We have investigated reversible single-wall carbon nanotube (SWNT) oxidation by quantitative analysis of the oxide-induced absorption bleaching and luminescence quenching at low pH. These data, in combination with DFT structure calculations, suggest that the nanotube oxide is a 1,4-endoperoxide. At low pH, the endoperoxide protonates to create a hydroperoxide carbocation, introducing a hole in the SWNT valence band. Nanotube luminescence is extremely sensitive to quenching by hole-doping, while the absorption is relatively robust.

A systematic study of the zeta (ζ)-potential distribution of surfactant-wrapped individual single-walled carbon nanotubes (SWNTs) dissolved in water is presented here. The surface charge on the SWNT micelles, as measured by the ζ-potential, has implications for the stability of the dispersions and for the electrophoretic and dielectrophoretic assembly and alignment of SWNTs. Very highly charged SWNTs are obtained by dispersing the nanotubes in high concentrations of anionic and cationic surfactants, whereas almost neutral SWNTs are obtained by using non-ionic surfactants. The ζ-potential of the dissolved SWNTs is tuned by adjusting the surfactant concentration, the alkyl chain length of the surfactant molecule, and the solution pH in different surfactant−SWNT systems.

We find that nearly monodisperse copper oxide nanoparticles prepared via the thermal decomposition of a Cu(I) precursor exhibit exceptional activity toward CO oxidation in CO/O 2 /N 2 mixtures. Greater than 99.5% conversion of CO to CO 2 could be achieved at temperatures less than 250°C for over 12 h. In addition, the phase diagram and pathway for CO oxidation on Cu 2 O (100) is computed by ab initio methods and found to be in qualitative agreement with the experimental findings.Nanoparticles offer a larger surface-to-volume ratio and a higher concentration of partially coordinated surface sites than the corresponding bulk materials. The unique properties of nanoparticles are due to a strong interplay between elastic, geometric, and electronic parameters, as well as the effects of interactions with the support. The result of these features is often improved physical and chemical properties compared to the bulk material. It is for these reasons that heterogeneous catalysis at nanoparticle surfaces is currently under intense investigation in the catalysis community at large. 1,2 Conventional supported catalysts are generally produced by impregnation of a support medium with the desired metal ions followed by thermal treatments that result in small and dispersed active catalytic sites. 3,4 Many traditional catalysts based on the impregnation method 5,6 rely on the noble metals, in particular platinum, as the source for high activity. Such metals are recognized as a scarce resource as well as a limiting step in the development of viable energy alternatives to petroleum. Automotive exhaust catalysts (the three way catalyst) and fuel cells are examples of this tenet. 5,6 Any new system that overcomes these limitations will be invaluable.There are several important processes in heterogeneous catalysis where removal of carbon monoxide is either desired or absolutely necessary, such as in the postprocessing of Syngas 7 to produce hydrogen as an energy source for use in fuel cells. 8,9 A byproduct of this reaction is CO; however, trace amounts of CO (>10 ppm) can poison a fuel cell electrode, drastically reducing its efficiency. [10][11][12] The CuCu 2 O-CuO system has been known to facilitate oxidation reactions in the bulk, suggesting it has potential as a costeffective substitute for noble metals in various catalytic systems. [13][14][15] Here we describe a cheap, effective method of using copper oxide nanoparticles loaded onto silica gel as an exceptional catalyst toward CO oxidation at relatively low temperatures. Over sustained periods of time, conversions of 99.5% of CO to CO 2 are routinely observed and the catalyst structure is retained during the reaction. For example, during a 50 h period with the same ∼10 mg sample of copper oxide nanoparticles, over 30 L of CO is converted to CO 2 with an average conversion of 98 ( 1%.With recent developments in nanoparticle synthesis leading to the ability to control size, reproducibility, and structural complexity, it becomes urgent to define specific target structu...

We report the controlled chemical vapor deposition (CVD) growth of single-walled carbon nanotubes (SWNTs), using ethanol as the carbon feedstock and bimetallic CoMo-doped mesoporous silica (SBA16) as the catalyst. Ultralong (up to 4 mm) and horizontally aligned SWNTs can be grown directly on flat substrates or across slits (20−120 μm apart), and the orientation of the nanotubes is always parallel to the gas flow direction. The control of the growth direction and length also enables us to fabricate parallel nanotube arrays or two-dimensional networks on flat surfaces. The growth of the carbon nanotubes is relatively fastit is attributed to the high reactivity of ethanol and high activity of the CoMo/SBA16 catalystand no doubt contributes to increased length and orientation control. Unlike previous procedures that have been used to grow well-oriented nanotubes, neither a strong external electrical field nor a fast-heating technique is required in this ethanol CVD process. Moreover, the as-grown SWNTs have a relatively narrow size distribution of 0.8−1.8 nm, which is a result of the narrow size distribution of the CoMo nanoparticles embedded in the mesoporous SBA16 silica.

We report a simple and efficient chemical vapor deposition (CVD) process that can grow oriented and long single-walled carbon nanotubes (SWNTs) using a cobalt ultrathin film ( approximately 1 nm) as the catalyst and ethanol as carbon feedstock. In the process, millimeter- to centimeter-long, oriented and high-quality SWNTs can grow horizontally on various flat substrate surfaces, traverse slits as large as hundreds of micrometers wide, or grow over vertical barriers as high as 20 microm. Such observations demonstrate that the carbon nanotubes are suspended in the gas flow during the growth. The trace amount of self-contained water (0.2-5 wt %) in ethanol may act as a mild oxidizer to clean the nanotubes and to elongate the lifetime of the catalysts, but no yield improvement was observed at the CVD temperature of 850 degrees C. We found that tilting the substrates supporting the Co ultrathin film catalysts can grow more, longer carbon nanotubes. A mechanism is discussed for the growth of long SWNTs.

The precise placement of single-walled carbon nanotubes ͑SWCNTs͒ in device architectures by ac dielectrophoresis involves the optimization of the electrode geometry, applied voltage and frequency, load resistance, and type of nanotube sample used. The authors have developed a toolkit to controllably integrate SWCNTs in device structures by the use of floating potential metal posts and appropriate electrode geometries, as designed using electric field simulations, and used it to fabricate structures such as crossed nanotube junctions.

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