Functionalization of carbon nanotubes by free radicals

Free radicals generated by decomposition of benzoyl peroxide in the presence of alkyl iodides have been used to derivatize small-diameter single-wall carbon nanotubes (HiPco tubes). The degree of functionalization, estimated by thermal gravimetric analysis, is as high as 1 in approximately 5 carbons in the nanotube framework. The derivatized nanotubes exhibits remarkably improved solubility in organic solvents. The attached groups can be removed by heating in an atmosphere of argon. Derivatization was also accomplished by treating SWNTs with various sulfoxides employing Fenton's reagent. [reaction: see text]     

Cutting of single-walled carbon nanotubes by ozonolysis

Cutting of single-walled carbon nanotubes (SWNT) has been achieved by extensive ozonolysis at room temperature. Perfluoropolyether (PFPE) was selected as a medium for cutting SWNT due to its high solubility for ozone (O3). A mixture of 9 wt % of O3 in O2 was bubbled through a homogeneous suspension of pristine SWNT in PFPE, at room temperature. The intense disorder mode in the Raman spectra of ozonated SWNT indicates that extensive reaction with the sidewalls of SWNT occurs during ozonolysis. Atomic force microscopy (AFM) images of SWNT, before and after ozonolysis, provided a measure of the extent of the cutting effects. Monitoring of the evolved gases for both pristine and purified SWNT indicates CO2 was produced during the ozonolysis process with a dependence on both system pressure and temperature. During heating, FTIR analysis of gases released indicated that carbon oxygen groups on the sidewalls of SWNT are released as CO2. SWNT was found to be extensively cut after an ozone treatment with a yield of approximately 80% of the original carbon.     

Hydrogen storage capacity characterization of carbon nanotubes by a microgravimetrical approach

An accurate gravimetric apparatus based on a contactless magnetic suspension microbalance was developed. This unit was used to measure the hydrogen storage capacity for a variety of carbon nanotubes (CNTs) at room temperature and hydrogen pressures up to 11.5 MPa. The results show that regardless of their synthesis methods, purities, and nanostructures all investigated CNT products possess relatively low hydrogen storage capacities (<0.2 wt %). For comparison, the adsorption characteristics of theses samples were also measured at a pressure of 0.1 MPa and liquid nitrogen temperature (approximately 77 K) by a conventional volumetric approach. The methodological aspects related to the accuracy of the hydrogen uptake measurements are also discussed.     

Sensitive electrochemical immunoassay for chlorpyrifos by using flake-like Fe3O4 modified carbon nanotubes as the enhanced multienzyme label

A highly sensitive electrochemical immunoassay of chlorpyrifos (CPF) was developed by using a biocompatible quinone-rich polydopamine nanospheres modified glass carbon electrode as the sensor platform and multi-horseradish peroxidase-flake like Fe₃O₄ coated carbon nanotube nanocomposites as the signal label. Due to the quinone-rich polydopamine nanospheres, the platform exhibited excellent fixing capacity by simple coating of sticky polydopamine nanospheres and subsequent oxidization. By coprecipitation of Fe³⁺ and Fe²⁺ on polydopamine modified carbon nanotubes (CNTs) with the aid of ethylene glycol (EG), the flake-like Fe₃O₄ coated CNTs (CNTs@f-Fe₃O₄) were synthesized and chosen as the carrier of multi-enzyme label due to the high loading of secondary antibody (Ab₂) and horseradish peroxidase (HRP) and also the peroxidase-mimic activity of Fe₃O₄. Under the optimum conditions, the immunosensor can detect CPF over a wide range with a detection limit of 6.3 pg/mL. Besides, the high specificity, reproducibility and stability of the proposed immunosensor were also proved. The preliminary application in real sample showed good recoveries, indicating it holds promise for fast analysis of CPF in aquatic environment.     

Improving ORR activity of carbon nanotubes by hydrothermal carbon deposition method

Nitrogen doped carbons are an important family of materials with ideal activity for oxygen reduction reaction(ORR). It is always interesting to search functional carbons with high heteroatom contents and desirable structure for ORR. Within this study, the surface modification of carbon nanotubes(CNTs) via hydrothermal carbonization(HTC) technique in the presence of glucose and urea was reported, where the surface of CNTs is successfully coated by nitrogen containing hydrothermal carbon layers. The resulting composite combines both advantages of the outstanding electrical conductivity of CNTs and the effective ORR active sites provided by doped nitrogen in the HTC carbon layers. By controlling the ratio of glucose and urea, the nitrogen contents coated on the surface of CNTs can reach up to 1.7 wt%. The resulting materials show outstanding electrochemical activity towards ORR in alkaline electrolyte, making it one of the valuable metal-free electrode materials and a competent alternative to the state-of-the-art Pt/C catalyst.     

Autonomous movement of silica and glass micro-objects based on a catalytic molecular propulsion system

A general approach for the easy functionalization of bare silica and glass surfaces with a synthetic manganese catalyst is reported. Decomposition of H(2)O(2) by this dinuclear metallic center into H(2)O and O(2) induced autonomous movement of silica microparticles and glass micro-sized fibers. Although several mechanisms have been proposed to rationalise movement of particles driven by H(2)O(2) decomposition to O(2) and water (recoil from O(2) bubbles, ([36,45]) interfacial tension gradient([37-42]), it is apparent in the present system that ballistic movement is due to the growth of O(2) bubbles.     

Pinning of single-walled carbon nanotubes by selective electrodeposition

A maskless method for the fabrication of electrical or mechanical contacts to the single-walled carbon nanotubes (SWNTs) by selective electrodeposition is reported. Both semiconducting SWNTs and metallic SWNTs can be pinned on prepatterned electrodes by the locally deposited metal, leaving the section of SWNTs between the electrodes clean. The distribution of deposited metal on the SWNTs is mainly determined by the covering power of the plating bath and the plating potential. This research provides a parallel method for the large-scale integration of SWNTs into electronic, optoelectronic, and sensing systems.     

Encapsulation of carbon nanotubes by self-assembling peptide amphiphiles

We demonstrate the dispersion and noncovalent functionalization of carbon nanotubes in water using peptide amphiphiles each consisting of a short hydrophobic alkyl tail coupled to a more hydrophilic peptide sequence. The assembly of peptide amphiphile molecules on the surfaces of carbon nanotubes adds biofunctionality to these one-dimensional conductors and simultaneously eliminates the hydrophobic nanotube-water interface, thus dispersing them in the aqueous medium. This should occur without the degradation of their structural, electronic, and optical properties caused by covalent functionalization and without the need for specific peptide sequences designed to bind with nanotube surfaces. The encapsulation by peptide amphiphiles is confirmed using transmission electron microscopy and optical absorbance spectroscopy and may have significant future applications in biosensing or medicine.     

Synthesis of polymer grafted carbon nanotubes by nitroxide mediated radical polymerization in the presence of spin-labeled carbon nanotubes

Multiwalled carbon nanotubes (MWCNT) were grafted with polystyrene by in situ nitroxide mediated radical polymerization in the presence of TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxyl) functionalized MWCNT, which was synthesized by the reaction between 4-hydroxyl-TEMPO (HO-TEMPO) and carbonyl chloride groups on the MWCNT. Although the controllability of the polymerization was not high, highly soluble grafted MWCNTs were indeed obtained, indicating that the graft polymerization was efficient. The resulting polystyrene grafted MWCNTs were easily defunctionalized at room temperature using 3-chloroperoxybenzioc acid. TEM, SEM, and TGA were employed to determine the structure, morphology, and the grafting quantities of the resulting products.     

Formation of carbon nanotubes from a silicon carbide/carbon composite

The reaction of a SiC/C composite powder in an arcing plasma forms carbon nanotubes in good yield. Besides carbon nanotubes, a Si/C composite composed of β SiC covered with a shell of graphite is formed. The graphitic carbon surface layers of the carbon shell of this composite reacts further to form carbon nanotubes when heated to 600 °C. This process seems highly effective since only a small overall low weight loss, indicative for a complete carbon shell oxidation is observed by thermal analysis. The formation of the carbon nanotubes from SiC is unlikely since no SiO₂ has been found when heating the SiC/C core shell composite to its reaction temperature of 600 °C under O₂. The CNTs formed are of good quality with 3 to 6 concentric walls and high aspect ratio. Occasionally even single walled carbon naotubes have been observed.     

Cytotoxicity of carbon nanotubes

With large-scale production and application at large scale, carbon nanotubes (CNTs) may cause ad-verse response to the environment and human health. Thus, study on bio-effects and safety of CNTs has attracted great attention from scientists and governments worldwide. This report briefly summa-rizes the main results from the in vitro toxicity study of CNTs. The emphasis is placed on the descrip-tion of a variety of factors affecting CNTs cytotoxicity, including species of CNTs, impurities contained, lengths of CNTs, aspect ratios, chemical modification, and assaying methods of cytotoxicity. However, experimental information obtained thus far on CNTs' cytotoxicity is lacking in comparability, and some-times there is controversy about it. In order to assess more accurately the potential risks of CNTs to human health, we suggest that care should be taken for issues such as chemical modification and quantitative characterization of CNTs in cytotoxicity assessment. More importantly, studies on physical and chemical mechanisms of CNTs' cytotoxicity should be strengthened; assaying methods and evaluating criteria characterized by nanotoxicology should be gradually established.     

Self-networking of carbon nanotubes

Carbon nanotube self-assembly into honeycomb-networks via controlling the ratio of the catalyst over hydrocarbon in the vapor phase using a tunable chemical vapor deposition process.     

Aromaticity of carbon nanotubes

Carbon nanotubes are composed of cylindrical graphite sheets. Both nanotubes and graphite sheets are benzenoid derivatives composed of sp2 carbon atoms arranged in a hexagonal pattern. Therefore both systems are aromatic. The extent of the aromatic character of a molecule G (here benzenoids) can be explained in terms of the number of possible Kekulé structures in G. In this work the Kekulé structures in carbon nanotubes and the corresponding, rectangular, graphite-sheets the tubes might originate from, were enumerated. It was shown that (2,2), (3,3), and (4,4) carbon nanotubes are more aromatic than the corresponding, rectangular, planar structures. This explains why it might be more difficult to saturate nanotubes by addition reactions than the respective, "narrow", graphite sheets.     

The conversion of polyaniline nanotubes to nitrogen-containing carbon nanotubes and their comparison with multi-walled carbon nanotubes

Polyaniline (PANI) nanotubes were prepared by the oxidation of aniline in solutions of acetic or succinic acid, and subsequently carbonized in a nitrogen atmosphere during thermogravimetric analysis running up to 830 °C. The nanotubular morphology of PANI was preserved after carbonization. The molecular structure of the original PANI and of the carbonized products has been analyzed by FTIR and Raman spectroscopies. Carbonized PANI nanotubes contained about 8 wt.% of nitrogen. The molecular structure, thermal stability, and morphology of carbonized PANI nanotubes were compared with the properties of commercial multi-walled carbon nanotubes.     

Tuning chirality of single-wall carbon nanotubes by selective etching with carbon dioxide

CO2 molecule chemisorbs selectively on the zigzag tube edge without an activation barrier, whereas it physisorbs on the armchair edge of nanotubes. In addition, carbon nanotubes can be etched by an adsorbed oxygen atom of CO2 molecule. From our results, we suggest a selective etching mechanism for tuning the chirality of the mass-produced carbon nanotubes.     

Anion recognition by functionalized single wall carbon nanotubes

Amidoferrocenyl-functionalised single wall carbon nanotubes (Fc-SWNT) are efficient exoreceptors for the redox recognition of H2PO4-.     

Photoinduced charge transfer mediated by DNA-wrapped carbon nanotubes

We report our observation of solution photochemical reactions catalyzed by carbon nanotubes. Addition of sub-millimolar Ag+ ions into a solution of DNA-wrapped carbon nanotubes (DNA-CNT) leads to a strong charge-transfer band in the UV region of the optical absorption spectrum. Light irradiation of the Ag+/DNA-CNT mixture results in reduction of Ag+ to Ag nanoparticles and concomitant oxidation of water.