applications for nanomaterials in critical technologies.pdf

149
APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES BY XUAN LI DISSERTATION Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Materials Science and Engineering in the Graduate College of the University of Illinois at Urbana-Champaign, 2010 Urbana, Illinois Doctoral Committee: Professor James Economy, Chair Professor Phillip H. Geil Professor Michael Plewa Associate Professor Moonsub Shim

Upload: swaroopexlnc

Post on 24-Dec-2015

239 views

Category:

Documents


2 download

TRANSCRIPT

Page 1: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES

BY

XUAN LI

DISSERTATION

Submitted in partial fulfillment of the requirements

for the degree of Doctor of Philosophy in Materials Science and Engineering

in the Graduate College of the

University of Illinois at Urbana-Champaign, 2010

Urbana, Illinois

Doctoral Committee:

Professor James Economy, Chair

Professor Phillip H. Geil

Professor Michael Plewa

Associate Professor Moonsub Shim

Page 2: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

ii

ABSTRACT

This thesis is devoted to the development, synthesis, properties, and applications

of nano materials for critical technologies, including three areas:

(1) Microbial contamination of drinking water is a serious problem of global

significance. About 51% of the waterborne disease outbreaks in the United States can be

attributed to contaminated ground water. Development of metal oxide nanoparticles, as

viricidal materials is of technological and fundamental scientific importance.

Nanoparticles with high surface areas and ultra small particle sizes have dramatically

enhanced efficiency and capacity of virus inactivation, which cannot be achieved by

their bulk counterparts. A series of metal oxide nanoparticles, such as iron oxide

nanoparticles, zinc oxide nanoparticles and iron oxide-silver nanoparticles, coated on

fiber substrates was developed in this research for evaluation of their viricidal activity.

We also carried out XRD, TEM, SEM, XPS, surface area measurements, and zeta

potential of these nanoparticles. MS2 virus inactivation experiments showed that these

metal oxide nanoparticle coated fibers were extremely powerful viricidal materials.

Results from this research suggest that zinc oxide nanoparticles with diameter of 3.5 nm,

showing an isoelectric point (IEP) at 9.0, were well dispersed on fiberglass. These fibers

offer an increase in capacity by orders of magnitude over all other materials. Compared to

iron oxide nanoparticles, zinc oxide nanoparticles didn‘t show an improvement in

inactivation kinetics but inactivation capacities did increase by two orders of magnitude to

99.99%. Furthermore, zinc oxide nanoparticles have higher affinity to viruses than the iron

oxide nanoparticles in presence of competing ions. The advantages of zinc oxide depend

on high surface charge density, small nanoparticle sizes and capabilities of generating

Page 3: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

iii

reactive oxygen species. The research at its present stage of development appears to offer

the best avenue to remove viruses from water. Without additional chemicals and energy

input, this system can be implemented by both points of use (POU) and large-scale use

water treatment technology, which will have a significant impact on the water purification

industry.

(2) A new family of aliphatic polyester lubricants has been developed for use in

micro-electromechanical systems (MEMS), specifically for hard disk drives that operate

at high spindle speeds (>15000rpm). Our program was initiated to address current

problems with spin-off of the perfluoroether (PFPE) lubricants. The new polyester

lubricant appears to alleviate spin-off problems and at the same time improves the

chemical and thermal stability. This new system provides a low cost alternative to PFPE

along with improved adhesion to the substrates. In addition, it displays a much lower

viscosity, which may be of importance to stiction related problems. The synthetic route

is readily scalable in case additional interest emerges in other areas including small

motors.

(3) The demand for increased signal transmission speed and device density for the

next generation of multilevel integrated circuits has placed stringent demands on

materials performance. Currently, integration of the ultra low-k materials in dual

Damascene processing requires chemical mechanical polishing (CMP) to planarize the

copper. Unfortunately, none of the commercially proposed dielectric candidates display

the desired mechanical and thermal properties for successful CMP. A new

polydiacetylene thermosetting polymer (DEB-TEB), which displays a low dielectric

constant (low-k) of 2.7, was recently developed. This novel material appears to offer the

Page 4: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

iv

only avenue for designing an ultra low k dielectric (1.85k), which can still display the

desired modulus (7.7Gpa) and hardness (2.0Gpa) sufficient to withstand the process of

CMP.

We focused on further characterization of the thermal properties of spin-on poly

(DEB-TEB) ultra-thin film. These include the coefficient of thermal expansion (CTE),

biaxial thermal stress, and thermal conductivity. Thus the CTE is 2.0*10-5

K-1

in the

perpendicular direction and 8.0*10-6

K-1

in the planar direction. The low CTE provides a

better match to the Si substrate which minimizes interfacial stress and greatly enhances the

reliability of the microprocessors. Initial experiments with oxygen plasma etching suggest

a high probability of success for achieving vertical profiles.

Page 5: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

v

To my dearest parents for their love and support …

Page 6: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

vi

ACKNOWLEDGEMENTS

I would like to express my sincere gratitude to my advisor, Professor James

Economy, for his support and guidance. I truly appreciated his leadership, inspiration

and encouragement in every stage during the Ph.D study, giving me the trust and freedom

to carry out the research. His vision, optimistic attitude, enthusiasm and continual pursuit

of scientific and industrial challenges have provided me with lifetime benefits.

I am so grateful to Professor Michael Plewa, Professor Philip Geil and Professor

Moonsub Shim in my thesis committee for reading my thesis despite their busy

schedules.

I had the great fortune to work with many intelligent, creative and highly motivated

people at the University of Illinois at Urbana-Champaign. I benefited from stimulating

interaction with colleagues in many different disciplines. I am truly grateful that

Professor Michael Plewa constantly challenged me to explore and understand phenomena

at the fundamental level and draw upon skills outside my formal education, all in search

of the truth. I also want to thank Dr. Elizabeth Wagner for her kind help, guidance and

assistance in carrying out the acute cytotoxcity tests. I would like to acknowledge

Professor Helen T. Nguyen, who has graciously offered permission to use the lab and

provided so many helpful and detailed comments on disinfection research. Without

them, these projects could not have been accomplished. It was a great pleasure working

and co-authoring journal articles with such outstanding professionals. I would also like

to express my sincere gratitude to Leonardo Gutierrez for the virus disinfection project,

who has offered me so much help.

Page 7: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

vii

There are many others at University of Illinois at Urbana and Champaign to whom I

am indebted for help. I would like to specially thank Dr. Xuan Zheng who has helped me

in the coefficient of thermal expansion for low-k dielectric materials, and Dr. Scott

Robison for his kind help and training for the mammalian cell TEM fixation and

embedding. I would also like to thank many friends in our department who have given

me assistance, including Dr. Matthew George, Dr. Margaret Shyer, Dr. Xindi Yu, Abby

Juhl, Dara Gough, and Dr. Qi Li.

Deep thanks must to be given to Dr. Zhongren Yue for his kind assistance with

numerous projects and his helpful discussion and suggestions during my Ph. D study. I

will never forget Dr. Gordon Nameni, Dr. Chaoyi Ba and Dr. Jinwen Wang, Dr.

Yongqing Huang, Samantha Bender, Dr. Jing Zhang, and Todd Martin for their

willingness to lend a helpful hand at the beginning of my study and for being good

friends. I appreciate the help from my undergraduate assistants, Brian Lin, Brent Smith,

Junghan Huang, Amanda Hedge, Michael Hebrew and Nicolas Pytle. I would also like to

extend my appreciation to other past and current members of Professor Economy‘s group

for being a friendly team and providing helpful insight, including Jacob Meyer, James

Langer, Zeba Farheen, Yaxuan Yao, Weihua Zheng and many others.

I want to take this opportunity to sincerely thank all the people in other departments

who have given me help and training. I need to thank Dr. Changhui Lei and; Dr. Jim

Mabon in the Center for Microanalysis of Materials Lab for help and training in TEM

and SEM, respectively. Without their help, my work would not have been nearly as

successful as it was.

Page 8: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

viii

I would like to express my gratitude to the business office personnel, Jay Menacher,

Judy Brewer, Debbie Kluge, Michelle Malloch, Cindy Byra, and Bryan Kieft for all their

help through all these years.

I want to acknowledge the moral support of my family. To my grandmother, you

were very kind in lending support. You let me know people should live kindly and

generously. To my grandfather, you taught me by example how to weather life’s

hardships, be strong, be brave, be persistent, never give up, and stay optimistic. Your

courage and passionate loyalty shows me how to mature and enjoy who I am. Your faith

inspired me to persevere through treacherous situations, and will guide me for the rest of

my life. To my uncles and cousins, you all provided me love, support and care, no matter

where I was.

Lastly, I would like to thank my parents for your unconditional love, support,

courage, dedication and selflessness. You made me believe the world was full of love

and sunshine. I felt fortunate that we could all live so close together and share this

memorable time. Without them, I couldn’t accomplish the things I have today. I thereby

dedicate this thesis to you, my dearest parents.

Page 9: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

ix

TABLE OF CONTENTS

LIST OF FIGURES ....................................................................................................... xii

LIST OF TABLES ........................................................................................................ xvi

CHAPTER 1 INTRODUCTION ....................................................................................1

1. 1 Background on nanomaterials ..................................................................................1

1. 2 Applications of nanomaterials for critical technologies .........................................3

1. 3 References ..............................................................................................................5

CHAPTER 2 METAL OXIDE NANOPARTICLES COATED ON FIBERGLASS TO

REMOVE VIRUSES FROM WATER ............................................................................7

2. 1 Introduction ............................................................................................................7

2.1.1 Background on water purification ....................................................................7

2.1.1.1 Billions suffer without improved water and sanitation services ...............7

2.1.1.2 Water disinfection .....................................................................................9

2.1.2 Background on viruses ...................................................................................11

2.1.2.1 What is a virus ........................................................................................11

2.1.2.2 Structure of viruses .................................................................................12

2.1.2.3 Cycle of life of viruses ............................................................................14

2.1.2.4 Prevention and treatment of viral disease in humans and other animals 15

2.1.2.5 Inactivation of viruses .............................................................................15

2. 2 Iron oxide nanoparticle coated on fiberglass to remove MS2 viruses from water 16

2.2.1 Introduction ....................................................................................................16

2.2.2 Mechanism of iron oxide nanoparticles virus removal from water ................18

2.2.3 Materials and methods ....................................................................................22

2.2.3.1 Synthesis of iron oxide nanoparticles coated on fiberglass ....................22

2.2.3.2 MS2 preparation and plaque forming unit (PFU) assay .........................24

2.2.4 Results and discussion ....................................................................................31

2.2.4.1 Characterization of iron oxide nanoparticles ..........................................31

2.2.4.2 Size of MS2 viruses ................................................................................35

2.2.4.3 Zeta potential of iron oxide nanoparticles and MS2 viruses ...................36

Page 10: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

x

2.2.4.4 Batch test results for MS2 viruses ..........................................................37

2.2.4.5 Flow-through test results for MS2 viruses ..............................................42

2.2.5 Summary .........................................................................................................46

2. 3 Iron oxide nanoparticle coated on fiberglass to remove rotaviruses from water 47

2.3.1 Introduction ....................................................................................................47

2.3.2 Materials and methods ....................................................................................47

2.3.3 Results and discussion ....................................................................................51

2.3.3.1 Size of rotaviruses ...................................................................................51

2.3.3.2 Diffusion coefficient of rotavirus ............................................................52

2.3.3.3 Zeta potential of rotavirus .......................................................................52

2.3.3.4 Batch test results for rotavirus ................................................................53

2.3.3.5 Flow-through test results for rotavirus ....................................................59

2.3.4 Summary .........................................................................................................61

2. 4 Silver-iron oxide nanoparticles coated on fiberglass to remove bacteria and viruses

from water ...........................................................................................................61

2.4.1 Introduction ....................................................................................................61

2.4.2 Materials and methods ....................................................................................62

2.4.3 Results and discussion ....................................................................................66

2.4.4 Summary .........................................................................................................70

2. 5 Zinc oxide nanoparticles coated on fiberglass removes MS2 viruses from water .70

2.5.1 Introduction ....................................................................................................70

2.5.2 Materials and methods ....................................................................................71

2.5.3 Results and discussion ....................................................................................74

2.5.3.1 Characterization of zinc oxide nanoparticles ..........................................74

2.5.3.2 Zeta potential of zinc oxide nanoparticles and MS2 viruses ..................79

2.5.3.3 TEM images of zinc oxide nanoparticles interact with MS2 viruses .....79

2.5.3.4 Batch test results for MS2 viruses ..........................................................80

2.5.3.5 Flow-through test results for MS2 viruses ..............................................85

2.5.4 Summary .........................................................................................................88

2. 6 Mammalian cell cytotoxicity and genotoxicity analysis of zinc oxide

nanoparticles .......................................................................................................88

Page 11: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

xi

2.6.1 Introduction ....................................................................................................88

2.6.2 Materials and methods ....................................................................................90

2.6.3 Results and discussion ....................................................................................94

2.6.4 Summary .........................................................................................................99

2. 7 References ..........................................................................................................100

CHAPTER 3 AN IMPROVED NANOTRIBOLOGICAL SYSTEM FOR HARD

DISK DRIVES ..............................................................................................................111

3. 1 Introduction ........................................................................................................111

3. 2 Materials and methods .......................................................................................112

3.2.1 Characterizations ..........................................................................................112

3.2.2 Material synthesis .........................................................................................114

3.2.2.1 Monomer synthesis ...............................................................................114

3.2.2.2 Polymer synthesis .................................................................................115

3. 3 Results and discussions ......................................................................................118

3. 4 Conclusions ........................................................................................................120

3. 5 References ..........................................................................................................120

CHAPTER 4 OPTIMIZATION OF NEW ULTRALOW-K MATERIALS FOR

ADVANCED INTERCONNECTIONS .......................................................................122

4. 1 Introduction ........................................................................................................122

4. 2 Materials and methods .......................................................................................125

4.2.1 Materials .......................................................................................................125

4.2.2 Synthesis and processing of poly (DEB-co-TEB) ........................................125

4.2.3 Thermal properties characterization .............................................................128

4. 3 Results and discussions ......................................................................................128

4. 4 Conclusions ........................................................................................................132

4. 5 References ..........................................................................................................132

Page 12: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

xii

LIST OF FIGURES

Figure 1.1. Schematic comparison of top-down and bottom-up approaches ....................3

Figure 2.1. Areas of physical and economic water scarcity .............................................8

Figure 2.2. Major components of a virus. The capsid encloses the viral genome; the

capsid, together with the RNA or DNA genome, is called the nucleocapsid .................12

Figure 2.3. Transmission electron microscope images of viruses. (a) tobacco mosaic

virus; (b) human rotavirus;(c) HIV-1 viruses; (d) smallpox virus. The brick-shaped virus

is covered with what looks like filaments .......................................................................13

Figure 2.4. The life cycle of an animal virus. (a) Viral capsid proteins bind with the host

receptor protein; (b) Entry into the host cytoplasm; (c) Biosynthesis of viral components;

(d) Assembly of viral components into complete viral units; (e) Budding from the host

cell ...................................................................................................................................14

Figure 2.5. Inactivation targets in virus ..........................................................................16

Figure 2.6. Development of charge at the iron oxide/solution interface ........................22

Figure 2.7. Synthesis of iron oxide nanoparticles coated on fiberglass ..........................23

Figure 2.8. Flow-through experimental set up ................................................................31

Figure 2.9. X-ray powder diffraction of iron oxide nanoparticles ..................................32

Figure 2.10.(a) TEM image of iron oxide nanoparticles; (b) TEM image of iron oxide

nanoparticle aggregate together; (c) HRTEM image of single iron oxide nanoparticles;

(d) SAED pattern of an iron oxide nanoparticle .............................................................33

Figure 2.11. SEM image shows iron oxide nanoparticles well attached to fiberglass ....34

Figure 2.12. XPS survey scan of iron oxide nanoparticles coated on fiberglass ............34

Figure 2.13. (a) TEM image shows the MS2 virus has a monodiperse diameter around

26nm; (b) TEM image shows MS viruses adsorbed to the surface of an aggregate of iron

oxide nanoparticles. There is no noticeable decrease in the diameter of the viral particles

and their integrity did not appear to be compromised ....................................................36

Figure 2.14. Zeta potential measurements for iron oxide nanoparticles and MS2 viruses in

1mM NaCl solution with different pHs ..........................................................................36

Figure 2.15. MS2 virus removal kinetics by iron oxide nanoparticles coated on fiberglass

in 1 mM NaCl at different pHs .......................................................................................38

Figure 2.16. MS2 virus removal kinetics and adsorption onto iron oxide nanoparticles

coated on fiberglass in 1 mM NaHCO3 solution .............................................................40

Page 13: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

xiii

Figure 2.17. MS2 virus removal kinetics and adsorption onto iron oxide nanoparticles

coated on fiberglass in 1 mg/L TOC NOM solution .......................................................41

Figure 2.18. Influence of Ca2+

or Mg2+

and NOM on the adsorption of MS2 viruses to

iron oxide nanoparticles ..................................................................................................43

Figure 2.19. Adsorption of MS2 viruses by iron oxide nanoparticles in DI water,

pH=6 ...............................................................................................................................43

Figure 2.20. Adsorption of MS2 viruses by iron oxide nanoparticles in artificial and

aquifer groundwater. Artificial groundwater presented fewer competitors than Newmark

groundwater for virus adsorption on available adsorption sites. ....................................44

Figure 2.21. Recovery of infectious MS2 viruses uses a solution of 1.5% beef extract in

50 mM glycine at pH 8 ...................................................................................................45

Figure 2.22. (a) TEM image shows rotavirus has monodiperse at diameter around 75nm

(b) TEM image shows rotavirus with compromised structure after coming into contact

with iron oxide nanoparticles in solution ........................................................................51

Figure 2.23. Zeta potential measurement for rotaviruses in 1mM NaCl solution with

different pHs ...................................................................................................................52

Figure 2.24. Rotavirus removal kinetics and adsorption onto iron oxide nanoparticles in

1m NaCl solution ............................................................................................................53

Figure 2.25. Rotavirus removal kinetics and adsorption onto iron oxide nanoparticles in

1m NaHCO3 solution ......................................................................................................54

Figure 2.26. Rotavirus removal kinetics and adsorption onto iron oxide nanoparticles in

1mg/L TOC of NOM solutions .......................................................................................55

Figure 2.27. Rotavirus removal kinetics and adsorption onto iron oxide nanoparticles in

AGW solutions ................................................................................................................57

Figure 2.28. Rotavirus removal kinetics and adsorption onto iron oxide nanoparticles in

divalent cation solutions .................................................................................................58

Figure 2.29. Adsorption of rotaviruses by iron oxide nanoparticles in artificial and aquifer

groundwater. ...................................................................................................................60

Figure 2.30. Recovery of infectious rotaviruses uses a solution of 1.5% beef extract in

50 mM glycine at pH 8 ...................................................................................................60

Figure 2.31. XPS Survey scan of silver-iron oxide nanoparticles coated on fiberglass .67

Figure 2.32. X SEM image shows that silver- iron oxide nanoparticles well attached to

fiberglass with a narrow size distribution .......................................................................68

Page 14: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

xiv

Figure 2.33. X-ray diffraction of silver-iron oxide nanoparticles coated on fiberglass ..68

Figure 2.34. Bactericidal activity of fiberglass coated with silver, iron oxide or silver-iron

oxide nanoparticles .........................................................................................................69

Figure 2.35. MS2 virus removal kinetics by fiberglass coated with silver, iron oxide and

silver-iron oxide nanoparticles in 1 mM NaCl at pH 6 ...................................................69

Figure 2.36. Synthesis of zinc oxide nanoparticles coated on fiberglass ........................72

Figure 2.37. X-ray diffraction of zinc oxide nanoparticles .............................................75

Figure 2.38. (a) TEM image of zinc oxide nanoparticles; (b) SAED pattern of selected

area of zinc oxide nanoparticles ......................................................................................76

Figure 2.39. FESEM image shows that zinc oxide nanoparticles are well attached to

fiberglass; (b) When FESEM is zoomed in, we can observed the nanoscale features of the

zinc oxide nanoparticles coating on fiberglass ...............................................................77

Figure 2.40. XPS survey scan of zinc oxide nanoparticles coated on fiberglass ............78

Figure 2.41. Zeta potential measurement for zinc oxide nanoparticles and MS2 viruses in

1mM NaCl solution with different pHs ..........................................................................79

Figure 2.42. (a) TEM shows that some areas of the MS2 viruses were destroyed and

busted after interacting with zinc oxide nanoparticles; (b) TEM image shows MS2 viruses

attach to the surface of zinc oxide nanoparticles. The shape indicated that damage had

occurred and their integrity appeared to be compromised. There is noticeable decrease in

the diameter of the viral particles to 20nm .....................................................................80

Figure 2.43. MS2 virus inactivation kinetics by zinc oxide nanoparticles coated on

fiberglass in 1 mM NaCl at different pHs .......................................................................82

Figure 2.44. MS2 virus inactivation kinetics and adsorption onto iron oxide nanoparticles

coated on fiberglass in 1 mM NaHCO3 solution .............................................................83

Figure 2.45. Influence of Ca2+

or Mg2+

and NOM on the inactivation of MS2 viruses by

zinc oxide nanoparticles ..................................................................................................84

Figure 2.46. Inactivation of MS2 viruses by zinc oxide nanoparticles in 1mM NaCl

solution at pH=6 .............................................................................................................85

Figure 2.47. Inactivation of MS2 viruses by zinc oxide nanoparticles in artificial and

aquifer groundwater. Artificial groundwater presented fewer competitors than Newmark

groundwater for virus adsorption on available adsorption sites .....................................86

Figure 2.48. Recovery of infectious MS2 viruses uses a solution of 1.5% beef extract in

50 mM glycine at pH 8 ...................................................................................................87

Page 15: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

xv

Figure 2.49. CHO cell chronic cytotoxicity concentration-response curve of zinc oxide

nanoparticles ...................................................................................................................95

Figure 2.50. CHO cell chronic genotoxicity concentration-response curve of zinc oxide

nanoparticles ...................................................................................................................96

Figure 2.51. TEM images to explore the uptake and subcellular localization of zinc oxide

nanoparticles: (a) cross section of CHO cell; (b) vacuoles are clear of any particles; (c)

interaction with 3.75 μg/mL zinc oxide nanoparticles over 72 h in the dark, the cell

membrane became much rougher as particles entered the cytoplasm; (d) zinc oxide

nanoparticles penetrating the vacuoles ...........................................................................97

Figure 2.52. Zinc oxide nanoparticles fall off from the fiberglass .................................99

Figure 3.1. Synthetic protocols for diacid monomers ...................................................114

Figure 3.2. Condensation and end-group conversion for polyester lubricants ................116

Figure 3.3. Tg of sterically hindered aliphatic copolyesters using a 5°C/min heating

rate .................................................................................................................................118

Figure 3.4. Thermal stability of sterically hindered aliphatic copolyester using a

10°C/min heating rate in air and in N2 ..........................................................................119

Figure 4.1. Schematic synthesis of DEB-co-TEB ........................................................123

Figure 4.2. Young‘s modulus and hardness of 700nm film on Si wafer ......................124

Figure 4.3. Plasma etching on the poly (DEB-co-TEB) 450nm thin films. a) contact UV

lithography technique to write the etching pattern; b)after etch by RIE O2 plasma; c)

remove photo-resist .......................................................................................................129

Figure 4.4. Thermal conductivity of poly (DEB-co-DEB) film used in the thermal model

are 0.33 Wm-1

K-1

.........................................................................................................130

Figure 4.5. Thermal capacity of poly (DEB-co-DEB) film used in the thermal model are

1.4Jcm-3

K-1

....................................................................................................................131

Page 16: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

xvi

LIST OF TABLES

Table 2.1. Newmark well chemistry at University of Illinois .........................................26

Table 2.2. Surface areas and pore volumes of iron oxide coated on fiberglass ..............35

Table 2.3. Surface areas and pore volumes of zinc oxide coated on fiberglass ..............78

Table 3.1. Monomers for sterically hindered aliphatic polyester lubricants .................116

Table 4.1. Electronic properties of cured poly (DEB-co-TEB) ....................................125

Table 4.2. Coefficient of thermal expansion of cured poly (DEB-co-TEB) .................131

Page 17: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

1

CHAPTER 1

INTRODUCTION

1.1 Background on nanomaterials

Nanotechnology is an emerging field that covers a wide range of disciplines,

including the frontiers of chemistry, materials, medicine, electronics, optics, sensors,

information storage, communication, energy conversion, environmental protection,

aerospace and more [4, 5, 6]. It focuses on the design, synthesis, characterization and

application of materials and devices at the nanoscale [1, 4, 5]. Nanomaterials are the

foundation of nanotechnology and are anticipated to open new avenues to numerous

emerging technological applications [4, 5]. Nanotechnology has grown very fast in the

past two decades because of the availability of new approaches and tools for the

synthesis, characterization, and manipulation of nanomaterials [5].

Nanomaterials with critical dimensions less than 100 nm may exhibit superior

chemical, biological, mechanical, electronic, magnetic, and optical properties that are

often significantly different from their corresponding micro counterparts [1, 4]. These

unique properties depend on the atomic structure, size confinement, composition,

microstructure, defects, and interfaces, all of which can be tailored by synthesis and other

processes [2, 3, 4, 5, 6].

The research on nanomaterials is highly interdisciplinary because it involves

many different synthetic methodologies and characterization techniques. Synthesis of

nanomaterials plays a significant role for cutting edge applications, and revolves around

the issue of assembling atoms or molecules into nanostructures of the desired

Page 18: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

2

coordination environment, size, and shape [6]. Many researchers are moving toward

such molecular based synthesis and applying engineered nanomaterials to novel uses [7].

In general, top-down and bottom-up are the two main approaches to

nanomaterials production (Figure 1.1) [2]. ‗Top-down‘ approaches are generated from the

macroscale to the nanoscale. They generally rely on physical attributes for their

processing - the combination of chemical, electrical or thermal processes. Top-down

methods include high-energy milling, ion implantation, lithography, laser ablation,

sputtering, vapor condensation, and etc. In contrast, ‗bottom-up‘ approaches are

synthesized and processed from the atomic or molecular scale to the nanoscale. It

requires a deep understanding of the individual molecular structures, their assemblies and

dynamic behaviors, and a broad multidisciplinary approach [1, 2]. Bottom-up methods

include sol-gel, precipitation, electrical deposition, cluster assembly/consolidation, self-

assembly, self-alignment, chemical vapor deposition, atomic layer deposition, anodizing,

and etc. [2, 5]. Innovations and inventions will emerge when researchers with diverse

backgrounds collaborate. Researchers have also combined top-down and bottom-up

approaches, developing new hybrid techniques to fabricate nanomaterials [2].

At the same time as new approaches to nanotechnology are being developed,

innovative applications are being discovered, as well. Nanomaterials have proven to

have great potential for improving environmental protection through an increased

adjustability within media, and higher selectivity and reactivity toward contaminants.

Both of these features extend nanotechnology‘s environmental applications via pollutant

removal and prevention, as well as environmentally conscious product and process

development.

Page 19: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

3

Figure 1.1 Schematic comparison of top-down and bottom-up approaches [2]

1.2 Applications of nanomaterials for critical technologies

The purification of drinking water is a primary environmental application of

nanotechnology. Contamination and overconsumption are depleting the planet‘s

freshwater resources. Seawater is becoming a recognized source for drinking water, as

freshwater becomes significantly scarce. Standard methods of salt removal are costly,

however, and cheaper and more reliable methods are necessary for effective water

treatment [8]. Today, approximately 1.1 billion people in developing countries do not

have access to clean water [9, 10]. Around 600,000 children die annually worldwide

because of intestinal complications due to rotavirus infection [11]. It is very critical for

public health to develop a new system to effectively remove viruses from drinking water.

The research at its present stage of development appears to offer the best avenue to

remove viruses from water. In Chapter 2, a new system is discussed that can be

implemented by both points of use (POU) and large-scale use water treatment technology

Page 20: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

4

without additional chemicals or energy input, which should have significant impact on

the water purification industry.

The status of nanotechnology‘s new role in the electronics industry is

unquestionably significant and far-reaching. Data-storage and batteries have been at the

forefront of nanotechnology developments in recent mobile device and computer product

releases [4, 6]. It is estimated that the hard disk drive industry will top $33 billion by

2011 [12]. The performance of the ultra-thin lubricant layer plays a critical role in the

long-term reliability and durability of the hard disk drive. In a recent study presented in

Chapter 3, a new family of sterically hindered polyester lubricants with improved thermal

stability and oxidation resistance, low glass transition temperature and crystallinity, and

good hydrolytic stability was successfully synthesized. These features dramatically

enhance the hard disk durability without sacrificing performance and at the same time

solve the spin off problems. Compared to the products currently available in the market,

the cost of this newly designed lubricant should be significantly lower [13].

The industrial manufacturing of microprocessors and semiconductors has been

another area that has grown by leaps and bounds with the help of nanotechnology [4, 6].

A newly developed process, detailed in Chapter 4, involving the modification of low-k

materials to match the CTE of substrates such as Si and Ta, sharply reduces stresses at

the interfaces which enhances the reliability of microprocessors. The system is currently

undergoing optimization, and the implementation of a plasma etching process will help

achieve vertical profiles at ultra fine line widths to meet the industry standards for next

generation architecture [14]. Success in this endeavor is expected to result in market

growth of at least 600 million dollars per year [15].

Page 21: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

5

1.3 References

1. Meier, W. Current Opinion in Colloid & Interface Science 1999, 4, 6-14.

2. Reithmaier, J.; Petkov, P.; Kulisch, W. Popov, Nanostructured Materials for

Advanced Technological Applications, 2009.

3. Bandyopadhyay, A. K. Nano Materials, New Age International (p) Limited,

2008.

4. Lhadi, M. Hybrid Nanocomposites for Nanotechnology. Electronic, Optical,

Magnetic and Biomedical Applications, 2009.

5. Yang, P.D. Chemistry of Nanostructured Materials, 2004.

6. Pradeep, T. Nano: The Essentials: Understanding Nanoscience and

Nanotechnology, 2008.

7. Pignataro, B. Tomorrow's Chemistry Today Concepts in Nanoscience, Organic

Materials and Environmental Chemistry, 2008.

8. Guobin, S., S. Yan, et al. (2009). "Applications of Nanomaterials in

Environmental Science and Engineering: Review." Practice Periodical of

Hazardous, Toxic & Radioactive Waste Management 13(2): 110-119.

9. Gleick, P. (2002) "Dirty Water: Estimated Deaths from Water-Related Disease

2000-2020" Pacific Institute for Studies in Development, Environment, and

Security.

10. Eisenburg, J. N. S.; Bartram, J.; Hunter, P. R. A Public Health Perspective for

Establishing Water-Related Guidelines and Standards. In Water Quality

Guidelines, Standards, and Health: Assessment of Risk and Risk Management for

Water-Related Infectious Disease; WHO: Geneva, 2001, 229–256. (18)

11. Parashar, U.D. and Gibson, C, J. and J.S. Bresee and et al. (2006) ―Rotavirus and severe childhood diarrhea‖, Emerging Infectious Diseases 12 (2): 304–306.

12. From website: http://www.itfacts.biz/hard-drive-industry-to-generate-33-bln-by-

2011/8300

13. Li , X. and Economy, J. ―An Improved Nanotribological System for Hard Disk

Drive‖, Materials Research Society Symposium Proceedings, (2009), 1139, 1139-

GG05-05

Page 22: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

6

14. Li, X. and Economy, J. ―Optimization of New Ultralow-k Materials for Advanced

Interconnection‖, Materials Research Society Symposium Proceedings, (2009),

1134, 1134-BB02-06.

15. Alternative Technologies Emerge in CMP (2002) : website:

http://www.icis.com/Articles/2002/07/12/177052/alternative-technologies-

emerge-in-cmp.html

Page 23: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

7

CHAPTER 2

METAL OXIDE NANOPARTICLES COATED ON FIBERGLASS TO REMOVE

VIRUSES FROM WATER

2. 1 Introduction

2.1.1 Background on water purification

Water is one of our most precious and valuable resources. Without it, we couldn‘t

survive. ―The world‘s 1.4 billion cubic kilometers of water are spread over a wide

variety of forms and locations. Of this water, the vast majority (nearly 97%) is salt water

in the oceans‖. The world‘s total freshwater reserves are estimated at around 35 million

cubic kilometers. Most freshwater is locked up in glaciers, permanent snow cover, or

deep groundwater and inaccessible to humans‖ [1].

2.1.1.1 Billions suffer without improved water and sanitation services

One of the most pervasive problems, afflicting people throughout the world, is

inadequate access to clean water and sanitation. 1.1 billion people lack access to safe

drinking water, 2.6 billion have little or no sanitation, and millions of people die annually

as a result [42]. The adverse health impacts attributable to lack of water and sanitation

are significant. Many of these effects are caused by exposure to pathogenic microbes.

The contaminated water is the major cause of death in developing countries [2, 3].

In both developing and industrialized countries, water resources strongly affect

energy and food production, industrial output, and the quality of our environment [1, 5].

Agriculture, livestock and energy consume more than 80% of all water for human use,

and demand for fresh water is expected to increase with population growth, further

stressing traditional sources [10]. Because of the enormous quantities necessary to

produce food, agriculture will remain the main user of water [59]. By 2020, water use is

Page 24: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

8

expected to increase by 40 percent, and the amount of water required for food production

to meet the needs of the growing population will increase by 17 percent [1].

Figure 2.1 Areas of physical and economic water scarcity [5]

Increasing amounts of contaminants are entering water supplies from human

activity. Many freshwater aquifers are being contaminated, overdrawn in populous

regions and suffering from saltwater intrusion. Water problems are expected to worsen in

the future, as water scarcity occurs globally (Figure 2.1) [5]. According to the United

Nations, 1.8 billion people will be living in regions with absolute water scarcity by 2025,

and two out of three people in the world will be living under conditions of water stress

[6]. Pressure on water resources will increase with rising demands from agricultural,

municipal, industrial and environmental usages [6, 10, 32, 59]. If better water

management and practices are not implemented, approximately 3 billion people will be

living below the water stress threshold [6].

Page 25: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

9

Conventional technologies of water and wastewater treatment can address many

of these problems with quality and supply. However, these traditional methods are often

chemically, energetically and operationally intensive. It requires considerable infusion of

capital to implement facilities, and both chemical and energy consumption are high. In

highly industrialized countries, the costs and time to implement conventional water and

wastewater treatment facilities make water purification expensive [59]. The developing

world greatly needs technologies with much less chemical and energy consumptions.

Moreover, intensive chemical treatments and the residuals and byproducts resulting from

treatment can cause other serious public health and environmental concerns [4, 54, 59].

It is very critical to develop new technologies for sustainable, affordable, safe and

robust water treatment methods to reduce water scarcity, improve health, and safeguard

the environment throughout the world. To reach these challenging goals, many open

research questions need to be addressed. A tremendous amount of effort has been put

into identifying more effective, efficient methods to purify waters at lower cost and with

less energy, while at the same time minimizing the use of chemicals and impact on the

environment [59].

2.1.1.2 Water disinfection

An overarching goal for providing safe water is to effectively and affordably

disinfect water to remove or destry traditional and emerging pathogens without intensive

use of chemicals or production of toxic byproducts [4, 12, 54, 59]. Waterborne

pathogens have a devastating effect on public health [3]. The vast majority of diarrheal

disease in the world (88%) is attributable to unsafe water, sanitation and hygiene.

Approximately 3.1% of annual deaths (1.7 million) and 3.7% of the annual health burden

Page 26: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

10

world-wide (54.2 million) are attributable to infected water [8]. Waterborne infectious

agents, including a variety of helminthes, protozoa, fungi, bacteria, rickettsiae, viruses

and prions, can cause many diseases [70]. Viruses are of particular concern, accounting

for nearly half of all emerging pathogens in the last two to three decades [71]. In 2000,

the U.S. Environmental Protection Agency (EPA) required that 99.99% of viruses be

removed or inactivated from publicly owned drinking water treatment facilities [72].

Chlorination has been the major disinfectant process for domestic drinking water

for many years. Concern about the potential health effects of the byproducts of

chlorination has prompted the research on the possible relationship between these

byproducts and incidence of human cancer, and even with adverse reproductive outcomes

[73]. Due to concern over the presence of trihalomethanes (THMs) and other chlorinated

byproducts in chlorinated drinking water, alternative disinfection methods are being

explored [75].

The current trend in water disinfection is the use of multiple-barrier drinking

water treatment plants. Such facilities utilize ultraviolet (UV) in water disinfection in the

filtration as the inactivation component to photochemically inactivate pathogens, such as

UV/combined chlorine and ozone/combined chlorine. Compared with free chlorine, both

UV and ozone are very effective in controlling waterborne bacteria and protozoa cysts

and oocysts [12, 59]. This approach has raised new concerns by changing disinfection

technologies, because some viruses can be effectively controlled by ozone but are

resistant to both UV and combined chlorine disinfection. Moreover, ozone can generate

the disinfection byproducts (DBP) in water containing bromide ions, and combined

chlorine can form other unregulated DBPs, including haloacetonitriles and iodoacetic

Page 27: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

11

acid [44,76]. These DBPs may be more toxic and carcinogenic than those associated

with free chlorine. New developed materials would be particularly beneficial in

developing countries. The new systems will provide a barrier against all pathogens by

inactivating viruses and trapping and inactivating any larger bacteria, protozoa cysts and

oocysts with relatively high resistance to chlorine and UV light inactivation, even without

producing DBPs or extensive use of chemicals [59].

2.1.2 Background on viruses

2.1.2.1 What is a virus

The word ―virus ―originally came from the Latin referring to toxin or poison [71].

Viruses are the smallest known infectious agents that can infect all types of organisms,

from animals and plants to bacteria and archaea [77]. Recent environmental studies have

shown that viruses, primarily bacteriophages, are the "most abundant biological entities

on the planet", with the total number of viruses exceeding the number of cells by at least

an order of magnitude [37, 78].

The major feature that distinguishes viruses from other microorganisms is a lack

of protein synthesis machinery and metabolism of their own [77]. Although viruses have

genes, they do not have a cellular structure, which is seen as the basic unit of life [71].

Viruses do not have their own metabolism, and they can replicate only inside the living

cells of other organisms [77]. Without a host cell, viruses cannot carry out their life-

sustaining functions or reproduce. They cannot synthesize proteins, because they lack

ribosomes and must use the ribosomes of their host cells to translate viral messenger

RNA into viral proteins [71]. Viruses get all metabolic functions from the host cells

since they cannot generate or store energy in the form of adenosine triphosphate (ATP) to

Page 28: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

12

derive their energy [79]. Viruses also parasitize the host cells for their basic building

materials, such as amino acids, nucleotides, and lipids [79].

2.1.2.2 Structure of viruses

Viruses display a wide diversity of shapes and sizes, called morphologies.

Viruses consist of nucleic acid (either DNA or RNA) encapsulated in a protective coat of

protein called a capsid and/or a cellular lipid outer coating. A virus contains a genome in

the form of one or more molecules of nucleic acid (Figure 2.2) [109]. Each nucleic acid

molecule is single-stranded (ss) or double-stranded (ds), giving four categories of virus

genome: dsDNA, ssDNA, dsRNA and ssRNA [77].

Figure 2.2 Major components of a virus. The capsid encloses the viral genome; the

capsid, together with the RNA or DNA genome, is called the nucleocapsid

[109].

Page 29: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

13

The capsids are composed of protein polypeptides that contain weakly

acidic

and/or basic functional groups (such as carboxyl and amino moieties) [26]. The capsid is

made from proteins encoded by the viral genome and its shape serves as the basis for

morphological distinction [31]. In general, there are four main morphological virus types

as shown in Figure 2.3: (a) helical, (b) icosahedral, (c) envelope, (d) complex virus [80,

81, 82, 83].

Figure 2.3 Transmission electron microscope images of viruses. (a) tobacco mosaic

virus [80]; (b) human rotavirus [81];(c) HIV-1 viruses[82]; (d) smallpox

virus. The brick-shaped virus is covered with what looks like filaments

[84].

Page 30: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

14

2.1.2.3 Cycle of life of viruses

Viruses are nanomachines built within the cell factory, designed to invade

neighboring cells. Their structure relies on the timely and dynamically regulated

assembly of individual components, including nucleic acids, proteins, and lipids, in

specific cell locations. Their invading strategies rely on complex interactions with the

cell plasma membrane, involving several viruses and cellular proteins organized in

dynamic complexes that are able to mediate viral penetration into the cell interior without

rupturing the outside-inside plasma membrane frontier required for cell survival [17, 84].

The life cycle of viruses differs greatly between species, but there are five basic stages in

the life cycle of viruses as shown in Figure 2.4 [25].

Figure 2.4 The life cycle of an animal virus. (a) Viral capsid proteins bind with the

host receptor protein; (b) Entry into the host cytoplasm; (c) Biosynthesis

of viral components; (d) Assembly of viral components into complete

viral units; (e) Budding from the host cell [25].

Page 31: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

15

2.1.2.4 Prevention and treatment of viral disease in humans and other animals

Many viruses cause little or no disease and are said to be "benign". The more

harmful viruses are described as virulent. Viruses cause different diseases depending on

the types of cells that they infect. Viruses have different mechanisms by which they

produce disease in an organism, which largely depends on the viral species [77].

Some viruses cause many important infectious diseases such as the common cold,

influenza, measles, diarrhea, hepatitis, yellow fever, polio, and AIDS. Some viruses can

cause life-long or chronic infections where the viruses continue to reproduce in the body

despite the host's defense mechanisms. This is common in hepatitis B virus and hepatitis

C virus infections, which are associated with liver cancer [71, 77].

Many viruses can cause disease in domestic animals and crop plants, which

significantly impacts the economy. Another area where viruses can cause economic

damage is in the dairy industry, where phages can infect the lactic acid bacteria that are

responsible for the fermentations that produce cheese, yogurt and other milk products.

To minimize the risk, procedures are required for treatment of the milk or whey to

inactivate any phages present, and for the disinfection of the factory environment.

Therefore the nature of viruses, the development of effective means for prevention, and

the diagnosis and treatment of viral diseases is very critical.

2.1.2.5 Inactivation of viruses

Viral inactivation makes viruses inactive or unable to infect. Many viruses contain

lipid or protein coats that can be inactivated by chemical alteration. Viruses can be

destroyed by the alteration or removal of its nucleic acid and/or one or more of its

proteins (Figure 2.5) [77]. A protein molecule may be altered by the induction of a

Page 32: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

16

conformational change or, more drastically, by the breaking of covalent bonds, such as

peptide and disulfide bonds. Alteration of a surface protein might prevent a virus from

attaching to or entering the cell. Stripping the envelope from an enveloped virus removes

the surface proteins and achieves the same outcome. Alteration of internal virus proteins

can destroy properties, such as enzyme activities, essential for the replication of the virus.

Some viral inactivation processes actually denature the virus completely.

Figure 2.5 Inactivation targets in virus [77]

2.2 Iron oxide nanoparticle coated on fiberglass to remove MS2 viruses from water

2.2.1 Introduction

The presence of pathogenic enteric viruses in water poses a significant risk to

human health, due to their low infectious dose. Enteric virus infections can not only

cause diarrhea and self-limiting gastroenteritis, but also cause respiratory infections,

conjunctivitis, hepatitis, and diseases that have high mortality rates. In addition, some

enteric viruses have been linked to chronic diseases such as insulin-dependent

diabetes

[12, 23]. Enteric viruses can be transmitted by food, water,

and human contact. Because

of the potential for contamination from a variety of sources, enteric viruses in water are of

Page 33: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

17

particular concern. Their extremely small size (23–80 nm) enables enteric viruses to

penetrate soil, contaminating aquifers, and travel long distances in groundwater [85].

The unique viral structure of enteric viruses makes them resistant to current water

treatment processes. They can pass through the gastrointestinal tract and are resistant to

environmental stresses, including heat and acid. Most enteric viruses are stable at pH 3.0,

in the presence of lipid solvents [51, 85]. They resist freezing and drying. For example

Picobirnaviruses are small non-enveloped viruses with bi-segmented double-stranded

RNA that are extremely resistant to UV light inactivation and parvoviruses are the

smallest known enteric viruses, with single-stranded RNA and high heat

resistance [85].

Polyomaviruses are non-enveloped double-stranded DNA viruses that have been found to

be very heat stable but are less resistant to chlorination than other enteric viruses [23, 85].

An alternative to using the virus itself is to use a model organism or surrogate for

lab testing for both safety and cost, which is likely to respond in a similar way to

environmental conditions or sanitizing treatments [86]. One option is to use a related

virus which may have similar properties. An alternative approach is to use bacteriophage

viruses, which do not require mammalian cell culture facilities, for growth and viability

determination [85]. Bacteriophages have long been used as indicators of water

contamination and used for disinfectant sensitivity studies, with the goal of modeling

properties of human pathogens in mind [87].

The MS2 virus belongs to group I of the RNA coliphages within the family

Leviviridae [77]. The bacterial host for MS2 is E. coli, therefore this bacteriophage is

found most frequently in sewage and animal feces [88]. Like enteric viruses, the MS2

virus is adapted to the intestinal tract. The MS2 virus is an icosahedral virus with 180

Page 34: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

18

copies of a coat protein, forming a shell around a single-stranded RNA molecule. The

coat protein subunits form a lattice with the triangulation number T = 3 [27]. The coat

protein has a fold which is different from the fold of all other viral coat proteins so far

known. It consists of a five-stranded β sheet facing the inside of the particle, and a

hairpin and two helices on the outside [51]. The MS2 virus is commonly utilized as a

model virus, due to its similarity to the human enteric viruses in shape, size, behavior,

and nucleic acid structure [51]. In addition, MS2 is usually more resistant to disinfection

processes than the majority of pathogen viruses, making it a suitable surrogate for

laboratory experimentation [85]. Finally, MS2 does not pose any risk to humans‘ health

since it only infects bacteria strains and it has been well characterized in previous studies.

In this investigation, E. coli (ATCC 15597) were used as the host.

Objective of this study was to evaluate the use of iron oxide nanoparticles coated

on fiberglass for virus removal under environmentally relevant conditions. This filter

could potentially be used as a point-of-use device for water treatment without producing

harmful disinfection by-products (DBPs). It would be significantly valuable in

developing nations in which water treatment facilities are unavailable. In this study,

bacteriophage MS2 viruses were used as surrogates to investigate the ability of iron oxide

nanoparticle coated fiberglass for virus removal [30].

2.2.2 Mechanism of iron oxide nanoparticles virus removal from water

Viruses behave as charged colloid particles in aqueous suspension, due to the

ionization of the protein capsids [89]. Increasing the pH of the medium will increase the

ionization of carboxyl groups (COOH → COO−) and sulfhydril groups (SH→S

−), and

decrease ionization of amine groups (NH4+ → NH3) at the capsid surface. Viruses

Page 35: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

19

typically have isoelectric points (IEP) in the range of 3–7 [52]. The IEP point is specific

to the individual virus type and strain. In aqueous environments, the net charge on the

viral surface is largely dependent on the pH of the medium and the surface chemistry of

the virus. Viruses may be positively or negatively charged in natural groundwater

(pH=4-9). Under most natural pHs, bacteriophage viruses are usually negatively charged

[92]. The electrophoretic mobility and zeta potential of viruses are dependent upon pH,

and the ionic strength of solution. The electrophoretic mobility in an electric potential

gradient is related to the surface charge and reflects the zeta potential [64]. Electrostatic

interactions between viruses and solid surfaces play important roles in influencing

sorption of viruses to sorbents [89]. However, localized regions on the virus surface can

vary widely in charge, as the surface is made up of multiple protein subunits, each of

which has its own unique hydrophilic and hydrophobic regions. Regions vary in the

ability to interact with adjacent protein subunits of different chemical composition and

associated hydrophilic and hydrophobic properties, as well, creating new domains with

uniquely charged and hydrophobic regions. At pH values greater than the IEP, the virus

carries a net negative charge. Depending on the pH and surface charge of other

interacting particles, electrostatic attraction can thus play an important role in virus fate

and transport [26, 64].

These interactions can be applied for (1) removal of viral pathogens from water

by coagulation and filtration, (2) detection of human viruses in clinical samples, (3) the

adsorption of viruses to soils and minerals and (4) even the binding of viruses to receptor

sites on host cells [52, 59]. ―Classical Derjaguin−Landau−Verwey−Overbeek (DLVO)

potential energy calculations describe the balance of electrostatic repulsion and van der

Page 36: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

20

Waals attraction forces as a function of virus − mineral separation distance‖ [52]. As a

first approximation, the interfacial interactions of spherical virus nanoparticles such as

bacteriophage MS2 viruses have been modeled within the DLVO paradigm when

modeling deposition of virus to mineral surfaces, and DLVO -like interactions have also

been used successfully in cases of bacteriophage PRD1and polio virus to describe their

sorption behavior on mineral surfaces [41, 56]. It is relatively well established that

electrostatic and van der Waals forces are important. Several recent studies have

demonstrated the importance of electrostatic interactions in the specific situation of

adsorption of viruses to solid interfaces [46].

The DLVO theory is based on the assumption of ideally spherical colloids and

smooth surfaces with uniform chemical properties, while real colloidal systems contain

both morphological and chemical heterogeneities [14]. In general, DLVO theory is

insufficient and often requires extensions to include contributions from other interactions

like Lewis acid-base interactions or steric interactions [14, 33]. Hydrophobic

interactions, factors relating to solution and surface chemistry, and other interactions are

also important in virus-media sorption and inactivation.

The interaction of MS2 virus particles with solid surfaces can be simplified to the

interaction of a charged colloidal particle with a charged surface. For a colloidal system,

the total interaction potential (Vtot), the critical parameter that determines the nature of

the interaction, may be written as Vtot = VvdW + Velect+ Vsteric + Vstructural, where VvdW is the

attractive potential arising from long range van der Waals forces, Velect is the potential

from electrostatic interactions, Vsteric is the steric hindrance of adsorbed layers, and

Page 37: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

21

Vstructural comes from short range structural forces from non adsorbed species in solution

[33, 38].

Virus attachment to various positively charged particles and surfaces is especially

prevalent in environments with metal oxides and positively charged media such as clays

that are rich in ferric oxides [16, 18, 67, 89]. Poliovirus can be removed from solution by

metal oxides such as α-SiO2, α-Fe2O3, α-Al2O3, β-MnO2, and CuO [18, 45]. Some

studies have shown that sand columns coated with metal oxides can remove significantly

more viruses than just sand alone. These metal oxide coatings change the surface charge

of media, which has potential to increase efficiency of virus removal in drinking water.

Virus removal by sorption to charged surfaces has been demonstrated to be strongly

associated with the charge differential. Once the viruses are absorbed to the surface, this

surface charge differential may lead to destructive chemical changes of the virus capsid

or nucleic acid. If the charge differential is great enough, viruses can be very effectively

removed and/or inactivated through sorption to charged media. Viruses are composed of

protein subunits that are arranged into a unique, directed and energy-stable pattern that is

created when the viruses are formed during replication. When external physical or

chemical stressors are applied to the virus, its structure can become altered, leading to

conformational changes and loss of integrity that result in loss of infectivity or in virus

inactivation [18, 57].

Natural removal of viruses by iron oxide / hydroxide coating on aquifer materials

has been studied [93]. Column packed with zero-valent iron or sand coated with ferric

hydroxides has been suggested as efficient means for virus removal [94].

Page 38: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

22

At the beginning of this research we selected iron oxide nanoparticles coated on

fiberglass as an initiative for the virus removal study. The charge on the iron oxide

surface results from the dissociation of surface hydroxyl groups. The adsorption or

desorption of protons depends on the pH of the solution. The situation can be treated as

acid/base equilibrium, represented by reactions shown in Figure 2.6 [24, 90]. Besides the

interaction between the surface hydroxyl group and protons, the underlying metal ion acts

as a Lewis acid and exchanges the OH group for other ligands to form surface complexes.

This process may be referred to as chemisorption, inner sphere adsorption, or ligand

exchange. This kind of adsorption is very strong and not easily broken. As a result,

adsorption may take place on a neutral surface or even with the same charge as the

adsorbing species. Both of the above interactions provide iron oxides with a high sorption

affinity toward MS2 viruses, which are Lewis bases (i.e., electron pair donors). Ions such

as nitrate and perchlorate do not exhibit Lewis acid–base characteristics, and are

adsorbed only through outer sphere complexes, or electrostatic interaction [24, 90].

Studies were also intended to aid in the identification of virus, media and water

characteristics affecting virus sorption to iron oxide nanoparticle coated fiberglass and

inactivation.

Figure2.6 Development of charge at the iron oxide/solution interface [24, 90]

2.2.3 Materials and methods

2.2.3.1 Synthesis of iron oxide nanoparticles coated on fiberglass

Page 39: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

23

Iron oxide was prepared by a precipitation method based on the procedure

described by Lin et al. with a modification for the deposition on fiberglass [110]. In a

typical procedure, a non-woven glass fiber mat with 7 wt% PVA binder (Crane glass 230

from Crane & Co. Inc.) was dipped into an aqueous solution of FeCl3 (0.05 mol in 100 ml

H2O) for 3min. After drying at 90oC for 5min, it was immersed into an aqueous solution

of NH4OH (15%). It was then heated at 90oC for 10min. This process was repeated two

more times. The resulting iron hydroxide was dried at 190oC for 4 h. After this, it was

washed several times with distilled water until the water was thoroughly clean. The

general process for the iron oxide coated fiberglass (IOCF) filter is illustrated in Figure

2.7 [90].

Figure 2.7 Synthesis of iron oxide nanoparticles coated on fiberglass [90]

Page 40: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

24

The final load of iron oxide nanoparticles in the fiberglass was ~25% in mass. For

batch experiments, the fiberglass coated with iron oxide nanoparticles was cut into

~0.050g pieces. For flow-through experiments the cartridge was packed in a column

measuring 1.5 cm in diameter and 13.2 cm high, the glass rod measuring 1.0 cm in

diameter [30].

2.2.3.2 MS2 preparation and plaque forming unit (PFU) assay

Preparation of Escherichia coli for further inoculation MS2 viruses

200 mL of tryptic soy broth (TSB) solution was prepared with 200 ml DI water

and 6 g Tryptic Soy Broth powder in a 1000 ml bottle to ensure that the solution had

enough surface area in contact with air. A stopper was used as a cap for a more efficient

aeration of the solution. After autoclaving, the solution was kept in the incubator at 37oC

until the temperature decreased to 37oC. A 2 ml sample of the solution was taken for

absorbance analysis. This sample was monitored at wavelength 420 nm. 5 ml of E. coli

(ATCC 15597) stock was added to the broth and incubation began at 37oC with a shake

speed of 200 rpm. The absorbance was monitored every 30 min at wavelength 420 nm

for the next 3 h, until absorbance ranges were between 0.8 and 1 [30].

Preparation and Plaque Forming Unit (PFU) Assay

The MS2 virus was replicated and purified following the modified procedure [35].

E. coli was grown in a TSB solution as its culture medium and afterward inoculated with

MS2 viruses. MS2 viruses were purified by sequential centrifugation and microfiltration

through 0.2-µm and 0.05-µm low-protein-binding polycarbonate track-etched membranes

(Whatman Nucleopore, USA) to remove debris. Nutrients, microbial products and small

debris in solution were removed by using a 100-kDa membrane (Koch Membranes,

Page 41: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

25

USA) in a Millipore ultra-filtration unit (Whatman Nucleopore, USA), using a previously

filtered and autoclaved 1mM NaCl solution. The final MS2 virus stock was stored at 4oC

at a concentration of ~1011

PFU mL-1

. The solutions were prepared immediately before

use by utilizing Nanopure water of a resistivity of 18 MΩ cm (Millipore, Barnstead,

USA) and high grade reagents, and then filtered using a 0.2-μm membrane. MS2

enumeration was performed following the double agar layer procedure [91]. Briefly, the

plaques indicating infection, formed due to the inoculation of E. coli with MS2 viruses at

37oC for 16 h were counted. Only the dishes that had from 20 to 300 plaques were used

for calculation of MS2 virus concentration [30].

Solution chemistries

Several chemically different solutions were prepared for testing MS2 with iron

oxide nanoparticles. The solutions were prepared immediately before use by utilizing

Nanopure water of a resistivity of 18 MΩ cm (Millipore, Barnstead, USA) and high grade

reagents, and then filtered using a 0.2μm membrane. Artificial groundwater (AGW,

Ionic strength ~ 1.5 mM) was synthesized according to specific parameters for

uncontaminated groundwater [30]. Newmark groundwater (NGW) was collected from a

natural aquifer located beneath the Newmark Civil Engineering Laboratory (205 N.

Matthews, Urbana, Illinois, 61801); its water has been characterized and used in previous

studies, as listed in Table 2.1[90].

Prior to use, NGW was greensand-filtered to remove manganese and iron and,

then passed through a 0.2-μm membrane to separate out large, suspended particles.

Content of dissolved organic carbon (DOC) was measured using a Phoenix 8000 TOC

Analyzer (Dohrmann, USA). Final total organic carbon (TOC) concentration of NGW

Page 42: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

26

was 2.35 mg/L.

Table 2.1 Newmark well chemistry at University of Illinois [90]

Solute

(mg/L)

Carbonate Bicarbonate Carbonic

acid Chloride Sulfate Sulfite Sulfide pH Nitrate

0.51 206 8.74 1 1.1 <0.5 <0.1 8.21 0.14

Potassium Magnesium Ammonia

(as N) Calcium Phosphate Sodium Silica DOC

Total

Dissolved

Iron

1.59 27.39 2 38.56 0.062 35 15.08 2.88 0.2

Suwannee river natural organic matter (SRNOM) from the International Humic

Substances Society (IHSS, St. Paul, MN) was used to simulate dissolved organic matter

(DOM) in solution. The procedure for NOM solution preparation has been previously

described [96].

NOM solution for fluorescence correlation spectroscopy (FCS)

experiments was prepared in the dark to prevent photodegradation. The TOC

concentration of the NOM solution, determined using a Phoenix 8000 TOC Analyzer

(Dohrmann, USA), was 101.4 mg/L. The stock of SRNOM solution was stored in the

dark at 4°C.

Measurement of electrophoretic mobility (EPM) for MS2 viruses and iron oxide

nanoparticles

Solutions were mixed with MS2 viruses or iron oxide nanoparticles to the final

concentrations of ~1010

PFU/mL and ~ 0.74 mg/mL, respectively. These concentrations

ensured an optimal signal for electrophoresis measurements. EPM was determined using

a ZS90 Zetasizer instrument (Malvern, UK) and 1-mL clear disposable zeta cells

(DTS1060C, Malvern). A minimum of 3 measurements was conducted for every

solution condition. Several solutions included the addition of iron oxide nanoparticles

Page 43: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

27

with SRNOM to measure changes to EPM in the presence of negatively charged NOM.

This set of measurements was converted to zeta potential with the Smoluchowski

equation, using Dispersion Technology Software (v5.10, Malvern 2008). Attenuation

index denotes the percentage of laser light that passes through the sample cuvette. For an

index of 10, only 30% of the nominal laser power is used. Polydispersity index is a width

parameter of the cumulant analysis of size. A minimum of three measurements per

sample was recorded and a total of three samples per each virus sample were processed

[30].

Transmission electron microscopy (TEM)

Most viruses cannot be seen with a light micoscope, so scanning and transmission

electron microscopes were used to visualize viruses. To increase the contrast between

viruses and the background, electron-dense "stains" are used. These are solutions of

heavy metal salts, such as tungsten, that scatter the electrons from regions covered with

the stain [71]. When viruses are reacted with stain (positive staining), fine detail is

obscured. Negative staining overcomes this problem by staining the background only.

MS2 samples with iron oxide nanoparticles were investigated using TEM technique.

Viruses and iron oxide nanoparticle suspensions were applied to holey-carbon-coated,

300-mesh, copper grids. Tungsten acetate was used as stains for MS2 viruses. All the

samples were examined using a Cryo TEM (JEM-2100, JEOL, Tokyo, Japan) at 200 kV

accelerated voltage [30].

Brunauer-Emmett-Teller (BET)

BET surface area and micro- and mesoporous volumes were carried out on an

Autosorb-1 apparatus (Quantachrome), following the standard procedure [95]. All

Page 44: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

28

samples were degassed at 100°C until the outgas pressure rise was below 5 μmHg/min

prior to analysis. Nitrogen isotherm obtained at 77 K in the appropriate relative pressure

ranges was used for subsequent calculations. The BET equation was used to determine

the surface area. The Dubinin-Radushkevich (DR) equation was used to deduce

micropore volumes, i.e., total volume of pores with diameter <2 nm. The total pore

volume was estimated from the amount of nitrogen adsorbed at P/Po = 0.95. The

mesopore volume (i.e., total volume of pores with diameter 2-50 nm) was calculated by

subtracting the volume of micropores from the total pore volume at a relative pressure of

0.95.

To find the IEP of iron oxide nanoparticles, EPM was measured using a 1 mM

NaCl solution. The range of pH from 3 to 9 and was adjusted by adding high grade

hydrochloric acid (0.1 M HCl) and sodium hydroxide (1 M NaOH). A minimum of 3

measurements was conducted for every pH selected. pH was determined using an Orion 3

Star pH meter (Thermo, USA).

Determination of hydrodynamic diameter of MS2 viruses by dynamic light

scattering (DLS)

Hydrodynamic diameter of MS2 viruses was determined using a ZS90 Zetasizer

instrument (Malvern, UK). For each solution tested in this study, MS2 was added to the

solutions until a final concentration was reached of ~1010

PFU/mL. These concentrations

allowed us to use an attenuation of 10 and a polydispersity index (PDI) close to 0.2.

Scanning electron microsope (SEM)

The morphology of the iron oxide nanoparticles coated on fiberglass was

examined with a Hitachi S-4700 high resolution SEM.

Page 45: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

29

Wide angle X-ray diffraction (WAXD)

WAXD experiments were carried out on a Rigaku D/Max-b diffractometer with a

copper X-ray source controlled by MDI's Data Scan (λ= 1.54178 Å). Zinc oxide

nanoparticle powders were evenly distributed on a piece of double-sided tape on a glass

slide. The parameters used were 45 kV and 20 mA, the scanning angle range (2θ) was

20°−80°, and the scanning rate was 0.6°/min, with a step increment of 0.05.

X-ray photoelectron spectroscopy (XPS)

XPS data were obtained from iron oxide coating on fiberglass using a Physical

Electronics PHI Model 5400 surface analysis system. Before analysis all samples were

washed with D.I. water and then fully dried. XPS spectra were obtained using an

achromatic Mg K (1253.6 eV) x-ray source operated at 300 W. Survey scans were

collected from 0 - 1100 eV with a pass energy equal to 178.95eV. The pressure inside

the vacuum system was maintained at approximately 10-9

Torr during all XPS

experiments. A non-linear least squares curve fitting program (XPSPEAK4.1 software)

with a symmetric Gaussian-Lorentzian sum function and Shirley background subtraction

was used to deconvolve the XPS peaks. The carbon 1s electron binding energy

corresponding to graphitic carbon was referenced at 284.5 eV for calibration.

Batch experiments

Batch tests were prepared using 300-mL Pyrex bottles for MS2 viruses. These

glass containers were cleaned using detergent and DI water and thereafter rinsed with

Nanopure water, dried in an oven, and autoclaved. The bottles were filled with viral

solution and varied mass of fiberglass coated with iron oxide nanoparticles. Air bubbles

were avoided by filling the container to the top with viral solution and then covering it

Page 46: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

30

with parafilm. The initial concentration of the solution was ~ 107 PFU/ mL. The bottles

were shaken at 200 rpm in a horizontal shaker and 0.25 mL samples were taken every

30 min for 3 h for kinetics experiments with MS2. The same volume of buffer solution

was added back to the bottles after removing solution. Control experiments, performed

for MS2 virus using fiberglass substrate with no coating of iron oxide nanoparticles,

showed no removal of viruses at 22°C during the 3 h of testing. First-order kinetic rate

constants (k) for virus removal were estimated by fitting the virus concentrations

measured throughout the experiment.

Reversibility of virus adsorption was studied by eluting with beef extract and

glycine, as previously reported. Batch reactors were prepared following the protocol

described in this section. However, only for these experiments, iron oxide nanoparticles

without the fiberglass were added to the solution containing ~107 PFU/mL, as colloidal

nanodispersed particles. After the adsorption experiments, beef extract and glycine were

added directly to the batch reactor at concentrations ranging from 1.5% (weight/volume)

to 3%, while raising the pH to 8 and 9. In addition, iron oxide nanoparticle samples after

adsorption and desorption of viruses were taken for TEM analysis.

Flow-through experiments

Flow-through experiments were conducted to test the adsorption capacity of

fiberglass coated with iron oxide nanoparticles under saturated flow conditions and

selected solution chemistries. We refer to the experiments in which virus-containing

solution was pumped continuously through the cartridge as flow-through experiments.

For every test, 1000 mL of ~107 PFU/mL MS2 suspensions were used. The viral solution

was pumped using a peristaltic pump at a flow rate of 3-4mL /min through to ensure a

Page 47: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

31

saturated flow at 22 °C. Samples from the outflow were collected every 5 min (1 mL).

Blank tests were also conducted to measure possible adsorption of viruses to tubing or

glass fiber with negative results. Finally, after the virus inflow was ceased, a 1.5% beef

extract and 50 mM glycine solution at a pH of 8 or 9 was used to elute the viruses

previously adsorbed by the iron oxide nanoparticles for testing viability.

Figure 2.8 Flow-through experimental set up [90]

2.2.4 Results and discussion

2.2.4.1 Characterization of iron oxide nanoparticles

According to XRD analysis, the particles were purely iron oxide, with no other

phases present. All of the peaks can be easily indexed to rhombohedral Fe2O3 with lattice

parameters a= 5.035 Å, C=13.747Å (space group: R3C) which are in agreement with the

reported values (JCPDS 86-0550) (Figure 2.9).

Page 48: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

32

20 30 40 50 60 70 80

Inte

ns

ity

(A

.U.)

Two Theta Angle ( Degree)

(012)

(104)

(110)

(113)

(024)

(116)

(018)

(214)

(300)

(1010)

a=5.035

c=13.747

(220)(208) (036)(202)

Figure 2.9 X-ray powder diffraction of iron oxide nanoparticles

The size and morphology of iron oxide nanoparticles were examined by TEM,

HRTEM, and SAED and SEM. TEM micrographs revealed a mean diameter of 10.78

(±0.72) nm (Figure 2.10 (a)). The nanoparticles were spherical with diameters ranging

from 3 to 20 nm. No monodispersion of nanoparticles was observed. Because of the high

surface energy, iron oxide nanoparticles in an aqueous medium tend to form aggregates

ranging on average from 100 to 300 nm in size (Figure 2.10 (b)). The HRTEM image of

a nanoparticle shows clear lattice fringes, without defects or dislocations, thus providing

additional confirmation that these nanoparticles are single crystals (Figure 2.10 (c)). The

clear lattice image indicates the high crystallinity and single crystalline nature of the iron

oxide nanoparticles. A lattice spacing of 0.368 nm corresponding to the (012) planes of

the rhombohedral iron oxide nanoparticle structure was resolved [55]. The SAED pattern

of α-Fe2O3 (Figure 2.10 (d)), which was taken from a single rhombohedron, shows that

the rhombohedra are single crystal. SEM images showed a coating of iron oxide

Page 49: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

33

nanoparticles on the fiberglass substrate. The fiberglass had a rod shape with a diameter

of 5-6 μm. Iron oxide nanoparticles were well attached to fiberglass (Figure 2.11). XPS

was also used to confirm the presence of the iron oxide coated on the fiberglass (Figure

2.12).

Figure 2.10 (a) TEM image of iron oxide nanoparticles; (b) TEM image of iron

oxide nanoparticle aggregate together; (c) HRTEM image of single

iron oxide nanoparticles; (d) SAED pattern of an iron oxide

nanoparticles

a

C d

b

Page 50: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

34

Figure 2.11 SEM image shows iron oxide nanoparticles well attached to fiberglass

1000 800 600 400 200 0

Inte

ns

ity

( A

.U.)

Binding Energy(eV)

O

Fe 2p

O 1s

Fe 3P

Figure 2.12 XPS survey scan of iron oxide nanoparticles coated on fiberglass

The BET surface area of the iron oxide nanoparticles was measured as

80.75 m2 g

−1, whereas the total pore volume (P/P0 = 0.95) was measured as

8.35 × 10−2

cm3 g

−1. The fraction of micropore volume is 34.1% (2.85 × 10

−2 cm

3 g

−1),

Page 51: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

35

while the mesopore volume is 65.9% (5.50 × 10−2

cm3 g

−1) [90]. The iron oxide

nanoparticles coating the fiberglass have small particle size, high surface area, and more

hydroxyl groups than granular particles. The BET surface area of iron oxide-coated sand

is only about 3–4 m2/g, which limits the system efficiency and the empty-bed contact

time [65]. The fiber form substrate provides the larger surface area needed to

significantly enhance the virus adsorption kinetic and capacity, and enables the assembly

filters to have much lower pressure drop compared to other forms of substrates.

Table 2.2 Surface areas and pore volumes of iron oxide coated on fiberglass [90]

Sample

BET surface

area (m2g

-1)

Total pore volume

(P/Po=0.95)

(10-2

cm3g

-1)

Micropore

volume

(10-2

cm3g

-1)

Mesopore

Volume

(10-2

cm3g

-1)

IOCF 46.71 8.35 2.85(34.1%) 5.50 (65.9%)

2.2.4.2 Size of MS2 viruses

Mean hydrodynamic diameters of the MS2 virus in all the solutions were

measured as 30.83 (±0.31) nm. A low polydispersity index of 0.15 for the MS2 virus

suggested a monodispersed population of MS2 viruses for every solution condition.

TEM images revealed mean MS2 diameters of 25.42 (±0.93) nm, which are in

accordance with previously reported data (Figure2.13(a)) [30, 97]. The difference in

diameter between DLS and TEM (~21% for MS2 virus) denotes the variation between

hydrodynamic diameter (hydrated particles) and dry virus diameter.

Page 52: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

36

Figure 2.13 (a) TEM image shows the MS2 virus has a monodiperse diameter

around 26nm; (b) TEM image shows MS2 viruses adsorbed to the

surface of an aggregate of iron oxide nanoparticles. There is no

noticeable decrease in the diameter of viruses and their integrity did

not appear to be compromised [30].

2.2.4.3 Zeta potential of iron oxide nanoparticles and MS2 viruses

2 3 4 5 6 7 8 9 10 11

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

30

35

40

45 MS2 Virus

Iron Oxide Nanoparticles

Ze

ta P

ote

nti

al

(mV

olt

s)

pH of Test Solutions

Figure 2.14 Zeta potential measurements for iron oxide nanoparticles and

MS2 viruses in 1mM NaCl solution with different pHs [30]

The IEP of iron oxide nanoparticles and MS2 viruses were determined as 6.9 and

3.6 respectively, which are consistent with previous studies [30]. Indeed, under the

a b

Page 53: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

37

environmental range of pH selected for this research (6–9), the MS2 virus showed a

highly negative potential, while iron oxide nanoparticles were positively charged until

reaching their IEP (0 mV at pH=6.9) (Figure 2.14).

2.2.4.4 Batch test results for MS2 viruses

Adsorption of MS2 virus by iron oxide nanoparticles under non-competing

conditions

We first measured viral adsorption on iron oxide nanoparticles in a solution

containing 1 mM NaCl as the basis for quantitative comparison of the effect of other ions

and NOM on adsorption. Adsorption capacity is defined as the number of infectious virus

particles (PFU) adsorbed per gram of iron oxide nanoparticles in solution. The 2-log

removal capacity for MS2 virus in a 1 mM NaCl solution was 2.33 × 1011

PFU/g for pH

= 6. The adsorption followed a pseudo-first-order reaction with kinetic rate constants (k)

of 0.035 min−1

(Figure 2.15). In most models, virus inactivation is portrayed simply as a

first-order decrease in the number of infectious viruses in a solution with a rate

coefficient solely dependent on temperature. It is recognized that many other factors,

such as virus type, pH, ionic strength, ion composition, microbial enzymes, virus

aggregation, and attachment to air/water and solid/water interfaces also affect virus

inactivation, but the effects of these factors are not known well enough to include in

models.

Another batch test under the same conditions was conducted, and the solution pH

(starting at pH 9.0) was monitored and continuously adjusted every 30 min to pH 9 using

1 M NaOH. The solution experienced a significant drop of four pH units during the first

30 min, showing that iron oxide acidifies the solution. Although under these conditions

the adsorption capacity still remained high for MS2 (1.79 × 1011

PFU/g), the kinetic rate

Page 54: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

38

decreased to 0.018 min−1

. These results suggest an almost negligible influence of proton

concentration at a pH range from 6 to 9 on the adsorption of MS2 with no competing ions

in the solution. Using classic DLVO calculations, for a 1 mM NaCl solution at pH 6 we

found no energy barrier, and at pH 7 we found an energy barrier of 0.9 kT. Adsorption of

MS2 to iron oxide nanoparticles at pH values below 7 is electrostatically favorable.

Above pH 7 the iron oxide nanoparticles acquired a negative charge, producing a small

energy barrier (up to 16.1 kT at pH 9). However, adsorption of MS2 to iron oxide

nanoparticles at pH 6 and 9 were similar.

0 30 60 90 120 150 180-2.5

-2.0

-1.5

-1.0

-0.5

0.0

Lo

g (

C/C

o)

Time (minutes)

1mM NaCl pH 6.0

1mM NaCl pH 6.9

1 mM NaCl pH 8.36

Figure 2.15 MS2 virus removal kinetics by iron oxide nanoparticles coated on

fiberglass in 1 mM NaCl at different pHs

These outcomes indicated that MS2 viruses adsorbed to iron oxide nanoparticles,

confirming the adsorption property of iron oxides [56, 68]. Due to their relatively high

surface area and IEP, iron oxide nanoparticles have shown fast kinetic rates and a high

Page 55: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

39

adsorption capacity for MS2 under non-competing conditions. Nevertheless, in natural

water systems many competitors for adsorption sites are found.

Effect of bicarbonate ions on adsorption of MS2 to iron oxide nanoparticles

We used 1 mM NaHCO3 to simulate typical groundwater found in North

America. When the background ion solution was 1 mM bicarbonate at pH 8.2, no

removal of MS2 virus was observed until the loading concentration of iron oxide

nanoparticles was increased 10 times to 0.43 g/L. The adsorption capacity decreased to

2.7 × 1010

PFU/g, and the kinetic was 0.0416 min−1

(Figure 2.16). Higher iron oxide

nanoparticle loading in the solution has a relatively higher adsorption surface area,

allowing more available sites for adsorption in comparison to granular media. According

to our results, 0.32 g/L of iron oxide nanoparticles reduced the pH of a 1 mM NaHCO3

solution from 8.2 to 7.6, which corresponds to a decrease in [HCO3-] of 0.9 mM. This

ratio is of particular importance for calculating the performance of iron oxide

nanoparticles in real systems. Iron oxide nanoparticles would be suitable for treated

water already equilibrated with the atmosphere and close to neutral pH. Therefore, the

removal of viruses decreased because many adsorption sites were occupied by the

adsorbed bicarbonate ions. Our results suggest a great affinity of iron oxide nanoparticles

for even low bicarbonate ions concentrations, implying that the attachment sites were

reached more efficiently by bicarbonate ions than by viruses. Therefore, the adsorption

capacity of iron oxide nanoparticles was consequently decreased by slightly more than

one order of magnitude.

Page 56: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

40

0 30 60 90 120 150 180

-7

-6

-5

-4

-3

-2

-1

0

0.32g/L Iron Oxide

0.43g/L Iron Oxide

Lo

g (

C/C

o)

Time (minutes)

Figure 2.16 MS2 virus removal kinetics and adsorption onto iron oxide

nanoparticles coated on fiberglass in 1 mM NaHCO3 solution

Competition by NOM with MS2 viruses for adsorption onto iron oxide

nanoparticles

To test for competition from NOM, a 1 mg/L TOC solution was prepared and

tested under the different concentrations of iron oxide until virus removal was detected.

Until the iron oxide concentration was further increased to 0.65 g/L, MS2 removal was

detected at a kinetic rate and adsorption capacity of 0.008 min−1

and 1.4 × 1010

PFU/g,

respectively (Figure 2.17). This result was one order of magnitude below non-competing

conditions and close to bicarbonate batch test values (Figure 2.16).

A second experiment was conducted in which the concentration of TOC was

decreased to 0.1 mg/L and the concentration of iron oxide nanoparticles was fixed at

0.043 g/L. No removal of viruses was detected at this low concentration of NOM. Note

that the zeta potential values for MS2 virus in the presence of 0.1 or 1 mg/L TOC were

Page 57: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

41

almost the same as in the absence of it (1 mM NaCl), suggesting a negligible influence of

NOM on the charge of viruses under these concentration conditions.

0 20 40 60 80 100 120 140 160 180

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.43 g/L

0.65 g/L

Lo

g (

C/C

o)

Time (minutes)

Figure 2.17 MS2 virus removal kinetics and adsorption onto iron oxide

nanoparticles coated on fiberglass in 1 mg/L TOC NOM solution

Under the range of concentrations tested in this set of experiments, NOM proved

to be an efficient competitor against MS2 viruses for available binding sites. The

diffusivity of SRNOM measured in this study (106.52 ± 3.32 μm2 s−1

) was higher than

the diffusivity for the MS2 virus. This high value of SRNOM diffusivity could allow

NOM to outcompete viruses for adsorption sites. As a result, the addition of NOM

provoked a dramatic drop of slightly more than one order of magnitude in the adsorption

capacity of iron oxide for both viruses. Nevertheless, the addition of more mass of iron

oxide was necessary to compensate for the competition effect for attachment sites for

MS2 viruses. However, iron oxide nanoparticles have the advantage of offering a more

Page 58: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

42

specific surface and, consequently, more available adsorption sites per gram than iron

oxide as granular media. In comparison to bicarbonate conditions, NOM solutions did

not experience change of pH at the end of the experiment, but did experience change in

the charge of iron oxide nanoparticles. According to our results, 1 mg/L TOC would be

sufficient to cover the adsorption sites of 0.43 g/L iron oxide nanoparticles and not allow

adsorption of MS2 viruses (Figure 2.17). Although this ratio might be high, the NOM

adsorbed to iron oxide nanoparticles is the charged fraction of the total population of

NOM. In drinking water treatment, most of the charged organic matter is coagulated and

flocculated in the first treatment steps, while uncharged species are absorbed to activated

carbon. Iron oxide nanoparticles would thus be a feasible option for a portable device for

virus removal for pretreated water.

Role of divalent cations in the adsorption of viruses to iron oxide nanoparticles

Divalent cations have been shown to enhance adsorption of MS2 viruses to silica

surface coated with NOM [53]. We conducted batch experiments to test whether divalent

cations allow improved performance of the studied glass fibers coated with iron oxide

nanoparticles. For MS2 viruses no enhanced adsorption was detected (Figure 2.18).

2.2.4.5 Flow-through test results for MS2 viruses

Adsorption of MS2 viruses to iron oxide nanoparticles under non-competing

conditions in solution

For a 1 mM NaCl solution, adjusted to pH 8 and a cartridge containing 0.060 g

iron oxide nanoparticles, breakthrough was observed for a minimum of 4-log removals

for MS2 viruses. The adsorption capacity for this condition was 1.7 × 1011

PFU/g. When

pH was kept at 6, the adsorption capacity dropped to 4.6 × 1010

PFU/g. These values

Page 59: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

43

0 20 40 60 80 100 120 140 160 180

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.1mM CaCl2

0.1mM MgCl2

0.1mMNaCl

Lo

g (

C/C

o)

Time (minutes)

Figure 2.18 Influence of Ca2+

or Mg2+

and NOM on the adsorption of MS2 viruses to

iron oxide nanoparticles

0 50 100 150 200 250 300

-9

-8

-7

-6

-5

-4

-3

-2

Lo

g(C

/Co

)

Bed Volume

Figure 2.19 Adsorption of MS2 viruses by iron oxide nanoparticles in DI water,

pH=6

Page 60: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

44

were similar to batch conditions at the same pH. For a cartridge containing 0.060 mg iron

oxide nanoparticles, no breakthrough was observed after 145 bed volumes.

The mass of iron oxide nanoparticles in the cartridge for both experiments with

AGW and NGW was 0.520 g. The adsorption capacity achieved until breakthrough was

1.1 × 109 PFU/mL and 8 × 10

8 PFU/mL for AGW and NGW, respectively (Figure 2.20).

These results are roughly more than 2 orders of magnitude below the adsorption capacity

of iron oxide under non-competing conditions. The high concentration of NOM and

other ions present in NGW or the bicarbonate and NOM content of AGW are responsible

for the reduced adsorption of MS2. These results suggest that this cartridge can be used

as a point-of-use device to remove viruses from water with similar characteristics to

groundwater.

0 10 20 30 40 50

-7.0

-6.5

-6.0

-5.5

-5.0

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0 Artificial Groundwater

Newmark Groundwater

Lo

g (

C/C

o)

Bed Volumes

Figure 2.20 Adsorption of MS2 viruses by iron oxide nanoparticles in artificial and

aquifer groundwater. Artificial groundwater presented fewer

competitors than Newmark groundwater for virus adsorption on

available adsorption sites.

Page 61: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

45

Desorption of MS2 viruses

Detachment of infectious MS2 viruses was also investigated using the same

reagents and conditions as in batch tests. Initially, a 2.0 × 106 PFU/mL solution was

injected into a column containing 0.130 g of iron oxide nanoparticles. The flow of viral

solution was stopped once 1 × 109 PFU had been injected into the column (500 mL) and,

consequently, no PFU were detected in the effluent. The viral solution was switched to a

beef extract–glycine solution and samples of the effluent were taken. High recoveries

ranging from 44.02% to 45.81% of infectious viruses were achieved (Figure 2.21),

suggesting that a considerable fraction of MS2 were able to remain infective during the

adsorption/desorption process. TEM micrographs of samples taken after the adsorption

period reveal intact MS2 virus adsorbed to the surface of iron oxides nanoparticle

aggregates (Figure 2.39(b)). These results suggest that MS2 virus adsorption to iron

oxide nanoparticles did not lead to inactivation of a significant portion of MS2 viruses.

0 30 60 90 120 150 180 210 240 270 300

-7

-6

-5

-4

-3

-2

-1

0

1 1 mM NaCl + 2x10^6 pfu/ml MS2

1 mM NaCl

1.5% Beef Extract + 50 mM Glycene - pH 8

Lo

g (

C/C

o)

Time (minutes)

Figure 2.21 Recovery of infectious MS2 viruses uses a solution of 1.5% beef extract

in 50 mM glycine at pH 8

Page 62: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

46

2.2.5 Summary

We successfully designed and analytically evaluated approach for coating iron

oxide nanoparticles on fiberglass. X-ray diffraction analysis showed that the particles

were hematite with no other phases present. TEM indicated that the nanoparticles are

spherical and their diameter was between 3-20 nm. MS2 viruses adsorbed to iron oxide

nanoparticles, confirming the adsorption property of iron oxides [56, 68]. Due to their

relatively high surface area and IEP, iron oxide nanoparticles showed fast kinetic rates

and a high adsorption capacity for MS2 under non-competing conditions. Iron oxide

nanoparticles showed high affinity for bicarbonate ions and NOM in solution.

Adsorption capacity of iron oxide nanoparticles was reduced down to 2-log units when

NOM and bicarbonate ions were present in the solution in comparison to non-competing

conditions. Because iron oxide nanoparticles have a high surface area, these particles

allow virus adsorption even in the presence of bicarbonate and NOM in natural water.

Adsorption on iron oxide nanoparticles by MS2 viruses was also tested with aquifer

groundwater under saturated flow conditions to mimic environmental conditions with

promising results of removal up to 8 × 108 PFU/g. Desorption of up to 63% of infectious

MS2 from iron oxide nanoparticles were achieved when an eluant solution containing

beef extract and glycine was used. TEM images showed evidence of electrostatic

adsorption of apparently intact MS2 viruses to iron oxide nanoparticles. Results from

this research suggest that a cartridge made of fiberglass coated with iron oxide

nanoparticles would be good but not ideal candidates to be used as a point-of-use device

for virus removal for drinking water treatment.

Page 63: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

47

2.3 Iron oxide nanoparticle coated on fiberglass to remove rotaviruses from water

2.3.1 Introduction

Rotavirus is an icosahedral non-enveloped double stranded RNA virus, measuring

approximately 75 nm in diameter [30, 97]. It is a genus of the Reoviridae family,

composed of a core, an inner layer and an outer layer [77]. When intact as a triple-

layered particle, the glycoproteins that structure the outer capsids are VP7 and VP4

(spiked protein) [98]. The last has been suggested to play a significant role in the

attachment of Rotavirus to host cells. Rotavirus is the most common enteric virus that

causes severe diarrhea, vomiting and acute dehydration among children. Approximately

600,000 children die worldwide every year because of intestinal complications due to

rotavirus infection [99]. Although efficient vaccines against rotaviruses have already

been developed, their high cost makes them inaccessible for certain markets, such as

Latin America, Asia and Africa [100,101]. Nevertheless, it is in developing countries

where rotavirus has a higher probability of infecting the general population because of

lack of access to sanitary water. However, although bacteriophages have long been used

as indicators of water pollution, similar behavior in ecological terms does not necessarily

indicate similarities with respect to survival on or decontamination of fresh produce. A

porcine rotavirus strain OSU was used to investigate the ability of fiberglass coated with

iron oxide nanoparticles for virus removal [30].

2.3.2 Materials and methods

Preparations of iron oxide nanoparticles coated on fiber glass and test solution

with different chemical concentrations followed the same protocol as the MS2 virus

experiments.

Page 64: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

48

Rotavirus preparation and focus forming unit (FFU) assay

Group A porcine rotavirus OSU strain was obtained from the American Type

Culture Collection. Rotavirus was propagated in embryonic African green monkey

kidney cells (MA-104 cells) and was extracted from culture as described. In lieu of

gradient centrifugation, rotavirus was purified following the same protocol as MS2

viruses, except the nanofiltration step, in which a 0.05-mm membrane was used. To

prevent the dissociation of the outercapsid proteins, rotavirus was processed and stored in

1 mM NaCl plus 0.1 mMCaCl2 during the 100 kDa ultrafiltration. The final rotavirus

stock was stored at 4oC at a concentration of >106 FFU mL

-1. This purification procedure

does not discriminate triple layer particles from double layer particles. Rotavirus

infectivity assays, or focus forming unit tests (FFU), were carried out following the

procedures described.

Measurement of EPM for rotaviruses

Solutions were mixed with MS2 viruses or iron oxide nanoparticles to the final

concentration of ~104 FFU/mL. These concentrations ensured an optimal signal for

electrophoresis measurements. EPM was determined using a ZS90 Zetasizer instrument

(Malvern, UK) and 1-mL clear disposable zeta cells (DTS1060C, Malvern). A minimum

of 3 measurements was conducted for every solution condition.

Determination of hydrodynamic diameter of rotaviruses by DLS

Hydrodynamic diameter of rotavirus was determined using a ZS90 Zetasizer

instrument (Malvern, UK) for each solution tested in this study. Rotavirus was added to

the solutions until a final concentration was reached of ~104 FFU/mL. These

concentrations allowed the use of an attenuation of 10 and a polydispersity index (PDI)

Page 65: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

49

close to 0.2. Attenuation index denotes the percentage of laser light that enters the sample

cuvette. For an index of 10, only 30% of the nominal laser power is used. Polydispersity

index is a width parameter of the cumulant analysis of size. A minimum of three

measurements per sample was recorded and a total of three samples were processed.

TEM

Rotavirus samples with iron oxide nanoparticles were investigated using TEM

technique by conventional negative staining. Pellets of rotavirus solution were obtained

by centrifugation at 24,000 rpm for one hour. To preserve rotavirus structural details, a

few drops of Karnovsky‘s fixative were added to the top of the pellet and allowed to set

for 20 min. Rotaviruses and iron oxide nanoparticle suspensions were applied to holey-

carbon-coated, 300-mesh, copper grids. Ural acetate was used as stains for rotaviruses.

All the samples were examined using a Cryo TEM (JEM-2100, JEOL, Tokyo, Japan) at

200 kV accelerated voltage.

Batch experiments

Batch tests were prepared using 50 mL Pyrex bottles for rotaviruses. These glass

containers were cleaned using detergent and DI water and thereafter rinsed with

Nanopure water, dried in an oven, and autoclaved. The bottles were filled with viral

solution and varied masses of fiberglass coated with iron oxide nanoparticles. Air bubbles

were avoided by filling the container to the top with viral solution and then covering it

with parafilm. The initial concentration of the solution was ~ 104 FFU/mL. The bottles

were shaken at 200 rpm in a horizontal shaker and 0.25mL samples were taken every

15min for 90min. Rotavirus solutions were removed for kinetics experiments with

rotaviruses. The same volume of buffer solution was added back to the bottles after

Page 66: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

50

removing solution. Control experiments, performed for rotaviruses using fiberglass

substrate with no coating of iron oxide nanoparticles, showed no removal of viruses at

22°C during the 90 min of testing. First-order kinetic rate constants (k) for virus removal

were estimated by fitting the virus concentrations measured throughout the experiment.

Reversibility of virus adsorption was studied by eluting with beef extract and

glycine as previously reported. Batch reactors were prepared following the protocol

described in this section. However only for these experiments iron oxide nanoparticles

without the fiberglass, as colloidal nanodispersed particles, were added to the solution

containing either ~ 104 FFU/mL. After the adsorption experiments, beef extract and

glycine were added directly to the batch reactor at concentrations ranging from 1.5%

(weight/volume) and 50 mM, while raising the pH to 8 and 9. In addition, iron oxide

nanoparticle samples after adsorption and desorption of viruses were taken for TEM

analysis.

Flow-through experiments

Flow-through experiments were conducted to test the adsorption capacity of

fiberglass coated with iron oxide nanoparticles under saturated flow conditions and

selected solution chemistries. We refer to the experiments in which virus containing

solution was pumped continuously through the cartridge as flow-through experiments.

For every test, 200 mL of ~ 105FF U/mL rotavirus suspensions were used. The viral

solution was pumped using a peristaltic pump at a flow rate of 3−4mL / min through the

flow-through to ensure a saturated flow at 22°C. Samples from the outflow were

collected every 5 min (1 mL). Blank tests were also conducted to measure possible

adsorption of viruses to tubing or glass fiber with negative results. Finally, after the virus

Page 67: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

51

inflow was terminated, a 1.5% beef extract and 50 mM glycine solution at a pH of 8 or 9

was used to elute the viruses previously adsorbed by the iron oxide nanoparticles for

testing viability.

2.3.3 Results and discussion

2.3.3.1 Size of rotaviruses

Mean hydrodynamic diameter of rotaviruses was measured as 127.15 (± 1.05) nm. Low

polydispersity index of 0.21 for rotavirus suggested monodispersed population of

rotavirus for every solution condition. TEM images revealed mean rotavirus diameters of

74.57 (± 1.32) nm, which are in accordance with previously reported data. The

difference in diameter between DLS and TEM denotes the variation between

hydrodynamic diameter (hydrated particles) and dry virus diameter [30].

Figure 2.22 (a) TEM image shows rotavirus is monodiperse at diameter around 75

nm (b) TEM image shows rotavirus with compromised structure after

coming into contact with iron oxide nanoparticles in solution [30]

b a

Page 68: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

52

2.3.3.2 Diffusion coefficient of rotavirus

Diffusion coefficient of SRNOM was averaged as 106.52 (± 3.32) um2s

-1, which

was assumed as a single macromolecule in solution. This value is comparable to

previously reported diffusivities for SRNOM fractions. The diffusivity of SRNOM was

particularly important in explaining the competition mechanism in the laminar film

between organic matters with rotaviruses for binding sites on iron oxide nanoparticles.

Because of the nearly-spherical icosahedral shape, the Stokes-Einstein relation was used

to convert the hydrodynamic diameters of rotavirus to diffusion coefficients. Diffusivity

for rotavirus was calculated as 3.37 μm2s

-1.

2.3.3.3 Zeta potential of rotavirus

3 4 5 6 7 8 9 10

-3

-2

-1

0

1

2

3

Ze

ta P

ote

nti

al

(mV

)

pH of Test Solutions

Figure 2.23 Zeta potential measurement for rotaviruses in 1mM NaCl solution with

different pHs [30]

IEP of rotavirus was estimated at 4.6 (Figure 2.23) [30]. Indeed, under the

environmental range of pH selected for this research (6 to 9), rotaviruses showed a highly

Page 69: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

53

0 15 30 45 60 75 90-6

-4

-2

0

Lo

g(C

/Co

)

Time (minutes)

0.26g/L Iron Oxide

1.95 g/L Iron Oxide

negative potential, while iron oxide nanoparticles were positively charged until reaching

their IEP (0 mV at pH 6.9).

2.3.3.4 Batch test results for rotavirus

Adsorption of rotavirus to iron oxide nanoparticles under non-competing conditions

in solution

Figure 2.24 Rotavirus removal kinetics and adsorption onto iron oxide

nanoparticles in 1mM NaCl solution

We first measured viral adsorption on iron oxide nanoparticles in solution

containing 1mM NaCl at pH = 6. Adsorption capacity is defined as the amount of

infectious virus particles (FFU) adsorbed per gram of iron oxide nanoparticles coated on

fiberglass. When the concentration of iron oxide nanoparticles in solution for the

rotavirus experiment was 0.26 g/L, the kinetics rate constant was 0.040 min-1

. When the

concentration of iron oxide nanoparticles in solution increase 7.5 times to 1.95 g/L, the

kinetics rate constant increased to 0.357 min-1

with a total removal of viruses (5 logs) and

Page 70: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

54

0 30 60 90-4

-2

0

Lo

g(C

/Co

)

Time (minutes)

2.0 g/L Iron Oxide

3.9 g/L Iron Oxide

an adsorption capacity of 8.9 × 106 FFU/g from solution within the first 45 min (Figure

2.24).

These outcomes indicated that iron oxide nanoparticles showed fast kinetic rates

and a high adsorption capacity for rotavirus under non-competing conditions, due to their

relatively high surface area and IEP. Nevertheless, in natural water systems many

competitors for adsorption sites are found.

Effect of bicarbonate ions on adsorption of rotavirus to iron oxide nanoparticles

For rotavirus removal by 2.0g/L iron oxide nanoparticles, the adsorption capacity

was reduced to 8.3 × 105 FFU/g and all adsorption sites were depleted, reaching only a

0.6 4-log removal of rotaviruses. When the concentration of iron oxide increased to 3.9

g/L, 5-log removal of rotavirus was observed after 90 min at a kinetic rate constant of

0.122 min-1

and an adsorption capacity of 7.5 × 105 FFU/g (Figure 2.25).

Figure 2.25 Rotavirus removal kinetics and adsorption onto iron oxide

nanoparticles in 1mM NaHCO3 solution

Page 71: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

55

Competition by NOM with rotavirus for adsorption onto iron oxide nanoparticles

For rotaviruses, the iron oxide nanoparticle concentration was increased to 3.9 g/L

to obtain an adsorption capacity of 1.2 × 105 FFU/g and a rate constant of 0.032 min

-1.

This result was one order of magnitude below non-competing conditions and close to

bicarbonate batch test values (Figure 2.26).

A second experiment was conducted in which the concentration of TOC was

decreased to 0.1 mg/L and the concentration of iron oxide nanoparticles was fixed at

0.260 g/L for rotavirus. No removal was detected at this low concentration of NOM.

Note that zeta potential values for rotavirus in the presence of 0.1 or 1 mg/L TOC were

almost the same as in the absence of it (1 mM NaCl), suggesting a negligible influence of

NOM on the charge of rotavirus under these concentration conditions.

0 15 30 45 60 75 90

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.3g/L Iron Oxide

2.0g/L Iron Oxide

Lo

g (

C/C

o)

Time (minutes)

Figure 2.26 Rotavirus removal kinetics and adsorption onto iron oxide

nanoparticles in 1mg/L TOC of NOM solutions

Page 72: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

56

Under the range of concentrations tested in this set of experiments, NOM proved

to be an efficient competitor against rotaviruses for available binding sites. The

diffusivity of SRNOM measured in this study (106.52 ± 3.32 μm2s

-1) was higher than the

diffusivity for rotavirus 3.37 μm2s

-1. The high value of SRNOM diffusivity could allow

NOM to outcompete viruses for adsorption sites. As a result, the addition of NOM

provoked a dramatic drop of slightly more than one order of magnitude in the adsorption

capacity of iron oxide for rotaviruses. Nevertheless, the addition of more iron oxide was

necessary to compensate for the competition effect of attachment sites for rotaviruses.

Adsorption of rotavirus in the presence of AGW

Once competition between bicarbonate ions and organic carbon and rotavirus was

confirmed, batch tests using AGW and NGW were conducted. AGW was also used as a

background for rotavirus. When 2.0 g/L of iron oxide nanoparticles were added, the

adsorption sites were depleted after 30 minutes and, as expected, the adsorption capacity

was decreased close to 2 orders of magnitude (5.4 × 104 FFU/g) in comparison to non-

competing conditions (Figure 2.27). A 0.66-log removal was achieved under this

condition. When the concentration of iron oxide was increased to 3.9 g/L, the adsorption

capacity increased to 2.1 × 105 FFU/g with 1.83-log removed. The adsorption capacity of

iron oxide nanoparticles experienced a drop of slightly 2 orders of magnitude in

groundwater, reflecting the possible presence of more competitors in solution for binding

sites than the previous conditions tested.

Page 73: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

57

0 30 60 90

-1

0

0.3g/L Iron Oxide

1.2g/L Iron Oxide

2.0g/L Iron Oxide

Lo

g(C

/Co

)

Time (minutes)

Figure 2.27 Rotavirus removal kinetics and adsorption onto iron oxide

nanoparticles in AGW solutions

Role of divalent cations in the adsorption of rotaviruses to iron oxide nanoparticles

Tests were conducted with 0.645 g/L of iron oxide nanoparticles filters, 106

FFU/mL rotavirus, 1 mg/L TOC of NOM, and 0.1 mM of NaCl, CaCl2, or MgCl2

solutions. In an experiment that used 1 mM NaCl as a background ion, no removal of

rotavirus was detected, since the NOM exhausted all the binding sites of iron oxide.

Therefore, we added 1 mM CaCl2 to the viral solution to investigate a possible binding of

MS2 to the NOM already adsorbed to the iron oxide layer by means of Ca2+

bridging.

However, after 90 minutes, no removal was detected. The same experiment was

conducted using 1 mM MgCl2 with negative adsorption results (Figure 2.28). A second

set of analogous experiments was conducted in which the mass of iron oxide

nanoparticles was increased to 3.9 g/L. Therefore, divalent cations were added to explore

a possible adsorption enhancement in comparison to the previous experiment.

Page 74: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

58

Nonetheless, the presence of Ca2+

or Mg2+

did not increase the removal of rotaviruses

(Figure 2.28).

0 60 120 180-3

-2

-1

0

0.1 mM CaCl2

0.1 mM MgCl2

0.1 mM NaCl

Lo

g(C

/Co

)

Time (minutes)

c

Figure 2.28 Rotavirus removal kinetics and adsorption onto iron oxide

nanoparticles in divalent cation solutions

Desorption of rotavirus

Rotavirus recoveries ranged from 0.5% to 2.1% and showed no dependence on

beef extract, glycine concentration, or pH level. These results suggest that rotavirus

irreversibly adsorbed or became inactivated during the attachment process to iron oxide

nanoparticles. Consequently, their outermost proteins, responsible for virulence, could

have been affected by the electrostatic forces of attraction or disintegration of the viral

particles. TEM micrographs showed rotaviruses with structural damage when iron oxide

nanoparticles were present in solution (Figure 2.22(b)). No rotavirus visibly adsorbed to

the surface of the iron oxide nanoparticles aggregates, suggesting that after the

electrostatic forces compromised the integrity of rotavirus, the viral particles broke apart

Page 75: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

59

and were released into solution. The observations that MS2 viruses and rotavirus

exhibited different behavior to the electrostatic forces of iron oxide nanoparticles suggest

that the inactivation of a given viral particle might depend on the proteins of its capsids or

the robustness of its structure.

2.3.3.5 Flow-through test results for rotavirus

Adsorption of rotavirus to iron oxide nanoparticles under non-competing conditions

in solution

For a 1 mM NaCl solution, adjusted to pH 8, with a cartridge containing 0.060 g

iron oxide nanoparticles, breakthrough was observed for a minimum of 4-log removal

conducted for rotavirus. For a cartridge containing 0.060 mg iron oxide nanoparticles, no

breakthrough was observed after 45 bed volumes. The adsorption capacity of 5 × 107

FFU/g for flow-through conditions is one order of magnitude higher than a batch test at

the same conditions, suggesting that flow-through is more efficient in rotavirus removal.

Adsorption of rotavirus in the presence of AGW and NGW

The mass of iron oxide nanoparticles in the cartridge for both experiments with

AGW and NGW was 0.520 g. The adsorption capacity until 4-log removal for rotavirus

reached 3 × 104 FFU/g for NGW and 9 × 10

4 FFU/g for AGW (Figure 2.29). These

results suggest that this cartridge can be used as a point-of-use device to remove viruses

from water with similar characteristics to groundwater.

Page 76: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

60

Figure 2.29 Adsorption of rotaviruses by iron oxide nanoparticles in artificial and

aquifer groundwater.

0 30 60 90 120

-6

-4

-2

0

2

10^5FFU/ml Rotavirus

3% Beef Extrat+100Mmol glycine PH8

Lo

g (

C/C

o)

Time (minutes)

Figure 2.30 Recovery of infectious rotaviruses uses a solution of 1.5% beef extract in

50 mM glycine at pH 8

Page 77: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

61

Desorption of rotavirus

Detachment of viable rotavirus was also investigated using the same reagents and

conditions as in batch tests. Desorption of rotavirus did not release a high fraction of

infectious viral particles. The highest recovery was in the order of 1.53% of viable

rotavirus (Figure 2.30). This result is also in accordance to batch tests.

2.3.4 Summary

These outcomes indicated that iron oxide nanoparticles showed fast kinetic rates

and a high adsorption capacity for rotavirus under non-competing conditions, due to their

relatively high surface area and IEP. Iron oxide nanoparticles showed high affinity for

bicarbonate ions and NOM in solution. Only a small fraction of infectious rotavirus was

successfully eluted in comparison to MS2 virus, possibly due to structural damage to the

capsid of rotaviruses when interacting with iron oxide. TEM micrographs also suggested

that after the electrostatic forces compromised the integrity of rotavirus, the viral particles

broke apart and were released into solution. The observations that MS2 viruses and

rotavirus exhibited different behavior to the electrostatic forces of iron oxide

nanoparticles suggest that the inactivation of a given viral particle might depend on the

proteins of its capsids or the robustness of its structure.

2.4 Silver-iron oxide nanoparticles coated on fiberglass to remove bacteria and

viruses from water

2.4.1 Introduction

Materials and methods

Iron oxide has been tested against water borne agents such as viruses, arsenic and

lead [30, 90]. Charges on iron oxide surfaces in aqueous solutions result from the

dissociation of surface hydroxyl groups, which can effectively remove viruses from water

Page 78: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

62

by electrostatic interactions and forming surface complexes [24]. Though iron oxide

nanoparticle coated fiberglass has shown strong antiviral potential, it has exhibited poor

antibacterial performance [30].

Silver is known for its bactericidal properties and has been used widely in water

to eliminate microorganisms [48, 50, 62]. Silver nanoparticles, with a large surface area

available for interaction, would give more bactericidal effect than the bulk contents.

Silver nanoparticles may attach to the surface of the cell membrane, disturbing

permeability and respiration functions of the cell [48]. It is also possible that silver

nanoparticles not only interact with the surface of cell membrane, but can also penetrate

the inside of the bacteria [50]. However, silver has shown poor viricidal performance.

In this study, we designed silver-iron oxide nanoparticles coated on fiberglass that

exhibited excellent bactericidal and viricidal properties. The aqueous hydrothermal

methods were applied to synthesize silver-iron oxide nanoparticles coated on fiberglass.

This hybrid system showed synergetic effects, while requiring less of each constituent

material for effectiveness. Both bactericidal performances evaluated against Escherichia

coli and viricidal performances against MS2 virus were carried out.

2.4.2 Materials and methods

Synthesis of silver nanoparticles coated on fiberglass

Silver nanoparticle coated fiberglass was prepared by the aqueous hydrothermal

method (2; 23). In a typical procedure, a nonwoven glass fiber mat with 7 wt% PVA

binder (Crane glass 230 from Crane & Co. Inc.) was dipped into an aqueous solution of

0.25M AgNO3 at room temperature in a 120 mL glass bottle covered in aluminum foil

and agitated at 150 rpm with a Tekmar VXR shaker (Janke & Kunkel, Staufen, Germany)

Page 79: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

63

for 12 h. The higher immersion temperature was selected to solicit greater reduction of

Ag+

in solution while the aluminum foil aided in metering the photon initiated reduction

of Ag+ to Ag

0. The treated fibers were then rinsed with DI water, and under N2

protection heated at 120oC for 1 h, and then the temperature was increased from 15

oC

min-1

to 300oC and held at 300

oC for 0.5 h. The final load of silver nanoparticles on the

glass fiber was 1.4% in mass.

Synthesis of silver-iron oxide nanoparticles coated on fiberglass

Iron oxide nanoparticles coated on fiberglass were prepared by aqueous

hydrothermal method. In a typical procedure, a nonwoven fiberglass mat with 7 wt%

PVA binder was dipped into an aqueous solution of FeCl3 (0.05 mol in 100 ml H2O) for

3min. After drying at 90oC for 5 min, it was immersed into an aqueous solution of

NH4OH (15%). It was then heated at 90oC for 10 min. This process was repeated two

more times. The resulting iron hydroxide was dried at 190oC for 4 h. After this, it was

washed several times with distilled water until the water became clean [90]. The load of

iron oxide nanoparticles on the fiberglass was 25% in mass [30].

Ag nanoparticles were incorporated onto the iron oxide coated fiberglass by

following the procedure described above for incorporating silver nanoparticles on the

iron oxide nanoparticles coated fiberglass. The final load of silver and iron oxide on

fiberglass was 0.1% and 9.1% in mass, respectively.

SEM

The morphology of the silver-iron oxide nanoparticles coated on fiberglass was

examined with a Hitachi S-4700 high resolution SEM.

WAXD

Page 80: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

64

WAXD experiments were carried out on a Rigaku D/Max-b diffractometer with a

copper X-ray source controlled by MDI's Data Scan (λ= 1.54178 Å). Silver-iron oxide

nanoparticle powders were evenly distributed on a piece of double-sided tape on a glass

slide. The parameters used were 45 kV and 20 mA, the scanning angle range (2θ) was

20°−80°, and the scanning rate was 0.6°/min, with a step increment of 0.05.

XPS

XPS data were obtained from silver-iron oxide nanoparticles coated on fiberglass

using a Physical Electronics PHI Model 5400 surface analysis system. Before analysis

all samples were washed with D.I. water and then fully dried. XPS spectra were obtained

using an achromatic Mg K (1253.6 eV) x-ray source operated at 300 W. Survey scans

were collected from 0 - 1100 eV with a pass energy equal to 178.95eV. The pressure

inside the vacuum system was maintained at approximately 10-9

Torr during all XPS

experiments. A non-linear least squares curve fitting program (XPSPEAK4.1 software)

with a symmetric Gaussian-Lorentzian sum function and Shirley background subtraction

was used to deconvolve the XPS peaks. The carbon 1s electron binding energy

corresponding to graphitic carbon was referenced at 284.5 eV for calibration.

Preparation of E.coli for bactericide experiments

The bacterial strain used in this work was E. coli (ATCC25404). The cells were

cultured at 37±0.1oC in Luria Bertani (LB) nutrient broth (10 g/L Bactotryptone, 5 g/L

yeast extract, 10 g/L NaCl, 0.2% glucose, pH 7.0). Cell densities were estimated by

measuring the optical density at 600 nm. Bacterial solutions consisting of 20 ppm CaCl2

solution and approximately 106

colony forming units (CFU)/mL of E. coli were used in

the static immersion and dynamic experiments. They were plated and grown on an R2A

Page 81: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

65

agar plate. R2A agar is composed of 0.5 g yeast extract, 0.5 g Difco Proteose Peptone no.

3 (Difco Laboratories, Detroit, MI), 0.5 g Casamino Acids (Difco), 0.5 g glucose, 0.5 g

soluble starch, 0.3 g K2HPO4, 0.05 g MgSO4 7H20, 0.3 g sodium pyruvate, and 15 g of

agar per liter of laboratory quality water and adjust to pH 7.2 with KH2PO4 and sterilized

at 121°C for 15 min [16]. Reasoner & Geldreich indicated that injured but still viable

bacteria displayed good recovery when plated on R2A agar for E. coli enumeration [16].

Bactericidal experiments

The bactericidal effect of the nanoparticles coated fiberglass systems was

determined against E.coli in an aerated environment. The antimicrobial materials were

added to bacterial suspensions which consisted of 50 mL of 106 CFU/mL E. coli in sterile

50 mL centrifuge tubes. The material silver for each run was approximately 0.05 mg/mL.

The test tubes were periodically agitated through the immersion test. A sample of

bacterial suspension was removed at each time interval (1, 5 and 15 min) and diluted 2:5

and 2:50. Each dilution was plated on LB agar and incubated for 24 h at 37± 0.1oC. The

viability of the bacteria was then determined by plate count of the colony forming units.

Preparation of E. coli for further inoculation MS2 viruses

200 mL of tryptic soy broth solution was prepared with 200 ml DI water and 6 g

Tryptic Soy Broth powder in a 1000 mL bottle to ensure that the solution had enough

surface area in contact with the air. A stopper was used as a cap for a more efficient

aeration of the solution. After autoclaving, the solution was kept in the incubator at 37oC

and until the temperature decreased to 37oC. A 2 mL sample of the solution was taken

for absorbance analysis. This sample was monitored at wavelength 420 nm. A 5 ml of E.

Coli (ATCC 15597) stock was added to the broth and incubation began at 37oC and a

Page 82: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

66

shake speed at 200 rpm. Absorbance was monitored every 30 min at wavelength 420 nm

for the next 3 to 3 ½ hours, approximately until absorbance ranged between 0.8 and 1.

Viricidal experiments

Batch tests were prepared using 300-mL Pyrex bottles for MS2 viruses. These

glass containers were cleaned using detergent and DI water and thereafter rinsed with

Nanopure water, dried in an oven, and autoclaved. The bottles were filled with viral

solution and air bubbles were avoided by filling the container to the top with viral

solution and then covering it with Parafilm. The initial concentration of the solution was

around107 PFU/mL of MS2 viruses. The viral solution was adjusted to pH 6 and 1mM

NaCl. The bottles were shaken at 200 rpm in a horizontal shaker and samples were taken

every 30 min for 3 h for MS2 virus. For kinetics experiments, 1 mL of the MS2 solution

was removed and the same volume of buffer solution was added back to the bottles after

removing the MS2 solution.

2.4.3 Results and discussion

Characterization of silver-iron oxide nanoparticles coated on fiberglass

Silver-iron oxide nanoparticles were successfully incorporated onto fiberglass as

low resolution XPS was used to confirm the presence of both silver and iron oxide on the

fiberglass. SEM images showed silver- iron oxide nanoparticles were well attached to

fiberglass with a narrow size distribution (Figure 2.32). The XRD pattern confirmed that

iron oxide present was in the hematite phase. The Ag peaks were confirmed to agree

with the face-centered-cubic form of metallic Ag with clear indexes at (111), (200), (220)

and (311). The Ag nanoparticles nucleating on the iron oxide nanoparticles appeared

Page 83: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

67

regular with readily identifiable (111) facets (Figure 2.33). XPS, SEM image and XRD

spectrum all display both silver and iron oxide nanoparticles coated on fiberglass.

1000 800 600 400 200 0

O 1s

Inte

ns

ity

(A

.U.)

Binding Energy (eV)

Ag

O

Fe 2p

Ag 3p3 Ag 3d5

Fe 3p

Figure 2.31 XPS Survey scan of silver-iron oxide nanoparticles coated on fiberglass

Page 84: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

68

Figure 2.32 SEM image shows that silver- iron oxide nanoparticles well attached to

fiberglass with a narrow size distribution

20 30 40 50 60 70 80

(116)

(110)

(104)

(311)(220)

(200)

Inte

ns

ity

(A

.U.)

Two Theta Angle(Degree)

(111)

Ag

Fe2O3

(024)

Figure 2.33 X-ray diffraction of silver-iron oxide nanoparticles coated on fiberglass

Page 85: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

69

0 3 6 9 12 15

-4

-3

-2

-1

0

Lo

g(C

/Co

)

Time (minutes)

Silver-Iron Oxide

Iron Oxide

Silver

Fiberglass

Figure 2.34 Bactericidal activity of fiberglass coated with silver, iron oxide or silver-

iron oxide nanoparticles

0 20 40 60 80 100 120 140

-2.0

-1.8

-1.6

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

Silver- Iron Oxide

Silver

Iron

Fiberglass

Lo

g(C

/Co

)

Time (Minutes)

Figure 2.35 MS2 virus removal kinetics by fiberglass coated with silver, iron oxide

and silver-iron oxide nanoparticles in 1 mM NaCl at pH=6

The control experiments, performed with plain fiberglass substrate, did not

display any virus removal at 22°C (Figure 2.35). The silver -iron oxide coating system

displayed enhanced effectiveness against MS2 virus compared to pure silver or iron oxide

Page 86: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

70

coating system. This is significant since it suggests that the new system can offer

effective disinfection at lower cost.

2.4.4 Summary

We have successfully developed silver-iron oxide nanoparticle coated fiberglass by

aqueous hydrothermal synthetic approach. The new system displayed synergistic

bactericidal and viricidal performance. With a small amount of silver-iron oxide coated

on fiberglass, the hybrid system displayed improved efficiency over fiberglass loaded

purely with each of the constituents of the hybrid system. Accordingly, the results imply

that these new systems would be less costly since a lower amount of nanoparticles are

needed to achieve the same disinfection efficiency. The lower silver amount necessary

for effectiveness also suggests that there is a greater chance to remain below the U.S.

Environmental Protection Agency secondary maximum contamination level of silver

and iron, 100 ppb and 300 ppb, respectively. These systems demonstrate their potential

use to complement existing disinfection systems in and outside the United States.

2.5 Zinc oxide nanoparticles coated on fiberglass removes MS2 viruses from water

2.5.1 Introduction

Zinc oxide, with a wide variety of physical properties, has been implemented in

photocatalysis, chemical sensors, solar cells, transparent electrodes, electroluminescent

devices, ultraviolet laser diodes, and more [49]. Research in the area of nanometer-scaled

zinc oxide has shown encouraging results that have demonstrated a clear dependence of

their electromagnetic, optical, and catalytic properties on their size [65]. This has

motivated burgeoning research on synthetic routes that allow a better control of particle

shape and size. Zinc oxide is currently being investigated as an antibactericide, both in

Page 87: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

71

microscale and nanoscale formulations. Results have indicated that ZnO nanoparticles

show antibacterial activity [102], apparently greater than that of microparticles [103]. As

the particle diameter approaches the nanoscale dimension, there is a dramatic increase in

surface area and presence of chemically reactive groups on the surface that have the

potential to enhance electron storage and can contribute to reactive oxygen species (ROS)

generation. ROS typically includes singlet oxygen (1O2), superoxide (O2

−), hydroxyl

radical (·OH), peroxyl radical (HO2−), and hydrogen peroxide (H2O2) [63]. ROS oxidize

proteins and cause the formation of carbonyl groups on protein molecules [57, 108].

Since ROS can be created by the radiation of water by photons [43], the sunlight and

ultraviolet light inactivation of viruses could also be attributed to the formation of

carbonyl groups on viral capsid protein. Since most noncultivatable enteric viruses are

nonenveloped, it would be possible to quantitatively detect the oxidative damages on

capsid protein of any enteric viruses.

In this research, we selected zinc oxide nanoparticles coated on fiberglass as the

candidate, because zinc oxide‘s high isoelectrical point (IEP) is around 9.0 in aqueous

solution and its bactericidal properties has been well studied.

2.5.2 Materials and methods

Synthesis of zinc oxide nanoparticles coated on fiberglass

Zinc acetate (Zn (O2CCH3)2•2H2O) from Aldrich Chemical Co. and absolute

ethanol were used as received, without further purification. The precursor was made as

follows: 0.5 L of ethanol containing 0.1 M Zn2+

was placed into a distillation apparatus,

fitted so that one could run the reaction under ambient atmospheric pressure, avoiding

moisture exposure and collection of condensation (1 L- flask, a column with calcium

Page 88: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

72

chloride trap. an adapter, and a condensate receiver). The solution was boiled at 80o

C

and stirred with a magnetic stirring bar for 3 hours. The solution was cooled to room

temperature and then 0.14 M LiOH•H2O powder was added to the solution. Finally, the

suspension was placed into an ultrasonic bath to break the weak soluble powder and

create a homogenous solution [107]. The nonwoven fiberglass mat with 7 wt% PVA

binder (Craneglass 230 from Crane & Co. Inc.) was dipped into this solution for 5 min

and then dried at 70oC for 5 min. This process was repeated two more times. Finally,

zinc oxide coated fiberglass mats were dried at 70oC over night. The general process for

the zinc oxide nanopartilces coated on fiberglass filter is illustrated in Figure 2.36.

Figure 2.36 Synthesis of zinc oxide nanoparticles coated on fiberglass

MS2 preparation and plaque forming unit (PFU) assay and test solution with

different chemical concentrations follow the same protocol as the MS2 virus removal by

iron oxide nanoparticles coated on fiberglass experiments. Both batch experiment and

flow-through experiment setups for zinc oxide coated on fiberglass are identical to iron

Page 89: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

73

oxide nanoparticles coated on fiberglass. In light of the aforementioned, the likely

reaction steps can be represented as follows:

Zn (O2CCH3) 2 • 2H2O Zn2+

+ 2 CH3CO2−

+ 2H2O

H2O H+ + OH

Zn2+

+2 OH−

Zn (OH) 2 ZnO + H2O

TEM

MS2 samples with zinc oxide nanoparticles were investigated using a TEM

technique. Viruses and zinc oxide nanoparticle suspensions were applied to holey-

carbon-coated, 300-mesh, copper grids. Tungsten acetate was used as a negative stain for

MS2 viruses. All the samples were examined using a Cryo TEM (JEM-2100, JEOL,

Tokyo, Japan) at 200 kV accelerated voltage. Selected area electron diffraction (SAED)

patterns were also taken to investigate the nanoparticles structure.

BET

BET surface area and micro- and mesoporous volumes were carried out on an

Autosorb-1 apparatus (Quantachrome), following the standard procedure. [] All samples

were degassed at 100 °C until the outgas pressure rise was below 5 μmHg/min prior to

analysis. Nitrogen isotherm obtained at 77K in the appropriate relative pressure ranges

was used for subsequent calculations. The BET equation was used to determine the

surface area. The Dubinin-Radushkevich (DR) equation was used to deduce micropore

volumes, i.e., total volume of pores with diameter less than 2 nm. The total pore volume

was estimated from the amount of nitrogen adsorbed at P/Po = 0.95. The mesopore

volume (i.e., total volume of pores with diameter 2-50 nm) was calculated by subtracting

the volume of micropores from the total pore volume at a relative pressure of 0.95.

Page 90: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

74

XPS

XPS data were obtained from zinc oxide nanoparticles coated on fiberglass using

a Physical Electronics PHI Model 5400 surface analysis system. Before analysis all

samples were washed with D.I. water and then fully dried. XPS spectra were obtained

using an achromatic Mg K (1253.6 eV) x-ray source operated at 300 W. Survey scans

were collected from 0 −1100 eV with a pass energy equal to 178.95eV. The pressure

inside the vacuum system was maintained at approximately 10-9

Torr during all XPS

experiments. A non-linear least squares curve fitting program (XPSPEAK4.1 software)

with a symmetric Gaussian-Lorentzian sum function and Shirley background subtraction

was used to deconvolve the XPS peaks. The carbon 1s electron binding energy

corresponding to graphitic carbon was referenced at 284.5 eV for calibration.

Field emission scanning electron microscope (FESEM)

Zinc oxide nanoparticles coated on fiberglass were characterized with a field

emission scanning electron microscope (Hitachi S-4700) operating at 10.0kV.

DLVO interaction energy profiles

According to the classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory,

the total interaction energy is the summation of the electrostatic and van der Waals

interactions. In this work, we used the Hogg et al. expression to calculate the electrostatic

double-layer interaction energy [104]. The retarded van der Waals attractive interaction

energy was calculated using Gregory‘s approximate expression [105]. The Hamaker

constant (A) of 4 × 10−21

J was used for the MS2-water-silica system [52,106].

2.5.3 Results and discussion

2.5.3.1 Characterization of zinc oxide nanoparticles

Page 91: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

75

X-ray diffraction patterns show that zinc oxide nanoparticles had a hexagonal

close packed (hcp) crystal structure (Figure 2.37). The crystallite size was about 3.5nm.

Data inferred from X-ray line broadening are quite similar compared to particle sizes

obtained from TEM. TEM indicates that the particles were nearly spherical with a

narrow size distribution, d-spacing = 2.814Å (100) (Figure 2.38 (a)). The SAED pattern

of the selected area exhibits a ring structure confirming that zinc oxide nanoparticles are

crystallized (Figure2.38 (b)).

30 40 50 60 70 80

Inte

ns

ity

(A

.U.)

Two Theta (Degree)

100

002

101

102

110103 112

Figure 2.37 X-ray diffraction of zinc oxide nanoparticles

Page 92: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

76

Figure 2.38 (a) TEM image of zinc oxide nanoparticles; (b) SAED pattern of

selected area of zinc oxide nanoparticles

The FESEM image showed zinc oxide nanoparticles were well attached to

fiberglass (Figure 2.39 (a)). When the FESEM is zoomed in, we can observe the

nanoscale features of the zinc oxide nanoparticles coating on fiberglass. The

nanoparticles are well dispersed on the fiberglass surface, although some aggregates

exhibited nanoscale features (Figure 2.39(b)). The particle size plays a primary role in

adhesion to the fiberglass, since smaller particles penetrate deeper and adhere strongly

into the fabric matrix. XPS was also used to confirm the presence of zinc oxide

nanoparticles coated on the fiberglass (Figure 2.40).

Page 93: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

77

Figure 2.39 (a) FESEM image shows that zinc oxide nanoparticles were well

attached to fiberglass; (b) When FESEM was zoomed in, we could

observe the nanoscale features of the zinc oxide nanoparticles coating

on fiberglass

Page 94: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

78

1000 800 600 400 200 0

0

10000

20000

30000

40000

50000

60000

O 1s

Inte

ns

ity

(A

.U.)

Binding Energy (eV)

Zn 2p3

O KLL

Zn 3p

Zn 2p1

Zn 3dZn 3s

Figure 2.40 XPS survey scan of zinc oxide nanoparticles coated on fiberglass

The BET surface area of the iron oxide nanoparticles was measured as

46.71m2 g

−1, whereas the total pore volume (P/P0 = 0.93) was measured as

8.35 × 10−2

cm3 g

−1. The fraction of micropore volume is 33.2% (4.91 × 10

−2 cm

3 g

−1),

while the mesopore volume is 66.8% (9.86 × 10−2

cm3 g

−1) (Table 2.3). The zinc oxide

nanoparticles coating the fiberglass have a small particle size and a high surface area. The

fiber form substrate provides the larger surface area needed to significantly enhance the

kinetic and capacity aspects of virus removal, and enables the assembled filters to have

much lower pressure drop compared to other substrates forms.

Table2.3. Surface areas and pore volumes of zinc oxide coated on fiberglass

Sample BET

surface area

(m2g

-1)

Total pore volume

(P/Po=0.93)

(10-2

cm3g

-1)

Micropore

volume

(10-2

cm3g

-1)

Mesopore

volume

(10-2

cm3g

-1)

ZOCF 46.71 14.77 4.91(33.2%) 9.86 (66.8%)

Page 95: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

79

2.5.3.2 Zeta potential of zinc oxide nanoparticles and MS2 viruses

IEP of zinc oxide nanoparticles and MS2 viruses were determined as 9.0 and 3.6

respectively, which are consistent with previous studies (Figure 2.41) [30]. Indeed, under

the environmental range of pH selected for this research (6–9), MS2 virus showed a

highly negative zeta potential, while zinc oxide nanoparticles were positively charged

until reaching their IEP (0 mV at pH=9.0).

2 3 4 5 6 7 8 9 10 11 12

-40

-30

-20

-10

0

10

20

30

40

ZnO Nanoparticle

MS2 virus

Ze

ta P

ote

nti

al

(mV

olt

s)

pH of Test Solution

Figure 2.41 Zeta potential measurements for zinc oxide nanoparticles and MS2

viruses in 1mM NaCl solution with different pHs

2.5.3.3 TEM images of zinc oxide nanoparticles interact with MS2 viruses

TEM images revealed mean MS2 diameters of 25.42 (±0.93) nm, which are in

accordance with previously reported data (Figure 2.13 (a)). After MS2 viruses interacted

with zinc oxide nanoparticles, the MS2 viruses were destroyed by zinc oxide

nanoparticles in most areas (Figure 2.43 (a)). Fortunately, in a particular area, we found

several MS2 viruses attached to the surface of zinc oxide nanoparticles. The shape

Page 96: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

80

indicated that damage had occurred and their integrity appeared to be compromised. The

diameter of MS2 virus was noticeably 23% decreased to 20 nm (Figure 2.42 (b)).

Figure 2.42 (a) TEM shows that some areas of the MS2 viruses were destroyed and

broken after interacting with zinc oxide nanoparticles; (b) TEM image

shows MS2 viruses attach to the surface of zinc oxide nanoparticles. The

shape indicated that damage had occurred and their integrity appeared

to be compromised. There is noticeable decrease in the diameter of the

viral particles to 20nm.

2.5.3.4 Batch test results for MS2 viruses

Inactivation of MS2 virus by zinc oxide nanoparticles coated on fiberglass under non-

competing conditions

We first measured viral inactivation by zinc oxide nanoparticles in solution

containing 1 mM NaCl as the basis for quantitative comparison of the effect of other ions

and NOM on adsorption. Inactivation capacity is defined as the number of infectious

virus particles (PFU) adsorbed per gram of zinc oxide nanoparticles in solution. The 2-

log inactivation capacity for MS2 virus in a 1 mM NaCl solution was 1.1× 1013

PFU/g for

pH = 6. MS2 virus inactivation process followed a pseudo-first-order reaction with

kinetic rate constants (k) of 0.025 min−1

(Figure 2.43).

Page 97: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

81

Another three batch tests at the solution pH of 7.0, 8.0, and 9.0 in 1mM NaCl

were conducted. Under these conditions, the removal capacity and the kinetic rate

constant decreased to 0.014 min−1

, 0.009 min−1

, and 0.016 min−1

, respectively. These

results suggest an almost negligible influence of proton concentration at a pH range from

6.0 to 9.0 on the inactivation of MS2 virus with no competing ions in solution. Using

classic DLVO calculations, for a 1 mM NaCl solution at a pH range from 6.0 to 9.0, we

found no energy barrier for all conditions.

These outcomes indicated that MS2 viruses were inactivated by zinc oxide

nanoparticles with fast kinetic rates and very high capacity under non-competing

conditions. The mechanism of the inactivation viruses by zinc oxide nanoparticles is

very complicated and needs further varification. Once the viruses were absorbed to the

surface of the zinc oxide nanoparticles, the charge differential led to destructive chemical

changes to the virus capsid or nucleic acid. If the charge differential is great enough,

viruses can be very effectively removed and/or inactivated through sorption to charged

media. Viruses are composed of protein subunits that are arranged into a unique, directed

and energy-stable pattern that is created when the viruses are formed during replication.

When external physical or chemical stressors are applied to the virus, its structure can

become altered, leading to conformational changes and loss of integrity that result in loss

of infectivity or virus inactivation. In aqueous suspensions, zinc oxide can produce ROS,

such as hydroxyl radicals (·OH), which are unselective and react with many organic

substrates at diffusion-limited rates [9, 20]. Hydroxyl radical also has been implicated to

cause MS2 virus inactivation during photocatalytic disinfection processes. As the

particle diameter approaches the nanoscale dimension, the dramatic increase in surface

Page 98: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

82

area and display of chemically reactive groups on zinc oxide nanoparticle surfaces could

produce much more ROS than bulk content [11, 40, 49]. The increased surface reactivity

of zinc oxide could lead to protein denaturation and RNA cleavage [40, 49]. The small

size of nanoparticles is also responsible for irreversible attachment by forming complexes

with viruses where they have a high rate of retention due to some surfaces having a

hydroxyl functional group, very high electrostatic charge, or van der Waals interactions

[11, 40, 49]. It is also possible that zinc oxide nanoparticles not only interact with the

protein capsid of viruses, but also can penetrate inside viruses.

0 30 60 90 120 150 180

-2.0

-1.5

-1.0

-0.5

0.0

Lo

g(C

/Co

)

Time( minutes)

PH9

PH8

PH6

PH7

Figure2.43 MS2 virus inactivation kinetics by zinc oxide nanoparticles coated on

fiberglass in 1 mM NaCl at different pHs

Effect of bicarbonate ions on inactivation of MS2 virus by zinc oxide nanoparticles

coated on fiberglass

We used 1 mM NaHCO3 to simulate typical groundwater found in North

America. According to our results, 0.015g of zinc oxide nanoparticles coated on

Page 99: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

83

fiberglass inactivated MS2 with a kinetics rate constant 0.011 min−1

and its 2-log

inactivation capacity was 6.93 × 1012

PFU/g (Figure 2.44). The slower inactivation

kinetic rate is mainly due to the high carbonate species in the test solution. HCO3−

and

CO32−

are known as effective hydroxyl radical scavengers and when pH values are above

8, the radical CO32−

becomes dominant (pKa, 8 of ·HCO3−

is 7.9) and reacts with O2−

to

terminate the reaction [15]. Their presence may reduce both the rate and capacity of

inactivation of MS2 viruses.

0 20 40 60 80 100 120 140 160 180

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

Lo

g(C

/Co

)

Time (minutes)

Figure 2.44 MS2 virus inactivation kinetics and adsorption onto zinc oxide

nanoparticles coated on fiberglass in 1 mM NaHCO3 solution

Competition by NOM with MS2 viruses for inactivation zinc oxide nanoparticles

coated on fiberglass

To test for competition from NOM, 0.015 g zinc oxide nanoparticles coated on

fiberglass was added into 1 mg/L TOC solution. Note that zeta potential values for MS2

virus in the presence of 1 mg/L TOC were almost the same as in the absence of it (1 mM

Page 100: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

84

NaCl), suggesting a negligible influence of NOM on the charge of viruses under these

concentration conditions. We detected that the MS2 virus removal kinetic rate was

0.0037 min−1

and 4-log inactivation capacity was 1.92 × 1012

PFU/g (Figure 2.45). The

slower inactivation kinetic rate and inactivation capacity were around one order of

magnitude below non-competing condition batch test values. This might be because

NOM is an effective hydroxyl radical scavenger and can absorb UV light sources,

slowing ROS formation [46,106].

0 20 40 60 80 100 120 140 160 180

-5.5

-5.0

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

NOM NaCl

NOM MgCl2

NOM CaCl2

Lo

g(C

/Co

)

Times (minutes)

Figure 2.45 Influence of Ca2+

or Mg2+

and NOM on the inactivation of MS2 viruses

by zinc oxide nanoparticles

We conducted batch experiments to test whether divalent cations allow improved

performance of the studied zinc oxide nanoparticles coated on fiberglass. With 1 mM

Ca2+

in 1mML

TOC solution, the MS2 virus inactivation kinetic rate increased

significantly to 0.0624 min−1

in the presence of Ca2+,

which can bind to negatively

Page 101: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

85

charged carboxylate groups on the NOM surface and the viral capsid proteins to form

complexes [52,53]. It reduces the interaction between NOM and ROS and also

potentially alters the structure of the moieties responsible for stabilizing the MS2 virus.

With 1 mM Mg 2+

in 1 mg/L TOC solution, the MS2 virus inactivation kinetic rate

increased to 0.0248 min−1

. Mg2+

was not as effective as Ca2+

in forming complexes with

carboxylate groups of NOM and MS2 viruses due to the stronger hydration sphere of

Mg2+

and its lower coordination number [53]. The interactions between Mg2+

and NOM

and MS2 viruses are electrostatic in water [52].

2.5.3.5 Flow-through test results for MS2 viruses

Removal of MS2 viruses by zinc oxide nanoparticles coated on fiberglass under non-

competing conditions in solution

0 50 100 150 200 250

-10

-9

-8

-7

-6

-5

-4

-3

-2

Lo

g (

C/C

o)

BedVolume

Figure 2.46 Inactivation of MS2 viruses by zinc oxide nanoparticles in 1 mM NaCl

solution at pH=6

For 1 mM NaCl solution, adjusted to pH =6 and with a cartridge containing 0.20g

zinc oxide nanoparticles coated on fiberglass, a breakthrough was observed for a

minimum of 4-log inactivation for MS2 viruses. The removal capacity for this condition

Page 102: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

86

was 1.11× 1013

PFU/g when pH was kept at 6 and no breakthrough was observed after

195 bed volumes (Figure 2.46).

Removal of MS2 viruses in the presence of aquifer and artificial groundwater

The mass of zinc oxide nanoparticles coated on fiberglass in the cartridge for both

experiments with AGW and NGW was 0.20g. The 4-log inactivation capacity achieved

until breakthrough was 7.94 × 1011

PFU/mL and 3.60× 1011

PFU/mL for AGW and

NGW, respectively (Figure 2.47). These results are roughly more than one order of

magnitude below the adsorption capacity of zinc oxide under non-competing conditions.

The high concentration of NOM and other ions present in NGW or the bicarbonate and

NOM content of AGW are responsible for the reduced adsorption of MS2 viruses. These

results suggest that this cartridge can be used as a point-of-use device to remove viruses

from water with similar characteristics to groundwater.

0 20 40 60 80 100

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

Artifical Groundwater

Newmark Groundwater

Lo

g(C

/Co

)

Bed Volumes

Figure 2.47 Inactivation of MS2 viruses by zinc oxide nanoparticles in artificial and

aquifer groundwater. Artificial groundwater presented fewer

competitors than Newmark groundwater for virus adsorption on

available adsorption sites

Page 103: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

87

Desorption of MS2 viruses

0 50 100 150 200 250 300

-9.5

-9.0

-8.5

-8.0

-7.5

-7.0

-6.5

-6.0

-5.5 MS2 virus 4.01E9PFU/ml

3% beef Extract +0.1 Mol/L Glycine PH=8

LO

G(C

/Co

)

Time (minutes)

Figure 2.48 Recovery of infectious MS2 viruses uses a solution of 1.5% beef extract

in 50 mM glycine at pH 8

Detachment of infectious MS2 viruses was also investigated using the same

reagents and conditions as in batch tests. Initially, a 4.01 × 109 PFU/mL MS2 virus

solution was injected into a column containing 0.20 g of zinc oxide nanoparticles. The

flow of viral solution was stopped when 1 × 109 PFU were injected into the column (500

mL) and, consequently, no PFU were detected in the effluent. The viral solution was

switched to a beef extract–glycine irreversible attachment by forming solution complexes

and samples of the effluent were taken. Less than 0.01% infectious viruses were

discovered by the desorption processes (Figure 2.48). This result is consistent with the

TEM image (Figure 2.42). TEM micrographs of samples taken after the adsorption period

reveal apparently intact but smaller MS2 viruses that were damaged by the zinc oxides

nanoparticles. These results suggested that zinc oxide nanoparticles and MS2 viruses can

form complexes by functional groups, very high electrostatic charge, or van der Waals

Page 104: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

88

interactions. The ROS releasing from zinc oxide nanoparticle surfaces can cause

permanent damages to MS2 viruses.

2.5.4 Summary

We have successfully synthesized the zinc oxide nanparticles coated on fiberglass

by a facile approach, which showed far better properties than any materials reported in the

literature. Zinc oxide nanoparticles with diameter of 3.5 nm show the IEP at 9.0 were well

dispersed on fiberglass. These fibers offer an increase in capacity by orders of magnitude

over all other materials. Compared to iron oxide nanoparticles, zinc oxide nanoparticles

didn‘t show improvement in inactivation kinetics but the 99.99% inactivation capacities

increase by two orders of magnitude. Furthermore, zinc oxide nanoparticles have higher

affinity to viruses than the iron oxide nanoparticles in presence of competing ions. The

advantages of zinc oxide depend on high surface charge density, small nanoparticle sizes

and capabilities of generating ROS.

2.6 Mammalian cell cytotoxicity and genotoxicity analysis of zinc oxide

nanoparticles

2.6.1 Introduction

Nanomaterials have been the subject of much recent praise for their potential

applications in environmental protection and biotechnology [111]. Nanoparticles also

provide new approaches to the development of cancer drugs, response monitoring, and

preventative care [121]. On the other hand, it has been shown that nanoparticles may be

harmful to cells [114, 118, 119]. There has been an increase in the public concern over

the effects of contact with nanomaterials, even as they appear in more and more

commercially-available products [111, 114, 118, 119]. Highly ionic metal oxide

nanoparticles are among some of the more interesting candidates, as they feature atypical

Page 105: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

89

crystal morphology, high surface areas and reactivity, yet they have still exhibited

behavior potentially dangerous to humans. Two extremely important steps must be taken

before the industry implements these nanomaterials for widespread commercial purposes:

the identification of the hazardous potential of nanoparticles, and the prevention of harm

to the public health and the environment [111].

Though many studies have suggested oxidative stress and lipid peroxidation

(LPO) may play an important role in nanoparticle-elicited DNA damage, cell membrane

disruption, and subsequent cell death, the exact mechanism behind nanoparticle

cytotoxicity and genotoxicity still needs to be explored further [111, 113, 114, 115, 118,

119]. Fundamentally understanding the mechanisms of these potential hazards associated

with these nanoparticle properties could help researchers further optimize materials

performance by improving safety and maintaining key nanoscale properties.

Some nanoparticles, such as zinc oxide nanoparticles, have also been subjects of

experiments involving the destruction of bacterial cells. The amount of eradicated

bacteria, cellular internalization, and defect concentration has been shown to be

dependent on the particle size, with more efficient antibacterial activity, more

internalization, and higher concentrations resulting from smaller nanoparticles [112]. A

complex surface area is most likely related to the reactivity of these oxygen species. For

instance, a recent study has revealed the clastogenic effects of zinc oxide nanoparticles on

Chinese hamster ovary (CHO) cells [113, 118]. Some studies have further described the

cytotoxicity of these particles in human CD4+T cells and lung mesothelioma cell line

[119].

Page 106: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

90

There are some studies that discuss the toxicity of zinc oxide nanoparticles but

there are very few significant studies evaluating cytotoxicity and genotoxicity of zinc

oxide nanoparticles in mammalian cells. In this study, we used CHO cells to evaluate

zinc oxide chronic cytotoxicity and study zinc oxide nanoparticles and in the DNA-

damaging potential of these particles was assessed by single cell gel electrophoresis

(SCGE). We also applied TEM to investigate the interaction between zinc oxide

nanoparticles and CHO cells.

2.6.2 Materials and methods

Biological and chemical reagents

General reagents were purchased from Fisher Scientific Co. (Itasca, IL) and

Sigma Chemical Co. (St. Louis, MO). Cell medium and fetal bovine serum (FBS) were

purchased from Hyclone Laboratories (Logan, UT) or from Fisher Scientific Co. (Itasca,

IL). 0.2 M Na-Cacodylate buffer (pH=7.4), 2.0 % paraformaldehyde, 2.5%

glutaraldehyde, and Poly/Bed 812 embedding media/ DMP-30Kid were purchased from

Polysciences, Inc.( Warrington, PA).

CHO cells

CHO cells, line AS52, clone 11-4-8 were used in this study Wanger et al 1998

[124]. The CHO cells were maintained in Ham‘s F12 medium containing 5% FBS at 37

°C in a humidified atmosphere of 5% CO2.

CHO cell chronic cytotoxicity assay

Over the course of 72 h (the length of three cell divisions), this assay measured

decreasing cell density in terms of the concentration of zinc oxide nanoparticles. A

modification of an assay that was developed for the analysis of water disinfection was

Page 107: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

91

used to measure the cytotoxicity in CHO cells. 96-well tissue culture microplates with

flat bottoms were used and eight duplicated wells were created for each concentration of

a particular zinc oxide particle. For the blank control group, eight wells with 200 μL of

F12 medium + 5% FBS were used. For the negative control group, eight wells with 100

μL of a titered CHO cell suspension (3×104 cells/mL) plus 100 μL F12 + FBS were used.

All of the other columns consisted of 200 μL of 3 × 103 CHO cells, F12 + FBS and a zinc

oxide nanoparticle concentration [112, 120].

AlumnaSeal™ (RPI Corporation, Mt. Prospect, IL) was put on top of the wells

before covering the microplate in order to hinder contamination. A rocking platform was

used to evenly distribute the cells for approximately 10 min, and they were then

incubated for 72 h. Wells were then aspirated and fixed for 10 min in 100% methanol,

and stained in a 1% crystal violet solution in 50% methanol for 20 min.

50 μL of dimethyl sulfoxide (DMSO) was added to each well after the microplate

was washed and aspirated. The microplate was then incubated for 20 min and analyzed

at 595 nm, using a BioRad microplate reader. The absorbance of each treatment group

was calculated as a percentage of the negative control absorbance, which was set to

100%.

A direct relationship was shown between the crystal violet dye absorbance and the

number of viable cells [122]. 8 reduplicated wells were analyzed for each zinc oxide

concentration and experiments were repeated two to three times.

SCGE

SCGE is a molecular assay that reveals the damage to DNA experienced by the

nuclei of treated cells [116, 117]. 2×104 CHO cells were added to each microplate well

Page 108: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

92

in 200 μL of F12+5% FBS and then incubated. The cells were washed using Hank‘s

balanced salt solution (HBSS) on the following day and treated with 25 μL of

concentrations of specific zinc oxide nanoparticles in F12 medium without FBS for 4 h at

37°C, 5% CO2. Sterile 5 AlumnaSeal™ was then applied to cover the wells [112, 120].

The wells were incubated and then washed twice with HBSS. 50 μL of 0.01%

trypsin with 53 μM EDTA was used to harvest the cells, and was inactivated using 70 μL

of F12 + FBS. A 10 μL aliquot of cell suspension with 10 μL of 0.05% trypan blue vital

dye in phosphate-buffered saline (PBS) was used to measure the acute cytotoxicity. If

the cytotoxicity exceeded 30% then SCGE data was not used.

1% normal melting point agarose prepared with DI water was dried and coated

onto microscope slides. A layer of low melting point agarose prepared with PBS was

used to embed the remaining cell suspensions on the slides. After an overnight

immersion in lysing solution at 4°C removed the cellular membranes, an alkaline buffer

of pH 13.5 was prepared in an electrophoresis tank. Slides were set inside the tank and

DNA was denatured for 20 min, and then the microgels were electrophoresed at 25 V,

300 mA (0.72 V/cm) for 40 min at 4°C. To prepare the microgels for storage, they were

neutralized with a Tris buffer of pH 7.5, rinsed in cold water, dehydrated in cold

methanol, and dried at 50°C [112, 120].

The microgels were stained with 65 μL of ethidium bromide (20 μg/mL) for 3

min, following 30 min of cold water hydration. A Zeiss fluorescence microscope with an

excitation filter of BP 546/10 nm and a barrier filter of 590 nm was used to analyze two

microgels for each treatment group, after they had been cold water rinsed. For every

microgel, 25 nuclei were chosen at random to be analyzed with a charged coupled device

Page 109: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

93

camera. To measure DNA damage, the migration distance was multiplied by the

integrated value of migrated DNA density, as determined by a computerized image

analysis system (Komet version 3.1, Kinetic Imaging Ltd., Liverpool, UK). The negative

control, positive control (3.8 mM ethylmethanesulfonate), and haloacetamide

concentrations were statistically analyzed using spreadsheets. Each experiment was

repeated at least 3 times for each zinc oxide nanoparticle.

TEM detection of cellular morphology

100 μl of CHO cells (2 × 105 cells/ml) and zinc oxide nanoparticles at the final

concentration (100 μg/ml) were incubated in 6-well tissue culture plate in CO2 incubator

for 24 h. CHO cells treated with PBS (pH = 7.4) were taken as the control. For TEM

analysis, CHO suspension was centrifuged at 800 rpm for 2 min. The pellet was washed

3 times by PBS (pH = 7.4) and fixed 2.0 % paraformaldehyde and 2.5% glutaraldehyde

(both E.M. grade) 0.1 M Na-Cacodylate buffer (pH= 7.4) in fridge for 4 h. After being

rinsed by the 0.1 M Na-Cacodylate buffer (pH=7.4), the cells were post-fixed for 90 min

with 1% osmium tetroxide in 0.1 M sodium cacodylate buffer (pH=7.4 in darkness. After

being rinsed by the 0.1 M Na-Cacodylate buffer (pH=7.4), then specimens were En-bloc

stained (tertiary fixation) by 2% aqueous uranyl acetate for 12 h in at 4°C and were

dehydrated in a series of ethanol solutions (37%, 67%, 95%, and 100%) for 10 min

separately.

After dehydrating, specimens were infiltrated in 1:1 100% ethanol:propylene

oxide, 1:2 100% ethanol: propylene oxide, 1:1 propylene oxide:Poly/Bed 812 embedding

media (without DMP-30), 1:2 propylene oxide:Poly/Bed 812 embedding (without DMP-

30), each solution for 10 min. Finally CHO cells were incubated in the mixture of 100%

Page 110: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

94

Poly/Bed 812 embedding media (without DMP-30), overnight in hood at room

temperature and then mixed with 100% Poly/Bed 812 embedding media with 1.5%

DMP-30 at 60ºC for 12h.

Ultrathin sections (70 nm) were cut with an ultramicrotome diamond knife and

transferred onto 200-mesh grids, stained with uranyl acetate, counter-stained with lead

citrate according to standard methods, and observed with the Philips CM200 TEM at

80KV.

Zinc oxide nanoparticles retention from fiberglass study

0.70g of zinc oxide nanoparticles coated on fiberglass was put in 1L DI water

with 10% zinc oxide mass loading, and stirred at room temperature. Samples were taken

daily, using inductively coupled plasma mass spectrometry (ICP-MS), from the first day

to the fourth day, and then weekly, starting on the seventh day, until the end of the first

month.

2.6.3 Results and discussion

CHO cell cytotoxicity.

Data from individual experiments were normalized to the averaged percent of the

concurrent negative control; these data were plotted as a concentration response curve

(Figure 2.49). An ANOVA test was conducted with normalized data representing each

microplate well. If a significant F value of ≤0.05 was obtained, a Holm-Sidak multiple

comparison analysis was conducted. The power of the test statistic (1-β) was maintained

at ≥0.8 at R=0.05. The lowest concentration that induced a significant cytotoxic response

concentration was 3.75 μg/mL. This concentration of significant response is much higher

Page 111: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

95

than reported cytotoxic response zinc oxide nanoparticles with 19.6 nm. The smaller zinc

oxide nanoparticles were more toxic than larger nanoparticles [122].

Regression analysis was conducted on each concentration-response curve; the

coefficient of determination (R2) ranged from 0.95 to 0.99. The %C½ value is the

concentration that induced a cell density of 50% as compared to the concurrent negative

control [112, 120].

Figure 2.49 CHO cell chronic cytotoxicity concentration–response curve of zinc

oxide nanoparticles

CHO cell genotoxicity

Acute genomic DNA damage was measured as SCGE tail moment values. Acute

cytotoxicity was determined with trypan blue vital dye; data were used within the range

that contained ≥70% viable cells Figure 2.50 The data were plotted, and regression

analysis was used to fit the curve; the coefficient of determination (R2) ranged from 0.97

to 0.99. SCGE tail moment values are not normally distributed, thus the median tail

Page 112: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

96

moment value for each microgel was determined and averaged. Averaged median values

express normal distributions according to the Central Limit theorem and were used with

an ANOVA test. If a significant F value of P ≤ 0.05 was obtained, a Holm−Sidak

multiple comparison analysis was conducted (1-β ≥ 0.8 at α = 0.05) [112, 120]. The

lowest concentration that induced a significant SCGE genotoxic response was 35 mg/mL

for zinc oxide nanoparticles. The SCGE genotoxic potency was calculated at the

midpoint of the concentration–response curve.

Figure 2.50 CHO cell chronic genotoxicity concentration–response curve of zinc

oxide nanoparticles

TEM

TEM images reveal the process of zinc oxide nanoparticle toxicity. Prior to

exposure, the cell membrane is well-structured and internal organelles are in a regular

state. The particles begin by penetrating and internalizing the CHO cells, resulting in an

irregular, jagged membrane. Particles then accumulate inside the food vacuoles. As

Page 113: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

97

Figure 2.51 TEM images to explore the uptake and subcellular localization of zinc

oxide nanoparticles: (a) cross section of CHO cell; (b) vacuoles are

clear of any particles; (c) interaction with 3.75 μg/mL zinc oxide

nanoparticles over 72 h in the dark, the cell membrane became much

rougher as particles entered the cytoplasm; (d) zinc oxide

nanoparticles penetrating the vacuoles

a b

c d

Page 114: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

98

shown in Figure 2.51 (a), the nucleus membrane is smooth before interaction with zinc

oxide nanoparticles. Figure 2.51 (b) shows that the vacuoles are clear of any particles, as

well. After interaction with 3.75 μg/mL zinc oxide nanoparticles over 72 h in the dark,

the cell membrane became much rougher as particles entered the cytoplasm, as shown in

Figure 2.51(c). This was followed by zinc oxide nanoparticles penetrating the vacuoles,

as shown in Figure 2.51(d).

Zinc oxide nanoparticles fall off from coating fiberglass test

Accumulated zinc oxide nanoparticles fell off from the fiberglass into the

solution. The amount of particles present in the solution increased over time. After first

day the concentration of zinc oxide nanoparticles was measured at 0.2 ppm and at the end

of the first month the concentration was measured as 2.27ppm (Figure 2.52). This result

is much lower than the cytotoxic response concentration of 3.75 μg/mL, which is

equivalent to 830 ppm. If the zinc oxide nanoparticles were coated on fiberglass, then the

concentration of particles would 1/366th

of the cytotoxic response concentration. The

zinc oxide nanoparticles were very strongly attached to the fiberglass, so zinc oxide

nanoparticle leakage was not a significant concern for this study. The Environmental

Protection Agency‘s (EPA) National Secondary Drinking Water Regulations specify that

the maximum contamination level of zinc oxide must not exceed 5 mg/L, which is far

above the concentration results achieved in this study [123].

Page 115: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

99

0 7 14 21 28

0.0

0.5

1.0

1.5

2.0

2.5

Zn

O i

n s

olu

tio

n (

pp

m)

Time (Day)

Figure 2.52 Zinc oxide nanoparticles fall off from the fiberglass

2.6.4 Summary

Zinc oxide nanoparticles with diameter of 3.5 nm showed significant cytotoxic

response at 3.75 μg/mL and genotoxitc response at 35 μg/mL. The TEM images showed

that zinc oxide nanoparticles can internalize the CHO cells. The smaller the size of the

particles, the more toxicity response they exhibited, most probably due to the more

active surface and increased ability of the particles to penetrate the cell membrane and

aggregate into the vacuoles. The leakage test for the zinc oxide nanoparticles

demonstrated that zinc oxide nanoparticles were well attached to the fiberglass substrate,

resulting in a very low concentration in the solution only 2.27 ppm over one month.

Page 116: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

100

2.7 References

1. Palaniappan, M., Gleick, P. et al. (2009). "Peak Water" The World‘s Water 2008-

2009.

2. Gleick, P.(2002) "Dirty Water: Estimated Deaths from Water-Related Disease

2000-2020" Pacific Institute for Studies in Development, Environment, and

Security.

3. Eisenburg, J. N. S.; Bartram, J.; Hunter, P. R. A Public Health Perspective for

Establishing Water-Related Guidelines and Standards. In Water Quality

Guidelines, Standards, and Health: Assessment of Risk and Risk Management for

Water-Related Infectious Disease; WHO: Geneva, 2001, 229–256. (18)

4. United States Environmental Protection Agency. 40 CFR parts 9, 141, & 142

National Primary Drinking Water Regulations: Stage 2 disinfectants and

disinfection byproducts rule; final rule. Federal Register 71, 388–493 (2006)

5. IMWI report. Insights from the Comprehensive Assessment of Water

Management in Agriculture (2006).

6. UN-Water. Coping with Water Scarcity: UN-Water Thematic Initiative. August

2006.Website : http://www.unwater.org/wwd2007.html

7. World Health Organization. Emerging Issues in Water and Infectious Disease 1–

22 (World Health Organization, Geneva, 2003)

8. Water, sanitation and hygiene links to health facts and figures. (2004)

9. Adams, L. K., D. Y. Lyon, et al. (2006). "Comparative eco-toxicity of nanoscale

TiO2, SiO2, and ZnO water suspensions." Water Research 40(19): 3527-3532.

10. Agriculture, C. A. o. W. M. i. (2006). "Water for food, water for life "Stockholm

World Water Week.

11. Applerot, G., A. Lipovsky, et al. (2009). "Enhanced Antibacterial Activity of

Nanocrystalline ZnO Due to Increased ROS-Mediated Cell Injury." Advanced

Functional Materials 19(6): 842-852.

12. Ashbolt, N. J. (2004). "Microbial contamination of drinking water and disease

outcomes in developing regions." Toxicology 198(1-3): 229-238.

13. Barrett Sylvia, E., W. Krasner Stuart, et al. (2000). Natural Organic Matter and

Disinfection By-Products: Characterization and Control in Drinking Water—An

Page 117: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

101

Overview. Natural Organic Matter and Disinfection By-Products. Washington,

DC, American Chemical Society: 2-14.

14. Bhattacharjee, S., C.-H. Ko, et al. (1998). "DLVO Interaction between Rough

Surfaces." Langmuir 14(12): 3365-3375.

15. Bielski, B. (1985). "Reactivity of perhydroxyl/superoxide radicals in aqueous

solution." Journal of physical and chemical reference data 14(4): 1041.

16. Brown, J. and Brown (2009). "Ceramic media amended with metal oxide for the

capture of viruses in drinking water." Environmental technology 30(4): 379.

17. Chazal, N. (2003). "Virus entry, assembly, budding, and membrane rafts."

Microbiology and molecular biology reviews 67(2): 226.

18. Chu, Y., Y. Jin, et al. (2001). "Mechanisms of Virus Removal During Transport

in Unsaturated Porous Media." Water Resour. Res. 37(2): 253-263.

19. Daneshvar, N. and Daneshvar (2004). "Photocatalytic degradation of azo dye

Acid red 14 in water on ZnO as an alternative catalyst to TiO2." Journal of

photochemistry and photobiology. Chemistry 162(2-3): 317.

20. Degen, A. and M. Kosec (2000). "Effect of pH and impurities on the surface

charge of zinc oxide in aqueous solution." Journal of the European Ceramic

Society 20(6): 667-673.

21. Di Virgilio, A. L., M. Reigosa, et al. (2010). "Comparative study of the cytotoxic

and genotoxic effects of titanium oxide and aluminium oxide nanoparticles in

Chinese hamster ovary (CHO-K1) cells." Journal of Hazardous Materials 177(1-

3): 711-718.

22. Fiksdal, L. (2006). "The effect of coagulation with MF/UF membrane filtration

for the removal of virus in drinking water." Journal of membrane science 279(1-

2): 364.

23. Fong, T.T and Lipp, E.K. (2005). "Enteric Viruses of Humans and Animals in

Aquatic Environments: Health Risks, Detection, and Potential Water Quality

Assessment Tools." Microbiol. Mol. Biol. Rev. 69(2): 357-371.

24. Cornell, R. M. andSchwertmann, U. (2003) The Iron Oxides: Structure,

Properties, Reactions, Occurrences and Uses Wiley VCH

Page 118: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

102

25. Gao, H., W. Shi, et al. (2005). "Mechanics of receptor-mediated endocytosis."

Proceedings of the National Academy of Sciences of the United States of America

102(27): 9469-9474.

26. Gerba, C. P. (1984). "APPLIED AND THEORETICAL ASPECTS OF VIRUS

ADSORPTION TO SURFACES." Advances in Applied Microbiology 30: 133-

168.

27. Golmohammadi, R. (1993). "The refined structure of bacteriophage MS2 at 2•8

à resolution." Journal of molecular biology 234(3): 620.

28. Guobin, S., S. Yan, et al. (2009). "Applications of Nanomaterials in

Environmental Science and Engineering: Review." Practice Periodical of

Hazardous, Toxic & Radioactive Waste Management 13(2): 110-119.

29. Gurr, J.-R., A. S. S. Wang, et al. (2005). "Ultrafine titanium dioxide particles in

the absence of photoactivation can induce oxidative damage to human bronchial

epithelial cells." Toxicology 213(1-2): 66-73.

30. Gutierrez, L., X. Li, et al. (2009). "Adsorption of rotavirus and bacteriophage

MS2 using glass fiber coated with hematite nanoparticles." Water Research

43(20): 5198-5208.

31. H, C. and F. H. Crick (1956). "Structure of small viruses." Nature 177(4506): 473.

32. Heimbuch, J. (2009). Water The India Story, Grail Research.

33. Hermansson, M. (1999). "The DLVO theory in microbial adhesion." Colloids and

Surfaces B: Biointerfaces 14(1-4): 105-119.

34. Hightower, M. and S. A. Pierce (2008). "The energy challenge." Nature

452(7185): 285-286.

35. Kitis, M. (2003). "Microbial removal and integrity monitoring of RO and NF

membranes." American Water Works Association. Journal 95(12): 105.

36. Kohn, T. and K. L. Nelson (2006). "Sunlight-Mediated Inactivation of MS2

Coliphage via Exogenous Singlet Oxygen Produced by Sensitizers in Natural

Waters." Environmental Science & Technology 41(1): 192-197.

37. Koonin, E., T. Senkevich, et al. (2006). "The ancient Virus World and evolution

of cells." Biology Direct 1(1): 29.

Page 119: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

103

38. Li, Q. (2007). "Modulation of MS2 virus adsorption on TiO2 semiconductor film

by nitrogen doping." Journal of materials research 22(11): 3036.

39. Liao (1995). "Chemical Oxidation by Photolytic Decomposition of Hydrogen

Peroxide." Environmental Science & Technology 29(12): 3007-3014.

40. Lin, W. (2009). "Toxicity of nano- and micro-sized ZnO particles in human lung

epithelial cells." Journal of nanoparticle research 11(1): 25.

41. Loveland, J. P., J. N. Ryan, et al. (1996). "The reversibility of virus attachment to

mineral surfaces." Colloids and Surfaces A: Physicochemical and Engineering

Aspects 107: 205-221.

42. Montgomery, M. A. and M. Elimelech (2007). "Water And Sanitation in

Developing Countries: Including Health in the Equation." Environmental Science

& Technology 41(1): 17-24.

43. Mostafavi, S. T., M. R. Mehrnia, et al. (2009). "Preparation of nanofilter from

carbon nanotubes for application in virus removal from water." Desalination

238(1-3): 271-280.

44. Muellner, M. G., E. D. Wagner, et al. (2006). "Haloacetonitriles vs. Regulated

Haloacetic Acids:  Are Nitrogen-Containing DBPs More Toxic?" Environmental

Science & Technology 41(2): 645-651.

45. Murray, J. P. and S. J. Laband (1979). "Degradation of poliovirus by adsorption

on inorganic surfaces." Appl. Environ. Microbiol. 37(3): 480-486.

46. Mylon, S. E., C. I. Rinciog, et al. (2009). "Influence of Salts and Natural Organic

Matter on the Stability of Bacteriophage MS2." Langmuir 26(2): 1035-1042.

47. Organization, W. H. (2004). Meeting the MDG Drinking Water and Sanitation

Target: A Mid-Term Assessment of Progress.

48. Ortiz-Ibarra, H., N. Casillas, et al. (2007). "Surface characterization of

electrodeposited silver on activated carbon for bactericidal purposes." Journal of

Colloid and Interface Science 314(2): 562-571.

49. Ostrovsky, S. (2009). "Selective cytotoxic effect of ZnO nanoparticles on glioma

cells." Nano Research 2(11): 882.

Page 120: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

104

50. Oyanedel-Craver, V. A. and J. A. Smith (2007). "Sustainable Colloidal-Silver-

Impregnated Ceramic Filter for Point-of-Use Water Treatment." Environmental

Science & Technology 42(3): 927-933.

51. Penrod, S. L., T. M. Olson, et al. (1995). "Whole Particle Microelectrophoresis

for Small Viruses." Journal of Colloid and Interface Science 173(2): 521-523.

52. Penrod, S. L., T. M. Olson, et al. (1996). "Deposition Kinetics of Two Viruses in

Packed Beds of Quartz Granular Media." Langmuir 12(23): 5576-5587.

53. Pham, M., E. A. Mintz, et al. (2009). "Deposition kinetics of bacteriophage MS2

to natural organic matter: Role of divalent cations." Journal of Colloid and

Interface Science 338(1): 1-9.

54. Plewa, M. J., M. G. Muellner, et al. (2007). "Occurrence, Synthesis, and

Mammalian Cell Cytotoxicity and Genotoxicity of Haloacetamides: An Emerging

Class of Nitrogenous Drinking Water Disinfection Byproducts." Environmental

Science & Technology 42(3): 955-961.

55. Pu, Z. (2006). "Controlled synthesis and growth mechanism of hematite

nanorhombohedra, nanorods and nanocubes." Nanotechnology 17(3): 799.

56. Ryan, J. N., R. W. Harvey, et al. (2002). "Field and Laboratory Investigations of

Inactivation of Viruses (PRD1 and MS2) Attached to Iron Oxide-Coated Quartz

Sand." Environmental Science & Technology 36(11): 2403-2413.

57. Sano, D., R. M. Pint , et al. (2009). "Detection of Oxidative Damages on Viral

Capsid Protein for Evaluating Structural Integrity and Infectivity of Human

Norovirus." Environmental Science & Technology 44(2): 808-812.

58. Sengupta, G., H. S. Ahluwalia, et al. (1979). "Chemisorption of water vapor on

zinc oxide." Journal of Colloid and Interface Science 69(2): 217-224.

59. Shannon, M. A., P. W. Bohn, et al. (2008). "Science and technology for water

purification in the coming decades." Nature 452(7185): 301-310.

60. Sharma, V. K., R. A. Yngard, et al. (2009). "Silver nanoparticles: Green synthesis

and their antimicrobial activities." Advances in Colloid and Interface Science

145(1-2): 83-96.

61. Sjogren, J. (1994). "Inactivation of phage MS2 by iron-aided titanium dioxide

photocatalysis." Applied and environmental microbiology 60(1): 344.

Page 121: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

105

62. Stadtman, E. R. and R. L. Levine (2003). "Free radical-mediated oxidation of free

amino acids and amino acid residues in proteins." Amino Acids 25(3): 207-218.

63. Tadic, M. and Tadic (2007). "Synthesis and magnetic properties of concentrated

α-Fe2O3 nanoparticles in a silica matrix." Journal of alloys and compounds

441(1-2): 291.

64. Taylor, D. H. and H. B. Bosmann (1981). "The electrokinetic properties of

reovirus type 3: electrophoretic mobility and zeta potential in dilute electrolytes."

Journal of Colloid and Interface Science 83(1): 153-162.

65. Tewari, S. (1956). "Studies on the nature of hydrated zinc oxide. Part II." Colloid

& Polymer Science 149(2): 65-67.

66. Xia, T., M. Kovochich, et al. (2006). "Comparison of the Abilities of Ambient

and Manufactured Nanoparticles to Induce Cellular Toxicity According to an

Oxidative Stress Paradigm." Nano Letters 6(8): 1794-1807.

67. Xu, W.-X., L.-C. Wang, et al. (1996). "Spontaneous Dispersion of Ag onto the

Fe3O4Surface." Journal of Colloid and Interface Science 179(2): 350-356.

68. Zhu, B., D. A. Clifford, et al. (2005). "Virus removal by iron coagulation-

microfiltration." Water Research 39(20): 5153-5161.

69. Zhu, R. R., S. L. Wang, et al. (2009). "Bio-effects of Nano-TiO2 on DNA and

cellular ultrastructure with different polymorph and size." Materials Science and

Engineering: C 29(3): 691-696.

70. Pitman, G. K. Bridging Troubled Waters — Assessing The World Bank Water

Resources Strategy (World Bank Publications, Washington DC, 2002)

71. From Website : http://en.wikipedia.org/wiki/Introduction_to_viruses

72. Water on Tap: What You Need To Know, EPA 816-K-09-002 U.S.

Environmental Protection Agency (2009)

73. Nieuwenhuijsen MJ, Toledano MB, et al. (2000). "Chlorination disinfection

byproducts in water and their association with adverse reproductive outcomes: a

review". Occupational Environmental Medince.57(2):73-85.

74. Center for Disease Control and Prevention. (2007)

Page 122: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

106

75. National Cancer Institute Report on Carcinogenesis Bioassay of Chloroform;

Carcinogenesis Program, Division of Cancer Cause and Prevention: Bethesda,

MD, Mar 1976.

76. Krasner, S. W. et al. (2006) Occurrence of a new generation of disinfection

byproducts. Environ. Sci. Technol. 40, 7175–7185

77. Carter, J. and Saunders, V. (2007). Virology: Principles and Applications

78. Edwards, R.A. and Rohwer, F. (2005). ―Viral metagenomics”. Nature Review

Microbiology, 3(6):504-510.

79. From website: http://micro.magnet.fsu.edu/cells/virus.html

80. From website :

http://www.mardre.com/homepage/mic/tem/samples/bio/virus/tmv1.htm

81. From website: http://rehydrate.org/rotavirus/index.html

82. Centers for Disease Control and Prevention‘s Public Health Image Library

83. From website: http://www.vetmed.ucdavis.edu/viruses/download.html

84. Chazal, N. and Gerlier, D (2003) ―Virus Entry, Assembly, Budding, and

Membrane Rafts‖ Microbiology and Molecular Biology Reviews, 67(2): 226-237.

85. Borchardt, M.A. and Bradbury, K., et al. (2007), Human enteric viruses in

groundwater from a confined bedrock aquifer, Environmental Science and

Technology 41: 6606–6612.

86. Dawson, D.J. and Paish.A, et al. (2005) ―Survival of viruses on fresh produce,

using MS2 as a surrogate for norovirus‖ Journal of Applied Microbiology 98,

203–209.

87. Research Plan for Microbial Pathogens and Disinfection By-Products in Drinking

Water U.S.EPA Office of Water EPA/600/R-97/122.(1997)

88. Brüssow, H. (2005) ―Phage therapy: the Escherichia coli experience‖

Microbiology 151: 2133-2140.

89. You, Y. and Vance, et al (2003). ―Sorption of MS2 Bacteriophage to Layered

Double Hydroxides‖, J. Environ. Qual. 32:2046-2053.

Page 123: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

107

90. Wang, J. and Li, X, et al. ―Iron Oxide-Coated on Glass Fibers for Arsenic

Removal‖, Separation Science and Technology, (2010), 45: 1058–1065.

91. Adams, M. (1959) ―Bacteriophages, Interscience‖ Publishers, New York.

92. Schulze-Makuch, D. and Bowman, R,et al (2007). ―Field Evaluation of the

Effectiveness of Surfactant Modified Zeolite and Iron-Oxide-Coated Sand for

Removing Viruses and Bacteria from Ground Water‖ Ground Water Monitoring

& Remediation. 23(4): 68-74.

93. Abudalo, R. and Bogatsu, Y. et al. (2005) ―Effect of ferric oxyhydroxide grain

coatings on the transport of bacteriophage PRD1 and Cryptosporidium parvum

oocysts in saturated porous media‖, Environmental Science and Technology 39,.

6412–6419.

94. Lukasik, J. and Cheng, Y. F. et al (1999) Removal of microorganisms from water

by columns containing sand coated with ferric and aluminum hydroxides, Water

Research 33 (3): 769–777.

95. Rouquerol, F. and Rouquerol, J., et al. (1999) ―Adsorption by Powders and

Porous Solids: Principle‖, Methodology and Application, Academic Press, New

York.

96. Nguyen, T. N. and Elimelech, N. (2007) ―Adsorption of plasmid DNA to a natural

organic matter-coated silica surface: kinetics, conformation, and reversibility‖,

Langmuir 23 (2007), pp. 3273–3279.

97. Bridger,J. and Clarke, I and et al. (1982) ―Characterization of an antigenically

distinct porcine rotavirus‖, Infection and Immunity 35 (3):1058–1062.

98. Ludert, J.E. and Ruiz, M.C. and et al. (2002) ―Antibodies to Rotavirus Outer

Capsid Glycoprotein VP7 Neutralize Infectivity by Inhibiting Virion

Decapsidation‖. J Virol.76 (13): 6643–6651.

99. Parashar, U.D. and Gibson, C, J. and J.S. Bresee and et al. (2006) ―Rotavirus and

severe childhood diarrhea‖, Emerging Infectious Diseases 12 (2): 304–306.

100. Dennehy, D.H. (2008). ―Rotavirus vaccines: an overview, Clinical Microbiology

Reviews 21 (1): 198–208.

Page 124: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

108

101. Gutierrez,M., Alvarado, M. and et al. (2007) ―Presence of viral proteins in

drinkable water—sufficient condition to consider water a vector of viral

transmission?‖, Water Research 41: 373–378.

102. Nair, S., et al., Role of size scale of ZnO nanoparticles and microparticles on

toxicity toward bacteria and osteoblast cancer cells. Journal of Materials Science:

Materials in Medicine,( 2009). 20 (0): 235-241.

103. Yamamoto, O., Influence of particle size on the antibacterial activity of zinc

oxide. International Journal of Inorganic Materials, (2001). 3 (7): 643-646.

104. Hogg, R.; Healy, T. W.; Fuersten, D. W. Mutual coagulation of colloidal

dispersions Trans. Faraday Soc. (1966) 62: 1638-1651.

105. Gregory, J., Approximate expressions for retarded van der waals interaction.

Journal of Colloid and Interface Science, 1981. 83(1): 138-145.

106. Yuan, B., M. Pham, and T.H. Nguyen, Deposition Kinetics of Bacteriophage

MS2 on a Silica Surface Coated with Natural Organic Matter in a Radial

Stagnation Point Flow Cell. Environmental Science & Technology, 2008. 42(20):

7628-7633.

107. Spanhel, L. and Anderson M.A., ―Semiconductor Clusters in the Sol-Gel

Process: Quantized Aggregation, Gelation, and Crystal Growth in Concentrated

ZnO Colloids‖, J. Am. Chem. Soc., 1991, 113, 2826-2833.

108. Stadtman, E.R. and R.L. Levine, Free radical-mediated oxidation of free amino

acids and amino acid residues in proteins. Amino Acids, 2003. 25(3): 207-218.

109. Kaplan, M. M. and Webster, R. G. (1977) The epidemiology of influenza.

Scientific American 237 (6), 88-106.

110. Lin, H. , Chen, Y. and Wang, W. (2005) Preparation of nanosized iron oxide and

its application in low temperature CO oxidation. J. Nanoparticle Research 7 , 249

111. Nel, A., et al., Toxic Potential of Materials at the Nanolevel. Science, 2006.

311(5761): p. 622-627.

112. Plewa, M.J., et al., Mammalian cell cytotoxicity and genotoxicity analysis of

drinking water disinfection by-products. Environmental and Molecular

Mutagenesis, 2002. 40(2): 134-142.

Page 125: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

109

113. Dufour, E.K., et al., Clastogenicity, photo-clastogenicity or pseudo-photo-

clastogenicity: Genotoxic effects of zinc oxide in the dark, in pre-irradiated or

simultaneously irradiated Chinese hamster ovary cells. Mutation

Research/Genetic Toxicology and Environmental Mutagenesis, 2006. 607(2):

215-224.

114. Yang, H., et al., Comparative study of cytotoxicity, oxidative stress and

genotoxicity induced by four typical nanomaterials: the role of particle size, shape

and composition. Journal of Applied Toxicology, 2009. 29(1): 69-78.

115. Sharma, V., et al., DNA damaging potential of zinc oxide nanoparticles in

human epidermal cells. Toxicology Letters, 2009. 185(3): 211-218

116. Rundell, M., et al, The comet assay: genotoxic damage or nuclear fragmentation

Environ. Mol. Mutagen. 2003, 42, (2), 61-67.

117. Tice, R. R., et al, Single cell gel/comet assay: guidelines for in vitro and in vivo

genetic toxicology testing. Environ. Mol. Mutagen. 2000, 35, (3), 206-221.

118. Ostrovsky, S., Selective cytotoxic effect of ZnO nanoparticles on glioma cells.

Nano Research, 2009. 2(11): 882.

119. Lin, W., Toxicity of nano- and micro-sized ZnO particles in human lung

epithelial cells. Journal of nanoparticle research, 2009. 11(1): 25.

120. Plewa, M.J., et al., Occurrence, Synthesis, and Mammalian Cell Cytotoxicity and

Genotoxicity of Haloacetamides: An Emerging Class of Nitrogenous Drinking

Water Disinfection Byproducts. Environmental Science & Technology, 2007.

42(3): 955-961.

121. George, S., et al., Use of a Rapid Cytotoxicity Screening Approach To Engineer

a Safer Zinc Oxide Nanoparticle through Iron Doping. ACS Nano, 2009. 4(1): 15-

29.

122. Oliver, M. H. A rapid and convenient assay for counting cells cultured in

microwell plates: application for assessment of growth factors. J. Cell Sci., 1989.

92: 513-518.

123. From Website: http://www.epa.gov/safewater/contaminants/index.htm

124. Wagner, E.D., et al., Analysis of mutagens with single cell gel electrophoresis,

flow cytometry, and forward mutation assays in an isolated clone of Chinese

Page 126: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

110

hamster ovary cells. Environmental and Molecular Mutagenesis, 1998. 32(4):

360-368

Page 127: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

111

CHAPTER 3

AN IMPROVED NANOTRIBOLOGICAL SYSTEM FOR HARD DISK DRIVES

3.1 Introduction

Future progress in the hard disc drive industry depends on achieving higher

storage densities and faster data access. This requires that the head-disk interface (HDI)

spacing be decreased to below 5nm and the spindle speed increased from 7,000 to over

15,000 rpm [1]. To achieve these spacings and spindle speeds, it is essential to come up

with a new and greatly improved lubricant [2, 3]. Perfluoropolyethers (PFPE) are almost

universally employed by the magnetic recording industry as hard disk lubricants. This is

due to several advantages of PFPE, including relatively low volatility, high thermal

stability, low surface energy, and excellent lubrication ability [4]. However, the

performance and lifetime of PFPE lubricants is proving to be inadequate for next

generation HDI. PFPE is mainly limited by insufficient chemical stability, a tendency for

stiction, and a tendency to spin off at the higher spindle speeds [5]. Recent research has

focused on trying to improve the tribology of the HDI by modifying PFPE lubricant end

groups, but none has led to molecularly thick uniform lubricant films with superior

thermal and tribochemical stability [6].

In this study, a new family of sterically hindered aliphatic polyester lubricants

was designed with the goal of overcoming some of the drawbacks of PFPE lubricants for

hard disk drive applications. Branching can greatly reduce the glass transition

temperature and crystallinity, while improving thermal and hydrolytic stability for more

severe HDI conditions. The polar ester groups in the polyester main chain should provide

sufficient dipole interactions between the lubricant and the substrate, minimizing the

Page 128: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

112

tendency for spin-off and dewetting [7]. In addition, polar lubricants may form a solid-

like boundary where the film thickness is under the 5nm range, and may possibly act to

reduce stiction problems [8]. The alkyl side groups will minimize the surface energy and

improve the interfacial interactions, leading to a stable uniform ultra-thin film. The polar

nature of esters also makes the polyester lubricant more miscible with a wide range of

solvents and dispersants. This allows the polyesters to dissolve easily and redistribute on

the carbon overcoat. In comparsion PFPE lubricants are relatively insoluble, and require

use of ozone-damaging solvents, such as Freon, during processing. The PFPE lubricants

also exhibit autophobicity, which can lead to formation of capillary wave patterns [9].

3.2 Materials and methods

2M lithium diisopropylamide in heptane /tetrahydrofuran /ethylbenzene,

isobutyric acid, 2-methyl butyric acid, 1, 3-dibromopropane, 1, 5-dibromopentane,

antimony oxide, triphenyl phosphate, trimethylacetyl chloride, 2,2,6,6-

tetramethylheptanedioic acid, 2,2-diethyl-1,3-dipropanediol, pyridine, chloroform and

hexane were all purchased from Aldrich. 2-ethyl-2-methyl-1, 3-propanediol was

purchased from Lancaster. The following materials were dried for 24hr under vacuum at

room temperature prior to use : 2,2,6,6-tetramethylheptanedioic acid, 2,2-diethyl-1,3-

dipropanediol and 2-ethyl-2-methyl-1,3-propanediol.

3.2.1 Characterizations

Fourier transform infrared spectroscopy (FT-TR)

FT-IR scans were acquired using a Nexus 670 FT-IR E.S.P. (Thermo Nicolet)

with 64 scans at 4 cm-1

resolution. Crystalline samples for FT-IR analysis were prepared

Page 129: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

113

by forming pellets with KBr powder. Liquid samples for FT-IR used chloroform as

solvent.

Nuclear magnetic resonance spectroscopy (NMR)

1H-NMR measurements were carried out using a Varian Unity 400NB NMR

system with CDCl3 as solvent.

Gel permeation chromatography (GPC)

GPC measurements were performed in tetrahydrofuran at 25°C with a Waters 515

HPLC pump, a Viscotek TDA model 300 triple detector, and a series of three Viscogel

7.8 × 300 mm columns (2 × GMHXL16141 and 1 × G3000HXL16136). Molecular

weights were determined using Viscotek's TriSEC software. The light scattering, mass,

and viscosity constants were determined from a single 96 kDa narrow polystyrene

standard and checked against other known polystyrene standards for accuracy. The

column exclusion limit was 1.0 × 107 Da, and the flow rate was 1.0 mL/min.

Differential scanning calorimetry (DSC)

DSC measurements were obtained with a Mettler Toledo Star System with a

heating rate of 10°C/min in a nitrogen atmosphere from -80°C to 80°C.

Thermal gravimetric analysis (TGA)

TGA measurements were made with a TA Instruments TGA 2950 with high

resolution option under a constant stream of nitrogen or air (100mL/min).

Hydrolytic stability characterization

Hydrolytic stability was characterized by saponification numbers using standard

test method ASTM-94. The lubricant sample was dissolved in 2-butane and refluxed with

KOH-ethanol solution. The excess alkali was titrated with standard acid and the

Page 130: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

114

saponification number was calculated and compared with the theoretical saponification

number, which represented 100% hydrolysis.

3.2.2 Materials synthesis

3.2.2.1 Monomer synthesis

Diacid monomers, 2, 2, 6, 6-tetramethylheptanedioic acid (I), 2, 6-diethyl-2, 6-

dimethylheptanedioic acid (II), and 2, 8-diethyl-2, 8-dimethylnonanedioic acid (III) were

synthesized according to the following protocols. (Scheme 1)

H3C CH1) LiN(iPr)2

Br(CH2)mBrCOOH

R

+ (CH2)m C

R

CH3

COOHC

R

CH3

HOOC2) H3O+

I: R=CH3, m =3,II: R=CH2CH3, m=3, III:R=CH2CH3, m=5

Figure 3.1 Synthetic protocols for diacid monomers

Representative synthesis, monomer I: 2,2,6,6-tetramethylheptanedioic acid.

2.0M solution of lithium diisopropylamide in heptane/tetrahydrofuran

/ethylbenzene (444.2mL) and hexane (250mL) were added into an oven-dried 1000ml 3-

neck round-bottomed flask at 0°C under dry nitrogen. The flask was equipped with a

pressure equalized dropping funnel and nitrogen inlet and outlet. The reaction mixture

was vigorously stirred throughout the entire reaction. Isobutyric acid (37.00g) and 1, 3-

dibromopropane (25g) were cooled to 0°C and then added sequentially dropwise over 30

min. The solution temperature was kept at 35°C for 1hr. The solution was washed with

HCl, deionized water, and extracted by chloroform. The chloroform layer was washed

with NaCl-saturated water solution and then dried over sodium sulfate. Evaporation of

chloroform yielded 31g (72%) of monomer I. The monomer I was further purified by

recrystallization from acetone/water mixture (1:1 volume ratio).

Page 131: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

115

Monomer I characterization

FT-IR analysis of monomer I showed three characteristic bands (caused by

COOH functional group). The broad band, centered in the range 2700-3000cm-1

, is

caused by the presence of OH, as well as CH stretch. Hydrogen bonding and resonance

weaken the C=O bond, resulting in absorption at a lower frequency than the monomer.

The band at 1701cm-1

is due to the C=O double bond stretch. Two bands arising from C-

O stretching and O-H bending appear in the spectra of carboxylic acids near 1320-1210

and 1440-1395 cm-1

, respectively.

1H-NMR of monomer I displayed four sets of functional groups: 1.18 (s, 12H,

CH3), 1.18-1.23 (m, 2H, CH2-CH2-CH2), 1.49 (t, 4H, CH2-CH2-CH2), 12.53 (s, 2H,

COOH). These results confirmed that 2, 2, 6, 6-tetramethylheptanedioic acid was

successfully synthesized and purified.

3.2.2.2 Polymer synthesis

Representative polymerization, copolymer 1

2,2,6,6-tetramethylheptanedioic acid (I)(28.85g ,150.26mmol), 2,2-diethyl-1,3-

dipropanediol(11.92g, 90.16mmol), and -ethyl-2-methyl-1,3-propanediol (10.66g,

90.16mmol) were melt polymerized in the presence of antimony oxide (0.5g) and

triphenyl phosphate (0.25g). The reaction mixture was held at 180°C at atmospheric

pressure for 15hr, and then at 190°C for 26hr. To complete the reaction, the pressure was

reduced to 1mm Hg with a vacuum pump over 2hr. The viscous fluid was cooled down

to room temperature, dissolved in chloroform, and then filtered to remove the antimony

oxide. A viscous transparent liquid lubricant was obtained by evaporation of chloroform

under vacuum at 70°C.

Page 132: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

116

HO C C

O CH3

CH3

(CH2)m C

CH3

CH3

C OH

O

HO CH2 C

CH2

(CH2)n

CH2 OH

CH3

CH3

H O CH2 C

CH2

(CH2)n

CH3

CH3

CH2 O C

O

C

CH3

CH3

HC

CH3

CH3

C

O

O CH2 C

CH2

(CH2)n

CH3

CH3

H2C OH

x

Sb2O

3, (PhO)

3P

H3C C

CH3

CH3

C

O

Cl

O CH2 C

CH2

(CH2)n

CH3

CH3

CH2 O C

O

C

CH3

CH3

(CH2)m C

CH3

CH3

C

O

O CH2

C

CH2

(CH2)n

CH3

CH3

CH2

x

H3C C

CH3

CH3

C

O

O C

O

C

CH3

CH3

CH3

+

(CH2)m

Figure 3.2 Condensation and end-group conversion for polyester lubricants

Copolyemer 1, copolyemer 2 and copolymer 3 are synthesized as the following: (Table

3.1)

Table3.1. Monomers for sterically hindered aliphatic polyester lubricants

Copolymers Diacid monomer Diol monomers(1:1 molar ratio) Copolymer1 2,2,6,6-tetramethyl heptanedioic acid 2,2-diethyl-1,3-propanediol,

2-ethyl-2-methyl-1,3-propanediol

Copolymer2 2,6-diethyl-2,6-dimethyl heptanedioic acid 2,2-diethyl-1,3-propanediol, 2-ethyl-2-methyl-1,3-propanediol

Copolymer3 2,6-diethyl-2,6-dimethyl heptanedioic acid, 2,8-diethyl-2,8-dimethyl nonanedioic acid

mixture(1:1 molar ratio)

2,2-diethyl-1,3-propanediol, 2-ethyl-2-methyl-1,3-propanediol

Coploymer 1 characterization

Page 133: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

117

The reaction was monitored by FT-IR. The strong broad OH stretch due to COOH

(2700-3000 cm-1

) disappeared. Carbonyl C=O double bond stretch in diacid monomers

had sharp absorption at 1701cm-1

. As the polymerization reaction progressed, the

absorption peak shifted to a higher value (1717cm-1

). The sharp adsorption peak at

1216cm-1

was due to the ester group formation.

1H-NMR of monomer I displayed five sets of functional groups: 1.18 (s, 12H,

CH3), 1.18-1.23 (m, 2H, CH2-CH2-CH2), 1.49 (t, 4H, CH2-CH2-CH2), 3.57-3.69 (t, 4H -

CH2OH), 3.82-4.199 (d, 2H-CH2OCO)

Representative capping of copolymer 1

Trimethylacetyl chloride (3.62 g, 30mmol) in chloroform (100mL) solvent was

added dropwise to a solution of copolyester I (6.83g) in chloroform (200mL) and

pyridine (2.77 g, 35mmol) at 5°C. The mixture was stirred for 1.5hr allowing the

solution to warm up to room temperature during the last hour; the solution was refluxed

for 2hr. The pyridinium chloride was filtered off after the reaction mixture was cooled

down to room temperature. 5% HCl solution (300mL) was added to the reaction mixture.

The organic layer was washed several times with water until it was acid free, and was

then dried with sodium sulfate. A yellowish viscous fluid was isolated from chloroform,

after drying with a water aspirator at 80°C.

Capped Copolymer 1 Characterization

The reaction was monitored by FT-IR. The peak at 2870-2980 cm-1

became

sharper. The carbonyl group in copolymer1 had sharp absorption at 1717cm-1

, and, as

esterification progressed, the absorption peak shifted to a higher value at 1729cm-1

.

Page 134: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

118

1H-NMR of monomer I displayed four sets of functional groups: 1.18 (s, 12H,

CH3), 1.18-1.23 (m, 2H, CH2-CH2-CH2), 1.49 (t, 4H, CH2-CH2-CH2), 3.82-4.20 (d, 2H-

CH2OCO). The disappearance of peak 3.57-3.69 (t, 4H -CH2OH) indicated that the

esterification was completed.

GPC (g/mol): Mw=820, PDI= 4.316

3.3 Results and discussions

Figure 3.3 Tg of sterically hindered aliphatic copolyesters using a 5°C/min heating

rate

DSC measurements on capped copolymer1, prepared from 2,2,6,6-

tetramethylheptanedioic acid (I), 2,2-dimethyl-1,3-propanediol and 2-ethyl-2-methyl-1,3-

propanediol (molar ratio 5:3:3) are shown in (Figure 3.3). As can be seen, there is a glass

transition at -47.35°C and a large melting endotherm at 42°C.

-60 -40 -20 0 20 40 60 80

Tg= -67.47

oC

Copolyester 3

Tg= -54.04

oC

Copolyester 2

DS

C H

ea

t F

low

(A

rbit

rary

Un

its

)

Temperature (oC)

m.p=42oC

Tg= -47.35

oC

Copolyester 1

Page 135: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

119

Introduction of ethyl groups in the diacid monomers will introduce further

irregularities into the main chain, and therefore could lower the crystallinity of the

polymers. Capped Copolyester2, which was prepared from 2,6,-diethyl-2,6-

dimethylheptanedioic acid, 2,2-dimethyl-1, 3-propanediol and 2-ethyl-2-methyl-1, 3-

propanediol (molar ratio 5:3:3), displayed a lower Tg at -54.04°C and no melting

endotherm was observed.

100 200 300 400

0

20

40

60

80

100

We

igh

t (%

)

Temperature (o

C)

In N2

In Air

Figure 3.4 Thermal stability of sterically hindered aliphatic copolyester using a

10°C/min heating rate in air and in N2

Additional asymmetry in the molecular structure could be achieved by

copolymerizing a mixture of monomers from copolymers1 and 2. Thus, capped

copolymer3, which was prepared from 2,6,-diethyl-2,6-dimethylheptanedioic acid(II), 2,8-

diethyl-2,8-dimethylnonanedioic acid(III), 2,2-dimethyl-1,3-propanediol and 2-ethyl-2-

Page 136: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

120

methyl-1,3-propanediol (molar ratio 1:1:1.2:1.2), the Tg was lowered to -67.47°C, and no

melting endotherm was observed (Figure 3.3).

The thermal degradation behavior of the sterically hindered copolyester3 in an

Al2O3 crucible shows no weight loss up to 230°C under N2 and no degradation up to

185°C in air. Isothermal measurements in air at four different temperatures for

copolyester3 demonstrate excellent long-term thermal stability from 100-150°C (Figure

3.4). In comparison, PFPE has a relatively weak physical absorption on the carbon

overcoat and shows up to 96% weight loss after 1hr at 200°C [10].

The hydrolytic stability was tested by refluxing 30 min in 0.5 N alcoholic KOH.

Copolyester1, copolyester2 and copolyester3 showed 20.7%, 5.7% and 4.9% hydrolysis,

respectively. In comparison, conventional polyesters would hydrolyze completely under

the test conditions.

3.4 Conclusions

In conclusion, we have successfully synthesized sterically hindered polyester

lubricants with improved thermal stability, oxidation resistance, low glass transition

temperature and crystallinity, and good hydrolytic stability. These new materials are a

promising alternative to PFPE for hard disk drive lubricants. We expect these aliphatic

polyester lubricants to have much stronger bonding to a carbon overcoat than PEFE,

which will effectively alleviate the spin-off and dewetting problem for the hard disk drive

industry.

3.5 References

1. Juang, J. and Bogy, D. (2005) ―Nanotechnology Advances and Applications

Information Storage‖, Microsyst Technol 11(8): 950-57.

Page 137: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

121

2. Economy, J. Professor Economy‘s Group Currently Pursues the Following Areas

of Research on Advanced Materials‘, ULR:

http://economy.mse.uiuc.edu/research.htm

3. Hitachi Global Storage Technologies, ‗Storage Technology‘, URL:

http://www.hitachigst.com/hdd/research/storage/adt/index.html

4. Chen, C. Bogy, D. and Singh, B. (2001) ‗Effects of Backbone and Endgroup on

the Decomposition Mechanisms of PFPE Lubricants and their Tribological

Performance at the Head-Disk Interface‘, Transaction of the ASM 123(2): 364-67.

5. Homola, A.M. (1996) ‗Lubrication Issues in Magnetic Disk Storage Devices‘,

IEEE Transactions on Magnetics 32(3):1812-18.

6. Xiao, W. (2005) New Materials Systems for Advanced Tribological and

Environmental Applications, University of Illinois at Urbana-Champaign

7. Hatco Corporation, About Ester Chemistry Web Site, URL:

www.hatcocorporation.com/pages/syntheticlubes/aboutesters.htm

8. Fabio, B. (1997) The Application of Advanced Materials to Four Unique

Problems Involving Surface Interfaces, University of Illinois at Urbana-

Champaign.

9. Karis, T. Kim, W. Jhon, M.S. (2005) Tribology Letter 18(1): 27-41.

10. Kasai, P. H. Tang, W. T.Wheeler, P. (1991) Applied Surface Science 51(3-4):

201-11.

Page 138: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

122

CHAPTER 4

OPTIMIZATION OF NEW ULTRALOW-K MATERIALS FOR ADVANCED

INTERCONNECTIONS

4.1 Introduction

The demand for increased signal transmission speed and device density in the

next generation of multilevel integrated circuits has placed stringent demands on

materials performance [1]. The International Technology Roadmap for Semiconductors

(ITRS), 2005 Update indicates that ultra-low k materials will be required for interlevel

metal insulators [2]. Currently, integration of the ultra low-k materials in dual

Damascene requires chemical mechanical polishing (CMP) to planarize the copper.

Unfortunately, none of the proposed dielectric candidates display the desired mechanical

and thermal properties for successful CMP [3].

Recent advances in the synthesis of a new family of aromatic polymers made in

our group allow, for the first time, the ability to design a dielectric with an ultra-low k

value, as well as excellent mechanical and thermal properties. Success in this endeavor

will result in new market opportunities worth at least 600 million dollars per year for low

k dielectrics [4].

Work in the past three years in our group has shown that a condensed aromatic

polynuclear based on diethynyl and triethynyl benzene has an extremely high modulus

and hardness [5, 6]. Such a system could provide a unique solution to the problem, as

compared to any other known family of polymers [7, 8]. The chemical nature of the

oligomer is shown below in Figure 1, with a proposed structure for the cured polymer [9].

As expected, such a polymer is very thermally stable, with practically zero weight loss at

400C. Curing of the oligomer was accompanied by a larger exotherm at 280C [10].

Page 139: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

123

Exotherm is not expected to be a problem, since the dielectric thickness is 1.0m or

lower, a level where excess heat would be easily dispersed. The oligomer is cured in the

presence of porogen, such as low Mw polystyrene or abietic acid to yield closed pores

from 18 nm (polystyrene) to 5nm (abietic acid).

Figure 4.1 Schematic synthesis of DEB-co-TEB [5, 9]

In Table 4.1 is a summary of the electrical properties of these films containing

poragen from zero to 40% [11]. This new family of polymers displays a very high

hardness and modulus, properties essential for successful CMP. As can be seen in Figure

4.2, the mechanical properties of samples containing up to 40% porogen are as good as

Ar

Ar

Ar Ar

Ar Ar

Proposed structure

C CH

C CH

n

C

C C

CH

HC CH

m+

CuCl / O2

Pyridine

CHC+

Capping agent

n

m

C CCC CC C C

C

C C

C C

C C

C

Ar

Ar

Ar Ar

Ar Ar

Proposed structure

Ar

Ar

Ar Ar

Ar Ar

Proposed structure

C CH

C CH

n

C

C C

CH

HC CH

m+

CuCl / O2

Pyridine

CHC+

Capping agent

n

m

C CCC CC C C

C

C C

C C

C C

C

C CH

C CH

n

C

C C

CH

HC CH

m+

CuCl / O2

Pyridine

CHC+

Capping agent

n

m

C CCC CC C C

C

C C

C C

C C

C

Page 140: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

124

nearly all of the candidate materials with no porogen, shown in Table 4.2. This means

that we appear to have met the original goals of the ITRS roadmap with respect to

achieving the desired low k material, with the requisite modulus and hardness.

Figure 4.2 Young’s modulus and hardness of 700nm film on Si wafer [5, 9]

The cured polymer with no porogen displays an outstanding thermal resistance

(1.56% weight loss at 425C after 8hours). An important goal was to show that use of

porogens, such as low MW polystyrene, yielded a closed micropore structure. This was

successfully demonstrated using scanning electron microscopy. There is a near-linear

relationship in a plot of dielectric constant with amount of porogen (Table 4.1). Most

importantly, values as low as 1.85 could be obtained with 40% porogen, which is

significantly lower than the goals of the ITRS roadmap [5, 9].

0 10 20 30 400

2

4

6

8

10

12

14

16

18

Har

dn

ess

(GP

a)

E

lastic m

od

ulu

s (

GP

a)

Loading weight percent of porogen (wt%)

0

2

4

6

8

10

16.8

3.5

0 10 20 30 400

2

4

6

8

10

12

14

16

18

Har

dn

ess

(GP

a)

E

lastic m

od

ulu

s (

GP

a)

Loading weight percent of porogen (wt%)

0

2

4

6

8

10

16.8

3.5

Page 141: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

125

Table 4.1 Electronic properties of cured DEB-co-TEB [5, 9]

Porogen

(wt%)

Capacitance

(pF)

Thickness

(m)

Dielectric

Constant

Dielectric

Loss

Breakdown

Strength

(V/m)

0 6.2 0.85 2.70 0.002 > 235

9% 5.89 0.86 2.59 0.02 > 232

15% 5.28 0.90 2.43 0.04 > 222

20% 4.92 0.95 2.39 0.03 > 211

25% 4.47 1.02 2.26 0.02 > 196

30% 4.17 1.00 2.13 0.02 > 192

35% - 0.92 2.03 0.03 > 217

40% - 0.91 1.85 0.02 > 220

Porogen: Polystyrene

4.2 Materials and methods

4.2.1 Materials

m-Diethynylbenzene monomer was purchased from Lancaster Synthesis Inc.

(Pelham, NH). 1, 3, 5-Triethynylbenzene was obtained from Alfa Aesar (Ward Hill,

MA). Polyimide (PI-2808) was purchased from HD MicroSystems (Parlin, NJ). Other

chemicals were purchased from Aldrich (Milwaukee, WI). All chemicals were used as

received, except for abietic acid, which was purified by heating to 260⁰C under vacuum

twice, and then partially collected at 260⁰C.

4.2.2 Synthesis and processing of poly (DEB-co-TEB)

Synthesis of oligomer (m-Diethynylbenzene)-co-(Triethynylbenzene) (DEB-co-TEB)

14.0 g (0.11 mol) of m-diethynylbenzene (DEB), 5.56 g (0.037 mol) of 1,3,5-

triethynylbenzene (TEB), extra phenylacetylene, and 8.3 mL of an acetone/pyridine

mixture (50:50 volume ratio) in 200 mL of acetone was added into a vigorously stirred

catalyst solution containing 13.3 g (0.13 mol) of Cu2Cl2, 8.3 mL of the acetone/pyridine

mixture (50:50 volume ratio), and 700 mL of acetone. The catalyst solution was pre-

Page 142: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

126

oxidized by bubbling O2 through for about 10 min before addition. The O2 flow was

continued throughout the rest of the reaction. 16.6 mL of the acetone/pyridine mixture

was added over a period of 10 min. The reaction was conducted in the dark by covering

the reaction flask with aluminum foil for 12 h. The reaction mixture was poured into

HCl/methanol solution. The precipitate was collected, washed with methanol, and

dissolved in chloroform. The solution was washed with HCl and deionized water, dried

with MgSO4, filtered, and precipitated from methanol. The solid was vacuum-dried at

50-55⁰C overnight to afford 10.2 g of a light-orange powder.

Fabrication of dense thin film

A 25-35 wt % DEB-co-TEB oligomer in cyclohexanone solution was spin-coated

onto a silicon wafer or GaAs wafer to form a thin film. The thin film was soft-baked at

110⁰C for 1 min in air, cured at 200⁰C for 30 min, and heated at 450⁰C for 30 min in a

vacuum annealer [5, 9].

Fabrication of porous film

Low molecular weight polystyrene (Mw = 780) was used as a porogen and

dissolved in THF to provide a 25 wt % solution A. Another type of solution A was

prepared by replacing polystyrene with abietic acid and selecting acetone as a solvent.

Solution B was prepared by dissolving DEB-co-TEB into cyclohexanone at a 25 wt %

concentration. Solutions A and B were mixed at various weight ratios to form a new

solution by stirring at room temperature for 2h and then allowing it to sit for over 12h.

The resulting solutions were spin-coated onto Si wafer dices or metal (gold)-deposited Si

wafer dies and soft-baked on a hot plate at 110⁰C for 1 min to remove most of the

solvent. The wafer was then cured in a vacuum annealer under controlled heating. A

Page 143: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

127

typical curing recipe for forming a porous film was as follows: ramp at 5⁰C/min to

200⁰C, hold at 200⁰C for 30 min, ramp at 5⁰C/min to 250⁰C and hold for 30 min, ramp at

5⁰C/min to 350⁰C and hold for 30 min, and then ramp at 5⁰C/min to 450⁰C and hold for

30 min to burn out the porogen. The film was then cooled to room temperature at

5⁰C/min [5, 9].

Oxygen plasma etching

The photo-resist AZ-5241E was spun at 4700rpm for 30s onto the 450 nm

thickness poly (DEB-co-TEB). The wafer was soft baked at 110 °C for 30s and then was

put on a cold plate to cool down to room temperature. These samples were covered by a

mask which measured 300 microns and exposed in a Karl Suss MJB3 UV365nm mask

aligner to UV light with an intensity of 11.0 mw/cm2

for 19s. After removing the mask,

the films were immersed into AZ-351B developer for 45s. Finally DI water was used to

rinse out all uncured monomer and the samples were air dried.

Poly (DEB-co-TEB) thin films coated with cured photo resistors were treated in

the PlasmaLab Freon/O2 Reactive Ion Etch (RIE) System. The flow of oxygen through

the system was adjusted with a volume flow controller, and the pressure was measured

with an absolute vacuum gauge. In our experiments, the oxygen flow was adjusted to

60.0sccm, which gave a pressure of 300 mtorr. The samples were etched at a

rate=40nm/min for 13mins.

Finally, the samples were soaked in acetone solution to remove cured photo-

resist.

Profilometer

Page 144: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

128

We used the AlphaStep 200 computerized surface profilometer auto-levels and

auto-scales step to measure thin film step heights with the vertical resolution at 5Å.

4.2.3 Thermal properties characterization

DSC

DSC measurements were obtained with a Mettler Toledo Star System with a

heating rate of 10°C/min in a nitrogen atmosphere from 20°C to 200°C.

Normal-to-plane coefficient of thermal expansion (CTE)

For Normal-to-Plane CTE of the poly (DEB-co-TEB), before thermal

measurements, the surface of the diffusion multiple was cleaned with polishing cloth to

remove the trace of the microprobe and then coated with an Al film of 116 nm thickness

by magnetron sputtering at room temperature. The thermal conductivity was measured

by time-domain thermoreflectance.

In-plane CTE

Identical 500nm poly (DEB-co-TEB) thin films were fabricated onto a 2‖ Si

wafer and a 2‖ GaAs wafer. A residual stress measurement tool (Frontier Semiconductor,

FSM 500 TC) was used to determine the residual tensile or compressive stress in the

films by measuring the changes of curvature induced in a wafer due to the deposited film.

A typical measure heat cycle is as follows: measure from at 20⁰C, then ramp at 1⁰C/min

to 400⁰C, then cool down to room temperature.

4.3 Results and discussions

The research at its present stage of development appears to offer an avenue for

designing an ultra low k dielectric, which display the desired modulus and hardness

values to withstand the process of CMP. Initial experiments with oxygen etching suggest

Page 145: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

129

Figure 4.3 Plasma etching on the poly (DEB-co-TEB) 450nm thin films. a) contact

UV lithography technique to write the etching pattern; b)after etch by

RIE O2 plasma; c) remove photo-resist.

Page 146: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

130

a high probability of success for achieving vertical profiles (Figure 4.3). This system can

potentially be implemented directly into an assembly line for dielectric films.

The unusually high modulus and hardness values observed suggest that they arise

from the formation of a layered aromatic structure, which implies an ability to match the

CTE of substrates such as Si and Ta. This would sharply reduce stresses at the interfaces.

However, in the perpendicular direction one would have to design around a somewhat

increased CTE. Efforts to further enhance the adhesive characteristics of the dielectric to

Si and Ta appear promising incorporating thermally resistant polyester groups into the

diacetylene oligomer [5]. The potential exists to further improve the thermal conductivity

over the measured value of 0.33 W/m, as shown in Figure 4.4 Experimental data (ο) and

calculated results (solid line). The thermal capacity of poly (DEB-co-DEB) is 1.4Jcm-3

K-1

(Figure 4.5).

Figure 4.4 Thermal conductivity of poly (DEB-co-DEB) film used in the thermal

model are 0.33 Wm-1

K-1

10-1

100

0.5

1

t (ns)

-Vin

/Vout

Page 147: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

131

The very high modulus and hardness values already observed suggest that the

formation of the layered aromatic structure may tend to match the CTE of substrates such

as Si and Ta, minimizing stresses at the interface. These include the coefficient of thermal

expansion (CTE), biaxial thermal stress, and thermal conductivity. Thus the CTE in the

perpendicular direction is 2.0*10-5

K-1

and in planar direction 8.0*10-6

K-1

(Table 4.1). The

low CTE provides a better match to the Si substrate which also minimizes interfacial

stress and greatly enhances the reliability of the microprocessors.

40 60 80 100 120 140 160 180

-1

0

1

2

3

4

He

at

Ca

pa

cit

y (

J c

m-3 K

-1)

Temperature (oC)

Figure 4.5 Thermal capacity of poly (DEB-co-DEB) film used in the thermal model

are 1.4Jcm-3

K-1

Table 4.2 Coefficient of Thermal Expansion of cured poly (DEB-co-TEB)

Film Thickness 510nm In-Plane (2‖Wafer) Normal-to-Plane

Intrinsic DEB-co-TEB 8.0*10

-6

K-1

2.0*10-5

K-1

DEB-co-TEB With 20% Porogen 7.3*10

-6

K-1

1.7 *10-5

K-1

Porogen: Polystyrene

Page 148: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

132

4.4 Conclusions

The research at its present stage of development appears to offer the avenue for

designing an ultra low k dielectric, which can display the desired modulus and hardness

values to withstand the process of CMP. Initial experiments with oxygen etching suggest

a high probability of success for achieving vertical profiles. This system can potentially

be implemented directly into an assembly line for spin coating of dielectric, followed by

porogen evolution to yield the desired dielectric. The formation of the layered aromatic

structure may tend to match the CTE of substrates such as Si and Ta, minimizing stresses

at the interface. The near and long term significance to the semiconductor industry

would be to reverse the current policy of compromise in the goals of the industry road

map and put the program back on its original path.

4.5 References

1. ITRS Roadmap for Semiconductors Interconnect (2005)

2. R.J.O.M. Hoofman, G.J.A.M. Verheijden, J. Michelon, F. Iacopi,Y. Travaly, M.R.

Baklanov, Zs. T kei, G.P. Beyer Microelectronic Engineering (2005), 80, 337–344

3. C.M. Garner G. Kloster, G. Atwood, L. Mosley, A.C. Palanduz, Microelectronics

Reliability (2005), 45, 919–924

4. Yongqing Huang, John McCormick, James Economy. Polymers for Advanced

Technologies (2005), 16(1), 1-5

5. Yongqing Huang, James Economy. Macromolecules (2006), 39, 5, 1850-1853.

6. Ken Schroeder. Future FAB international (2005), 19,18-21

7. Thomas Neenan, Matthew Callstrom, Louis Scarmoutzos, George Whitesides.

Macromolecules (1988), 21, 3528-3530

8. James Economy. High Temperature Polymers for Electronic Applications, Plenum

Press, Contemporary Topics in Polymer Science (1984), 5, 351-375

9. Yongqing Huang. PhD Dissertation: Design of Novel High Temperature

Thermosetting Resins Tailored to Specific Needs (2004).

Page 149: APPLICATIONS FOR NANOMATERIALS IN CRITICAL TECHNOLOGIES.pdf

133

10. A.C. Diebold. Handbook of Silicon Semiconductor Metrology (2001)

11. From website: URL: http://www.physorg.com/news5067.html