Solvent-free functionalization of carbon nanotubes

A fundamentally new single-walled and multiwalled carbon nanotube sidewall functionalization technique has been developed in which solvent is not required and the reaction times are greatly shortened (1 h at 60 degrees C). Exploiting the long linear dimension of the nanotube ropes by macroscopic mechanical deformation, reactive sites are generated merely by mechanically deforming the tubes using a stir bar. This approach eliminates the need for large volumes of solvent ( approximately 2 L/g), which were formerly considered essential due to the insolubility of carbon nanotubes. Using a series of 4-substituted anilines and a nitrite, the aryl diazonium intermediates were generated in situ and permitted to react with the tubes. Raman, IR, and UV spectroscopies, coupled with thermogravimetric analyses and solubility studies, support the assignments.     

Organic functionalization of carbon nanotubes

A very general and versatile method for functionalizing different types of carbon nanotubes is described, using the 1,3-dipolar cycloaddition of azomethine ylides. Approximately one organic group per 100 carbon atoms of the nanotube is introduced, to yield remakably soluble bundles of nanotubes, as seen in transmission electron micrographs. The solubilization of the nanotubes generates a novel, interesting class of materials, which combines the properties of the nanotubes and the organic moiety, thus offering new opportunities for applications in materials science, including the preparation of nanocomposites.     

Microwave-induced multiple functionalization of carbon nanotubes

We describe a new synthetic strategy to produce multifunctionalized carbon nanotubes using a combination of two different addition reactions, the 1,3-dipolar cycloaddition of azomethine ylides and the addition of diazonium salts, both via a simple and fast microwave-induced method. The presence of multifunctionality on the SWNTs has been confirmed using the most useful techniques for the characterization of carbon nanotubes. The doubly functionalized SWNTs can be considered potentially useful for many interesting applications.     

One-pot triple functionalization of carbon nanotubes

Carbon nanotubes (CNTs) are very promising as carriers for the delivery of bioactive molecules. The multifunctionalization of CNTs is necessary to impart multimodalities for the development of future CNT-based multipotent therapeutic constructs. In this context, we report the first example of covalent trifunctionalization of different types of CNTs. Our strategy is a simple and efficient methodology based on the simultaneous functionalization of the nanotube surface with three different active groups. The reaction is performed in one step by arylation with diazonium salts generated in situ. The CNTs are functionalized with benzylamine moieties blocked with three different protecting groups that can be selectively removed under specific conditions. The trifunctionalized CNTs were characterized by TEM, thermogravimetric analysis, and Raman and UV/Vis/NIR spectroscopy, while the amine loading was determined by using the Kaiser test. The sequential removal of the protecting groups of the amine functions allows the grafting of the molecules of interest on the nanotube surface to be controlled.     

Organic functionalization of sidewall of carbon nanotubes

Using density functional theory, we have theoretically studied sidewall functionalization of carbon nanotubes (CNT) with a nucleophilic organic carbene, dipyridyl imidazolidene (DPI). When compared to the dissociated system, formation of the adduct from defect-free (5,5) tube and the DPI is weakly exothermic. However, introduction of (5,7,7,5) defect or nitrogen doping at the CNT stabilizes the adduct in both physical and chemical senses, suggesting a possible way to enrich the chemistry of sidewall functionalization. The work function of the adducts is found to decrease by approximately 0.4 eV per DPI/80 atoms. Upon binding of the DPI, electronic structures are modified in such a way that small gaps are introduced, where the size of the gap depends upon the degree of functionalization.     

Polymer-masking for controlled functionalization of carbon nanotubes

An effective and versatile method for tube-length-specific functionalization of carbon nanotubes through a controllable embedment of vertically-aligned carbon nanotubes into polymer matrices is reported, which allows not only asymmetric functionalization of nanotube sidewalls, but also facile introduction of new properties (e.g. magnetic) onto the region-selectively functionalized carbon nanotubes.     

Covalent sidewall functionalization of single wall carbon nanotubes

Alkyllithium reagents may be used to attach alkyl groups to the sidewalls of fluoro nanotubes. Thermal gravimetric analysis combined with UV-vis-Nir spectroscopy has been used to provide a quantitative measure of the degree of functionalization. SWNTs prepared using the HiPco process exhibit a higher degree of alkylation than SWNTs from the laser-oven method, indicating that the smaller diameter fluoro tubes are alkylated more readily. The spectral signature of the pristine SWNTs can be regenerated when the alkylated SWNTs are heated in Ar at 500 degrees C, demonstrating that dealkylation occurs at this temperature. TGA-MS analysis using a sample of n-butylated h-SWNTs showed that 1-butene and n-butane are formed during thermolysis.     

Microwave-assisted covalent sidewall functionalization of multiwalled carbon nanotubes

Thermal cycloaddition of 1,3-dipolar azomethine ylides to the sidewalls of multiwalled carbon nanotubes (MWNTs) has been used to prepare MWNTs that contain 2-methylenethiol-4-(4-octadecyloxyphenyl) (4), N-octyl-2-(4-octadecyloxyphenyl) (5) or 2-(4-octadecyloxyphenyl)pyrrolidine (6) units. All these contain the 4-octadecyloxyphenyl substituent that acts as a solubilizing group. Microwave (MiW)-assisted heating was found to be highly efficient for soluble MWNTs, for which the amount of added groups after only 2 h of MiW heating at 200 degrees C, determined by using thermogravimetric analysis, was found to be in the same range as that obtained after 100-120 h of conventional heating of soluble and insoluble MWNTs. Solubility is a key feature for a successful MiW-heated reaction; MWNTs insoluble in the reaction medium yielded considerably less addends in the MiW-heated reactions than in the conventionally heated reaction. The location and even distribution of the pyrrolidine units over the outermost layer of the MWNTs was verified by transmission electron microscopy analysis of 4 that had been treated with gold nanoparticles and thoroughly washed to remove gold particles adsorbed on nonfunctionalized parts of the MWNTs.     

Purification of HiPCO carbon nanotubes via organic functionalization

We report a new method for the purification of HiPCO single-wall carbon nanotubes (SWNT), which consists of the following sequence: (a) organic functionalization of the as-produced nanotubes (pristine tubes, p-SWNT), (b) purification of the soluble functionalized nanotubes (f-SWNT), (c) removal of the functional groups and recovery of purified nanotubes (r-SWNT) by thermal treatment at 350 degrees C, followed by annealing to 900 degrees C. Each of these steps contributes to the purification, but only their sequential combination leads to high-purity materials. Organic functionalization makes the SWNT more easy to handle, which results in a better manipulation for potential practical uses. The electronic properties of the purified tubes are investigated via Raman and NIR spectroscopies along with transmission electron microscopy.     

Sidewall carboxylic acid functionalization of single-walled carbon nanotubes

The reactions of single-walled carbon nanotubes (SWNTs) with succinic or glutaric acid acyl peroxides in o-dichlorobenzene at 80-90 degrees C resulted in the addition of 2-carboxyethyl or 3-carboxypropyl groups, respectively, to the sidewalls of the SWNT. These acid-functionalized SWNTs were converted to acid chlorides by derivatization with SOCl(2) and then to amides with terminal diamines such as ethylenediamine, 4,4'-methylenebis(cyclohexylamine), and diethyltoluenediamine. The acid-functionalized SWNTs and the amide derivatives were characterized by a set of materials characterization methods including attenuated total reflectance (ATR) FTIR, Raman and solid state (13)C NMR spectroscopy, transmission electron microscopy (TEM), and thermal gravimetry-mass spectrometry (TG-MS). The degree of SWNT sidewall functionalization with the acid-terminated groups was estimated as 1 in 24 carbons on the basis of TG-MS data. In comparison with the pristine SWNTs, the acid-functionalized SWNTs show an improved solubility in polar solvents, for example, alcohols and water, which enables their processing for incorporation into polymer composite structures as well as for a variety of biomedical applications.     

Coordination and organometallic compounds in the functionalization of carbon nanotubes

Various methods for functionalization of carbon nanotubes (CNTs) using classic coordination complexes, as well as organometallic compounds as precursors, are discussed. CNTs can form hybrids via covalent or non-covalent interaction with metal complexes of crown ethers, carboxylates, amines, polypyridyl compounds, a host of N,O-containing ligands, derivatives of phosphonic acid, porphyrins, phthalocyanines, carbonyls, cyclopentadienyls, pyrene-containing moieties, and other aromatic structures. Several applications of synthesized composites/hybrids are emphasized.     

Noncovalent functionalization of single-walled carbon nanotubes with water-soluble porphyrins

We have employed water-soluble porphyrin molecules [meso-(tetrakis-4-sulfonatophenyl) porphine dihydrochloride] to solubilize single-walled carbon nanotubes (SWNTs), resulting in aqueous solutions that are stable for several weeks. The porphyrin-nanotube complexes have been characterized with absorption and fluorescence spectroscopy and with AFM. We find that the porphyrin/SWNT interaction is selective for the free base form, and that this interaction stabilizes the free base against protonation to the diacid. Under mildly acidic conditions nanotube-mediated J-aggregates form, which are unstable in solution and result in precipitation of the nanotubes over the course of a few days. Porphyrin-coated SWNTs can be precisely aligned on hydrophilic poly(dimethylsiloxane) (PDMS) surfaces by combing SWNT solution along a desired direction and then transferred to silicon substrates by stamping. Parallel SWNT patterns have been fabricated in this manner.     

Optimizing functionalization of multiwalled carbon nanotubes using sodium lignosulfonate

Multiwalled carbon nanotubes (MWCNTs) were functionalized with sodium lignosulfonate (SLS) at various SLS/MWCNT ratios, and the solubility of the functionalized MWCNTs was examined using ultraviolet-visible (UV-Vis) spectroscopy. Then, the effects of SLS on the dispersion and conductivity of MWCNTs were investigated. A calibration curve was constructed to measure the concentration of MWCNTs in water using the absorbance measured from UV-Vis spectroscopy. Using the curve, the change in the functionalized MWCNT concentration was investigated as a function of time. The results showed that the solubility of the MWCNTs did not increase significantly with further increases in SLS after the appropriate amount of SLS was employed. Excessive use of SLS rather decreased the conductivity of functionalized MWNTs. Also, the solubility of MWCNTs was influenced by dispersing method even when the same amount of SLS was used. Our method could functionalize the MWCNTs with a small amount of SLS, and the solution could remain stable for lengthy periods of time.     

Multiple functionalization of single-walled carbon nanotubes by dip coating

Single walled carbon nanotubes were functionalized with different functionalities by simple dip coating. This fast and reproducible procedure was realized with nanotube coated electrodes for the construction of polyvalent biosensors. Three different pyrene derivatives were attached to the nanotube sidewalls by π-stacking interactions in a one-step reaction.     

Sidewall functionalization of single-walled carbon nanotubes with organic peroxides

Single-wall carbon nanotubes (SWNTs) and their fluorinated derivatives (F-SWNTs) were reacted with organic peroxides including benzoyl and lauroyl peroxide to produce phenyl and undecyl sidewall functionalized SWNTs, respectively, which were characterized by Raman, FTIR, and UV-Vis-NIR spectra as well as TGA/MS, TGA/FTIR, and TEM data.     

Sidewall functionalization of single-walled carbon nanotubes through electrophilic addition

Electrophilic addition of chloroform to SWNTs followed by hydrolysis resulted in the addition of hydroxy groups to the surface of the nanotubes; further esterification with propionyl chloride led to the corresponding ester derivatives, which allowed us to identify their structure, also providing better solubility in organic solvents.     

Double functionalization of carbon nanotubes for multimodal drug delivery

Multi-walled carbon nanotubes have been covalently functionalized via 1,3-dipolar cycloaddition of azomethine ylides with orthogonally protected amino functions that can be selectively deprotected and subsequently modified with drugs and fluorescent probes.     

Nucleophilic-alkylation-reoxidation: a functionalization sequence for single-wall carbon nanotubes

A new reaction sequence for the chemical functionalization of single-wall carbon nanotubes (SWNTs) consisting of the nucleophilic addition of t-BuLi to the sidewalls of the tubes and the subsequent reoxidation of the intermediates t-Bu(n)SWNT(n-) leading to t-Bu(n)SWNT was developed. During the formation of the t-Bu(n)SWNT(n-), a homogeneous dispersion in benzene was formed due to the electrostatic repulsion of the negatively charged intermediates causing debundling. The entire reaction sequence can be repeated, and the degree of functionalization of the products (t-Bu(n))(m)SWNT (m = 1-3) increases with increasing m. Degrees of functionalization expressed as the carbon-to-addend ratio of up to 31 were reached. The reaction was studied in detail by photoelectron spectroscopy, Raman spectroscopy, and scanning tunneling microscopy (STM). The C 1s core level spectra reveal that the nucleophilic attack of the t-BuLi leads to negatively charged SWNTs. Upon oxidation, this negative charge is removed. The valence band spectra of the functionalized samples exhibit a significant reduction in the pi-derived density of states. In STM, the covalently bonded t-butyl groups attached to the sidewalls have been visualized. Raman spectroscopy reveals that addition of the nucleophile to metallic tubes is preferred over the addition to semiconducting tubes.     

Sidewall functionalization of single-walled carbon nanotubes by addition of dichlorocarbene

We report the sidewall functionalization of soluble HiPco single-walled carbon nanotubes (SWNTs) by addition of dichlorocarbene. The dichlorocarbene-functionalized SWNTs [(s-SWNT)CCl(2)] retain their solubility in organic solvents such as tetrahydrofuran and dichlorobenzene. The degree of dichlorocarbene functionalization was varied between 12% and 23% by using different amounts of the dichlorocarbene precursor. Because the addition of dichlorocarbene saturates the carbon atoms on the sidewall of the SWNTs and effectively replaces the delocalized partial double bonds with a cyclopropane functionality, the optical spectra of the SWNTs change dramatically. We estimate that the saturation of 25% of the pi-network electronic structure of the SWNTs is sufficient to remove all vestiges of the interband transitions in the infrared spectrum. The transitions at the Fermi level in the metallic SWNTs that appear in the far-infrared (FIR) region of the spectrum show a dramatic decrease of intensity on dichlorocarbene functionalization. The FIR region of the spectrum allows a clear differentiation between the covalent and the ionic chemistry of SWNTs. In contrast with covalent functionalization, we show that reaction of the SWNTs with bromine vapor leads to a strong increase in absorptions at the Fermi level that is observable in the FIR due to hole doping of the semiconducting SWNTs. Thermal treatment of the (s-SWNT)CCl(2) above 300 degrees C resulted in the breakage of C-Cl bonds, but did not restore the original electronic structure of the SWNTs.