Debundling and dissolution of single-walled carbon nanotubes in amide solvents

Multicomponent solubility parameters for single-walled carbon nanotube-solvent mixtures

We have measured the dispersibility of single-walled carbon nanotubes in a range of solvents, observing values as high as 3.5 mg/mL. By plotting the nanotube dispersibility as a function of the Hansen solubility parameters of the solvents, we have confirmed that successful solvents occupy a well-defined range of Hansen parameter space. The level of dispersibility is more sensitive to the dispersive Hansen parameter than the polar or H-bonding Hansen parameter. We estimate the dispersion, polar, and hydrogen bonding Hansen parameter for the nanotubes to be <delta(D)> = 17.8 MPa(1/2), <delta(P)> = 7.5 MPa(1/2), and <delta(H)> = 7.6 MPa(1/2). We find that the nanotube dispersibility in good solvents decays smoothly with the distance in Hansen space from solvent to nanotube solubility parameters. Finally, we propose that neither Hildebrand nor Hansen solubility parameters are fundamental quantities when it comes to nanotube-solvent interactions. We show that the previously calculated dependence of nanotube Hildebrand parameter on nanotube diameter can be reproduced by deriving a simple expression based on the nanotube surface energy. We show that solubility parameters based on surface energy give equivalent results to Hansen solubility parameters. However, we note that, contrary to solubility theory, a number of nonsolvents for nanotubes have both Hansen and surface energy solubility parameters similar to those calculated for nanotubes. The nature of the distinction between solvents and nonsolvents remains to be fully understood.

High population of individualized SWCNTs through the adsorption of water-soluble perylenes

The aqueous dispersion of SWCNTs in the presence of the water-soluble perylene derivatives 1-3 is reported. Significantly, even very low concentrations of the perylenes such as 0.01 wt% of the amphiphilic derivative 3, cause an efficient dissolution of the SWCNTs in water accompanied by a very pronounced individualization. The individualization of SWCNTs in water after ultrasonication in the presence of water-soluble aromatic perylenes was investigated in detail by absorption, emission, and Raman spectroscopy as well as by AFM and cryo-TEM. These studies also revealed that the individualization of the SWCNTs caused by the adsorption of 3 is much more effective than that induced by SDBS, which is the most frequently used surfactant for SWCNT dispersion in water. The pi-pi-stacking interaction and the electronic interaction between the perylene unit and the nanotube surface is reflected, for example, by the distinct absorption and emission features in the UV/vis/nIR, which differ significantly from those observed for SWNTs dispersed in the presence of SDBS and by the quenching of the perylene fluorescence of 3 when being in contact with the tubes.

A nitrite biosensor based on the immobilization of cytochrome c on multi-walled carbon nanotubes-PAMAM-chitosan nanocomposite modified glass carbon electrode

A novel nitrite biosensor was successfully prepared via immobilizing Cytochrome c (Cyt c) onto the multi-walled carbon nanotubes-poly(amidoamine) (PAMAM)-chitosan (MWNT-PAMAM-Chit) nanocomposite modified glass carbon electrode (GCE). Ultraviolet and visible (UV-vis) absorption spectrum, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to examine the native conformation and bioactivity of the immobilized Cyt c, and the electrochemical properties of the modified electrodes, respectively. The results indicate that the immobilized Cyt c retained its native characters, and the MWNT-PAMAM-Chit nanocomposite is a good platform for the immobilization of Cyt c as well as an excellent promoter for the electron transfer between Cyt c and electrode. The high reactive Cyt c pi-cation, which can oxidize NO(2)(-) into NO(3)(-) in the solution, is generated at higher potential (>0.7 V) based on the further oxidation of Cyt c. The nitrite biosensor showed a fast response to nitrite (about 5 s) in two concentration intervals, one was from 0.1 to 29 microM, and the other from 29 to 254 microM. The low detection limit of 0.01 microM was obtained.

Direct deposition of single-walled carbon nanotube thin films via electrostatic spray assisted chemical vapor deposition

In this work, electrostatic spray assisted chemical vapor deposition is used to directly deposit single-walled carbon nanotube (SWNT) thin films on a substrate. The catalyst solution was finely dispersed by a strong electrical field and injected into the heated reaction zone (950-1100 degrees C) during the growth. It was found that under optimized growth conditions, the deposited material consists of SWNTs while only small amounts of impurities are observed. The growth at different temperatures results in nanotubes of different length and morphology. The location at which the SWNTs deposit at the downstream end of the growth chamber is found to be affected by the nanotube length and the growth temperature, which can be understood by considering different forces acting on the floating aerosol particles inside the furnace. These results suggest a potential for in situ separation of the SWNTs by applying different forces to the floating SWNTs.

Efficient dispersion and exfoliation of single-walled nanotubes in 3-aminopropyltriethoxysilane and its derivatives

A novel amine solvent, 3-aminopropyltriethoxysilane, has been used to disperse single-walled carbon nanotubes. Well-dispersed nanotubes in the form of small bundles coexist in the liquid phase with large nanotube aggregates. A mild centrifugation step can be used to remove the aggregates. By measurement of the absorbance before and after centrifugation as a function of concentration, the fraction of the dispersed nanotube phase can be estimated. As measured by atomic force microscopy, the mean bundle diameter tends to decrease with decreasing concentration and levels off below a concentration of ∼0.012 mg ml(-1). Individual nanotubes are always observed, whose population increases with decreasing concentration before saturating at a concentration of ∼0.012 mg ml(-1). The absolute number of individual nanotubes per volume of dispersion initially increases with decreasing concentration, and then reaches a peak at a concentration of ∼0.024 mg ml(-1). Further experimental results showed that nanotubes can also be effectively dispersed in a series of aminoalkoxylsilane derivatives. In the light of these findings, possible solvent-nanotube interaction mechanisms are discussed.

Graphene oxide dispersions in organic solvents

The dispersion behavior of graphene oxide in different organic solvents has been investigated. As-prepared graphite oxide could be dispersed in N, N-dimethylformamide, N-methyl-2-pyrrolidone, tetrahydrofuran, and ethylene glycol. In all of these solvents, full exfoliation of the graphite oxide material into individual, single-layer graphene oxide sheets was achieved by sonication. The graphene oxide dispersions exhibited long-term stability and were made of sheets between a few hundred nanometers and a few micrometers large, similar to the case of graphene oxide dispersions in water. These results should facilitate the manipulation and processing of graphene-based materials for different applications.

Physicochemical determinants of multiwalled carbon nanotube bacterial cytotoxicity

Rational modification of carbon nanotubes (CNTs) to isolate their specific physical and chemical properties will inform a mechanistic understanding of observed CNT toxicity in bacterial systems. The present study compares the toxicity of commercially obtained multiwalled carbon nanotubes (MWNTs) before and after physicochemical modification via common purification and functionalization routes, including dry oxidation, acid treatment functionalization, and annealing. Experimental results support a correlation between bacterial cytotoxicity and physicochemical properties that enhance MWNT-cell contact opportunities. For example, we observe higher toxicity when the nanotubes are uncapped, debundled, short, and dispersed in solution. These conclusions demonstrate that physicochemical modifications of MWNTs alter their cytotoxicity in bacterial systems and underline the need for careful documentation of physical and chemical characteristics when reporting the toxicity of carbon-based nanomaterials.

A novel density-tunable nanocomposites of CdTe quantum dots linked to dendrimer-tethered multi-wall carbon nanotubes

A novel nanocomposite of CdTe-PAMAM-MWNT was synthesized by covalently linking CdTe quantum dots (QDs) onto highly water-soluble multi-wall carbon nanotubes (MWNTs) functionalized with dendritic poly(amidoamine) (PAMAM). The IR, UV-vis and TEM methods has been used for the characterization of the composites. A facile method for controlling the density of QDs in the composite by simply changing the ratio of CdTe QDs/PAMAM-MWNT, as was verified by the TEM images. The experiments revealed that PAMAM and PAMAM-MWNT, once covalently linked with CdTe QDs, had remarkable effect on their fluorescence property. The fluorescence intensity of the CdTe-PAMAM hybrid was substantially enhanced as a compared to that of QDs, and the fluorescence was quenched greatly when QDs reacted with PAMAM-MWNT. The experimentally observed phenomena indicate that electron and energy transfer took place efficiently between CdTe QDs, PAMAM and MWNTs in the novel composite. These nanocomposits might hold great potential in photoelectron device and biotechnology applications.

Transparent boron-doped carbon nanotube films

We report results of studies on the sheet resistance and optical transmission of thin films of boron-doped single-walled carbon nanotubes (SWNTs). Boron doping was carried out by exposure of SWNTs to B 2O 3 and NH 3 at 900 degrees C and 1-3 atom % boron was found in the SWNT bundles via electron energy loss spectroscopy (EELS). Boron doping was found to downshift the positions of the optical absorption bands associated with the van Hove singularities (E 11 (s) E 22 (s) and E 11 (m)) by approximately 30 meV relative to their positions in acid-treated and annealed SWNTs. Raman spectroscopy, EELS, and optical data are consistent with the picture that a few atom % boron has been substituted for carbon in the sp (2) framework of SWNTs. Finally, our results show that boron doping does not significantly affect the optical transmittance in the visible region. However, boron doping lowers the sheet resistance by approximately 30% relative to pristine SWNT films from the same batch. Boron-doped SWNT may provide a better approach to touch-screen technology.

High-yield production of graphene by liquid-phase exfoliation of graphite

Fully exploiting the properties of graphene will require a method for the mass production of this remarkable material. Two main routes are possible: large-scale growth or large-scale exfoliation. Here, we demonstrate graphene dispersions with concentrations up to approximately 0.01 mg ml(-1), produced by dispersion and exfoliation of graphite in organic solvents such as N-methyl-pyrrolidone. This is possible because the energy required to exfoliate graphene is balanced by the solvent-graphene interaction for solvents whose surface energies match that of graphene. We confirm the presence of individual graphene sheets by Raman spectroscopy, transmission electron microscopy and electron diffraction. Our method results in a monolayer yield of approximately 1 wt%, which could potentially be improved to 7-12 wt% with further processing. The absence of defects or oxides is confirmed by X-ray photoelectron, infrared and Raman spectroscopies. We are able to produce semi-transparent conducting films and conducting composites. Solution processing of graphene opens up a range of potential large-area applications, from device and sensor fabrication to liquid-phase chemistry.

Surface design of carbon nanotubes for optimizing the adsorption and electrochemical response of analytes

Carbon nanotubes (CNTs) from different sources were dissolved in water with high solubility by Congo red (CR) via strong noncovalent pi-stacking interactions. The resulting CNTs were capable of forming uniform, compact, stable films on various substrates. This provided a chance to explore the relationship between the surface property of CNTs and the adsorptive behavior of analytes on CNTs without considering the influence of film structures or free additives. Electrochemical behaviors of several small biomolecules and glucose oxidase (GOD) on various CR-functionalized CNT films were examined. The results showed that both the hydrophobic structural defect sites and the hydrophilic oxygen-containing groups were the electroactive sites of CNTs, which was further proven by UV-vis and FTIR spectra. Moreover, the surface properties of CNTs could be conveniently designed by simple pretreatments for optimizing the adsorption and the electrochemical response of analytes. For instance, the hydrophobic defect sites created during the growth or the workup of CNTs were favorable to the adsorption and the electrochemical response of hydrophobic analytes, whereas the hydrophilic oxygen-containing groups produced by acid treatment facilitated the stable adsorption and the direct electrochemistry of redox proteins.

Investigation of the inner environment of carbon nanotubes with a fullerene-nitroxide probe

A fulleropyrrolidine bearing a nitroxide free radical has been inserted into single-walled carbon nanotubes with the aid of supercritical CO2. Thanks to the encapsulated paramagnetic probes, it has been possible to detect and characterize the resulting peapod-like structure through electron paramagnetic resonance (EPR) spectroscopy. In particular, the analysis of spectral parameters derived from extensive EPR studies has elucidated the orientation and the residual rotational dynamics of the molecules embedded in the nanotubes. A limited anisotropic rotational freedom of the encapsulated fullerene nitroxide reveals a rather strong interaction of the probe with the surrounding nanotube walls. The interaction seems to involve the fullerene cage (as confirmed by Raman spectroscopy) and not the nitroxide moiety, whose EPR spectral characteristics, such as the isotropic hyperfine constant and the g-tensor, remain unaltered after encapsulation.

Carbon Nanotubes for Electronic and Electrochemical Detection of Biomolecules

The unique electronic and optical properties of carbon nanotubes, in conjunction with their size and mechanically robust nature, make these nanomaterials crucial to the development of next-generation biosensing platforms. In this Review, we present recent innovations in carbon nanotube-assisted biosensing technologies, such as DNA-hybridization, protein-binding, antibody-antigen and aptamers. Following a brief introduction on the diameter- and chirality-derived electronic characteristics of single-walled carbon nanotubes, the discussion is focused on the two major schemes for electronic biodetection, namely biotransistor- and electrochemistry-based sensors. Key fabrication methodologies are contrasted in light of device operation and performance, along with strategies for amplifying the signal while minimizing nonspecific binding. This Review is concluded with a perspective on future optimization based on array integration as well as exercising a better control in nanotube structure and biomolecular integration.

An Unexpected New Optimum in the Structure Space of DNA Solubilizing Single-Walled Carbon Nanotubes

Here we report quantitative data on the amount of single-walled carbon nanotubes that can be suspended with oligodeoxynucleotides in aqueous buffer, together with rate constants for the thermal denaturation of the resulting DNA-nanotube complexes at elevated temperatures. Sequence motifs d(GT)n and d(AC)n with n=2, 3, 5, 10, 20, or 40 were employed, both individually and as equimolar mixtures of the complementary strands. Unexpectedly, the greatest suspending efficiency was found for the mixture of short, complementary oligonucleotides d(GT)3 and d(AC)3. Unlike the suspending efficiency, the kinetic stability of the nanotube suspensions increases with increasing chain length of the DNA, with half life times of >25 h at 90 degrees C for the complexes of the longest strands. Our results identify a new, unexpected optimum in DNA sequence space for suspending carbon nanotubes. They also demonstrate that suspending power depends on the presence of complementary strands. Exploratory assays suggest that nanotubes can be deposited site-selectively from suspensions formed with short DNA sequences.

Debundling of Single-Walled Nanotubes by Dilution: Observation of Large Populations of Individual Nanotubes in Amide Solvent Dispersions

Large-scale debundling of single-walled nanotubes has been demonstrated by dilution of nanotube dispersions in the solvent N-methyl-2-pyrrolidone (NMP). At high concentrations some very large (approximately 100 s of micrometers) nanotube aggregates exist that can be removed by mild centrifugation. By measurement of the absorbance before and after centrifugation as a function of concentration the relative aggregate and dispersed nanotube concentrations can be monitored. No aggregates are observed below CNT approximately 0.02 mg/mL, suggesting that this can be considered the nanotube dispersion limit in NMP. After centrifugation, the dispersions are stable against sedimentation and further aggregation for a period of weeks at least. Atomic force microscopy (AFM) studies on deposited films reveal that the bundle diameter distribution decreases dramatically as concentration is decreased. Detailed data analysis suggests the presence of an equilibrium bundle number density and that the dispersions self-arrange themselves to always remain close to the dilute/semidilute boundary. A population of individual nanotubes is always observed that increases with decreasing concentration until almost 70% of all dispersed objects are individual nanotubes at a concentration of 0.004 mg/mL. The number density of individual nanotubes peaks at a concentration of approximately 10(-2) mg/mL. Both the mass fraction and the partial concentration of individual nanotubes can also be measured and behave in similar fashion. Comparison of the number density and partial concentration also of individual nanotubes reveals that the individual nanotubes have average molar masses of approximately 700,000 g/mol. The presence of individual nanotubes in NMP dispersion was confirmed by photoluminescence spectroscopy. Concentration dependence of the photoluminescence intensity confirms that the AFM measurements reflect the diameter distributions in situ. In addition, Raman spectroscopy confirms the presence of large quantities of individual nanotubes in the deposited films. Finally, the nature of the solvent properties required for dispersion are discussed.

Infrared spectroscopic study of O2 interaction with carbon nanotubes

Infrared reflection-absorption spectroscopic measurements have been performed on single-wall carbon nanotubes (SWNTs), cleaned by heating to approximately 500 degrees C in vacuo, during exposure to pure 16O2 or 18O2 at room temperature and at pressures of up to approximately 630 Torr. No vibrational signature of any form of adsorbed O is detected. However, structure is seen which is very similar to that observed for the adsorption of atomic H or D and which indicates changes in the SWNT vibrational spectrum. The close similarity between the spectra for atomic H and D, on one hand, and O2 on the other is an unexpected result. Changes are also noted in the broad background extending throughout the mid-IR which arises from the Drude contribution to the reflectance. All these effects increase with O2 exposure and are essentially irreversible upon evacuation of the gas. The results are consistent with other data indicating that O2 interacts only weakly with, and does not chemisorb on, pristine regions of the SWNT under these conditions. The small and irreversible effects seen upon O2 exposure are interpreted in terms of enhanced chemisorption, at or near defective regions of the SWNT wall, which saturates at a low O coverage.

Diameter and metallicity dependent redox influences on the separation of single-wall carbon nanotubes

Recently, it has become possible to separate and/or enrich fractions of single-wall carbon nanotubes (SWNTs) according to type (or otherwise termed "metallicity") and diameter (d(t)). Exposure of acid-treated SWNTs to amines has shown such separation. In this contribution, we describe the underlying mechanism for this separation and provide a better description of the physicochemical properties of charge-stabilized SWNT dispersions in polar aprotic media, such as N,N-dimethylformide (DMF). With the establishment of the reversible nature of the redox chemistry, SWNT(n+) + (n/2)H2O <==> SWNT + nH(+) + (n/4)O2, amine-induced pH changes as well as variations in H2O and O2 concentration in DMF are shown to cause differential partial-reduction trends according to d(t) and metallicity. At a pH of 10, the (n,m)-SWNTs that resist complete reduction to their undoped state remain in suspension while the rest that lose their charges populate the precipitate. These d(t)- and metallicity-dependent redox and separation trends are modeled based on the Gibbs free energy and charge loss as it pertains to the (n,m)-dependent SWNT integrated density of states (I(DOS)) across the corresponding pH-induced redox jump. At a given redox potential, the relative placement of the van Hove singularities and continuum determines the amount of charge left on various (n,m)-SWNTs that governs their relative dispersion stability in DMF.

Effect of the Tube Diameter Distribution on the High-Temperature Structural Modification of Bundled Single-Walled Carbon Nanotubes

We present results of a systematic high-resolution transmission electron microscopy study of the thermal evolution of bundled single-walled carbon nanotubes (SWNTs) subjected to approximately 4-h high-temperature heat treatment (HTT) in a vacuum at successively higher temperatures up to 2200 degrees C. We have examined purified SWNT material derived from the HiPCO and ARC processes. These samples were found to thermally evolve along very different pathways that we propose depend on three factors: (1) initial diameter distribution, (2) concomitant tightness of the packing of the tubes in a bundle, and (3) the bundle size. Graphitic nanoribbons (GNR) were found to be the dominant high-temperature filament in ARC material after HTT = 2000 degrees C; they were not observed in any heat-treated HiPCO material. The first two major steps in the thermal evolution of HiPCO and ARC material agree with the literature, i.e., coalescence followed by the formation of multiwall carbon nanotubes (MWNTs). However, ARC material evolves to bundled MWNTs, while HiPCO evolves to isolated MWNTs. In ARC material, we find that the MWNTs collapse into multishell GNRs. The thermal evolution of these carbon systems is discussed in terms of the diameter distribution, nanotube coalescence pathways, C-C bond rearrangement, diffusion of carbon and subsequent island formation, as well as the nanotube collapse driven by van der Waals forces.

Thermal conversion of bundled carbon nanotubes into graphitic ribbons

High temperature heat treatment (HTT) of bundled single-walled carbon nanotubes (SWNTs) in vacuum ( approximately 10(-5) Torr) has been found to lead to the formation of two types of graphitic nanoribbons (GNRs), as observed by high-resolution transmission electron microscopy. Purified SWNT bundles were first found to follow two evolutionary steps, as reported previously, that is, tube coalescence (HTT approximately 1400 degrees C) and then massive bond rearrangement (HTT approximately 1600 degrees C), leading to the formation of bundled multiwall nanotubes (MWNTs) with 3-12 shells. At HTT > 1800 degrees C, we find that these MWNTs collapse into multishell GNRs. The first type of GNR we observed is driven by the collapse of diameter-doubled single-wall nanotubes, and their production is terminated at HTT approximately 1600 degrees C when the MWNTs also start to form. We propose that the collapse is driven by van der Waals forces between adjacent tubes in the same bundle. For HTT > 2000 degrees C, the heat-treated material is found to be almost completely in the multishell GNR form.

Individualization of single-walled carbon nanotubes: is the solvent important?

The influence of different solvents on the individualization of single-walled carbon nanotubes (SWNTs) was investigated by several methods. A stable solution of individual SWNTs in o-dichlorobenzene was obtained by a combination of ultrasonication and ultracentrifugation. Atomic force microscopy height analysis confirmed that the final supernatant solution contained 85 % of individual tubes with a diameter equal to or less than 1.5 nm, which is consistent with the average diameter of arc-discharge tubes. Both the solvent and the ultracentrifugation speed are important parameters in determining the final degree of individualized SWNTs. Notably, the SWNTs were stable in o-dichlorobenzene for more than eight months. This technique for obtaining highly individualized SWNTs in an organic solvent is expected to have great potential in many applications, such as functional materials and nanoelectronics.

Raman and IR Spectroscopy of Chemically Processed Single-Walled Carbon Nanotubes

IR and Raman spectroscopy has been used to study the evolution of the vibrational spectrum of bundled single-walled carbon nanotubes (SWNTs) during the purification process needed to remove metal catalyst and amorphous carbon present in arc-derived SWNT soot. We have carried out a systematic study to define the different outcomes stemming from the purification protocol (e.g., DO, DO/HCl, DO/HNO(3), H(2)O(2), H(2)O(2)/HCl), where dry oxidation (DO) or refluxing in H(2)O(2) was used in a first purification step to remove amorphous carbon. The second step involves acid reflux (HCl or HNO(3)) to remove the residual growth catalyst (Ni-Y). During strong chemical processing, it appears possible to create additional defects where carbon atoms are eliminated, the ring structure is now open, localized C=C bonds are created, and O-containing groups can be added to this defect to stabilize the structure. Evolution of SWNT skeletal disorder obtained via chemical processing was studied by Raman scattering. Higher intensity ratios of R- and G-band (I(R)/I(G)) are more typically found in SWNT materials with low D-band intensity and narrow G-band components. Using IR transmission through thin films of nanotubes, we can resolve the structure due to functional groups that were present in the starting material or added through chemical processing. After high-temperature vacuum annealing of the purified material at 1100 degrees C, IR spectroscopy shows that most of the added functional groups can be removed and that the structure that remains is assigned to the one- and two-phonon modes of SWNTs.

Infrared-active vibrational modes of single-walled carbon nanotubes

The IR-active vibrational modes of single-walled carbon nanotubes have been observed by optical transmission through thin films of bundled nanotubes. Because IR-active chemical functional groups, e.g., -COOH, -OH, might be attached to the tube walls and contribute additional spectral features, we have also studied the effects of chemical purification and long-term high-temperature vacuum annealing on the IR spectrum. Through comparison with theory, we are able to assign much of the sharp structure observed in our IR spectra.

Substituted Carborane-Appended Water-Soluble Single-Wall Carbon Nanotubes: New Approach to Boron Neutron Capture Therapy Drug Delivery

Substituted C(2)B(10) carborane cages have been successfully attached to the side walls of single-wall carbon nanotubes (SWCNTs) via nitrene cycloaddition. The decapitations of these C(2)B(10) carborane cages, with the appended SWCNTs intact, were accomplished by the reaction with sodium hydroxide in refluxing ethanol. During base reflux, the three-membered ring formed by the nitrene and SWCNT was opened to produce water-soluble SWCNTs in which the side walls are functionalized by both substituted nido-C(2)B(9) carborane units and ethoxide moieties. All new compounds are characterized by EA, SEM, TEM, UV, NMR, and IR spectra and chemical analyses. Selected tissue distribution studies on one of these nanotubes, {([Na(+)][1-Me-2-((CH(2))(4)NH-)-1,2-C(2)B(9)H(10)][OEt])(n)(SWCNT)} (Va), show that the boron atoms are concentrated more in tumors cells than in blood and other organs, making it an attractive nanovehicle for the delivery of boron to tumor cells for an effective boron neutron capture therapy in the treatment of cancer.

Discrete dispersion of single-walled carbon nanotubes

Single-walled carbon nanotubes (SWNTs) have been effectively wetted and dispersed in saturated sodium hydroxide (NaOH) alcohol-water solutions with little surface damage or shortening of the tubes; the treated material was dissolvable as individual tubes in many common organic solvents.

Chemically functionalized carbon nanotubes

Since their discovery, carbon nanotubes have attracted the attention of many a scientist around the world. This extraordinary interest stems from their outstanding structural, mechanical, and electronic properties. In fact, apart from being the best and most easily available one-dimensional (1D) model system, carbon nanotubes show strong application potential in electronics, scanning probe microscopy, chemical and biological sensing, reinforced composite materials, and in many more areas. While some of the proposed applications remain still a far-off dream, others are close to technical realization. Recent advances in the development of reliable methods for the chemical functionalization of the nanotubes provide an additional impetus towards extending the scope of their application spectrum. In particular, covalent modification schemes allow persistent alteration of the electronic properties of the tubes, as well as to chemically tailor their surface properties, whereby new functions can be implemented that cannot otherwise be acquired by pristine nanotubes.