Fate and Transport of Multiwalled Carbon Nanotubes in ... Loon... · Factories producing CNTs and...

Fate and Transport of Multiwalled Carbon Nanotubes in

Aquatic Systems

Kai Loon ChenDepartment of Geography and Environmental Engineering

Johns Hopkins University

1

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

2

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

3

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

4

–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

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

6

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

– – ––

7

Objective

To investigate the influence of surface oxidation and solution chemistry on the aggregation and deposition of MWNTs in aqueous solutions

8

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

9

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

10

–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

11

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

Time-Resolved Dynamic Light Scattering

Brookhaven BI-200SM goniometerLexel 95 argon laser Wavelength 488 nmScattering angle 90

13

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

14

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

15

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


10 100 1000

10-2

10-1

100CCC=210 mM

LO-MWNTs HO-MWNTs

Atta

chm

ent E

ffici

ency


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



10 100 1000

10-2

10-1

100CCC=210 mM

LO-MWNTs HO-MWNTs

Atta

chm

ent E

ffici

ency


CCC=53 mM

A lower NaCl concentration is required to destabilize the less negatively charged LO-MWNTs


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


10 100 1000

10-2

10-1

100CCC=210 mM

LO-MWNTs HO-MWNTs

Atta

chm

ent E

ffici

ency


CCC=53 mM

Ca2+ binds to carboxyl groups, effectively neutralizing the surface charge of MWNTs


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

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)

21

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

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

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

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

25

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

0.1 1 10

10-2

10-1

100

dD

(3) /d

t (10

-6/m

in)


Deposition Rates on Silica Surfaces

0.1 1 1010-2

10-1

100

df (3

) /dt

(Hz/

min

)


HO-MWNTs HO-MWNTs

Silica (–)

27

Favorable (Transport-Limited) Deposition Rates

0.1 1 1010-2

10-1

100

df (3

) /dt

(Hz/

min

)


HO-MWNTs

0.1 1 10

10-2

10-1

100

dD

(3) /d

t (10

-6/m

in)


HO-MWNTs

Silica (–)Poly-L-lysine (+)

28

100 1000

10-1

100

HO-MWNTs F

Atta

chm

ent E

ffici

ency


Attachment Efficiency α and Critical Deposition Concentration (CDC)

favdtfddtfd

//

Attachment Efficiency:


100 1000

10-1

100

HO-MWNTs F HO-MWNTs D

Atta

chm

ent E

ffici

ency



favdtfddtfd

//

favdtDddtDd

//



100 1000

10-1

100


Atta

chm

ent E

ffici

ency



Qualitative agreement with classical DLVO deposition behavior

favdtfddtfd

//

favdtDddtDd

//


Unfavorable Favorable

CDC~330 mM


100 1000

10-1

100


Atta

chm

ent E

ffici

ency



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


Atta

chm

ent E

ffici

ency



0.1 1 10

10-1

100

Atta

chm

ent E

ffici

ency


Influence of Surface Oxidation on Deposition Kinetics of MWNTs

100 1000

10-1

100


Atta

chm

ent E

ffici

ency


CDC~330 mM

CDC NaCl CaCl2

HO-MWNTs 330 mM 1.1 mM

CDC~1.1 mM


0.1 1 10

10-1

100

Atta

chm

ent E

ffici

ency


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


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


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

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

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

)


37

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

)


38

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


39

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

40

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/

Fate and Transport of Multiwalled Carbon Nanotubes in ... Loon... · Factories producing CNTs and...

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