Nano Res

1

Covalent functionalization/polycarboxylation of

tungsten disulfide inorganic nanotubes (INTs-WS2)

Daniel Raichman, David A. Strawser, and Jean-Paul Lellouche ()

Nano Res., Just Accepted Manuscript • DOI: 10.1007/s12274-014-0630-9

http://www.thenanoresearch.com on November 7 2014

© Tsinghua University Press 2014

Just Accepted

This is a “Just Accepted” manuscript, which has been examined by the peer-review process and has been

accepted for publication. A “Just Accepted” manuscript is published online shortly after its acceptance,

which is prior to technical editing and formatting and author proofing. Tsinghua University Press (TUP)

provides “Just Accepted” as an optional and free service which allows authors to make their results available

to the research community as soon as possible after acceptance. After a manuscript has been technically

edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP

article. Please note that technical editing may introduce minor changes to the manuscript text and/or

graphics which may affect the content, and all legal disclaimers that apply to the journal pertain. In no event

shall TUP be held responsible for errors or consequences arising from the use of any information contained

in these “Just Accepted” manuscripts. To cite this manuscript please use its Digital Object Identifier (DOI®),

which is identical for all formats of publication.

Nano Research

DOI 10.1007/s12274-014-0630-9

Covalent

functionalization/

polycarboxylation

of tungsten

disulfide

inorganic

nanotubes

(INT-WS2)

Daniel Raichman,

David A. Strawser,

and Jean-Paul

Lellouche*

Department of

Chemistry,

Nanomaterials

Research Center,

Institute of

Nanotechnology &

Advanced Materials,

Bar-Ilan University,

Ramat-Gan

5290002, Israel

Efficient polycarboxylation of surface shell S atoms of WS2 inorganic nanotubes (INT-WS2) by a

modified, acidic, highly electrophilic Vilsmeier-Haack (VH) reagent.

Covalent functionalization/polycarboxylation of

tungsten disulfide inorganic nanotubes (INTs-WS2)

Daniel Raichman, David A. Strawser, and Jean-Paul Lellouche ()

Received: day month year

Revised: day month year

Accepted: day month year

(automatically inserted by

the publisher)

© Tsinghua University Press

and Springer-Verlag Berlin

Heidelberg 2014

KEYWORDS

Tungsten disulfide

nanotubes, INT-WS2,

Vilsmeier-Haack reagents,

polycarboxylation,

inorganic nanotube

functionalization

ABSTRACT

Inorganic nanotubes of tungsten disulfide (INT-WS2) are insoluble in common

solvents and practically inert, hindering their usefulness in both research and

commercial applications. The covalent attachment of functional species onto the

surface of INT-WS2 is a critical first step in realizing the potential that INT-WS2

offer for high-performance materials and products. Although a few attempts

have been reported regarding preparing modified nanotubes, only a limited

range of surface functionalities is possible with these methods. We have

developed a versatile method, based on a modified, highly electrophilic acidic

Vilsmeier-Haack reagent, to produce covalently bonded, polycarboxylated

functional WS2 nanotubes that are dispersible in polar liquids, including water.

The surface polycarboxylated shell provides a means for additional

derivatization, enabling matching compatibility of derivatized nanotubes to

both hydrophobic and hydrophilic materials. Nanocomposites incorporating

derivatized INT-WS2 are expected to show improved properties as a result of

enhanced interfacial compatibility, made possible by the large number of classes

of functionalization available through the initial polycarboxylation step.

1. Introduction

Nanomaterials are of great interest to the scientific

community due to the unique properties that result

from their small size (< 100 nm in at least one

dimension). For example, small nanoparticles

(NPs) typically exhibit very large surface areas,

with 1 mg of NPs of 1 nm3 containing the same

surface area as 1 kg of particles of 1 mm3. Although

this large surface area is valuable in applications,

such as nanocomposites that rely on optimal

interfacial interactions between all of the

components, it is a challenge to prepare

well-dispersed NP-based suspensions that are

required to obtain optimum performance of the

final product.

In order to study the chemical and physical

properties of NPs or to produce useful products,

especially nanocomposites that incorporate

nanoscale fillers, the NPs must be compatible with

a variety of media. For example, carbon nanotubes

(CNTs) are insoluble, nearly inert, and difficult to

disperse into most common liquids. However,

today, various commercial products are available

that incorporate CNTs including bicycle

components, anti-fouling paints for ships, flexible

transistors, and electrostatic discharge shields used

in spacecraft technology [1]. These products were

made possible only through research that led to

methods of dispersing the CNTs in a variety of

Nano Research

DOI (automatically inserted by the publisher)

Research Article

Address correspondence to Jean-Paul Lellouche, lellouj@biu.ac.il

| www.editorialmanager.com/nare/default.asp

2 Nano Res.

liquids as well as polymers. CNTs can be made

dispersible through physisorption of surfactants

[2-7] or via surface functionalization [8-14]. From

Iijima’s report of the discovery of CNTs in 1991 [15],

extensive research was conducted on surface

modifications of CNTs, particularly regarding the

best process to oxidize CNTs in a manner that

would produce desired surface functional groups,

such as hydroxyls (-OH), acids (-COOH), and

carbonyls (R(R’)C=O), while at the same time

minimizing damage, such as etching of the CNT

surface or even complete cutting of the tubes into

smaller pieces [16-18]. In addition to modifying the

interactions with other materials, these surface

functionalizations enable surface properties to be

tailored even further by attachment of additional

chemical groups through reaction with the above

“anchor” chemical groups.

Inorganic transition metal dichalcogenide

materials, such as tungsten and molybdenum

disulfides (WS2 and MoS2, respectively), are of

interest to the scientific community because of their

unique layered structure and functional properties,

with nano-sized particles (NPs) tending to exhibit a

different set of properties compared to the bulk

forms. These metal dichalcogenide nanomaterials

have emerged as one of the most promising classes

of nanomaterials since the discovery of CNTs. As

with early research in the field of CNTs, a number

of potential applications have been proposed [19]

including areas such as energy storage [20], field

effect transistors [21], nanocomposite coatings [22,

23], battery anodes [24], light-emitting diodes [25],

self-lubricating medical devices [26], and

high-performance lubricants [27-34]. In addition,

the outstanding shock absorbing ability of WS2 NPs

[35-37] holds potential for new impact and shock

resistant materials. Nanocomposite materials,

formed by adding small amounts (less than 5% by

weight) of nano-sized fillers into a polymer matrix,

are of particular interest, showing improved

mechanical properties, higher thermal properties,

and improved performance as barriers to heat,

moisture, and solvents [23, 38, 39] than composites

prepared with conventional fillers [21, 22].

Considerable research has been conducted on

polymer-nanocomposites that incorporate WS2 NPs

into matrices of epoxy [40],

polystyrene/poly(methylmethacrylate) [41],

poly(propylene fumarate) [42], nylon 12 [43], and

poly(phenylene) sulphide [44]. Due to the superior

mechanical properties of WS2 NPs, such as high

stiffness and strength [45], ultrahigh-performance

polymer nanocomposites have been produced [46].

In addition, commercial lubricants are presently

available that include WS2 NPs that impart unique

tribological properties [47] to the final products.

Although there are many potential applications

in a variety of fields for these metal dichalcogenide

NPs and INTs, research has been hampered

analogously to early CNT research because these

dichalcogenide materials are insoluble in common

solvents, difficult to disperse into most liquids and

resins, and tend to have limited compatibility when

admixed with common polymers. This directly

mirrors the difficulties that were encountered in

the early years of research with CNTs. And

although the CNT literature contains a number of

methods to functionalize the CNTs, as presented

above, few of these methods are readily adaptable

to metal dichalcogenides because of the difference

in composition between the two.

To overcome these limitations due to phase

incompatibility, considerable effort has been made

to functionalize metal dichalcogenide NPs, as first

reported by Tahir et al. in 2006 [48]. Chemically

modified MoS2 NPs were produced that were

dispersible both in water and common organic

solvents. This was accomplished by attaching a

cationic Ni(II) complex with chelating ligands to

the outer sulfur layer/atoms of the MoS2 NPs. This

approach of using a cationic metal with high sulfur

affinity to coordinate with the sulfur was chosen

because they believed that “… a direct anchoring of

organic ligands to the sulfur surface is not

possible…” Although successful, this method lacks

versatility due to the limited selection of chelating

ligands as well as rather weak bonding between

the Ni(II) and S reactive centers. Another method

to introduce covalently bound functional groups

onto WS2 NPs was developed by Shahar et al. [49].

This method relies on inherent hydroxylated

surface defects that are few in number, thereby

severely limiting the quantity of functional groups

that serve as anchors for further modification in

subsequent functionalization steps.

In contrast to these studies, we have

successfully developed a functionalization method

for INT-WS2 that uses readily available materials

and equipment to produce an acidic, covalently

bound shell of polyCOOH functional groups. This

breakthrough in efficient, robust functionalization

www.theNanoResearch.com∣www.Springer.com/journal/12274 | Nano Research

3 Nano Res.

of INT-WS2 provides researchers with a highly

versatile tool to tailor the compatibility of

functionalized INT-WS2 (f-INT-WS2) with nearly

any other material. This functionalization method

produces polycarboxylated INT-WS2 (polyCOOH

f-INT-WS2) that are readily dispersible in polar

liquids, including water. Thus, these

polycarboxylation sites can serve as anchor points

for secondary-step derivatizations, providing a

versatile route to additional surface modifications

through the well-known reactivity of carboxylic

acid groups. These surface modifications enable

matching interfacial compatibility to both

hydrophilic and hydrophobic materials. In

addition, subsequent functionalizations can include

bis- or multi-reactive species that enable covalent

bonding with other materials/polymeric phases in

specific compositions. This is an especially

important feature for the controlled fabrication of

hybrid nanocomposites that may contain both

co-fillers and polymerizable monomers, for

example.

Realizing the important ramifications of this

new derivatization method, we undertook in

parallel with the present study an optimization

study [50], via design of experiments (DoE)

methodology of several reaction parameters to

maximize the yield of polyCOOH f-INT-WS2. In

addition to finding optimum values of reaction

factors, an interaction analysis indicated that

reaction parameters might be adjusted to tune the

level of poly-carboxylation obtained.

While screening various solvents and reagents

to try to produce surface functionalized INTs, we

found that DMF in combination with halogenated

acetic acid produced readily dispersible INTs.

Finding this to be reproducible, a more extensive

study using a variety of solvents revealed that

DMF was an essential component in this

polycarboxylation reaction. More specifically, this

innovative polycarboxylation functionalization

method exploits the high electrophilic reactivity of

a modified Vilsmeier-Haack (VH) reagent [51].

Classical VH reactions generally use in situ

generated VH iminium salts/reagents arising from

cold (-50–0 °C) mixtures of dimethyl formamide

(DMF, secondary N-formyl amine) and POCl3 or

SOCl2, that are effective in formylating a large

variety of electron rich substrates via iminium salts

of type A (Scheme 1a).

These types of VH reactions have been

extensively studied and found to be extremely

versatile, producing not only formylated products

but also various oxygen and nitrogen heterocycles

[52-57] as well.

In this context, we discovered that a mixture

containing DMF (secondary N-formyl amine),

O-alkylating 2-bromoacetic acid (2-BrCH2COOH),

and silver acetate (Ag(I)OAc) as a bromophilic

agent to enhance abstracting the halogen from

bromoacetic acid, very effectively polycarboxylates

INT-WS2 according to the mechanism presented in

Scheme 1(c). The essential role of anhydrous DMF

in this reaction was demonstrated by either its

removal from the reaction mixture or replacement

with other polar, non-protic solvents (e.g., DME,

1,4-dioxane, THF, etc.), resulting in unsuccessful

polycarboxylation. This strict requirement of DMF

(secondary N-formyl amine) as an essential

component in the reaction mixture led us to

propose the VH-like reaction mechanism, detailed

in Scheme 1(c), with emphasis on the key

ionization assistance induced by bromophilic Ag(I)

cations.

The presence and chemical reactivity of the

grafted carboxylic acid groups covalently bound

onto the outer S layer of INT-WS2 were quantified

via the quite sensitive UV-spectrophotometric

Kaiser test for reactive primary amines [56] after

derivatization of the polycarboxylated shell with a

diamine (1,3-diaminopropane), thereby producing

polyNH2 f-INT-WS2 comprising a

poly(amido-primary NH2) shell for fluorescence

coupling. In addition and quite similarly,

polyCOOH f-INT-WS2 have been reacted with

cysteamine, resulting in polySH f-INT-WS2

containing a terminal polySH shell that was

quantified using Ellman’ s fluorescence based test

[59].

| www.editorialmanager.com/nare/default.asp

4 Nano Res.

(a)

(b)

(c)

Scheme 1 (a) Classical highly electrophilic Vilsmeier-Haack (VH) iminium salt intermediate A; (b) generation of the electrophilic

VH iminium complex B with 2-bromoacetic acid (POCl3 replacement) and halide (Br) abstraction mediated by the Ag(I)OAc salt;

(c) sulfur mediated nucleophilic addition of the electrophilic VH iminium complex B onto the outermost layer of S atoms of

INT-WS2 to produce polyCOOH f-INT-WS2.

2. Experimental

2.1. Materials

Tungsten disulfide inorganic nanotubes

(INT-WS2) have been provided by NanoMaterials

Ltd (Yavne, Israel). All reagents and solvents

were purchased from commercial sources and

used without further purification.

Thermogravimetric analysis was performed on a

TA Q600-0348, model SDT Q600

(Thermofinnigan) using a temperature profile of

25–800 °C at 10 °C/min under nitrogen flow (180

mL/min) with sample masses of 5-15 mg. IR

spectra were recorded on an FT-IR Tensor 27

spectrometer (Bruker) using ATR. Nanomaterial

surface charges were evaluated by ξ potential

measurements with a Zetasizer Nano-ZS

(Malvern Instruments Ltd., Worcestershire, UK)

in water (pH unadjusted) at 25 °C and 150 V.

Untreated and VH-treated INTs were

characterized with a G2, FEI High Resolution

| www.editorialmanager.com/nare/default.asp

Nano Res.

TEM (Tecnai). Dispersions of INT-WS2 and

f-INT-WS2 were prepared with a low-power

ElmaSonic S30 bath sonicator (Elma GmbH & Co.,

Singen, DE). The chemically accessible

polyCOOH shell present on the surface of the

polyCOOH f-INT-WS2 was quantified by (i) the

Kaiser test after shell derivatization using

1,3-diaminopropane and by (ii) Ellman’ s test

after a subsequent similar shell derivatization

with cysteamine.

2.2. Polycarboxylation of INT-WS2 (polyCOOH

f-INT-WS2)

To a solution of 2-bromoacetic acid

(2-BrCH2COOH, 1.0 g, 7.19 mmol) in anhydrous

DMF (3 mL) was added AgOAc (10 mg, 0.059

mmol) and dry INT-WS2 (200 mg). The mixture

was heated in an oil bath to 80 °C and stirred

over 2 days at the same temperature. After

cooling to room temperature, the mixture was

centrifuged (11,000 RPM, 5 min) and the

supernatant discarded. The solids were cleaned

by 5 cycles of washing with EtOH followed by

centrifugation (11,000 rpm, 5 minutes). The

cleaned solids were dried under vacuum to

obtain 190 mg of polyCOOH f-INT-WS2.

2.3. Diamine coupling onto polyCOOH f-INT-WS2

(polyNH2 f-INT-WS2)

To a solution of

1-ethyl-3-(3-dimethylaminopropyl)carbodiimide

(EDC, 20 mg, 4 mmol) in dichloromethane (DCM,

12 mL) was added polyCOOH f-INT-WS2 (200

mg) and 4-dimethylaminopyridine (DMAP, 10

mg, 0.08 mmol). The mixture was stirred for 2

hours at room temperature followed by addition

of 1, 3-diaminopropane (NH2-(CH2)3-NH2, 800 µl,

9.58 mmol) and stirring continued at room

temperature overnight. The mixture was

centrifuged (11,000 RPM, 5 min) and the

supernatant discarded. The solids were worked

up as described for polyCOOH f-INT-WS2. The

product contained 0.77 mmol NH2 groups/g of

polyNH2 f-INT-WS2, as determined by the Kaiser

Test [45].

2.4. Cysteamine Coupling onto polyCOOH

f-INT-WS2 (polySH f-INT-WS2)

To a solution of EDC (3.0 g, 19.32 mmol) in DCM

(40 mL) was added polyCOOH f-INT-WS2 (1.8 g).

The suspension was stirred for 2 hours at room

temperature followed by addition of cysteamine

(NH2-(CH2)2-SH, 4 g, 51.85 mmol) and DMAP (20

mg, 0.16 mmol) and stirring continued for 2 days

at room temperature. The mixture was

centrifuged (11,000 RPM, 5 min) and the

supernatant discarded. The solids were worked

up as described for polyCOOH f-INT-WS2 to

obtain 1.6 g of product. The product contained

0.80 mmol SH groups/g of polySH f-INT-WS2, as

determined by Ellman’s Test [46].

3. Results and discussion

INT-WS2 were functionalized with a shell of

carboxylic acid groups followed by further shell

modifications with 1,3-diaminopropane or

cysteamine species, resulting in f-INT-WS2 with

surfaces decorated with terminal polyCOOH,

polyNH2, or polySH functional shells. A large

excess of 1,3-diaminopropane was used to

suppress cross-linking between INTs and to

ensure all accessible carboxyl sites were

derivatized. Likewise, a large excess of

cysteamine was used to ensure all accessible

carboxyl sites were derivatized

The polycarboxylation was accomplished by

reaction of INT-WS2 with 2-bromoacetic acid in

dry DMF (as both solvent and reagent) using

Ag(I)OAc to assist in bromide abstraction/DMF

ionization. The presence of carboxylic acid

groups (polyCOOH shell) on polyCOOH

f-INT-WS2 was confirmed by characterizations

including thermogravimetric analysis (TGA),

Fourier-transform infrared spectroscopy (FTIR),

Kaiser and Ellman’ s tests, as well as Zeta

potential. Zeta potential was measured in water

with no adjustment to pH.

Stability of dispersions in water of

polyCOOH f-INT-WS2 was superior to

dispersions of unmodified INT-WS2. The

dispersions were prepared in water by low

power sonication (37 kHz, 280 W, 1 minute) in a

bath sonicator.

Thermogravimetric analyses were performed

in order to determine the amount of organic

material bound to the functionalized INTs.

Figure 1(a) displays the TGA graphs of

unfunctionalized and functionalized INT-WS2

(polyCOOH f-INT-WS2, polyNH2 f-INT-WS2, and

polySH f-INT-WS2), and Figure 1(b) displays the

www.theNanoResearch.com∣www.Springer.com/journal/12274 | Nano Research

Nano Res.

first-derivative plots. The unfunctionalized

material shows a total weight loss of less than 3%

(25-800 °C under nitrogen). As expected, the

three functionalized samples all display

significant weight losses, ranging between 11%

and 19% (25-800 °C under nitrogen). In addition,

the weight loss profiles for polyNH2 f-INT-WS2

and polySH f-INT-WS2 are significantly different,

which supports the fact that different species

have been grafted.

(a)

(b)

Figure 1 TGA graphs of unfunctionalized and

functionalized INT-WS2. (a) Weight (%) vs. temperature

(°C). (b) First-derivative curves of TGA graphs displayed in

Figure 1(a).

FTIR spectroscopy was used to confirm the

presence of characteristic absorptions of the

chemically modified f-INT-WS2. Figure 2 displays

stacked spectra of the untreated INT-WS2 and the

three functionalized samples. The spectrum of

unmodified INT-WS2 is nearly featureless,

whereas the other three spectra show

characteristic peaks that indicate the presence of

carboxyl, amine, and thiol groups, respectively.

Figure 2 FTIR spectra of unfunctionalized and

functionalized INT-WS2. (1) INT-WS2; (2) polyCOOH

f-INT-WS2; (3) poly NH2 f-INT-WS2; (4) polySH

f-INT-WS2.

The significant peaks can be assigned as

follows: 1730 cm-1 to 1640 cm-1, C=O of carboxylic

acid and amide functions, respectively; 2972 cm-1

and 1454 cm-1, C-H bend and C-H stretch

respectively; 3500 cm-1 to 3600 cm-1, O-H, N-H,

and S-H stretch; 867 cm-1, C-S stretch; 1039 and

1267 cm-1, C=S stretch; 2052 cm-1 results from

protonated primary amines (-NH3+).

potential analyses were performed to assess

changes in surface charges of the chemically

modified f-INT-WS2. The pH of the dispersions

was not adjusted. As expected, the incorporation

of the polyCOOH shell onto the surface of

modified f-INT-WS2 increased the negative

charge ( potential) on this material as well as

lowered the pH. The incorporation of the

polyNH2 shell resulted in a decrease of the

potential as well as an increase in pH. The

potential was -25 mV @pH 6.1, -34.7 mV @pH 5.9,

and -18.9 mV @pH 6.5 for unmodified INT-WS2,

polyCOOH f-INT-WS2, and polyNH2 f-INT-WS2,

respectively. These significant changes in the

potential values for the functionalized INTs

clearly indicate that subsequent surface

modifications have occurred.

XRD analyses were performed to determine

if a change in the crystallographic properties of

the polyCOOH f-INT-WS2 occurs due to the

VH-based chemical treatment. The resulting XRD

spectra (Figure 3, black: untreated control, red:

polyCOOH f-INT-WS2) agree well with the

literature reference spectrum (red vertical bars)

for unmodified INT-WS2, indicating that the

chemical treatment causes no significant change

in crystal structure.

| www.editorialmanager.com/nare/default.asp

Nano Res.

Figure 3 XRD plot of unfunctionalized INT-WS2 (black) and polyCOOH f-INT-WS2 (red), showing good agreement with the

literature reference (red vertical bars JCPDS 08-0237).

Figure 4 displays HRTEM images, at low-

and high-magnifications, of polyCOOH

f-INT-WS2 and unmodified INT-WS2. No

discernible difference in the morphologies of

either of the two materials is revealed, indicating

that the polycarboxylation procedure does not

result in damage to the INTs.

(a) (b)

(c) (d)

Figure 4 HRTEM images at low- and high-magnification

respectively of (a, c) unmodified and (b, d) polyCOOH

f-INT-WS2. No change in the morphology of the INTs is

evident due to the chemical modification.

The stability of suspensions of unmodified

INT-WS2 and polyCOOH f-INT-WS2 in water was

compared by dispersing ultrasonically (low

power bath sonicator) for one minute 5 mg of

INTs in 1.5 mL of distilled water in capped vials

while leaving the suspensions undisturbed at

room ambient. Figure 5 displays a photograph of

the two suspensions after 18 h. A significant

portion of the unmodified INT-WS2 has settled

out, while the polyCOOH f-INT-WS2 remain

suspended with no visual evidence of

sedimentation.

Figure 5. Suspensions of (A) unmodified INT-WS2 and (B)

polyCOOH f-INT-WS2 in H2O after low-power sonication

and standing undisturbed 18 h at room temperature.

4. Conclusions

A novel method for the polycarboxyl surface

functionalization (polyCOOH shell) of INT-WS2

via an electrophilic reactive modified

Vilsmeier-Haack reagent is described. This

polycarboxylated shell can serve as an anchoring

shell for subsequent second-step attachment of a

wide variety of organic molecules/polymers,

including other components such as NPs, for

| www.editorialmanager.com/nare/default.asp

Nano Res.

example, onto the nanotube surface using quite

versatile, simple organic chemistry (EDC

activation of polyCOOH), enabling surface

property tuning to match those of any contacting

material (polymeric phases, solvents, etc.).

Moreover, by employing reactive functional

groups such as those described in this study

(polyNH2/polySH shells), the chemically

modified f-INT-WS2 can be covalently bound to a

variety of reactivity-complementing materials.

These surface modifications should prove quite

useful in a wide range of applications in which

interfacial phase/component compatibility is

presently problematic. For example,

nanocomposite materials that incorporate such

functional f-INT-WS2 in any given polymer

matrix are expected to display significantly

improved properties such as mechanical strength,

impact resistance, and fracture performance

compared to those obtained when using

unmodified INT-WS2. A wide range of research

areas and applications can now benefit from (i)

the inclusion of these functionalized nanotubes

and (ii) the very versatile chemistry-tailored

platform.

Acknowledgements

We thank NanoMaterials Ltd. for their generous

gift of WS2 nanotubes and the Israel National

Nanotechnology Initiative Focal Technology Area

proposal “Inorganic Nanotubes: From

Nanomechanics to Improved Nanocomposites”

for partial funding of this research. References

[1] De Volder, M. F. L.; Tawfick, S. H.; Baughman, R.

H.; Hart, A. J. Carbon nanotubes: present and future

applications. Science 2013, 339, 535-539.

[2] Bandyopadhyaya, R.; Nativ-Roth, E.; Regev, O.;

Yerushalmi-Rozen, R. Stabilization of individual

carbon nanotubes in aqueous solutions. Nano Lett.

2002, 2, 25-28.

[3] Samanta, S. K.; Fritsch, M.; Scherf, U.; Gomulya, W.;

Bisri, S. C.; Loi, M. A. Conjugated polymer-assisted

dispersion of single-wall carbon nanotubes: The

power of polymer wrapping. Acc. Chem. Res. 2014,

in press, DOI: 10.1021/ar500141j.

[4] Krstic, V.; Duesberg, G. S.; Muster, J.; Burghard, M.;

Roth, S. Langmuir-Blodgett films of matrix-diluted

single-walled carbon nanotubes. Chem. Mater. 1998,

10, 2338-2340.

[5] Bandow, S.; Rao, A. M.; Williams, K. A.; Thess, A.;

Smalley, R. E.; Eklund, P. C. Purification of

single-wall carbon nanotubes by microfiltration. J.

Phys. Chem. B 1997, 101, 8839-8842.

[6] O’Connell, M. J.; Boul, P.; Ericson, L. M.; Huffman,

C.; Wang, Y.; Haroz, E.; Kuper, C.; Tour, J.; Ausman,

K. D.; Smalley, R. E. Reversible water-solubilization

of single-walled carbon nanotubes by polymer

wrapping. Chem. Phys. Lett. 2001, 342, 265-271.

[7] Duesberg, G. S.; Burghard, M.; Muster, J.; Philipp, G.

Separation of carbon nanotubes by size exclusion

chromatography. Chem. Commun. 1998, 435-436.

[8] Barton, S. S.; Evans, M. J. B.; Halliop, E.;

MacDonald, J. A. F. Acidic and basic sites on the

surface of porous carbon. Carbon 1997, 35,

1361-1366.

[9] Chen, J.; Hamon, M. A.; Hu, H.; Chen, Y.; Rao, A.

M.; Eklund, P. C.; Haddon, R. C. Solution properties

of single-walled carbon nanotubes. Science 1998, 282,

95-98.

[10] Hamon, M. A .; Chen, J.; Hu, H.; Chen, Y.; Itkis, M.

E.; Rao, A. M.; Eklund, P. C.; Haddon, R. C.

Dissolution of single-walled carbon nanotubes. Adv.

Mater. 1999, 11, 834-840.

[11] Park, S-J.; Kim, M-H. Effect of acidic anode

treatment on carbon fibers for increasing fiber-matrix

adhesion and its relationship to interlaminar shear

strength of composites. J. Mater. Sci. 2000, 35,

1901-1905.

[12] Holzinger, M.; Vostrowsky, O.; Hirsch, A.; Hennrich,

F.; Kappes, M.; Weiss, R.; Jellen, F.

Seitenwandfunctionalisierung von

kohlenstoff-nanorohren. Angew. Chem. 2001, 113,

4132-4136.

[13] Georgakilas, V.; Kordatos, K.; Prato, M.; Guldi, D.

M.; Holzinger, M.; Hirsch, A. Organic

functionalization of carbon nanotubes. J. Am. Chem.

Soc. 2002, 124, 760-761.

[14] Tan, L.; Chen, Y.; Zhou, W.; Ye, S.; Wei, J. Novel

approach toward poly(butylene

succinate)/single-walled carbon nanotubes

nanocomposites with interfacial-induced

crystallization behaviors and mechanical strength.

Polymer 2011, 52, 3587-3596.

[15] Iijima, S. Helical microtubules of graphitic carbon.

Nature 1991, 354, 56-58.

[16] Wu, Z.; Pitman, Jr., C. R.; Gardner, S. D. Bonding

epoxide functions to nitric acid-oxidized carbon

fibers using epichlorohydrin; a reliable analytical

determination of epoxide functions of fiber surfaces.

Carbon 1995, 33, 607-616.

[17] Esumi, K.; Ishigami, M.; Nakajima, A.; Sawada, K.;

Honda, H. Chemical treatment of carbon nanotubes.

Carbon 1996, 34, 279-281.

www.theNanoResearch.com∣www.Springer.com/journal/12274 | Nano Research

Nano Res.

[18] Yu, R.; Chen, L.; Liu, Q.; Lin, J.; Tan, K.-L.; Ng, S.

C.; Chan, H. S. O.; Xu, G.-Q.; Hor, T. S. A. Platinum

deposition on carbon nanotubes via chemical

modification. Chem. Mater. 1998, 10, 718-722.

[19] Tenne, R.; Redlich, M. Recent progress in the

research of inorganic fullerene-like nanoparticles and

inorganic nanotubes. Chem. Soc. Rev. 2010, 39, 1423.

[20] Zhao, H. Y.; Oyama, S. T.; Naeemi, E. D. Hydrogen

storage by using heterocyclic compounds: The

hydrogenation of 2-methylthiophene. Catal. Today

2010, 149, 172−184.

[21] Radisavljevic, B.; Radenovic, A.; Brivio, J.;

Giacometti, V.; Kis, A. Single-layer MoS2 transistors.

Nat. Nanotechnol. 2011, 6, 147−150.

[22] Hubert, T.; Hattermann, H.; Griepentrog, M.

Sol-gel-derived nanocomposite coatings filled with

inorganic fullerene-like WS2. J. Sol-Gel. Sci. Technol.

2009, 51(3), 295–300.

[23] Polcar, T.; Nossa, A.; Evaristo, M.; Cavaleiro, A.

Nanocomposite coatings of carbon-based and

transition metal dichalcogenides phases: a review.

Rev. Adv. Mater. Sci. 2007, 15, 118−126.

[24] Feng, C.; Huang, L.; Guo, Z.; Liu, H. Synthesis of

tungsten disulfide (WS2) nanoflakes for lithium ion

battery application. Electrochem. Commun. 2007, 9,

119−122.

[25] Frey, G. L.; Reynolds, K. J.; Friend, R. H.; Cohen, H.;

Feldman, Y. Solution-processed anodes from

layer-structure materials for high-efficiency polymer

light-emitting diodes. J. Am. Chem. Soc. 2003, 125,

5998−6007.

[26] Katz, A.; Redlich, M.; Rapoport, L.; Wagner, H. D.;

Tenne, R. Self-lubricating coatings containing

fullerene-like WS2 nanoparticles for orthodontic

wires and other possible medical applications. Tribol.

Lett. 2006, 21, 135.

[27] Ratoi, M.; Niste, V.B.; Walker, J.; Zekonyte, J.

Mechanism of action of WS2 lubricant nanoadditives

in high-pressure contacts. Tribol. Lett. 2013, 52,

81-91.

[28] Greenberg, R.; Halperin, G.; Etsion, I.; Tenne, R.

Effect of WS2 nanoparticles on friction reduction in

various lubrication regimes. Tribol. Lett. 2004, 17(2),

179–186.

[29] Eidelman, O.; Friedman, H.; Rosentveig, R.;

Moshkovith, A.; Perfiliev, V.; Cohen, S. R.; Feldman,

Y.; Rapoport, L.; Tenne, R. Chromium-rich coatings

with WS2 nanoparticles containing fullerene-like

structure. NANO. 2011, 6(4), 313–324.

[30] Wu, J. F.; Zhai, W. S.; Jie, G. F. Preparation and

tribological properties of WS2 nanoparticles modified

by trioctylamine. Proc. Inst. Mech. Eng. Part J 2009,

223(4), 695–703.

[31] Wu, J.; Zhai, W.; Jie, G. Preparation and tribological

properties of tungsten disulfide hollow spheres

assisted by methyltrioctylammonium chloride. Tribol.

Int. 2010, 43(9), 1650–1658.

[32] Abate, F.; D’Agostino, V.; Di Giuda, R.; Senatore, A.

Tribological behaviour of MoS2 and inorganic

fullerene-like WS2 nanoparticles under boundary and

mixed lubrication regimes. Tribology 2010, 4(2),

91–98.

[33] Rapoport, L.; Bilik, Y.; Feldman, Y.; Homyonfer, M.;

Cohen, S. R.; Tenne, R. Hollow nanoparticles of WS2

as potential solid-state lubricants. Nature 1997, 387,

791–793.

[34] Rapoport, L.; Feldman, Y.; Homyonfer, M.; Cohen,

H.; Sloan, J.; Hutchinson, J. L.; Tenne, R. Inorganic

fullerene-like material as additives to lubricants:

structure-function relationship. Wear 1999, 225–229.

[35] Zhu, .Y. Q.; Sekine, T.; Brigatti, S.; Firth, S.; Tenne,

R.; Rosentsveig, R.; Kroto, H. W.; Walton, D. R. M.

Shock-wave resistance of WS2 nanotubes. J. Am.

Chem. Soc. 2003, 125, 1329-1333.

[36] Zhu, Y. Q.; Sekine, T.; Li, Y. H.; Fay, M. W.; Zhao,

Y. M.; Poa, C. H. P.; Wang, W. X.; Roe, M. J.;

Brown, P. D.; Fleischer, N.; Tenne, R.

Shock-absorbing and failure mechanisms of WS2 and

MoS2 nanoparticles with fullerene-like structures

under shock wave pressure. J. Am. Chem. Soc. 2005,

127, 16263-16272.

[37] Cook, J.; Rhyans, S.; Roncase, L.; Hobson, G.; Luhrs,

C. C. Microstructural studies of IF-WS2 failure

modes. Inorganics 2014, 2, 377-395.

[38] Chang, L.; Yang, H.; Fu, W.; Yang, N.; Chen, J.; Li,

M.; Zou, G.; Li, J. Synthesis and thermal stability of

W/WS2 inorganic fullerene-like nanoparticles with

core-shell structure. Mater. Res. Bull. 2006, 41(7),

1242–1248.

[39] Naffakh, M.; Diez-Pascual, A. M. Thermoplastic

polymer nanocomposites based on inorganic

fullerene-like nanoparticles and inorganic nanotubes.

Inorganics 2014, 2, 291-312.

[40] Zohar, E.; Baruch, S.; Shneider, M.; Dodiuk, H.;

Kenig, S.; Tenne, R.; Wagner, H. D. The effect of

WS2 nanotubes on the properties of epoxy-based

nanocomposites. J. Adhes. Sci. and Technol. 2011, 25,

1603-1617.

[41] Zhang, W.; Ge, S.; Wang, Y.; Rafailovitch, M. H.;

Dhez, O.; Winesett, D. A.; Ade, H.; Shafi, K. V. P.

M.; Ulman, A,; Popvitz-Biro, R.; Tenne, R.; Sokolov,

J. Use of funtionalized WS2 nanotubes to produce

new polystyrene/ polymethylmethacrylate

nanocomposites. Polymer. 2003, 44, 2109-2015.

[42] Lalwani, G.; Henslee, A. M.; Farshid, B.; Parmar, P.;

Lin, L.; Qin, Y-X.; Kasper, F. K.; Mikos, A. G.;

Sitharamn, B. Tungsten disulfide nanotubes

reinforced biodegradable polymers for bone tissue

engineering. Acta Biomater. 2013, 9, 8365−8373.

[43] Xu, F.; Yan, C.; Shyng, Y-T.; Chang, H.; Xia, Y.;

Zhu, Y. Ultra-toughened nylon 12 nanocomposites

reinforced with IF-WS2. Nanotechnology 2014, 25,

325701-325711.

| www.editorialmanager.com/nare/default.asp

Nano Res.

[44] Diez-Pascual, A. M.; Naffakh, M. Inorganic

nanoparticle-modified poly(phenylene sulphide)

carbon fiber laminates: thermomechanical behavior.

Materials 2013, 6, 3171-3193.

[45] Tevet, O.; Goldbart, O.; Cohen, S. R.; Rosentsveig,

R.; Popovitz-Biro, R.; Wagner, H. D.; Tenne, R.

Nanocompression of individual multilayered

polyhedral nanoparticles. Nanotechnology 2010, 21,

365705−365710.

[46] Naffakh, M.; Díez-Pascual, A. M.; Marco, C.; Ellis,

G. J.; Gomez- Fatou, M. A. Opportunities and

challenges in the use of inorganic fullerene-like

nanoparticles to produce advanced polymer

nanocomposites. Prog. Polym. Sci. 2013, 38,

1163−1231.

[47] http://www.nanotechproject.org/cpi/search-products/?

title=nanolub (accessed Jul 20, 2014).

[48] Tahir, M. N.; Zink, N.; Eberhardt, M.; Therese, H. A.;

Kolb, U.; Theato, P.; Tremel, W. Overcoming the

insolubility of molybdenum disulfide nanoparticles

through a high degree of sidewall functionalization

using polymeric chelating ligands. Angew. Chem., Int.

Ed. 2006, 45 (29), 4809-4815.

[49] Shahar, C.; Zbaida, D.; Rapoport, L.; Cohen, H.;

Bendikov, T.; Tannous, J.; Dassenoy, F.; Tenne, R.

Surface functionalization of WS2 fullerene-like

nanoparticles. Langmuir 2010, 26(6), 4409-4414.

[50] Raichman, D.; Strawser, D. A.; Lellouche, J.-P.

Design of experiments: Optimizing the

polycarboxylation/functionalization of tungsten

disulfide nanotubes. Inorganics 2014, 2, 455-467.

[51] Vilsmeier, A.; Haack, A. Uber die Einwirkung von

halogen phosphor auf alkyl-formanilide. Ein neue

methode zur darstellung sekundarer und tertiarer

p-alkylamino-benzaldehyde. Chem. Berichts. 1927,

60, 119–122.

[52] Sreenivasulu, M.; Rao, K. G. S. Vilsmeier reaction

studies on some α,β-unsaturated alkenones. Indian J.

Chem. Sect. B 1989, 28, 594–595.

[53] Lilienkampf, A.; Johansson, M. P.; Wahala, K.

(Z)-1-Aryl-1-haloalkenes as intermediates in the

vilsmeier haloformylation of aryl ketones. Org. Lett.

2003, 5, 3387–3390.

[54] Ali, M. M.; Tasneem; Rajanna, K. C.; Saiprakash, P.

K. An efficient and facile synthesis of

2-chloro-3-formyl quinolines from acetanilides in

micellar media by Vilsmeier–Haack cyclisation.

Synlett 2001, 2, 251–253.

[55] Quiroga, J.; Trilleras, J.; Galvez, J.; Insuasty, B.;

Abonıa, R.; Nogueras, M.; Cobo, J.; Marchal, A. C-

and N-cyanoacetylation of 6-aminopyrimidines with

cyanoacetic acid and acetic anhydride. Tetrahedron

Lett. 2008, 49, 5672–5675.

[56] Giles, C. M. M. A. P. R. Synthesis Using Vilsmeier

Reagents. New Directions in Organic and Biological

Chemistry, 1st ed; CRC Press: Boca Raton, FL, USA,

1994.

[57] Rajanna, K. C.; Ali, M. M.; Solomon, F.; Saiprakash,

P. K. Vilsmeier-Haack formylation of coumarin

derivatives. A solvent dependent kinetic study. Int. J.

Chem. Kinet. 1996, 28, 865–872.

[58] Kaiser, E.; Colescott, R. L.; Bossiriger, C.D.; Cook,

P.I. Color test for the detection of free terminal amino

groups in the solid-phase synthesis of peptides. Anal.

Biochem. 1970, 34, 595–598.

[59] Ellman, G. L. Tissue sulfhydryl groups. Arch.

Biochem. Biophys. 1959, 82(1), 70-77.