Al Azhar University

Faculty of Science Chemistry Department

Nanotechnology and Its Applications

Submitted By

Mahmoud Ahmed Abd El-Maabud Abo Omar

4th Year Special Chemistry

Under Supervision of

Dr. Essam Shawky Abd El Hady Khattab

Doctor of Medical Biochemistry

And Molecular Biology

2014 - 2015

Contents

Introduction

1.1 Definition 1

1.2 Origins

2

Characterization of Nanotechnology 5

2.1 Observing with photons 5

2.1.1 The optical microscope in visible light 5

2.1.2 X-ray machines. 6

2.2 Observing with electrons: 7

2.2.1 The transmission electron microscope (TEM). 8

2.2.2 The scanning electron microscope (SEM).

9

Synthesis of Nanocrystals 10

3.1 Physical Methods 10

3.1.1 Inert Gas Condensation 10

3.1.2 Arc Discharge 10

3.1.3 Ion Sputtering 11

3.1.4 Laser Ablation 11

3.1.5 Pyrolysis and Other Methods 11

3.1.6 Spray Pyrolysis 12

3.2 Chemical Methods 12

3.2.1 Metal Nanocrystals by Reduction 12

3.2.2 Solvothermal Synthesis 15

3.2.3 Photochemical Synthesis 16

3.2.4 Electrochemical Synthesis 17

3.2.5 Nanocrystals of Semiconductors and Other

Materials by Arrested Precipitation 20

3.2.6 Thermolysis Routes 21

3.2.7 Sonochemical Routes 25

3.2.8 The Liquid–Liquid Interface 26

3.3 Biological Methods 27

APPLICATIONS OF NANOTECHNOLOGY

4.1 History 30

4.2 Nano-medicine 31

4.2.1 Cancer treatment 32

4.3 Nano-biotechnology 34

4.4 Green nanotechnology 36

4.4.1 Current research 36

4.5 Energy applications 38

4.6 Industrial applications 39

4.6.1 Military 40

4.6.2 Construction 42

5 References 51

1

Introduction

1.1 Nanotechnology:

It is defined as the study and use of structures between 1 nanometer

and 100 nanometers in size. To get an idea of how small that is, it would

take eight hundred 100 nanometer particles side by side to match the

width of a human hair.

A nanometer is one billionth of a meter (10-9

m) and is the unit of length

that is generally most appropriate for describing the size of single

molecules. The nanoscale marks the nebulous boundary between the

classical and quantum mechanical worlds; thus, realization of

nanotechnology promises to bring revolutionary capabilities. Fabrication

of nanomachines, nanoelectronics and other nanodevices will

undoubtedly solve an enormous amount of the problems faced by

mankind today.

If one looks at current forecasts for nanotechnology, often reads

outstanding sentences such as “Small is Big”, “Big Plans for the Tiny

World”, “Nanotechnology: It’s a small, small, small world” etc. Several

countries have been steadily allocating more resources for

nanotechnology R&D studies. The reason behind is that forecasters have

already projected that expertise in nanotechnology will be a key factor of

the economical leadership in the 21st century.

Nanoscience is an interdisciplinary field that seeks to bring about

mature nanotechnology. Focusing on the nanoscale intersection of fields

2

such as physics, biology, engineering, chemistry, computer science and

more, nano science is rapidly expanding. Nanotechnology centers are

popping up around the world as more funding is provided and

nanotechnology market share increases. The rapid progress is apparent by

the increasing appearance of the prefix "nano" in scientific journals and

the news. Thus, as we increase our ability to fabricate computer chips

with smaller features and improve our ability to cure disease at the

molecular level, nanotechnology is here.

1.2 Origins:

The concepts that seeded nanotechnology were first discussed in 1959

by renowned physicist Richard Feynman in his talk There's Plenty of

Room at the Bottom, in which he described the possibility of synthesis

via direct manipulation of atoms. The term "nano-technology" was first

used by Norio Taniguchi in 1974, though it was not widely known.

Inspired by Feynman's concepts, K. Eric Drexler used the term

"nanotechnology" in his 1986 book Engines of Creation: The Coming Era

of Nanotechnology, which proposed the idea of a nanoscale "assembler"

which would be able to build a copy of itself and of other items of

arbitrary complexity with atomic control. Also in 1986, Drexler co-

founded The Foresight Institute (with which he is no longer affiliated) to

help increase public awareness and understanding of nanotechnology

concepts and implications.

Thus, emergence of nanotechnology as a field in the 1980s occurred

through convergence of Drexler's theoretical and public work, which

3

developed and popularized a conceptual framework for nanotechnology,

and high-visibility experimental advances that drew additional wide-scale

attention to the prospects of atomic control of matter. In 1980s two major

breakthroughs incepted the growth of nanotechnology in modern era.

First, the invention of the scanning tunneling microscope in 1981

which provided unprecedented visualization of individual atoms and

bonds, and was successfully used to manipulate individual atoms in 1989.

The microscope's developers Gerd Binnig and Heinrich Rohrer at IBM

Zurich Research Laboratory received a Nobel Prize in Physics in 1986.

Binnig, Quate and Gerber also invented the analogous atomic force

microscope that year.

Second, Fullerenes were discovered in 1985 by Harry Kroto, Richard

Smalley, and Robert Curl, who together won the 1996 Nobel Prize in

Chemistry. C60 was not initially described as nanotechnology; the term

was used regarding subsequent work with related graphene tubes (called

carbon nanotubes and sometimes called Bucky tubes) which suggested

potential applications for nanoscale electronics and devices.

In the early 2000s, the field garnered increased scientific, political,

and commercial attention that led to both controversy and progress.

Controversies emerged regarding the definitions and potential

implications of nanotechnologies, exemplified by the Royal Society's

report on nanotechnology.Challenges were raised regarding the feasibility

of applications envisioned by advocates of molecular nanotechnology,

4

which culminated in a public debate between Drexler and Smalley in

2001 and 2003.

Meanwhile, commercialization of products based on advancements in

nanoscale technologies began emerging. These products are limited to

bulk applications of nanomaterials and do not involve atomic control of

matter. Some examples include the Silver Nano platform for using silver

nanoparticles as an antibacterial agent, nanoparticle-based transparent

sunscreens, and carbon nanotubes for stain-resistant textiles.

Governments moved to promote and fund research into

nanotechnology, beginning in the U.S. with the National Nanotechnology

Initiative, which formalized a size-based definition of nanotechnology

and established funding for research on the nanoscale.

By the mid-2000s new and serious scientific attention began to

flourish. Projects emerged to produce nanotechnology roadmaps which

center on atomically precise manipulation of matter and discuss existing

and projected capabilities, goals, and applications.

5

Characterization of Nanoparticles

What is characterization?

-Characterization refers to study of materials features such as its

composition, structure, and various properties like physical, electrical,

magnetic, etc.

Why is characterization of nanoparticles important?

-Nanoparticle properties vary significantly with size and shape

-Accurate measurement of nanoparticles size and shape is, therefore,

critical to its applications

2.1 Observing with photon:

2.1.1 The optical microscope in visible light

The optical microscope was the first instrument that enabled man

to observe objects normally invisible to the naked eye. As the microscope

is subject to the laws of optics, its resolution is limited to several tenths of

a micron. In order to study samples from living organisms, the samples

must be prepared with coloration techniques

A new generation of microscope which uses laser light appeared in

the 1980s. It has enabled scientists to create three dimensional images at

different levels of depth of the matter being studied by using focalization

and laser beam scanning. This type of microscope is known as a confocal

microscope1 and is particularly adapted for use in the natural world

One very interesting use of these microscopes corresponds to their

ability to work with fluorescent markers. The laser beam excites a

fluorescent substance which has been added to the sample, for which we

know the affinity for certain molecular sites. Thanks to these markers we

6

can, for example, selectively view certain reactions. The fluorescent

signals are detected by electronic

2.1.2 X-ray machines

X-rays are photons with a wavelength that is much shorter than the

wavelength of ultraviolet light. X-rays are produced from an accelerated

shock of electrons against a metallic target.

One of the first applications of machines using X-rays was in the

macroscopic domain. The X-rays benefit from the fact that this radiation

has a strong penetrating power in materials with the rate of absorption

depending on the density of the material. Radiation transmitted through a

body coated with a phosphorescent or photosensitive substance is

commonly known as radio waves. A sophisticated version of this type of

machine is the X-ray scanner. The transmitter turns around the object at

the same time as the receptor does, measuring the intensity of the X-rays

7

transmitted. The data is processed by a computer which reconstructs

cross- sections of the object, in other words 3-D imagery. The resolution

is determined by the quality of the X-ray beam used. This type of

machine is used in many applications, especially in medical imagery .

Another type of machine, which uses the interactive properties of

X-rays with crystalline structures, is used in X-ray spectroscopy. These

machines enable scientists to investigate objects in the nanoworld. Their

operation rests on the following principle: a crystal is made up of

identical patterns of atoms following a particular lattice whose chain is

the same size as the wavelength of the X-ray. The X-rays are realigned by

selective reflection in predetermined directions and then form diffraction

figures. The information contained in the diffraction figures clearly deals

with the structure of the lattice and, more specifically, the rather complex

three-dimensional structures of atomic patterns. This analysis is possible,

firstly, due to the quality of today’s machines and, secondly, because of

the sophisticated calculation techniques used. This type of machine is an

essential tool for chemists who want to assemble molecules in crystalline

form in order to study their atomic pattern. This method enabled the

discovery of the double helix by Francis Crick and James Watson in

19532

2.2 Observing with electrons

Electron microscopy uses the wave properties of electrons.

However, as particles they need a vacuum in order to travel. Microscopes

are in the form of a metal vacuum enclosure in which the following can

be found:

– The electron gun, such as in cathode ray tubes used in television sets.

8

– The different elements of electronic optics, such as electromagnetic

lenses (equivalent to traditional optic lenses) which control the

trajectories of the electrons as well as the support of the object to be

studied .

There are two types of electron microscope

The transmission electron microscope (TEM)

The scanning electron microscope (SEM)

2.2.1 Transmission Electron Microscope(TEM):

-Operation: Image is generated based on the interaction pattern of

electrons that transmit through the specimen

-Variation: Scanning Transmission Electron Microscope

-Advantages: Additional analysis techniques like X-ray spectrometry are

possible with the STEM, high-resolution , 3-D image construction

possible but aberrant

-Limitations: Needs high-vacuum chamber, sample preparation necessary,

mostly used for 2-D images

9

2.2.2 Scanning Electron Microscope (SEM):

-Operation: Generates image by scanning the surface of the sample in a

raster pattern, using an electron beam

-Modes of operation:

-i. Secondary electrons

-ii. Back-scattered electrons (BSE)

-iii. X-rays

-Advantages: Bulk-samples can be observed and larger sample area can

be viewed, generates photo-like images, very high-resolution images

are possible

-Disadvantages: Samples must have surface electrical conductivity, non-

conductive samples need to be coated with a conductive layer

11

Synthesis of Nanocrystals

Modern materials science is characterized by a close interplay with

physics, chemistry, and biology. This is especially true of nanomaterials,

as vividly demonstrated by the methods of synthesis employed for these

materials. On the one hand, are the top-down methods which rely on

continuous breakup of bulk matter while on the other are the bottom-up

methods that build up nanomaterials from their constituent atoms. The

top-down and bottom-up approaches can also be considered as physical

and chemical methods, respectively. A variety of hybrid methods have

since come into being.

3.1- Physical Methods

3.1.1 Inert Gas Condensation

This method is most widely used and provides straightforward

means to prepare nanosized clusters, especially of metals. A metal foil or

ingot is heated in a ceramic crucible placed in a chamber filled with an

inert gas, typically a few torr of argon. Thme etal vapor cools rapidly

losing energy on collision with argon atoms, thereby producing

nanoparticles.

3.1.2 Arc Discharge

Another means of vaporizing metals is to strike an arc between

metal electrodes in the presence of an inert gas. Weber used this method

to prepare Ni nanoparticles and studied the in situ catalytic properties

without interference from a substrate. Nanoparticles of metal oxides,

11

carbides, and nitrides can be prepared by carrying out the discharge in a

suitable

gas medium or by loading the electrodes with suitable precursor

3.1.3 Ion Sputtering

In this method, accelerated ions such as Ar+ are directed toward

the surface of a target to eject atoms and small clusters from its surface.

The ions are carried to the substrate under a relatively high pressure

(∼1mTorr) of an inert gas, causing aggregation of the species.

Nanoparticles of metals and alloys as well as semiconductors have been

prepared using this method

3.1.4 Laser Ablation

A variant of the method is the supersonic expansion method where

the plume produced by the laser pulse is carried by an inert gas pulse

through a narrow orifice to cause adiabatic expansion. This results in the

formation of nanoclusters. Harfenist prepared mass-selected Ag

nanoparticles from this method and collected them in the form of a sol

outside the preparation chamber. Because of spatial and temporal

confinement of the gaseous species with supersonic speeds, the method

calls for extreme sophistication in instrumentation.

3.1.5 Pyrolysis and Other Methods

In laser pyrolysis, a precursor in the gaseous form is mixed with an

inert gas and heated with CO2 infrared laser (continuous or pulsed),

whose energy is either absorbed by the precursor or by an inert

photosensitizer such as SF6.

12

3.1.6 Spray Pyrolysis

In spray pyrolysis, small droplets of a solution containing a desired

precursor are injected into the hot zone of a furnace to obtain

nanoparticles. The droplets are generated by using a nebulizer, generally

by making use of a transducer. By controlling the nebulizer energy, the

relative vapor pressures of the gases and the temperature of the furnace,

the particle size is controlled

3.2 Chemical Method

3.2.1 Metal Nanocrystals by Reduction

A variety of reducing agents are used to reduce soluble metal salts

to obtain the corresponding metals. By terminating the growth with

appropriate surfactants or ions, metal nanoparticles are produced. We

shall discuss the use of a few representative reducing agents in this

section. Some of the older methods of preparing nanoparticles were

reviewed by Turkevich in 1951

Borohydride Reduction

The basic reaction involves the hydrolysis of the borohydride

accompanied by the evolution of hydrogen.

BH− 4 + 2H2 O −→ BO− 2 + 4H2 (2.1)

13

Fig. 2.1. TEM image of Cr nanocrystals synthesized by borohydride reduction. The scale bar

corresponds to 20nm (reproduced with permission from [150])

Nanocrystals of a variety of metals have been made by borohydride

reduction. Thus, Pt nanocrystals with mean diameter 2.8nm were

prepared by the reduction of chloroplatinic acid with sodium borohydride.

Homiyama and coworkers made Cu sols by the borohydride reduction of

Cu salts. Green and O’Brien prepared Cr and Ni nanoparticles by

carrying out the reduction with Li or Na borohydride at high temperatures

in coordinating solvents (see Fig. 2.3).

Citrate Reduction

Synthesis by the citrate method involves the addition of chloroauric

acid to a boiling solution of sodium citrate. A wine red color indicates the

onset of reduction. The average diameter of the nanoparticles can be

varied over a range of 10–100nm by varying the concentration ratio

between chloroauric acid and sodium citrate (see Fig. 2.3).

Fig. 2.3. TEM image of Au nanocrystals synthesized by citrate reduction. The magnification is 50,000

(reproduced with permission from [144])

14

Alcohol Reduction

This reaction is further catalyzed by a base and requires the

presence of α-hydrogen in the alcohol. By making use of polymeric

capping agents such as PVP, the growth of metal particles can be

arrested.

The polyol method of Figlarz and coworkers [183, 184] involves

the reduction of metal salts with high boiling polyols such as ethylene

glycol. The polyol serves both as the reducing agent and the stabilizing

agent. Particles of Co, Ni, Cu, Au, Ag, and their alloys in the size range

of 100nm to a few microns have been obtained by this method (see Fig.

2.4) .

Fig. 2.4. TEM image of large Ag nanocrystals synthesized by the polyol method (reproduced with

permis [185])

15

3.2.2 Solvothermal Synthesis

The solvothermal method provides a means of using solvents at

temperatures well above their boiling points, by carrying out the reaction

in a sealed vessel. The pressure generated in the vessel due to the solvent

vapors elevates the boiling point of the solvent. Typically, solvothermal

methods make use of solvents such as ethanol, toluene, and water, and are

widely used to synthesize zeolites, inorganic open-framework structures,

and other solid materials. Due to the high-pressures employed, one often

obtains high-pressure phases of the materials. In the past few years,

solvothermal synthesis has emerged to become the chosen method to

synthesize nanocrystals of inorganic materials. Numerous solvothermal

schemes have been employed to produce nanocrystalline powders as well

as nanocrystals dispersible in a liquid. Qian and coworkers have reported

several solvothermal routes to chalcogenide nanocrystals. CdS

nanocrystals of 6nm diameter have been made using cadmium

sulphate/nitrate as the Cd source, thiourea as the S source and

ethyleneglycol as the solvent. The reaction was carried out for 12 h at

180◦C. Chen and Fan have prepared transition metal dichalcogenides

(MS2; M = Fe, Co, Ni, Mo; S = S or Se) with diameters in the range 4–

200nm by a hydrothermal route (water as solvent). Fe, Co, and Ni

chalcogenides were obtained by treating the corresponding halide with

Na2S2O3 (sodium thiosulphate) or Na2SeSO3 (sodium selenosulphate)

for 12 h at 140–150◦C. Mo chalcogenides were prepared starting from

Na2MoO4, sodium thio or seleno sulphate and hydrazine.

By employing a metal salt, elemental Se or S and a reducing agent

(to reduce Se or S), it is possible to produce metal chalcogenide

nanocrystals (see Table 2.3). Control over size is rendered possible by the

16

slow release of sulphide or selenide ions. Nanocrystal dispersions are

often obtained even without a capping agent. In some cases, S or Se can

be caused to disproptionate, making the reducing agent redundant. Thus,

CdSe nanocrystals have been prepared solvothermally by reacting Cd

stearate with elemental Se in toluene in the presence of tetralin (see Fig.

2.5)

Fig. 2.5. TEM image of CdSe nanocrystals synthesized by solvothermal method. The

scale bar corresponds to 50 nm. The inset shows a histogram of particle size

distribution (reproduced with permission from)

3.2.3 Photochemical Synthesis

Photochemical synthesis of nanoparticles is carried out by the

light-induced decomposition of a metal complex or the reduction of a

metal salt by photogenerated reducing agents such as solvated electrons.

The former is called photolysis and the latter radiolysis. The formation of

photographic images on a AgBr film is a familiar photolysis reaction.

Henglein, Belloni, and their coworkers have pioneered the use of

photolysis and radiolysis for the preparation of nanoscale metals.

17

Metals such as Cd and Tl have been obtained by photolysis. PVP-

covered Au nanocrystals are produced by the reduction of HAuCl4 in

formamide by UV-irradiation. The reaction is free radical mediated, with

the radicals being generated by photodegradation of formamide. This

provides a route to ion-free reduction of HAuCl4. Radiolysis of Ag salts

in the presence of polyphosphates produces extremely small clusters that

are stable in solution for several hours. Effective control can be exercised

over the reduction process by controlling the radiation dosage.

Marandi et al. have shown that the size of CdS nanocrystals could

be controlled photochemically in the reaction of CdSO4 and Na2S2O3.

Radiolysis also provides a means for the simultaneous generation of a

larger number of metal nuclei at the start of the reaction, thereby yielding

a fine dispersion of nanocrystals. Studies of the reduction pathways by

radiolysis have been carried out.

3.2.4 Electrochemical Synthesis

Reetz and coworkers have pioneered the electrochemical synthesis

of metal nanocrystals. Their method represents a refinement of the

classical electrorefining process and consists of six elementary steps they

are oxidative dissolution of anode, migration of metal ions to the

cathodes, reduction of ions to zero-valent state, formation of particles by

nucleation and growth, arrest of growth by capping agents, and

precipitation of particles.

18

Fig. 2.11. Schematic illustration of the steps involved in the electrochemical reduction

of metal nanocrystals by the Reetz method (reproduced with permission from [265])

The steps are schematically illustrated in Fig. 2.11. The capping

agents are typically quaternary ammonium salts containing long-chain

alkanes such as tetraoctylammonium bromide. The size of the

nanocrystals could be tuned by altering the current density, the distance

between the electrodes, the reaction time, the temperature, and the

polarity of the solvent. Thus, using tetraoctylammonium bromide as

stabilizer, Pd nanocrystals in the size range of 1–5nm have been obtained.

Low current densities yield larger particles (∼4.8 nm) while large current

densities yield smaller particles (∼1.4 nm). Larger Pd nanoparticles

stabilized by the solvent (propylene carbonate) have also been obtained

[259]. This method has been used to synthesize Ni, Co, Fe, Ti, Ag, and

nanoparticles. Bimetallic colloids such as Pd–Ni, Fe–Co, and Fe–Ni have

been prepared using two anodes consisting of either metals [260]. Mono

and bimetallic particles consisting of Pt, Rh, Ru, and Mo could be

prepared by reduction of their salts dissolved in the electrolyte (see Table

2.4) .

19

Bimetallic particles could be prepared by using two ions, one of which

was from the anode and the other from the metal salt dissolved in the

electrolyte

Table 2.4. Metal particles synthesized by the electrochemical

reduction of salts

Table 2.5. Bimetallic particles synthesized by the combination of anodic

oxidation and salt reduction

(see Table 2.5). Pascal et al. synthesized maghemite nanocrystals

in the size range of 3–8nm by the use of an Fe electrode in an aqueous

solution containing DMF and cationic surfactants.

21

3.2.5 Nanocrystals of Semiconductors and Other Materials

by Arrested Precipitation

Nanocrystals can be obtained from solutions that precipitate the

bulk matter under conditions unfavorable for the growth of particulates in

the precipitate. For example, the precipitation of metal salts by

chalcogens can be arrested by employing a high pH. The groups of Brus,

Henglein, and Weller have prepared CdS nanocrystals by adopting this

strategy. Typically, CdSO4 is reacted with (NH4)2S in water at high pH

to obtain CdS particles of diameter around 5 nm. Other sulfur sources

such as H2S and Na2S are also used to obtain CdS. Capping agents (e.g.,

sodium polyphosphate) stabilize such dispersions. In addition to water,

methanol, acetonitrile and such solvents can be used to obtain CdS and

ZnS nanocrystals by arrested precipitation. Weller and coworkers have

pioneered the use of water soluble thiols, such as 1-thioglycerol, 2-

mercaptoethanol, 1-mercapto-2-propanol, 1,2-dimercapto- 3-propanol,

thioglycolic acid, thiolactic acid, and cysteamine as capping agents to

prepare CdS, CdSe, CdTe, HgSe, HgTe, and CdHgTe nanocrystals.

Typically, a solution containing a metal salt (e.g., perchlorate) and the

capping agent is treated with NaOH to raise the pH, degassed by bubbling

inert gas (to prevent the oxidation of chalcogen source), followed by the

introduction of the chalcogen in the form of Na2S, NaHSe, etc. under

inert conditions (see Fig. 2.12).

21

Fig. 2.12. TEM images of thioglycerol–capped CdSe nanocrystals prepared by

arrested precipitation reaction. Insets show a HRTEM image and a Fourier transform

of one of the HRTEM images (reproduced with permission from [272

3.1.6 Thermolysis Routes

Thermolys is routes are related to chemical vapor deposition

(CVD)-based methods to prepare thin films. By carrying out thermolysis

reactions in high boiling solvents in the presence of capping agents,

nanocrystals of various materials are obtained. Thermal decomposition

provides remarkable control over size and is well suited for scale up to

gram quantities.

22

Metal and Metal Oxide Nanocrystals

Various metal nanoparticles have been prepared by decomposition

of low-valent complexes involving olefinic ligands, such as

cyclooctatetraene (COT), cycloocta-1,5-diene (COD), and carbonyls. It

has been known since long that colloidal Co can be prepared by the

decomposition of Co carbonyls . Bawendi and coworkers [288] carried

out a similar reaction with Co2(CO)8, in the presence of tri-n-

octylphosphine oxide (TOPO) and obtained Co nanoparticles with an

average diameter of 20 nm. By using capping agents such as carboxylic

acids and alkyl amines the size of the nanoparticles can be tuned to be in

the range of 3–20nm . Decomposition of carbonyls has been used to

prepare nanocrystals of Fe

Fig. 2.13. TEM image of large Au nanocrystals prepared by decomposition of Au

thiolate [C14H29(CH3)3N][Au(SC12H25)2] (reproduced with permission from

[300])

FeCo [, FeMo , FePt , CoPt , FePd , and SmCo , as well. Large Au

nanoparticles with diameters of tens of nanometers have been prepared by

Nakamoto. by the thermolysis of Au(I) thiolate complexes –

[R(CH3)3N][Au(SC12H25)2],[R(CH3)3N][Au(SC6H4–p–R_)2]

(R=C14H29, C12H25); (R_=C8H17, CH3)(see Fig. 2.13)

23

Semiconductor Nanocrystals

The synthesis of some of the semiconducting metal chalcogenide

nanocrystals was discussed in an earlier section. Murray and coworkers in

a pathbreaking paper described a method for synthesizing CdSe

nanocrystals by reacting a metal alkyl (dimethylcadmium) with TOPSe

(tri-octylphosphineselenide) in TOP (tri-n-octylphosphine), a

coordinating solvent that also acts as the capping agent (see Fig. 2.14).

This method readily yields CdS and CdTe nanocrystals as well. The

reaction scheme of Murray succeeds to some extent in separating the

nucleation and growth steps. When the chalcogen source is injected into

the hot solution, explosive nucleation occurs, accompanied by a fall in

temperature. Further growth occurs by maintaining the reagents around

100K or lower, the final size depending on the growth temperature. The

scheme of

Murray has proved to be extraordinarily popular and has received

extensive attention from numerous groups.

Fig. 2.14. TEM image of CdSe nanocrystals produced by the Murray method. The

nanocrystals are elongated along one axis (reproduced with permission from

24

Single Molecule Precursors

Decomposition of single molecular precursors provides convenient

and effective routes for the synthesis of semiconductor nanocrystals. In

this method, a molecular complex consisting of both the metal and the

chalcogen is thermally decomposed in a coordinating solvent. Initial

attempts with dithio and diselno carbamates, [Cd(E2CNEt2)]2 (E=S,Se)

gave nanoparticles of CdS . The nanoparticles were capped with TOPO,

the reaction medium. CdSe nanocrystals have been produced starting with

compounds of the form RCd(S2CNEt2)(R = neopentyl, methyl)(see Fig.

2.15). Diselenocarbamates with unsymmetrical R groups such as hexyl

and methyl (CdSe2CNMeHex)2 were found to be good air stable

precursors for CdSe nanoparticles . ZnS and ZnSe nanoparticles were

prepared starting from [EtZn(E2NEt2)]2 .

Fig. 2.15. TEM image of CdSe nanocrystals produced by the thermal decomposition

25

3.2.7 Sonochemical Routes

The effect of ultrasound on a colloidal system has been known for

sometime although its use for the preparation of nanosized matter is of

relatively recent origin. Numerous methods have been discussed in the

literature for the sonochemical synthesis of nanosized particles. However,

not all the nanosized particles so obtained have been dispersed in a liquid

medium. Progress in sonochemical synthesis made over the last two

decades is illustrated by the set of examples discussed later. In order to

carry out sonochemical reactions, a mix of reagents dissolved

in a solvent is subjected to ultrasound radiation (20 kHz–10 MHz).

Acoustic cavitation leads to the creation, growth, and collapse of bubbles

in the liquid medium. The creation of bubbles is due to the suspended

particulate matter and impurities in the solvent. The growth of a bubble

by expansion leads to the creation of a vacuum that induces the diffusion

of volatile reagents into the bubble. The growth step is followed by the

collapse of the bubble which takes places rapidly accompanied by a

temperature change of 5,000–25,000K in about a nanosecond. Collapse of

the bubble triggers the decomposition of the matter within the bubble.

The rapid cooling rate often hinders crystallization, and amorphous

Table2.5. Bimetallic particles synthesized by the combination of anodic oxidation and salt

reduction

26

products are usually obtained. The collapse of the bubble does not signal

the end of the reaction. The collapse is frequently accompanied by the

formation of free radicals that cause further reactions. A few of the

sonochemical reactions are, in fact, mediated by free radicals

3.2.7 The Liquid–Liquid Interface

Rao and coworkers have used reactions taking place at the

interface of two liquids such as toluene and water to produce nanocrystals

and films of metals, semiconductors, and oxides. In this method, a

suitable organic derivative of the metal taken in the organic layer reacts at

the interface with the appropriate reagent present in the aqueous layer to

yield the desired product. For example, by reacting Au(PPh3)Cl in

toluene with THPC in water, nanocrystals of Au can be obtained at the

interface of two liquids. This method has been extended to prepare

nanocrystals of Ag and Pd, Au–Ag alloys, semiconducting sulphides such

as CdS, ZnS, and CoS, and oxides such as Fe2O3 and CuO (see Fig.

2.17).

By an appropriate choice of the reaction parameters, it has been

possible to obtain isolated nanocrystals with narrow size distribution or

well-formed films of the nanocrystals. By varying parameters such as the

reaction temperature, and the reactant concentrations, the size of the

nanocrystals and the coverage of the films can be modified. Thus, a

change in the reaction temperature from 298 to 348 K, increases the size

of Au nanocrystals from 7 to 16nm (see Fig. 2.18). Starting with a

mixture of metal precursors, it has been possible using this method to

prepare Au–Ag alloy nanocrystalline films of varying compositions

27

Biological Methods

Of the templates and systems used for the synthesis of nanocrystals,

microbes offer an interesting possibility. The innards of a microorganism

can be a tiny

Fig. 2.17. Nanocrystals of: (a) Au, (b) CdS, and (c) γ–Fe2O3 formed at the toluenewater

interface (reproduced with permission from)

Fig. 2.18. Transmission electron micrographs of ultrathin nanocrystalline Au films prepared

at the liquid–liquid interface at (a) 303K (b) 318K (c) 333 K, and (d) 348 K. The histograms

of particle size distribution are also shown. The scale bars

28

correspond to 50 nm. A high-resolution image of an individual particle is

shown in the center (reproduced with permission from)

reactor as well as a container. Elementary reactions such as reduction are

generally mediated by enzymes. Synthesis can therefore be carried out by

simply incubating a solution of metal ions in the right microbial culture.

The ability of microbes to accumulate inorganic particles such as Au ,

CdS , ZnS , and magnetite is well documented in the literature. It is also

known that microorganisms put nanoscale particles to use as UV shields

(CdS particles) and direction indicators (magnetite). The possibility of

harnessing microorganisms for the synthesis of nanocrystals was realized

only recently .

Nair and Pradeep have utilized Lactobacillus present in yogurt to

synthesize Au, Ag, and Au–Ag alloy nanoparticles. The nanoparticles

thus produced were in the size range of 15–500 nm. Joerger and

coworkers have synthesized Ag nanoparticles in the size range 2–200nm

by using Pseudomonas Stutzeri. Klebsiella aerogenes has been used to

synthesize CdS nanoparticles in the size range 20–200nm . Roh and

coworkers have substituted metal ions such as Co, Cr, and Ni in

magnetite nanocrystals synthesized using the iron-reducing bacteria

Thermoanaerobacter ethanolium.

Enzymes act as catalysts for the growth of metal nanoparticles. Enzyme

58 2 Synthesis of Nanocrystals mediated growth of metallic nanoparticles

can be exploited for various purposes in biology involving dip pen

lithography .

Apart from bacteria, yeast, and fungi have been used to obtain

nanoparticles.

Yeasts, Candida glabrata and Schizosaccharomyces pombe have been

29

shown to yield CdS nanoparticles. Kowshik . have identified the ability of

yeast Torulopsis sp. to produce nanoscale PbS nanoparticles.

Sastry and coworkers have identified two fungi species, Fusarium

oxysporum and Verticillium sp. to produce Au and Ag nanoparticles.

Fusarium oxysporum also reduces CdSO4 to CdS to yield CdS

nanoparticles. CdS nanoparticles have been produced in the extracellular

space. Highly luminescent, water-soluble and biocompatible CdTe

nanocrystals have been prepared by using glutathione as a stabilizer.

Quantitum yields in excess of 60% have been observed with these

nanoparticles .

A novel nature of such biological synthetic schemes is that they produce

nanoparticles at room temperature in aqueous medium, although poor

size and morphology control also appear to be characteristic of these

routes.

Besides control over size and morphology, identification of the active

biological ingredient that brings about the reaction remains unknown.

31

Application of Nanotechnology

4.1 History:

The 2000s have seen the beginnings of the applications of

nanotechnology in commercial products, although most applications are

limited to the bulk use of passive Nanomaterials. Examples include

titanium dioxide and zinc oxide nanoparticles in sunscreen, cosmetics and

some food products; silver nanoparticles in food packaging, clothing,

disinfectants and household appliances such as Silver Nano; carbon

nanotubes for stain-resistant textiles; and cerium oxide as a fuel catalyst.

As of March 10, 2011, the Project on Emerging Nanotechnologies

estimated that over 1300 manufacturer-identified nanotech products are

publicly available, with new ones hitting the market at a pace of 3–4 per

week.

Nanotechnology is being used in developing countries to help treat

disease and prevent health issues. The umbrella term for this kind of

nanotechnology is Nano medicine.

Nanotechnology is also being applied to or developed for

application to a variety of industrial and purification processes.

Purification and environmental cleanup applications include the

desalination of water, water filtration, wastewater treatment, groundwater

treatment, and other Nano remediation. In industry, applications may

include construction materials, military goods, and nano-machining of

nano-wires, nano-rods, few layers of graphene, etc.

31

Different fields of nanotechnology application

4.2 Nano-medicine:

Nanomedicine is the medical application of nanotechnology.

Nanomedicine ranges from the medical applications of nanomaterials, to

nanoelectronic biosensors, and even possible future applications of

molecular nanotechnology. Current problems for nanomedicine involve

understanding the issues related to toxicity and environmental impact of

nanoscale materials (materials whose structure is on the scale of

nanometers, i.e. billionths of a meter).

Functionalities can be added to nanomaterials by interfacing them

with biological molecules or structures. The size of nanomaterials is

similar to that of most biological molecules and structures; therefore,

nanomaterials can be useful for both in vivo and in vitro biomedical

research and applications. Thus far, the integration of nanomaterials with

biology has led to the development of diagnostic devices, contrast agents,

analytical tools, physical therapy applications, and drug delivery vehicles.

32

Nanomedicine seeks to deliver a valuable set of research tools and

clinically useful devices in the near future. The National Nanotechnology

Initiative expects new commercial applications in the pharmaceutical

industry that may include advanced drug delivery systems, new therapies,

and in vivo imaging. Nanomedicine research is receiving funding from

the US National Institutes of Health, including the funding in 2005 of a

five-year plan to set up four nanomedicine centers.

Nanomedicine is a large industry, with nanomedicine sales

reaching $6.8 billion in 2004, and with over 200 companies and 38

products worldwide, a minimum of $3.8 billion in nanotechnology R&D

is being invested every year. In April 2006, the journal Nature Materials

estimated that 130 nanotech-based drugs and delivery systems were being

developed worldwide. As the nanomedicine industry continues to grow, it

is expected to have a significant impact on the economy.

2.2.1 Cancer:

Another nanoproperty, high surface area to volume ratio, allows

many functional groups to be attached to a nanoparticle, which can seek

out and bind to certain tumor cells. Additionally, the small size of

nanoparticles (10 to 100 nanometers), allows them to preferentially

accumulate at tumor sites (because tumors lack an effective lymphatic

drainage system). Limitations to conventional cancer chemotherapy

include drug resistance, lack of selectivity, and lack of solubility.

Nanoparticles have the potential to overcome these problems.

In photodynamic therapy, a particle is placed within the body and

is illuminated with light from the outside. The light gets absorbed by the

33

particle and if the particle is metal, energy from the light will heat the

particle and surrounding tissue. Light may also be used to produce high

energy oxygen molecules which will chemically react with and destroy

most organic molecules that are next to them (like tumors). This therapy

is appealing for many reasons. It does not leave a "toxic trail" of reactive

molecules throughout the body (chemotherapy) because it is directed

where only the light is shined and the particles exist. Photodynamic

therapy has potential for a noninvasive procedure for dealing with

diseases, growth and tumors. Kanzius RF therapy is one example of such

therapy.[citation needed] Also, gold nanoparticles have the potential to

join numerous therapeutic functions into a single platform, by targeting

specific tumor cells, tissues and organs.

A schematic illustration showing how nanoparticales or other cancer

Druges might be used to treat cancer

34

4.3 Nano-biotechnology:

Nanobiotechnology, bionanotechnology, and nanobiology are

terms that refer to the intersection of nanotechnology and biology. Given

that the subject is one that has only emerged very recently,

bionanotechnology and nanobiotechnology serve as blanket terms for

various related technologies.

This discipline helps to indicate the merger of biological research

with various fields of nanotechnology. Concepts that are enhanced

through nanobiology include: nanodevices, nanoparticles, and nanoscale

phenomena that occurs within the discipline of nanotechnology. This

technical approach to biology allows scientists to imagine and create

systems that can be used for biological research. Biologically inspired

nanotechnology uses biological systems as the inspirations for

technologies not yet created. However, as with nanotechnology and

biotechnology, bionanotechnology does have many potential ethical

issues associated with it.

The most important objectives that are frequently found in

nanobiology involve applying nanotools to relevant medical/biological

problems and refining these applications. Developing new tools, such as

peptoid nanosheets, for medical and biological purposes is another

primary objective in nanotechnology. New nanotools are often made by

refining the applications of the nanotools that are already being used. The

imaging of native biomolecules, biological membranes, and tissues is also

a major topic for the nanobiology researchers. Other topics concerning

nanobiology include the use of cantilever array sensors and the

35

application of nanophotonics for manipulating molecular processes in

living cells.

Recently, the use of microorganisms to synthesize functional

nanoparticles has been of great interest. Microorganisms can change the

oxidation state of metals. These microbial processes have opened up new

opportunities for us to explore novel applications, for example, the

biosynthesis of metal nanomaterials. In contrast to chemical and physical

methods, microbial processes for synthesizing nanomaterials can be

achieved in aqueous phase under gentle and environmentally benign

conditions. This approach has become an attractive focus in current green

bionanotechnology research towards sustainable development.

36

4.4 Green nanotechnology:

Green nanotechnology refers to the use of nanotechnology to enhance

the environmental sustainability of processes producing negative

externalities. It also refers to the use of the products of nanotechnology to

enhance sustainability. It includes making green nano-products and using

nano-products in support of sustainability.

Green nanotechnology has been described as the development of clean

technologies, "to minimize potential environmental and human health

risks associated with the manufacture and use of nanotechnology

products, and to encourage replacement of existing products with new

nano-products that are more environmentally friendly throughout their

lifecycle."

2.4.1 Current research:

Solar cells:

One major project that is being worked on is the development of

nanotechnology in solar cells. Solar cells are more efficient as they get

tinier and solar energy is a renewable resource. The price per watt of solar

energy is lower than one dollar.

Nanotechnology is already used to provide improved performance

coatings for photovoltaic (PV) and solar thermal panels. Hydrophobic and

self-cleaning properties combine to create more efficient solar panels,

especially during inclement weather. PV covered with nanotechnology

coatings are said to stay cleaner for longer to ensure maximum energy

efficiency is maintained.

37

Nanoremediation and water treatment:

Nanotechnology offers the potential of novel nanomaterials for the

treatment of surface water, groundwater, wastewater, and other

environmental materials contaminated by toxic metal ions, organic and

inorganic solutes, and microorganisms. Due to their unique activity

toward recalcitrant contaminants, many nanomaterials are under active

research and development for use in the treatment of water and

contaminated sites. The present market of nanotech-based technologies

applied in water treatment consists of reverse osmosis, nanofiltration,

ultrafiltration membranes. Indeed, among emerging products one can

name nanofiber filters, carbon nanotubes and various nanoparticles.

Nanotechnology is expected to deal more efficiently with contaminants

which convectional water treatment systems struggle to treat, including

bacteria, viruses and heavy metals. This efficiency generally stems from

the very high specific surface area of nanomaterials which increases

dissolution, reactivity and sorption of contaminants.

Some potential applications include:

To maintain public health, pathogens in water need to be identified

rapidly and reliably. Unfortunately, traditional laboratory culture

tests take days to complete. Faster methods involving enzymes,

immunological or genetic tests are under development.

Water filtration may be improved with the use of nanofiber

membranes and the use of nanobiocides, which appear promisingly

effective.

Biofilms are mats of bacteria wrapped in natural polymers. These

can be difficult to treat with antimicrobials or other chemicals.

They can be cleaned up mechanically, but at the cost of substantial

38

down-time and labour. Work is in progress to develop enzyme

treatments that may be able to break down such biofilms.

Pollution:

Scientists have been researching the capabilities of

buckminsterfullerene in controlling pollution, as it may be able to control

certain chemical reactions. Buckminsterfullerene has been demonstrated

as having the ability of inducing the protection of reactive oxygen species

and causing lipid peroxidation. This material may allow for hydrogen fuel

to be more accessible to consumers.

2.5 Energy applications of nanotechnology:

Over the past few decades, the fields of science and engineering have

been seeking to develop new and improved types of energy technologies

that have the capability of improving life all over the world. In order to

make the next leap forward from the current generation of technology,

scientists and engineers have been developing energy applications of

nanotechnology.

Nanotechnology, a new field in science, is any technology that

contains components smaller than 100 nanometers. For scale, a single

virus particle is about 100 nanometers in width.

An important subfield of nanotechnology related to energy is

nanofabrication. Nanofabrication is the process of designing and creating

devices on the nanoscale. Creating devices smaller than 100 nanometers

39

opens many doors for the development of new ways to capture, store, and

transfer energy. The inherent level of control that nanofabrication could

give scientists and engineers would be critical in providing the capability

of solving many of the problems that the world is facing today related to

the current generation of energy technologies.

People in the fields of science and engineering have already begun

developing ways of utilizing nanotechnology for the development of

consumer products. Benefits already observed from the design of these

products are an increased efficiency of lighting and heating, increased

electrical storage capacity, and a decrease in the amount of pollution from

the use of energy. Benefits such as these make the investment of capital

in the research and development of nanotechnology a top priority.

2.6 Industrial applications of nanotechnology:

Nanotechnology is impacting the field of consumer goods, providing

products with novel functions ranging from easy-to-clean to scratch-

resistant. Modern textiles are wrinkle-resistant and stain-repellent; in the

mid-term clothes will become "smart", through embedded "wearable

electronics". Several products that incorporate nanomaterials are already

in use. Nanomaterials are in a variety of items, many of which people do

not even realize contain nanoparticles. For example, car bumpers are

made lighter, clothing is more stain repellant, sunscreen is more radiation

resistant, synthetic bones are stronger, cell phone screens are lighter

weight, glass packaging for drinks leads to a longer shelf-life, and balls

for various sports are made more durable. Such novel products have a

41

promising potential especially in the field of cosmetics. Nanotechnology

also has numerous potential applications in heavy industry.

Nanotechnology is predicted to be a main driver of technology and

business in this century and holds the promise of higher performance

materials, intelligent systems and new production methods with

significant impact for all aspects of society.

2.6.1 Military:

Biological sensors:

Nanotechnology can improve the military’s ability to detect

biological agents. By using nanotechnology, the military would be able to

create sensor systems that could detect biological agents.[10] The sensor

systems are already well developed and will be one of the first forms of

nanotechnology that the military will start to use.

Uniform material:

Nanoparticles can be injected into the material on soldiers’

uniforms to not only make the material more durable, but also to protect

soldiers from many different dangers such as high temperatures, impacts

and chemicals. The nanoparticles in the material protect soldiers from

these dangers by grouping together when something strikes the armor and

stiffening the area of impact. This stiffness helps lessen the impact of

whatever hit the armor, whether it was extreme heat or a blunt force. By

reducing the force of the impact, the nanoparticles protect the soldier

wearing the uniform from any injury the impact could have caused.

41

Another way nanotechnology can improve soldiers’ uniforms is by

creating a better form of camouflage. Mobile pigment nanoparticles

injected into the material can produce a better form of camouflage. These

mobile pigment particles would be able to change the color of the

uniforms depending upon the area that the soldiers are in. There is still

much research being done on this self-changing camouflage.

Nanotechnology can improve thermal camouflage. Thermal

camouflage helps protect soldiers from people who are using night vision

technology. Surfaces of many different military items can be designed in

a way that electromagnetic radiation can help lower the infrared

signatures of the object that the surface is on. Surfaces of soldiers’

uniforms and surfaces of military vehicle are a few surfaces that can be

designed in this way. By lowering the infrared signature of both the

soldiers and the military vehicles the soldiers are using, it will provide

better protection from infrared guided weapons or infrared surveillance

sensors.

Communication method:

There is a way to use nanoparticles to create coated polymer

threads that can be woven into soldiers’ uniforms. These polymer threads

could be used as a form of communication between the soldiers. The

system of threads in the uniforms could be set to different light

wavelengths, eliminating the ability for anyone else to listen in. This

would lower the risk of having anything intercepted by unwanted

listeners.

42

Medical system:

A medical surveillance system for soldiers to wear can be made

using nanotechnology. This system would be able to watch over their

health and stress levels. The systems would be able to react to medical

situations by releasing drugs or compressing wounds as necessary. This

means that if the system detected an injury that was bleeding, it would be

able to compress around the wound until further medical treatment could

be received. The system would also be able to release drugs into the

soldier’s body for health reasons, such as pain killers for an injury. The

system would be able to inform the medics at base of the soldier’s health

status at all times that the soldier is wearing the system. The energy

needed to communicate this information back to base would be produced

through the soldier’s body movements.

Weapons:

Nano-weapon is the name given to military technology currently

under development which seeks to exploit the power of nanotechnology

in the modern battlefield.

2.6.2 Construction:

Nanotechnology has the potential to make construction faster,

cheaper, safer, and more varied. Automation of nanotechnology

construction can allow for the creation of structures from advanced

homes to massive skyscrapers much more quickly and at much lower

cost. In the near future, Nanotechnology can be used to sense cracks in

foundations of architecture and can send nanobots to repair them.

43

Nanotechnology is an active research area that encompasses a

number of disciplines such as electronics, bio-mechanics and coatings.

These disciplines assist in the areas of civil engineering and construction

materials.[25] If nanotechnology is implemented in the construction of

homes and infrastructure, such structures will be stronger. If buildings are

stronger, then less of them will require reconstruction and less waste will

be produced.

Nanotechnology in construction involves using nanoparticles such

as alumina and silica. Manufacturers are also investigating the methods of

producing nano-cement. If cement with nano-size particles can be

manufactured and processed, it will open up a large number of

opportunities in the fields of ceramics, high strength composites and

electronic applications.

Nanomaterials still have a high cost relative to conventional

materials, meaning that they are not likely to feature in high-volume

building materials. The day when this technology slashes the

consumption of structural steel has not yet been contemplated.

Cement:

Much analysis of concrete is being done at the nano-level in order

to understand its structure. Such analysis uses various techniques

developed for study at that scale such as Atomic Force Microscopy

(AFM), Scanning Electron Microscopy (SEM) and Focused Ion Beam

(FIB). This has come about as a side benefit of the development of these

44

instruments to study the nanoscale in general, but the understanding of

the structure and behavior of concrete at the fundamental level is an

important and very appropriate use of nanotechnology. One of the

fundamental aspects of nanotechnology is its interdisciplinary nature and

there has already been cross over research between the mechanical

modeling of bones for medical engineering to that of concrete which has

enabled the study of chloride diffusion in concrete (which causes

corrosion of reinforcement). Concrete is, after all, a macro-material

strongly influenced by its nano-properties and understanding it at this

new level is yielding new avenues for improvement of strength, durability

and monitoring as outlined in the following paragraphs

Silica (SiO2) is present in conventional concrete as part of the

normal mix. However, one of the advancements made by the study of

concrete at the nanoscale is that particle packing in concrete can be

improved by using nano-silica which leads to a densifying of the micro

and nanostructure resulting in improved mechanical properties. Nano-

silica addition to cement based materials can also control the degradation

of the fundamental C-S-H (calcium-silicatehydrate) reaction of concrete

caused by calcium leaching in water as well as block water penetration

and therefore lead to improvements in durability. Related to improved

particle packing, high energy milling of ordinary Portland cement (OPC)

clinker and standard sand, produces a greater particle size diminution

with respect to conventional OPC and, as a result, the compressive

strength of the refined material is also 3 to 6 times higher (at different

ages).

45

Steel:

Steel is a widely available material that has a major role in the

construction industry. The use of nanotechnology in steel helps to

improve the physical properties of steel. Fatigue, or the structural failure

of steel, is due to cyclic loading. Current steel designs are based on the

reduction in the allowable stress, service life or regular inspection regime.

This has a significant impact on the life-cycle costs of structures and

limits the effective use of resources. Stress risers are responsible for

initiating cracks from which fatigue failure results. The addition of

copper nanoparticles reduces the surface un-evenness of steel, which then

limits the number of stress risers and hence fatigue cracking.

Advancements in this technology through the use of nanoparticles would

lead to increased safety, less need for regular inspection, and more

efficient materials free from fatigue issues for construction.

Steel cables can be strengthened using carbon nanotubes. Stronger

cables reduce the costs and period of construction, especially in

suspension bridges, as the cables are run from end to end of the span.

The use of vanadium and molybdenum nanoparticles improves the

delayed fracture problems associated with high strength bolts. This

reduces the effects of hydrogen embrittlement and improves steel micro-

structure by reducing the effects of the inter-granular cementite phase.

Welds and the Heat Affected Zone (HAZ) adjacent to welds can be

brittle and fail without warning when subjected to sudden dynamic

loading. The addition of nanoparticles such as magnesium and calcium

46

makes the HAZ grains finer in plate steel. This nanoparticle addition

leads to an increase in weld strength. The increase in strength results in a

smaller resource requirement because less material is required in order to

keep stresses within allowable limits.

Wood:

Nanotechnology represents a major opportunity for the wood

industry to develop new products, substantially reduce processing costs,

and open new markets for biobased materials.

Wood is also composed of nanotubes or “nanofibrils”; namely,

lignocellulosic (woody tissue) elements which are twice as strong as

steel. Harvesting these nanofibrils would lead to a new paradigm in

sustainable construction as both the production and use would be part of a

renewable cycle. Some developers have speculated that building

functionality onto lignocellulosic surfaces at the nanoscale could open

new opportunities for such things as self-sterilizing surfaces, internal self-

repair, and electronic lignocellulosic devices. These non-obtrusive active

or passive nanoscale sensors would provide feedback on product

performance and environmental conditions during service by monitoring

structural loads, temperatures, moisture content, decay fungi, heat losses

or gains, and loss of conditioned air. Currently, however, research in

these areas appears limited.

Due to its natural origins, wood is leading the way in cross-

disciplinary research and modelling techniques. BASF have developed a

highly water repellent coating based on the actions of the lotus leaf as a

result of the incorporation of silica and alumina nanoparticles and

47

hydrophobic polymers. Mechanical studies of bones have been adapted to

model wood, for instance in the drying process.

Glass:

Research is being carried out on the application of nanotechnology

to glass, another important material in construction. Titanium dioxide

(TiO2) nanoparticles are used to coat glazing since it has sterilizing and

anti-fouling properties. The particles catalyze powerful reactions that

break down organic pollutants, volatile organic compounds and bacterial

membranes. TiO2 is hydrophilic (attraction to water), which can attract

rain drops that then wash off the dirt particles. Thus the introduction of

nanotechnology in the Glass industry, incorporates the self-cleaning

property of glass.

Fire-protective glass is another application of nanotechnology. This

is achieved by using a clear intumescent layer sandwiched between glass

panels (an interlayer) formed of silica nanoparticles (SiO2), which turns

into a rigid and opaque fire shield when heated. Most of glass in

construction is on the exterior surface of buildings. So the light and heat

entering the building through glass has to be prevented. The

nanotechnology can provide a better solution to block light and heat

coming through windows.

Coatings:

Coatings is an important area in construction coatings are

extensively use to paint the walls, doors, and windows. Coatings should

provide a protective layer bound to the base material to produce a surface

48

of the desired protective or functional properties. The coatings should

have self-healing capabilities through a process of "self-assembly".

Nanotechnology is being applied to paints to obtained the coatings having

self-healing capabilities and corrosion protection under insulation. Since

these coatings are hydrophobic and repel water from the metal pipe and

can also protect metal from salt water attack.

Nanoparticle based systems can provide better adhesion and

transparency. The TiO2 coating captures and breaks down organic and

inorganic air pollutants by a photo-catalytic process, which leads to

putting roads to good environmental use.

Fire Protection and detection:

Fire resistance of steel structures is often provided by a coating

produced by a spray-on-cementitious process. The nano-cement has the

potential to create a new paradigm in this area of application because the

resulting material can be used as a tough, durable, high temperature

coating. It provides a good method of increasing fire resistance and this is

a cheaper option than conventional insulation.

Risks in construction:

In building construction nanomaterials are widely used from self-

cleaning windows to flexible solar panels to wi-fi blocking paint. The

self-healing concrete, materials to block ultraviolet and infrared radiation,

smog-eating coatings and light-emitting walls and ceilings are the new

nanomaterials in construction. Nanotechnology is a promise for making

the "smart home" a reality. Nanotech-enabled sensors can monitor

49

temperature, humidity, and airborne toxins, which needs nanotech-based

improved batteries. The building components will be intelligent and

interactive since the sensor uses wireless components, it can collect the

wide range of data.

If nanosensors and nanomaterials become an everyday part of the

buildings, as with smart homes, what are the consequences of these

materials on human beings?

Effect of nanoparticles on health and environment: Nanoparticles

may also enter the body if building water supplies are filtered

through commercially available nano-filters. Airborne and

waterborne nanoparticles enter from building ventilation and

wastewater systems.

Effect of nanoparticles on societal issues:

As sensors become commonplace, a loss of privacy and autonomy

may result from users interacting with increasingly intelligent

building com

51

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