Geckeler K.E., Nishide H. (Eds.) Advanced Nanomaterials

18.4 Summary 609

18.4

Summary

The “ nanotechnology revolution ” has spurred interest and concern regarding the

safety of engineered nanoparticles. In particular, attention has been paid to the

potential effects that such materials might have on humans, either through

the use of consumer products containing “ nanotechnology, ” or through occupa-

tional exposure during the manufacturing process. Unfortunately, less attention

has been paid to the potential impacts that these materials might have on ecologi-

cal systems, despite the increased manufacture of engineered carbon nanomateri-

als being likely to result in their deposition into aquatic ecosystems, either from

spills or as a result of the waste stream, in a fashion similar to other chemicals

and consumer products [7, 9] . As noted in this chapter, there is a paucity of data

regarding the behavior and fate of engineered carbon nanoparticles in aquatic

Figure 18.7 (a,b) Representative images of the caudal ﬁ ns for

(a) control and (b) 200 ppb nC

60

- exposed animals; (c,d)

Representative images of (c) 1% dimethylsulfoxide - exposed

control larval head and (d) 200 ppb nC

60

- exposed larval head.

The arrows indicate the pericardial edema ( PE ) and yolk sac

edema ( YSE ). Reproduced from Ref. [43] .

610 18 Ecological Toxicology of Engineered Carbon Nanoparticles

ecosystems, their potential bioavailability to aquatic organisms, and the effects that

they might have on those organisms.

The ﬁ eld of ecotoxicology generally operates within the framework of ecological

risk assessment in order to determine the risk posed by a particular chemical to

the natural environment. This framework relies on accurate exposure assess-

ment – How much of the material is likely to be found in the environment and is

the material bioavailable? – as well as accurate effects assessment – At what expo-

sure concentrations does the material result in harm? Although preliminary inves-

tigations have indicated that fullerenes and nanotubes can be taken up by aquatic

organisms, and result in deleterious effects under certain conditions, the realism

of these exposure scenarios, and particularly of the exposure concentrations, is

unknown. Are these exposure concentrations environmentally relevant? Are we

likely to see these concentrations of fullerenes and nanotubes being discharged

into aquatic systems? The effects that site - speciﬁ c parameters such as pH, hard-

ness, and temperature (which all have major impacts on the bioavailability of other

contaminants) have on the bioavailability of engineered carbon nanomaterials are

unknown. Until questions regarding these bioavailability and exposure scenarios

are answered, it will remain difﬁ cult to ascertain the risk and potential effects that

engineered carbon nanomaterials might have on aquatic ecosystems.

References

1 Daroczi , B. , Kari , G. , McAleer , M.F. ,

Wolf , J.C. , Rodeck , U. and Dicker , A.P.

( 2006 ) In vivo radioprotection by the

fullerene nanoparticle DF - 1 as assessed in

a zebraﬁ sh model . Clin. Cancer Res. , 12 ,

7086 – 7091 .

2 Kohli , P. and Martin , C.R. ( 2005 )

Template - synthesized nanotubes for

biotechnology and biomedical

applications . J. Drug Deliv. Sci. Technol. ,

15 , 49 – 57 .

3 Mroz , P. , Pawlak , A. , Satti , M. , Lee , H. ,

Wharton , T. , Gali , H. , Sarna , T. and

Hamblin , M.R. ( 2007 ) Functionalized

fullerenes mediate photodynamic killing

of cancer cells: Type I versus Type II

photochemical mechanism . Free Radic.

Biol. Med. , 43 , 711 – 719 .

4 Nohynek , G.J. , Lademann , J. , Ribaud , C.

and Roberts , M.S. ( 2007 ) Grey goo on

the skin? Nanotechnology, cosmetic and

sunscreen safety . Crit. Rev. Toxicol. , 37 ,

251 – 277 .

5 Nel , A. , Xia , T. , Madler , L. and Li , N.

( 2006 ) Toxic potential of materials at

the nanolevel . Science , 311 , 622 – 627 .

6 Council , N.R. ( 2006 ) A Matter of Size:

Triennial Review of the National

Nanotechnology Initiative , National

Academies Press , p. 130 .

7 Kolpin , D.W. , Furlong , E.T. , Meyer , M.T. ,

Thurman , E.M. , Zaugg , S.D. , Barber , L.B.

and Buxton , H.T. ( 2002 ) Pharmaceuticals,

hormones, and other organic wastewater

contaminants in US streams, 1999 – 2000:

a national reconnaissance . Environ. Sci.

Technol. , 36 , 1202 – 1211 .

8 Maynard , A.D. , Aitken , R.J. , Butz , T. ,

Colvin , V. , Donaldson , K. , Oberdorster , G. ,

Philbert , M.A. , Ryan , J. , Seaton , A. , Stone ,

V. , Tinkle , S.S. , Tran , L. , Walker , N.J. and

Warheit , D.B. ( 2006 ) Safe handling of

nanotechnology . Nature , 444 , 267 – 269 .

9 Moore , M.N. , Lowe , D.M. , Soverchia , C. ,

Haigh , S.D. and Hales , S.G. ( 1997 ) Uptake

of a non - caloriﬁ c, edible sucrose polyester

oil and olive oil by marine mussels and

their inﬂ uence on uptake and effects of

anthracene . Aquat. Toxicol ., 39 , 307 – 320 .

10 Hyung , H. , Fortner , J.D. , Hughes , J.B.

and Kim , J.H. ( 2007 ) Natural organic

matter stabilizes carbon nanotubes in

References 611

the aqueous phase . Environ. Sci. Technol. ,

41 , 179 – 184 .

11 Oberdorster , E. ( 2004 ) Manufactured

nanomaterials (Fullerenes, C - 60) induce

oxidative stress in the brain of juvenile

largemouth bass . Environ. Health.

Perspect. , 112 , 1058 – 1062 .

12 Roberts , A.P. , Seda , B. , Mount , A.S. , Lin ,

S.J. , Ke , P.C. , Qiao , R. and Klaine , S.J.

( 2007 ) In vivo biomodiﬁ cation of a lipid

coated carbon nanotube by Daphnia

magna . Environ. Sci. Technol. , 41 ,

3025 – 3029 .

13 Wu , Y. , Hudson , J.S. , Lu , Q. , Moore , J.M. ,

Mount , A.S. , Rao , A.M. , Alexov , E. and

Ke , P.C. ( 2006 ) Coating single - walled

carbon nanotubes with phospholipids . J.

Phys. Chem. B , 110 , 2475 – 2478 .

14 Brinkman , S.F. and Hansen , D.L. ( 2007 )

Toxicity of cadmium to early life stages of

brown trout ( Salmo trutta ) at multiple

water hardnesses . Environ. Toxicol. Chem. ,

26 , 1666 – 1671 .

15 Van Genderen , E. , Gensemer , R. , Smith ,

C. , Santore , R. and Ryan , A. ( 2007 )

Evaluation of the Biotic Ligand Model

relative to other site - speciﬁ c criteria

derivation methods for copper in surface

waters with elevated hardness . Aquat.

Toxicol. , 84 , 279 – 291 .

16 Ogendi , G.M. , Brumbaugh , W.G. ,

Hannigan , R.E. and Farris , J.L. ( 2007 )

Effects of acid - volatile sulﬁ de on metal

bioavailability and toxicity to midge

( Chironomus tentans ) larvae in black shale

sediments . Environ. Toxicol. Chem. , 26 ,

325 – 334 .

17 Weinstein , J.E. and Oris , J.T. ( 1999 )

Humic acids reduce the bioaccumulation

and photoinduced toxicity of ﬂ uoranthene

ﬁ sh . Environ. Toxicol. Chem. , 18 ,

2087 – 2094 .

18 Templeton , R.C. , Ferguson , P.L. ,

Washburn , K.M. , Scrivens , W.A. and

Chandler , G.T. ( 2006 ) Life - cycle effects of

single - walled carbon nanotubes (SWNTs)

on an estuarine meiobenthic copepod .

Environ. Sci. Technol. , 40 , 7387 – 7393 .

19 Smith , C.J. , Shaw , B.J. and Handy , R.D.

( 2007 ) Toxicity of single walled carbon

nanotubes to rainbow trout ( Oncorhynchus

mykiss ): respiratory toxicity, organ

pathologies, and other physiological

effects . Aquat. Toxicol. , 82 , 94 – 109 .

20 Braun , M. and Hirsch , A. ( 2000 )

Fullerene derivatives in bilayer

membranes: an overview . Carbon , 38 ,

1565 – 1572 .

21 Oberdorster , E. , Zhu , S.Q. , Blickley , T.M. ,

McClellan - Green , P. and Haasch , M.L.

( 2006 ) Ecotoxicology of carbon - based

engineered nanoparticles: effects of

fullerene (C - 60) on aquatic organisms .

Carbon , 44 , 1112 – 1120 .

22 Cagle , D.W. , Kennel , S.J. , Mirzadeh , S. ,

Alford , J.M. and Wilson , L.J. ( 1999 ) In

vivo studies of fullerene - based materials

using endohedral metallofullerene

radiotracers . Proc. Natl Acad. Sci. USA ,

96 , 5182 – 5187 .

23 Chen , X. , Tam , U.C. , Czlapinski , J.L. , Lee ,

G.S. , Rabuka , D. , Zettl , A. and Bertozzi ,

C.R. ( 2006 ) Interfacing carbon nanotubes

with living cells . J. Am. Chem. Soc. , 128 ,

6292 – 6293 .

24 Qiao , R. , Roberts , A.P. , Mount , A.S. ,

Klaine , S.J. and Ke , P.C. ( 2007 )

Translocation of C60 and its derivatives

across a lipid bilayer . Nano Lett. , 7 ,

614 – 619 .

25 Kashiwada , S. ( 2006 ) Distribution of

nanoparticles in the see - through medaka

( Oryzias latipes ) . Environ. Health Perspect. ,

114 , 1697 – 1702 .

26 Yamago , S. , Tokuyama , H. , Nakamura ,

E. , Kikuchi , K. , Kananishi , S. , Sueki , K. ,

Nakahara , H. , Enomoto , S. and Ambe , F.

( 1995 ) In - vivo biological behavior of a

water - miscible fullerene – C - 14 labeling,

absorption, distribution, excretion and

acute toxicity . Chem. Biol. , 2 , 385 – 389 .

27 Cleckner , L.B. , Garrison , P.J. , Hurley ,

J.P. , Olson , M.L. and Krabbenhoft , D.P.

( 1998 ) Trophic transfer of methyl mercury

in the northern Florida Everglades .

Biogeochemistry , 40 , 347 – 361 .

28 Drevnick , P.E. , Horgan , M.J. , Oris , J.T.

and Kynard , B.E. ( 2006 ) Ontogenetic

dynamics of mercury accumulation in

Northwest Atlantic sea lamprey

( Petromyzon marinus ) . Can. J. Fish. Aquat.

Sci. , 63 , 1058 – 1066 .

29 Johnson - Restrepo , B. , Kannan , K. ,

Addink , R. and Adams , D.H. ( 2005 )

Polybrominated diphenyl ethers and

polychlorinated biphenyls in a marine

foodweb of coastal Florida . Environ. Sci.

Technol. , 39 , 8243 – 8250 .

612 18 Ecological Toxicology of Engineered Carbon Nanoparticles

30 Donato , F. , Magoni , M. , Bergonzi , R. ,

Scarcella , C. , Indelicato , A. , Carasi , S. and

Apostoli , P. ( 2006 ) Exposure to

polychlorinated biphenyls in residents

near a chemical factory in Italy: The food

chain as main source of contamination .

Chemosphere , 64 , 1562 – 1572 .

31 Drevnick , P.E. and Sandheinrich , M.B.

( 2003 ) Effects of dietary methylmercury

on reproductive endocrinology of fathead

minnows . Environ. Sci. Technol. , 37 ,

4390 – 4396 .

32 Drevnick , P.E. , Sandheinrich , M.B. and

Oris , J.T. ( 2006 ) Increased ovarian

follicular apoptosis in fathead minnows

( Pimephales promelas ) exposed to dietary

methylmercury . Aquat. Toxicol. , 79 ,

49 – 54 .

33 Langer , P. , Kocan , A. , Tajtakova , M. ,

Petrik , J. , Chovancova , J. , Drobna , B. ,

Jursa , S. , Radikova , Z. , Koska , J. ,

Ksinantova , L. , Huckova , M. , Imrich , R. ,

Wimmerova , S. , Gasperikova , D. ,

Shishiba , Y. , Trnovec , T. , Sebokova , E.

and Klimes , I. ( 2007 ) Fish from

industrially polluted freshwater as the

main source of organochlorinated

pollutants and increased frequency of

thyroid disorders and dysglycemia .

Chemosphere , 67 , S379 – S385 .

34 Tillitt , D.E. , Ankley , G.T. , Giesy , J.P. ,

Ludwig , J.P. , Kurita - Matsuba , H. , Weseloh ,

D.V. , Ross , P.S. , Bishop , C.A. , Sileo , L. et

al . ( 1992 ) Polychlorinated biphenyl

residues and egg mortality in double -

crested cormorants from the Great Lakes .

Environ. Toxicol. Chem. , 11 , 1281 – 1288 .

35 Hoffmann , J.L. and Oris , J.T. ( 2006 )

Altered gene expression: a mechanism for

reproductive toxicity in zebraﬁ sh exposed

to benzo[a]pyrene . Aquat. Toxicol. , 78 ,

332 – 3340 .

36 Neff , J.M. , ( 1979 ) Polycyclic Aromatic

Hydrocarbons in the Aquatic Environment ,

Applied Science , London .

37 Oris , J.T. and Giesy , J.P. ( 1987 ) The

photo - induced toxicity of polycyclic

aromatic hydrocarbons to larvae of the

fathead minnow Pimephales promelas .

Chemosphere , 16 , 1395 – 1404 .

38 Yang , K. , Zhu , L.Z. and Xing , B.S.

( 2006 ) Adsorption of polycyclic aromatic

hydrocarbons by carbon nanomaterials .

Environ. Sci. Technol. , 40 , 1855 – 1861 .

39 Lam , C.W. , James , J.T. , McCluskey , R.

and Hunter , R.L. ( 2004 ) Pulmonary

toxicity of single - wall carbon nanotubes in

mice 7 and 90 days after intratracheal

instillation . Toxicol. Sci. , 77 , 126 – 134 .

40 Shvedova , A.A. , Castranova , V. , Kisin ,

E.R. , Schwegler - Berry , D. , Murray , A.R. ,

Gandelsman , V.Z. , Maynard , A. and

Baron , P. ( 2003 ) Exposure to carbon

nanotube material: assessment of

nanotube cytotoxicity using human

keratinocyte cells . J. Toxicol. Environ.

Health A , 66 , 1909 – 1926 .

41 Lovern , S.B. and Klaper , R. ( 2006 )

Daphnia magna mortality when exposed

to titanium dioxide and fullerene (C - 60)

nanoparticles . Environ. Toxicol. Chem. , 25 ,

1132 – 1137 .

42 Zhu , X.S. , Zhu , L. , Li , Y. , Duan , Z.H. ,

Chen , W. and Alvarez , P.J.J. ( 2007 )

Developmental toxicity in zebraﬁ sh

( Danio rerio ) embryos after exposure to

manufactured nanomaterials:

Buckminsterfullerene aggregates (nC(60))

and fullerol . Environ. Toxicol. Chem. , 26 ,

976 – 979 .

43 Usenko , C.Y. , Harper , S.L. and Tanguay ,

R.L. ( 2007 ) In vivo evaluation of carbon

fullerene toxicity using embryonic

zebraﬁ sh . Carbon , 45 , 1891 – 1898 .

44 Fortner , J.D. , Lyon , D.Y. , Sayes , C.M. ,

Boyd , A.M. , Falkner , J.C. , Hotze , E.M. ,

Alemany , L.B. , Tao , Y.J. , Guo , W. ,

Ausman , K.D. , Colvin , V.L. and Hughes ,

J.B. ( 2005 ) C60 in water: nanocrystal

formation and microbial response .

Environ. Sci. Technol ., 39 , 4307 – 4316 .

45 Henry , T.B. , Menn , F.M. , Fleming , J.T. ,

Wilgus , J. , Compton , R.N. and Sayler ,

G.S. ( 2007 ) Attributing effects of aqueous

C - 60 nano - aggregates to tetrahydrofuran

decomposition products in larval

zebraﬁ sh by assessment of gene

expression . Environ. Health Perspect. , 115 ,

1059 – 1065 .

46 Lovern , S.B. , Strickler , J.R. and Klaper , R.

( 2007 ) Behavioral and physiological

changes in Daphnia magna when exposed

to nanoparticle suspensions (titanium

dioxide, nano - C - 60, and C(60)HxC(70)

Hx) . Environ. Sci. Technol. , 41 , 4465 – 70 .

47 Choi , J. and Oris , J.T. ( 2000 ) Anthracene

photoinduced toxicity to PLHC - 1 cell line

( Poeciliopsis lucida ) and the role of lipid

References 613

peroxidation in toxicity . Environ. Toxicol.

Chem. , 19 , 2699 – 2706 .

48 Choi , J. and Oris , J.T. ( 2000 ) Evidence of

oxidative stress in bluegill sunﬁ sh

( Lepomis macrochirus ) liver microsomes

simultaneously exposed to solar

ultraviolet radiation and anthracene .

Environ. Toxicol. Chem. , 19 , 1795 – 1799 .

49 Roberts , A.P. and Oris , J.T. ( 2004 )

Multiple biomarker response in rainbow

trout during exposure to hexavalent

chromium . Comparative Biochemistry and

Physiology C: Toxicology and Pharmacology ,

138 , 221 – 228 .

50 Lehmann , D.W. , Levine , J.F. and Law ,

J.M. ( 2007 ) Polychlorinated biphenyl

exposure causes gonadal atrophy and

oxidative stress in Corbicula ﬂ uminea

clams . Toxicol. Pathol. , 35 , 356 – 365 .

51 Possamai , F.P. , Fortunato , J.J. , Feier , G. ,

Agostinho , F.R. , Quevedo , J. , Wilhelm , D.

and Dal - Pizzol , F. ( 2007 ) Oxidative stress

after acute and sub - chronic malathion

intoxication in Wistar rats . Environ.

Toxicol. Pharmacol. , 23 , 198 – 204 .

52 Verlecar , X.N. , Jena , K.B. and Chainy ,

G.B.N. ( 2007 ) Biochemical markers of

oxidative stress in Perna viridis exposed to

mercury and temperature . Chem. Biol.

Interact. , 167 , 219 – 226 .

53 Gharbi , N. , Pressac , M. , Hadchouel , M. ,

Szwarc , H. , Wilson , S.R. and Moussa , F.

( 2005 ) [60]Fullerene is a powerful

antioxidant in vivo with no acute or

subacute toxicity . Nano Lett. , 5 , 2578 – 2585 .

54 Handy , R.D. , Sims , D.W. , Giles , A. ,

Campbell , H.A. and Musonda , M.M.

( 1999 ) Metabolic trade - off between

locomotion and detoxiﬁ cation for

maintenance of blood chemistry and

growth parameters by rainbow trout

( Oncorhynchus mykiss ) during chronic

dietary exposure to copper . Aquat.

Toxicol. , 47 , 23 – 41 .

Carbon Nanotubes as Adsorbents for the Removal of Surface

Water Contaminants

Jose E. Herrera and Jing Cheng

615

Advanced Nanomaterials. Edited by Kurt E. Geckeler and Hiroyuki Nishide

ISBN: 978-3-527-31794-3

19

19.1

Introduction

The level and complexity of water contamination worldwide has reached unprec-

edented levels in such a way that the complexity of this problem seems intractable.

While there is a wide variety of different contaminant species, the US environ-

mental protection agency divides most of the common contaminants found in

surface water into six categories [1] :

• Inorganic compounds: these include toxic heavy metal ions (e.g., cadmium,

chromium, lead, copper, mercury), oxoanions (arsenates, chromates) and

nonmetal anions such as ﬂ uoride.

• Organic compounds: benzene, 1,2 - dichloroethene ( 1,2 - DCE ), dioxins, polyaro-

matic hydrocarbon s ( PAH s), tetrachloroethene ( PCE ), trichloroethene ( TCE ),

polychlorinated biphenyl s ( PCB s), etc.

• Disinfection byproducts: trihalomethanes and haloacetic acids.

• Disinfectants: chlorine (as Cl

2

), chloramines (as Cl

2

) and chlorine dioxide.

• Radionuclide: atoms with unstable potentially radioactive nuclei, such as

phosphorus - 32, promethium - 147 or americium - 243.

• Microorganisms: these include bacteria, fungi and archaea, but not viruses nor

prions.

Different methods employed for the removal of pollutants from water include

chemical precipitation, membrane ﬁ ltration, ion exchange, and adsorption. Many

types of adsorbent, such as silica, alumina, activated carbon, rare earth oxides,

amorphous iron hydroxide, polymers, ion - exchange ﬁ bers, and lanthanum - based

compounds, have been developed as adsorbents for the removal of pollutants from

water [2 – 7] . Recently, carbon nanotube s ( CNT s) have been considered as materials

for the removal of trace pollutants from water. A number of contributions in this

ﬁ eld have been devoted to the experimental and theoretical study of contaminant

616 19 Carbon Nanotubes as Adsorbents for the Removal of Surface Water Contaminants

adsorption by CNTs. One of the earliest studies, conducted by Long et al . [8] ,

reported that CNTs had a signiﬁ cantly higher dioxin removal efﬁ ciency than acti-

vated carbon. One year later Li et al . [9] suggested that CNTs had a high adsorption

capacity for the removal of lead from water. The same group [10] also showed

CNTs to be excellent ﬂ uoride adsorbents, with a removal capability superior to that

of activated carbon. Peng et al . [11] indicated that CNTs were efﬁ cient adsorbents

for the removal of 1, 2 - dichlorobenzene ( 1, 2 - DCB ) from water, and could be used

over a wide pH range. Lu and coworkers [12] noted that CNTs also displayed sig-

niﬁ cant high trihalomethane removal efﬁ ciencies.

Together, the results of these studies have indicated that CNTs possess an enor-

mous potential for applications in environmental remediation. Consequently, we

present in this chapter a comprehensive overview of recent progress in laboratory

studies of CNTs for contaminant removal from water. Particular aspects concen-

trate on the preparation, characterization and adsorption results of the nanotube

materials, while speciﬁ c examples of experimental studies with CNTs for the

adsorption of common environmental contaminants in water are also discussed.

19.2

Structure and Synthesis of Carbon Nanotubes

Carbon nanotubes can be formally depicted as a graphene honeycomb rolled either

into a seamless single - walled cylinder or into several concentric cylinders. The

former structure is termed single - walled nanotube ( SWNT ) (Figure 19.1 ), and the

latter multi - walled nanotube ( MWNT ) (Figure 19.2 ). The diameter of a typical

Figure 19.1 Transmission electronic microscopy image of a

single - walled carbon nanotube rope. Reproduced from F.L.

Darkrima, P. Malbrunot, G.P. Tartaglia, Int. J. Hydrogen Energy

(2002), 27 , 193 – 202.

19.2 Structure and Synthesis of Carbon Nanotubes 617

MWNT ranges from a few to a few tens of nanometers, while their length is of

the order of one micron. In the case of SWNTs, the diameter is in the order of one

nanometer, but the length can reach several micrometers, or more.

Each SWNT structure is fully described by two integers ( n , m ) which specify the

number of unit vectors

→

a

1

and

→

a

2

in the graphene structure that constitute the chiral

vector

→

V = n

→

a

1

+ m

→

a

2

. The graphene structure is rolled - up in such a way that the

chiral vector

→

V

forms the nanotube circumference. These indices determine the

nanotube diameter, and also the orientation of the carbon hexagons with respect to

the nanotube axis; this orientation is the termed the “ chirality ” of the nanotube.

Single - walled CNTs have unique chemical, electronic and mechanical proper-

ties, combined with a very light weight. Depending on their chirality and diameter,

the nanotubes may be either electrically metallic or semiconductor. At the same

time, they have shown evidence for high stiffness (Young ’ s modulus), a very high

resilience, and an ability to reversibly buckle and collapse. These properties have

led to SWNTs becoming promising candidates in the fabrication of strong ﬁ bers

with a light weight and high electrical conductivity. Nanotubes can also be func-

tionalized with different chemical moieties, and this greatly broadened the scope

of their applications in ﬁ elds ranging from conductive coatings to molecule -

speciﬁ c nanosensing.

The synthesis of CNT materials can be divided into high - temperature routes

(laser ablation, arc discharge) [13 – 18] and medium - temperature processes, based

on either catalytic decomposition or a carbon - containing molecule (a saturated or

Figure 19.2 Multiwalled carbon nanotube (MWNT) as seen by

transmission electron microscopy. The different walls

constituting the material appear in a longitudinal view. A

micrograph of a SWNT is included for comparison.

Reproduced from B. Bai, A. - L. Hamon, A. Marrauda, B.

Jouffreya, V. Zymlab, Chem. Phys. Lett. (2002), 365 , 184.

618 19 Carbon Nanotubes as Adsorbents for the Removal of Surface Water Contaminants

unsaturated hydrocarbon or carbon monoxide) [19, 20] . For the high - temperature

routes, pure graphite or a mixture of graphite and a metallic catalyst are vaporized

at very high temperatures (2000 – 4000 ° C), and the nanotubes are formed during

the cooling process at lower temperatures [21] . The catalytic decomposition of a

carbon - containing molecule requires a relatively low temperature, and has the

potential for high - yield productions.

Iijima [13] was the ﬁ rst to report the presence of multi - walled CNTs in the soot

of an arc - discharge chamber. The tubes were produced using an electric arc -

discharge evaporation method similar to that used for the synthesis of fullerene.

In this method, an electric arc discharge is generated between two graphite elec-

trodes under an inert atmosphere of helium or argon. (Figure 19.3 a) [22] . The ﬁ rst

successful production of MWNTs at the gram level was developed in 1992 by

Ebbesen and Ajayan [23] . To synthesize SWNTs, a metal catalyst is required [24] ,

and the ﬁ rst report of the synthesis of substantial amounts of these materials, by

Bethune and coworkers, appeared in 1993 [25] .

In 1996, Smalley and coworkers produced high yields ( > 70%) of SWNTs by

utilizing the laser - ablation (vaporization) of graphite rods doped with small

amounts of Ni and Co catalysts (Figure 19.3 b) [26] . In this process, a piece of

graphite is vaporized by laser irradiation under an inert atmosphere. The resultant

soot containing the nanotubes is deposited on the walls of a quartz tube when the

reaction mixture has cooled. Although this process is known to produce CNTs of

the highest quality and highest purity, a puriﬁ cation step is generally required to

eliminate any carbonaceous impurities from the as - produced material. This puri-

ﬁ cation is normally achieved by carbon gasiﬁ cation.

Since 1960, carbon ﬁ laments and ﬁ bers have also been produced by the thermal

decomposition of carbon - containing molecules (this process is also known as

chemical vapor decomposition ; CVD ) in the presence of a catalyst [27, 28] . A

similar approach was used by Yacaman [29] in 1993, and later by Nagy and col-

laborators [30, 31] , to grow MWNTs. Following these initial reports, the CVD

technique has been subsequently improved and optimized. In general, these proc-

esses involve the catalyst - assisted decomposition of hydrocarbons (usually ethyl-

ene or acetylene) in a tube reactor at temperatures between 550 – 1000 ° C. The

growth of CNTs occurs on the catalyst surface as the gas molecule decomposes

(Figure 19.3 c). This process has several advantages over the arc discharge and laser

ablation techniques. In fact, its amenable nature has led to its use in the large - scale

synthesis of aligned CNTs [32, 33] .

Since all of these synthesis methods generate, in addition to the nanotubes,

relatively large amounts of impurities, a number of techniques have been pro-

posed to improve the quality of the materials through post - synthesis puriﬁ cation.

These methods range from concentrated acid treatments, dispersion by sonication

in a surfactant and ﬁ ltration, to high - temperature heating under neutral or lightly

oxidizing conditions [34, 35] . A detailed account of the different methods for CNT

synthesis and puriﬁ cation is beyond the scope of this chapter, and these topics

will be addressed only in the context of the synthesis or chemical treatment affect-

ing the adsorption properties of the materials.

Geckeler K.E., Nishide H. (Eds.) Advanced Nanomaterials

Подождите немного. Документ загружается.