fate and transport of multiwalled carbon nanotubes in ... loon... · factories producing cnts and...
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Fate and Transport of Multiwalled Carbon Nanotubes in
Aquatic Systems
Kai Loon ChenDepartment of Geography and Environmental Engineering
Johns Hopkins University
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OverviewBackground on carbon nanotubes (CNTs)
Objective
Preparation and characterization of multiwalled carbon nanotubes (MWNTs)
Aggregation kinetics of MWNTs
Kinetics and reversibility of MWNT deposition on silica surfaces
Conclusions
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Carbon Nanotubes
www.bayerus.com
Mechanical properties:high strength;light weight
Electronic properties:semiconducting or metallic
Sekitani et al., Nature Materials,2009, 494-499
www.basesciences.commrbarlow.wordpress.com
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Toxicity of Carbon Nanotubes Cause pulmonary inflammation and fibrosis in lungs of miceDamage bacterial membrane and inhibit bacterial growth
Kang et al., Langmuir 2007, 23, 8670-8673
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–COOH
–OH
=O
Release of Carbon Nanotubes into the Environment
Consumer products that contain CNTs as they undergo wear and tearFactories producing CNTs and CNT-based productsCNT-based products disposed in waste disposal facilities, e.g., incinerators and landfills
Potential Routes of Release
Surface of CNTs can be oxidized in natural and engineered aquatic systems
5
oxidants
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Aggregation and Deposition Behavior Controls Fate and Transport of CNTs
Aggregation and deposition can be conceptualized as a two-stage process: transport and attachment
Mineral Surfaces
River Bed
Aggregation Deposition
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Attachment Depends on Surface and Solution Chemistries
Derjaguin–Landau–Verwey–Overbeek (DLVO) Theory:
Total energy of interaction = van der Waals attraction + electrostatic interaction
Particle shape and size, material, surface properties, solution chemistry
0 5 10 15 20-10
-5
0
5
10
Inte
ract
ion
Ene
rgy
(kT)
Separation Distance (nm)
Low IS High IS
– – ––
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Objective
To investigate the influence of surface oxidation and solution chemistry on the aggregation and deposition of MWNTs in aqueous solutions
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Preparation of Two MWNTs with Different Degrees of Surface OxidationMWNTs purchased from NanoLab (8 to 10 walls) were used as starting materialExpose MWNTs to a 3:1 mixture of 98% H2SO4and 69% HNO3 or a 4-time diluted acid mixture at 70oC for 8 hoursRepeated cycles of dilution with DI water, centrifugation, and decantation of the supernatantThe highly and lowly oxidized MWNTs (HO-MWNTs and LO-MWNTs) were dried overnight at 100oC and then pulverized in a ball-mill
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Surface Characterization of MWNTsThe distribution of carboxyl (COOH), hydroxyl (C-OH), and carbonyl (C=O) groups was quantified by X-ray photoelectron spectroscopy (XPS) in conjunction with vapor phase chemical derivatization
+
HO CF3
NN
Trifluoroethanol
1,3-di-tert-butyl-carbodiimide
Pyridine
O
O
CF3O
NC(CH3)3
CNHC(CH3)3
O
+H2N NH CF3
Carbonyl
N NH CF3
TrifluoroethylHydrazine
O CF3
O O
F3C+
O
O
CF3
OHO
Carboxyl
OH O
O
OH
HydroxylTrifluoroacetic
Anhydride
Surface Oxide
DerivatizingAgent
Surface Product
Chen et al., Environmental Chemistry 2010, 7, 10-27
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–CO
OH
–OH
=O
O(Total)
O(C=O
)O(C
OOH)O(C
-OH)
O(Othe
rs)
-2
0
2
4
6
8
10
12
Oxy
gen
Com
posi
tion
(ato
mic
%)
Oxygen-Containing Functional Groups
HO-MWNTs LO-MWNTs
Surface Characterization of MWNTsThe distribution of carboxyl (COOH), hydroxyl (C-OH), and carbonyl (C=O) groups was quantified by X-ray photoelectron spectroscopy (XPS) in conjunction with vapor phase chemical derivatization
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Electrokinetic Properties of MWNTs in NaCl and CaCl2 Solutions
Electrophoretic mobility (EPM)Brookhaven ZetaPALSpH 7.1 – carboxyl groups are
deprotonated
0.1 1 10 100
-4
-3
-2
-1
0
LO-MWNTs in CaCl2 HO-MWNTs in CaCl2 LO-MWNTs in NaCl HO-MWNTs in NaCl
EP
M (1
0-8m
2 /Vs)
Electrolyte Concentration (mM)
12
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Time-Resolved Dynamic Light Scattering
Brookhaven BI-200SM goniometerLexel 95 argon laser Wavelength 488 nmScattering angle 90
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Determining Aggregation Kinetics using Time-Resolved Dynamic Light Scattering
0 1 2 3 4 5 6 7 8 9
100
150
200
250
300 600 mM NaCl 300 mM NaCl 200 mM NaCl 160 mM NaCl 100 mM NaCl
Hyd
rody
nam
ic D
iam
eter
(nm
)
Time (min)
HO-MWNTs
Particle concentration = 0.1 mg/LpH = 7.1
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Determining Aggregation Kinetics using Time-Resolved Dynamic Light Scattering
Initial aggregation kinetics:
Attachment efficiency:
0 1 2 3 4 5 6 7 8 9
100
150
200
250
300 600 mM NaCl 300 mM NaCl 200 mM NaCl 160 mM NaCl 100 mM NaCl
Hyd
rody
nam
ic D
iam
eter
(nm
)
Time (min)
HO-MWNTs
0
t
h
dttdDk
fastkk
Particle concentration = 0.1 mg/LpH = 7.1
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Influence of Surface Oxidation on Colloidal Stability of MWNTs
10 100 1000
10-2
10-1
100CCC=210 mM
LO-MWNTs HO-MWNTs
Atta
chm
ent E
ffici
ency
NaCl Concentration (mM)
CCC=53 mM
Na+ screens the surface charge of MWNTs, and results in an increase in aggregation kinetics
Yi and Chen, Langmuir 2011, 27, 3588–3599.16
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Influence of Surface Oxidation on Colloidal Stability of MWNTs
10 100 1000
10-2
10-1
100CCC=210 mM
LO-MWNTs HO-MWNTs
Atta
chm
ent E
ffici
ency
NaCl Concentration (mM)
CCC=53 mM
Na+ screens the surface charge of MWNTs, and results in an increase in aggregation kinetics
CCC = 210 mM
Diffusion-limited
Reaction-limited
Yi and Chen, Langmuir 2011, 27, 3588–3599.17
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Influence of Surface Oxidation on Colloidal Stability of MWNTs
10 100 1000
10-2
10-1
100CCC=210 mM
LO-MWNTs HO-MWNTs
Atta
chm
ent E
ffici
ency
NaCl Concentration (mM)
CCC=53 mM
A lower NaCl concentration is required to destabilize the less negatively charged LO-MWNTs
Yi and Chen, Langmuir 2011, 27, 3588–3599.18
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0.1 1 10
10-2
10-1
100
LO-MWNTs HO-MWNTs
Atta
chm
ent E
ffici
ency
CaCl2 Concentration (mM)
CCC=1.0 mMCCC=0.9 mM
Influence of Surface Oxidation on Colloidal Stability of MWNTs
10 100 1000
10-2
10-1
100CCC=210 mM
LO-MWNTs HO-MWNTs
Atta
chm
ent E
ffici
ency
NaCl Concentration (mM)
CCC=53 mM
Ca2+ binds to carboxyl groups, effectively neutralizing the surface charge of MWNTs
Yi and Chen, Langmuir 2011, 27, 3588–3599.19
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Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D)
Laminar flow at 0.6 mL/min[MWNT] = 0.5–1.2 mg/LT = 25oC, pH = 7.1
From Q-Sense20
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Principle of QCM-D: Frequency
Quartz crystal
AC
Flow Cell:
Sauerbrey relationship:
nfCm Silica coating
Deposited mass is proportional to frequency shift with C as the constant of proportionality
where C = 17.7 ng/(Hz.cm2)
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Principle of QCM-D: Dissipation
Quartz crystal
AC
Flow Cell:
Oscillatory motion in attached film results in energy dissipationD is related to viscoelastic properties of film
stored
dissipated
EE
D2
Time
Am
plitu
de
A(t)=A0exp(-t/)sin(2ft+)
D=1/f
From Q-Sense22
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0 10 20 30 40 50 60 70-20
-15
-10
-5
0
5
Frequency Dissipation
Time (min)
Freq
uenc
y S
hift,
f (3
)(Hz)
-2
0
2
4
6
8
10
Dis
sipa
tion
Shi
ft,
D(3
)(10-6
)
Deposition of MWNTs on Silica Surfaces
DIwater
Backgroundsolution
MWNTsuspension
23
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0 10 20 30 40 50 60 70-20
-15
-10
-5
0
5
Time (min)
Freq
uenc
y S
hift,
f (3
)(Hz)
-2
0
2
4
6
8
10
Dis
sipa
tion
Shi
ft,
D(3
)(10-6
)
d∆f/dt
d∆D/dt
Deposition of MWNTs on Silica Surfaces
24
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Scanning Electron Microscopy (SEM) Imaging of MWNTs
HO-MWNTs deposited on poly-L-lysine (PLL)-coated silica surface at 1.5 mM CaCl2
Corresponds to∆f(3) of –36 Hz and ∆D(3) of 1.7 × 10–5
2 µm2 µm
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Rates of Frequency and Dissipation Shift are Proportional to Deposition Rate
0.0 0.2 0.4 0.6 0.8 1.00.0
0.2
0.4
0.6
0.8
df (3
) /dt (
Hz/
min
)
MWNT Concentration (mg/L)
LO-MWNTs
0.0 0.2 0.4 0.6 0.8 1.00.0
0.1
0.2
0.3
0.4
0.5
dD
(3) /
dt (1
0-6/m
in)
MWNT Concentration (mg/L)
LO-MWNTs
Deposition on PLL-modified surfaces at 1 mM NaCl and pH 7.1
26
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0.1 1 10
10-2
10-1
100
dD
(3) /d
t (10
-6/m
in)
CaCl2 Concentration (mM)
Deposition Rates on Silica Surfaces
0.1 1 1010-2
10-1
100
df (3
) /dt
(Hz/
min
)
CaCl2 Concentration (mM)
HO-MWNTs HO-MWNTs
Silica (–)
27
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Favorable (Transport-Limited) Deposition Rates
0.1 1 1010-2
10-1
100
df (3
) /dt
(Hz/
min
)
CaCl2 Concentration (mM)
HO-MWNTs
0.1 1 10
10-2
10-1
100
dD
(3) /d
t (10
-6/m
in)
CaCl2 Concentration (mM)
HO-MWNTs
Silica (–)Poly-L-lysine (+)
28
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100 1000
10-1
100
HO-MWNTs F
Atta
chm
ent E
ffici
ency
NaCl Concentration (mM)
Attachment Efficiency α and Critical Deposition Concentration (CDC)
favdtfddtfd
//
Attachment Efficiency:
Yi and Chen, Langmuir 2011, 27, 3588–3599.29
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100 1000
10-1
100
HO-MWNTs F HO-MWNTs D
Atta
chm
ent E
ffici
ency
NaCl Concentration (mM)
Attachment Efficiency α and Critical Deposition Concentration (CDC)
favdtfddtfd
//
favdtDddtDd
//
Attachment Efficiency:
Yi and Chen, Langmuir 2011, 27, 3588–3599.30
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100 1000
10-1
100
HO-MWNTs F HO-MWNTs D
Atta
chm
ent E
ffici
ency
NaCl Concentration (mM)
Attachment Efficiency α and Critical Deposition Concentration (CDC)
Qualitative agreement with classical DLVO deposition behavior
favdtfddtfd
//
favdtDddtDd
//
Attachment Efficiency:
Unfavorable Favorable
CDC~330 mM
Yi and Chen, Langmuir 2011, 27, 3588–3599.31
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100 1000
10-1
100
HO-MWNTs F HO-MWNTs D
Atta
chm
ent E
ffici
ency
NaCl Concentration (mM)
Attachment Efficiency α and Critical Deposition Concentration (CDC)
The CDC in NaCl is much higher than the CDC in CaCl2
CDC~1.1 mM
Unfavorable FavorableUnfavorable Favorable
CDC~330 mM
0.1 1 10
10-1
100
HO-MWNTs F HO-MWNTs D
Atta
chm
ent E
ffici
ency
CaCl2 Concentration (mM)
Yi and Chen, Langmuir 2011, 27, 3588–3599.32
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0.1 1 10
10-1
100
Atta
chm
ent E
ffici
ency
CaCl2 Concentration (mM)
Influence of Surface Oxidation on Deposition Kinetics of MWNTs
100 1000
10-1
100
HO-MWNTs F HO-MWNTs D
Atta
chm
ent E
ffici
ency
NaCl Concentration (mM)
CDC~330 mM
CDC NaCl CaCl2
HO-MWNTs 330 mM 1.1 mM
CDC~1.1 mM
Yi and Chen, Langmuir 2011, 27, 3588–3599.33
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0.1 1 10
10-1
100
Atta
chm
ent E
ffici
ency
CaCl2 Concentration (mM)
Influence of Surface Oxidation on Deposition Kinetics of MWNTs
100 1000
10-1
100
LO-MWNTs F LO-MWNTs D HO-MWNTs F HO-MWNTs D
Atta
chm
ent E
ffici
ency
NaCl Concentration (mM)
CDC~150 mM
CDC~330 mM
CDC~1.1 mM
CDC~1.6 mM
CDC NaCl CaCl2LO-MWNTs 150 mM 1.6 mMHO-MWNTs 330 mM 1.1 mM
Yi and Chen, Langmuir 2011, 27, 3588–3599.34
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Release of MWNTs from Silica Surfaces1.
5mM
CaC
l 2
HO
-MW
NTs
1.5m
M C
aCl 2
1.5m
M C
aCl 2
DI w
ater
0 50 100 150 200 250 300 350 400 450 500 550-40
-35
-30
-25
-20
-15
-10
-5
0
5
Release F Release D
Time (min)
Freq
uenc
y S
hift,
f (3
)(Hz)
0
5
10
15
20
25
Dis
sipa
tion
Shi
ft,
D(3
)(10-6
)
35
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1.5m
M C
aCl 2
HO
-MW
NTs
1.5m
M C
aCl 2
1.5m
M C
aCl 2
DI w
ater
0.7m
M C
aCl 2
0.4m
M C
aCl 2
0.1m
M C
aCl 2
0.01
mM
CaC
l 2
0 50 100 150 200 250 300 350 400 450 500 550-40
-35
-30
-25
-20
-15
-10
-5
0
5
Release F Release D
Time (min)
Freq
uenc
y S
hift,
f (3
)(Hz)
0
5
10
15
20
25
Dis
sipa
tion
Shi
ft,
D(3
)(10-6
)
Release of MWNTs from Silica Surfaces
36
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1.5m
M C
aCl 2
HO
-MW
NTs
1.5m
M C
aCl 2
1.5m
M C
aCl 2
DI w
ater
1 m
M N
aCl
pH 7
.1
0.7m
M C
aCl 2
0.4m
M C
aCl 2
0.1m
M C
aCl 2
0.01
mM
CaC
l 2
0 50 100 150 200 250 300 350 400 450 500 550-40
-35
-30
-25
-20
-15
-10
-5
0
5
Release F Release D
Time (min)
Freq
uenc
y S
hift,
f (3
)(Hz)
0
5
10
15
20
25
Dis
sipa
tion
Shi
ft,
D(3
)(10-6
)
Release of MWNTs from Silica Surfaces
37
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1.5m
M C
aCl 2
HO
-MW
NTs
1.5m
M C
aCl 2
1.5m
M C
aCl 2
DI w
ater
pH
10
DI w
ater
1 m
M N
aCl
pH 7
.1
0.7m
M C
aCl 2
0.4m
M C
aCl 2
0.1m
M C
aCl 2
0.01
mM
CaC
l 2
0 50 100 150 200 250 300 350 400 450 500 550-40
-35
-30
-25
-20
-15
-10
-5
0
5
Release F Release D
Time (min)
Freq
uenc
y S
hift,
f (3
)(Hz)
0
5
10
15
20
25
Dis
sipa
tion
Shi
ft,
D(3
)(10-6
)
Release of MWNTs from Silica Surfaces
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Degree of release increases
when:
CaCl2 Concentration
CaCl2 NaCl
pH of solution
Increase in surface potential of both MWNTs and silica surface may lead to decrease in the depth of primary energy minimum
Ruckenstein and Prieve, AIChE Journal, 1976, 276-283
Release of MWNTs from Silica Surfaces
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ConclusionsClassic aggregation and deposition behavior with favorable and unfavorable regimes is observed for MWNTsHO-MWNTs are more stable to aggregation and deposition than LO-MWNTs in NaCl. However, stabilities of both MWNTs are similar in CaCl2.Deposited MWNTs are released from silica surfaces during a change in solution chemistry that leads to an increase in the magnitude of their surface potential
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Acknowledgements
Ph.D. student Peng YiDr. Howard Fairbrother’s group (Dept. of Chemistry)Oak Ridge Associated Universities
41
E-mail: [email protected]: http://jhu.edu/crg/
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