aggregation and deposition behavior of carbon-based nanomaterials … · 2007-12-18 · aggregation...
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Aggregation and Deposition Behavior of Carbon-Based Nanomaterials
in Aquatic Environments
Menachem ElimelechDepartment of Chemical EngineeringEnvironmental Engineering Program
Yale University
2007 NSF Nanoscale Science and Engineering Grantees Conference, Arlington, VA, December 3-6, 2007
NSF BES 0504258NSF BES-0646247
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Engineered Carbon-Based Nanomaterials
Exponential growth in production and potential applications Unique properties (shape, surface charge, reactivity)Environmental and health impacts are not known
SWNT MWNT
100 nm
C60Nanoparticles
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Aggregation and Deposition Behavior Determines Fate and Transport
Influences rate of settling and transport
Removal from aqueous phase
May influence reactivity and toxicity
Mineral Surfaces
Sediment
Aggregation
Deposition/ Attachment
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NOM, biomolecules, minerals/suspended solids
IonsNa+
Cl-Ca2+
Mg2+
Nanomaterials
Complex Interactions in Aquatic Systems
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Aggregation Kinetics of Fullerene Nanoparticles
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Fullerene Nanoparticles
200 nm
Buckminsterfullerene C60 nC60
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Ordered Structure of C60 Molecules
10 nm
Buckminsterfullerene C60 nC60
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Two Synthesis MethodsSonicated C60 Nanoparticles (Son-C60)
Dissolve fullerene in
toluene
Sonicate with water and
ethanol for 3 hr
Filter with 0.45 then 0.2
µm filters
Fullerene (99.9% purity)
Aqueous C60 Nanoparticles (Aq-C60)Stirring fullerene in deionized water for 40 days before filtration
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Physical CharacterizationSon-C60 Aq-C60
RH = 50.5 nm RH = 83.1 nm
20 nm 50 nm
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Physical CharacterizationSon-C60 Aq-C60
10 nm10 nm
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Electrophoretic Mobility (EPM) in KCl
Negatively charged Aq-C60 more negatively charged than Son-C60
EPM becomes less negative as KCl concentration increases
1 10 100
-4
-3
-2
-1
0
Son-C60 pH 5.5 Aq-C60 pH 5.5
EP
M (1
0-8 m
2 /Vs)
KCl Conc. (mM)
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ALV Light Scattering SetupDynamic light scattering to derive hydrodynamic radiusYAG laser with wavelength of 532 nmScattered light intensity measured at 90° from incident beam
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Time-Resolved Dynamic Light Scattering
( )0→
⎟⎠⎞
⎜⎝⎛∝
t
hA dt
tdrk
fastA
A
kkW,
/1 ==α0 400 800 1200
60
70
80
90
200 mM NaCl 145 mM NaCl 100 mM NaCl 80 mM NaCl
Hyd
rody
nam
ic R
adiu
s (n
m)
Time (s)
kA, fast
kA
Initial aggregation kinetics:
Attachment Efficiency or Inverse Stability Ratio:
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Aggregation Kinetics in KCl
0.01 0.1 10.01
0.1
1
Son-C60
Aq-C60
Inve
rse
Sta
bilit
y R
atio
, 1/W
KCl Conc. (M)
pH 5.550 mM
200 mM
Classic slow and fast aggregation regimesAq-C60 are much more stable (CCC of 200 mM)
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Aggregation Kinetics in KCl and CaCl2
0.01 0.1 10.01
0.1
1
Son-C60
Aq-C60
Inve
rse
Sta
bilit
y R
atio
, 1/W
KCl Conc. (M)10-3 10-2 10-10.01
0.1
1
Son-C60
Aq-C60
Inve
rse
Sta
bilit
y R
atio
, 1/W
CaCl2 Conc. (M)
pH 5.5 pH 5.550 mM
200 mM
4.3 mM
6.0 mM
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Increased Stability in Humic Acid with NaCl
0 800 1600 2400 3200
60
80
100
120
No humic acid 1 mg/L TOC 5 mg/L TOC
Hyd
rody
nam
ic R
adiu
s (n
m)
Time (s)
NaCl concentration = 650 mMpH 8
Chen and Elimelech, J. Colloid Interface Sci. 2007, 309, 126-134
Diffusion-limited
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Increased Stability in Humic Acid with NaCl and MgCl2
0 800 1600 2400 3200
60
80
100
120
No humic acid 1 mg/L TOC 5 mg/L TOC
Hyd
rody
nam
ic R
adiu
s (n
m)
Time (s)0.01 0.1
0.1
1
No humic acid 1 mg/L TOC
Atta
chm
ent E
ffici
ency
, αMgCl2 Concentration (M)
NaCl concentration = 650 mMpH 8
CCC increases in humic acid
pH 8
Chen and Elimelech, J. Colloid Interface Sci. 2007, 309, 126-134
Diffusion-limited
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Steric Stabilization with Humic Acid in NaCl and MgCl2
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
EP
M (1
0-8 m
2 /Vs)
No humic acid Humic acid
10 mM 3 mM 3 mMNaCl CaCl2 MgCl2
Electrophoretic mobility (EPM) similar with and without humic acid
Indication of steric stabilization
pH 8
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Enhanced Aggregation at High CaCl2 Concentrations
0 400 800 1200
60
80
100
120
1 mg/L TOC No humic acid
Hyd
rody
nam
ic R
adiu
s (n
m)
Time (s)
Diffusion-limited
Enhanced aggregation
CaCl2 concentration = 40 mMpH 8
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Enhanced Aggregation at High CaCl2 Concentrations
1E-3 0.01 0.1
0.1
1
10 No humic acid 1 mg/L TOC
Atta
chm
ent E
ffici
ency
, αCaCl2 Concentration (M)
0.0010 400 800 1200
60
80
100
120
1 mg/L TOC No humic acid
Hyd
rody
nam
ic R
adiu
s (n
m)
Time (s)
Diffusion-limited
Enhanced aggregation
pH 8
At 1 mg/L TOC, enhanced aggregation occurs above 10 mM CaCl2
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Humic Acid Clusters Bridge Fullerene Nanoparticles
200 nm
100 mM MgCl2
500 nm
40 mM CaCl2
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Humic Acid Clusters Bridge Fullerene Nanoparticles
500 nm
40 mM CaCl2
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Aggregation Kinetics of Multi-Walled Carbon Nanotubes (MWNTs)
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MWNT Sample Preparation
10 mg MWNTs added to 100 mL DI water
Sonicated for 30 minutes using ultrasonicating probe
Supernatant collected
Re-sonicated for 5 more cycles (30 minutes each) to obtain final sample
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TEM Images of Untreated and Treated MWNTs
100nm 500nm
Tubes are bundled and long before treatmentSonication debundles and reduces average length
Untreated Treated
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Diameter and Length Distributions of Treated MWNTs
Diameter and length distributions are obtained with TEMAverage diameter 18 nm and average length 1.5 μm
2 4 6 8 100
5
10
15
20
25
% M
WC
NT
Length (μm)10 20 30 40 50
0
2
4
6
8
10
% M
WC
NT
Diameter (nm)
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Aggregation Kinetics with Monovalent Salt (NaCl)
10-3 10-2 10-1
0.01
0.1
1
A
ttach
men
t Effi
cien
cy, α
NaCl Conc. (M)
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Aggregation Kinetics with CaCl2and MgCl2
10-5 10-4 10-3 10-2 10-10.01
0.1
1
Atta
chm
ent E
ffici
ency
, α
MgCl2 Conc. (M)
10-5 10-4 10-3 10-2 10-10.01
0.1
1
Atta
chm
ent E
ffici
ency
, α
CaCl2 Concentration (M)
Classic aggregation behavior with slow and fast regimes
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Deposition Kinetics of Fullerene Nanoparticles
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Aggregation and Deposition Behavior Determines Fate and Transport
Mineral Surfaces
Sediment
Aggregation
Deposition/ Attachment
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Quartz Crystal Microbalance (QCM)
Quartz crystal
AC
Flow Cell: Sauerbrey relationship:
nfC
m nΔ−=Δ
0 10 20 30 40 50-25
-20
-15
-10
-5
0
Freq
uenc
y S
hift
(Hz)
Time (min)
Deposition starts
Silica coating
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0 10 20 30 40 50-30
-25
-20
-15
-10
-5
01 mM
10 mM
30 mM
Fr
eque
ncy
Shi
ft (H
z)
Time (min)
Deposition Kinetics
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0 10 20 30 40 50-30
-25
-20
-15
-10
-5
01 mM
10 mM
30 mMPLL
Fr
eque
ncy
Shi
ft (H
z)
Time (min)
Attachment Efficiency
fastD
DD k
k
,
=α
Favorable (fast) deposition:
Quartz crystal
Pre-adsorption of +ve charged poly-L-lysine (PLL) on silica surface
PLL
kD, fast
kD
Deposition attachment efficiency:
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Influence of NaCl and CaCl2 on Deposition Kinetics
Below CCC, as electrolyte concentration increases – faster deposition through charge shielding
Towards CCC and above – significant drop in deposition rate
0.01
0.1
1
0.0001 0.001
Dep
ositi
on R
ate
(Hz/
min
)
CaCl2 Concentration (M)
0.01
0.1
1
Attachm
ent Efficiency, α
D1E-3 0.01 0.1 1
0.01
0.1
1
Dep
ositi
on R
ate
(Hz/
min
)
NaCl Concentration (M)0.001
CCC
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Simultaneous Deposition and Aggregation at Higher Ionic Strength
0 20 40 60 80 100
-2.0
-1.5
-1.0
-0.5
0.0
0.5
Freq
uenc
y S
hift
(Hz)
Time (min)
Non-linear deposition behavior
At 100 mM NaCl:
Bigger aggregates formed at later stages –deposition rate decreases even more
Quartz crystal
Aggregate formation –lower convective-diffusive transport towards silica surface
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Release of Deposited Nanoparticles
0 100 200 300
-30
-20
-10
0
10FEDCBA
Fr
eque
ncy
Cha
nge
(Hz)
Time (min)
0 100 200 300-60
-40
-20
0FEDCBA
Freq
uenc
y C
hang
e (H
z)
Time (min)
A – Baseline (pH 5.7)
B – Deposition at 30 mM NaCl and 0.6 mM CaCl2 (both αD ~ 1)
C – Rinsing with respective electrolytes
D – Rinsing with 1 mM NaCl
E – Rinsing with DI water
F – Rinsing with DI water (pH 12.3)
Release at Stage F – sudden increase in surface potential of C60 nanoparticles and silica surface
NaCl
CaCl2
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Concluding RemarksEelectrostatic interactions control the aggregation and deposition behavior of carbon-based nanomaterials (CBNs)Humic substances stabilize CBNs by electrosteric repulsion Under solution chemistries of natural waters, CBNs are stable and thus expected to be mobile
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Acknowledgments
NSF BES 0504258NSF BES-0646247