Hangsheng Yang

Structure and Lithium Insertion Properties of Carbon Nanotubes

Carbon nanotubes were obtained by pyrolysis of acetylene or ethylene catalyzed by iron or iron oxide nanoparticles. The morphology, microstructure, and lithium insertion properties of these carbon nanotubes were investigated by transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and electrochemical measurements, respectively. The results showed that the structures of the carbon nanotubes play major roles in both specific capacity and cycle life. Slightly graphitized carbon nanotubes showed a specific capacity of 640 mAh/g during the first charge, whereas well-graphitized carbon nanotubes showed a specific capacity of 282 mAh/g during the first charge. After 20 charge/discharge cycles the charge capacity of the slightly graphitized samples degraded to 65.3% of their original charge capacities, but the well-graphitized samples maintained 91.5% of their original charge capacities. The effects of charge-discharge rates and cycling temperature on lithium insertion properties of carbon nanotubes with different extents of graphitization are discussed.

Catalytic reduction of NOx with NH3 over different-shaped MnO2 at low temperature

MnO(2) nanotubes, nanorods, and nanoparticles were prepared using a hydrothermal method, after which the different activities for selective catalytic reduction (SCR) of nitrogen oxides (NO(x)) were compared. MnO(2) nanorods performed the highest activity for reduction of NO(x) under a gas hourly space velocity of 36,000 h(-1) with conversion efficiencies of above 90% between 250 and 300 °C; it also had the highest removal efficiency of 98.2% at 300 °C. From the analysis of X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, temperature-programmed desorption, and temperature-programmed reduction, we can ascribe the high activity of MnO(2) nanorods to low crystallinity, more lattice oxygen, high reducibility, and a large number of strong acid sites. The apparent activation energy of the SCR reaction on the surface of nanorods was calculated to be 20.9 kJ/mol, which favored the reaction better than the other catalysts.

New method of carbon onion growth by radio-frequency plasma-enhanced chemical vapor deposition

Large quantities of carbon onions with high purity were synthesized by radio-frequency plasma-enhanced chemical vapor deposition. The produced carbon onions are solid, clean and can be separated easily from the catalytic particles. The formation of onions is based on the formation of many cages in successive stages from the core to the surface. Around the edge of a carbon onion, discontinuous curved lines are shown in the high-resolution TEM image, reflecting the wavy behavior of carbon onions.

Generation of curved or closed-shell carbon nanostructures by ball-milling of graphite

Abstract Curved or closed-shell carbon nanostructures were produced by ball-milling of graphite. A high resolution indicates that the ball-milling not only produces bend of graphite sheets, forming carbon nanoarches, but also produces closed-shell carbon nanostructures, nearly carbon ‘onions’. The possible formation mechanism is proposed.

Synthesis of CuO nanowalnuts and nanoribbons from aqueous solution and their catalytic and electrochemical properties

One dimensional copper hydroxide nanostrands, two dimensional Cu(2)(OH)(3)NO(3) nanoribbons and three dimensional CuO nanowalnuts were synthesized from the same diluted copper nitrate solution with ethanolamine at room temperature and 10 °C, respectively. The Cu(2)(OH)(3)NO(3) nanoribbons were formed by slowly hydrolyzing ethanolamine at low temperature. The CuO nanowalnuts were formed through dehydration of copper hydroxide nanostrands in aqueous solution at room temperature. Although their average size is about 500 nm, the specific surface area of the CuO nanowalnuts can be as large as 61.24 m(2) g(-1), due to their particular morphology with assembling of 8 nm grains. The Cu(2)(OH)(3)NO(3) nanoribbons were converted to CuO porous nanoribbons, keeping the shape. The catalytic performance of the CuO nanowalnuts for CO oxidation is 160 mL h(-1) g(cat)(-1) which is 23 times higher than those of the CuO porous nanoribbons and 40 nm commercial CuO nanoparticles, respectively. The electrochemical properties of the CuO nanowalnuts were also examined in a lithium-ion battery. After 30 cycles, the capacity of the as-prepared CuO nanowalnuts could sustain 67.1% (407 mA h g(-1)) of the second cycle (607 mA h g(-1)) at a rate of 0.1 C.

Promotional effects of carbon nanotubes on V2O5/TiO2 for NOX removal.

A series of V(2)O(5)/TiO(2)-carbon nanotube (CNT) catalysts were synthesized by sol-gel method, and their activities for NO(X) removal were compared. A catalytic promotional effect was observed by adding CNTs to V(2)O(5)/TiO(2). The catalyst V(2)O(5)/TiO(2)-CNTs (10wt.%) showed an NO(X) removal efficiency of 89% at 300°C under a GHSV of 22,500h(-1). Based on X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, NH(3)-temperature-programmed desorption, temperature-programmed reduction, Brunauer-Emmett-Teller surface area measurements, differential scanning calorimetry, and thermogravimetric analysis, the increased acidity and reducibility, which could promote NH(3) adsorption and oxidation of NO to NO(2), respectively, contributed to this promotion.

High-quality cBN thin films prepared by plasma chemical vapor deposition with time-dependent biasing technique

Cubic boron nitride thin films were deposited on silicon (111) wafers by inductively coupled plasma-enhanced chemical vapor deposition. The influences of Ar flow rate and the time-dependent substrate biasing condition on the composition and the transition layers thickness of cBN films were systematically investigated. By using the time-dependent biasing technique, with decreasing the substrate bias voltage gradually from sputtering mode to a final appropriate value for cBN deposition mode, 600 nm thick high quality and stoichiometric cBN films consisting of more than 98% cubic phase were successfully deposited with the deposition rate of 1.5 nm/s. The transition layer consisted of an amorphous layer and a turbostratic boron nitride layer that could be reduced less than 10 nm, which proved that, by using proper deposition technique, high-quality cBN films similar to those prepared by physical vapor deposition methods can be prepared even by chemical vapor deposition.

Preparation of MnOx/TiO2 composites and their properties for catalytic oxidation of chlorobenzene

MnO(x)/TiO(2) composites with different atomic ratio of Mn/Ti were prepared by sol-gel, solvothermal and coprecipitation method, respectively. The catalytic tests on chlorobenzene (CB) removal ability of all 15 catalysts were performed in a fixed-bed flow reactor and compared to each other. Experimental results showed that when the atomic ratio of Mn/Ti reached 1:4, the activity of the catalysts prepared by three methods reached their highest value, particularly the catalyst with the Mn/Ti atomic ratio of 1:4 prepared by sol-gel method showed higher catalytic activity than the catalysts with the same atomic ratio prepared by other methods at temperature between 100 and 300 degrees C. From the microstructure characterization by XRD, SEM, EDS, BET, and TPR, it could be known that the combined TiO(2) phases of anatase and rutile and a good dispersion of manganese oxides contributed to a good catalytic performance in the catalyst prepared by the sol-gel method.

Mass spectrometric study of low-pressure inductively coupled plasma for chemical vapor deposition of cubic boron nitride films

Abstract Chemical species in plasma are crucial for understanding the mechanism of cubic boron nitride film vapor phase deposition and controlling the film structure. In this study, the plasma condition for cubic boron nitride deposition by low-pressure inductively coupled plasmaenhanced chemical vapor deposition using B2H6,N2, and Ar as reactant gases has been diagnosed by a quadrupole mass spectrometer with an ion energy analyzer. The ionization potentials of BxHy (X = 1-2, Y = 0-6) decomposed from B2H6 have been measured to be between 11.6 and 18.9 eV. B2H6 was totally ionized to B+ together with small amounts of BH+, and in plasma above the 2 kW input power. N2 was only partially ionized, and the degree of ionization increased with increasing Ar partial pressure. Neutral species under the present plasma environment were N2, Ar and He, but N and H were not detected even by appearance mass spectrometry. Our results demonstrate that the main sources for cubic boron nitride formation are ions produced in plasma. The interaction between N2 and the growth surface suppresses the cubic boron nitride formation by enhancing the tBN growth, and this surface interference can be reduced by introducing Ar into the system.

Interface engineering of cBN films deposited on silicon substrates

We could determine the substrate pretreatment conditions required for the deposition of cubic boron nitride films without an interfacial amorphous layer by investigating nanostructures, chemical composition, and bonding states of the amorphous layer, which inevitably grew prior to the growth of cubic BN in ion-assisted chemical vapor deposition. The amorphous layer was composed of a native Si oxide layer and a complex oxide layer consisting of B, N, Si, and 10–20 at.u200a% oxygen. However, by the substrate pretreatment, 1200 K heating in 20 mTorr H2 atmosphere for 120 min, the crystallinity of the Si substrate surface could be retained throughout the removal of the native oxide layer, and turbostratic BN was revealed to grow directly on the Si substrate. In addition, we could reduce the thickness of the turbostratic BN layer to less than 3 nm, and increase the adhesion strength markedly. The formation of the amorphous layer was found to be caused by two factors: the native oxide layer and the ion bombardment ...