Advanced Materials Research Vols. 750-752

Abstract: Polyaniline (PANI) nanofibers were fabricated via rapid initiated polymerization in a binary oxidant system consisting of ammonium peroxydisulfate (APS) and hydrogen peroxide (H₂O₂). The influence of the ratios of APS to H₂O₂ on the morphologies and optical properties of PANI nanofibers were discussed. It is found that the minimum optical band gap of PANI nanofibers with a relatively uniform diameter of 40 nm can be obtained for the ratio of 1:3.

Abstract: TiO₂ has large potential ability in Lithium-ion batteries due to its high energy density and safety. The main reasons that limit the performance of TiO₂ electrode is its low real capacity which caused by poor conductivity and other factors. Varying bulk TiO₂ materials to nanoscale is believed a promising method as it could increase Li insertion sites, short the ions diffusion distance and enhance the kinetics. In addition, doping heterogeneous elements or compositing other conductivity materials could enable TiO₂ to improve electron transfer ability. In this paper, we reviewed the electrochemical performance of some nanostructured TiO₂ and analyzed the merits and weaknesses. Some challenges and perspectives for future research were also discussed.

Abstract: Vanadium-doped TiO₂ hollow spheres (V-THs) were successfully synthesized by hydrothermally process using carbon spheres as templates. The physicochemical properties of the catalysts were characterized by XRD, TEM, UV-Vis diffuse reflectance spectra, N₂ adsorption-desorption isotherms. The photocatalytic activities of the prepared samples were evaluated for the degradation of 4-chlorophenol (4-CP) aqueous solution under visible light (λ>400 nm) irradiation, and was compared to undoped TiO₂ hollow spheres (THs). It was found that vanadium ions doping sample showed the highest photocatalytic activity with an optimal doping concentration of 1.5% under visible light irradiation.

Abstract: Fine polystyrene fibers have been generated from electrospinning of PS/molybdophosphoric acid in THF and DMF solution. The fiber diameters ranged from 500 nm and increased by adjusting the volume of DMF, the amount of the PS/ molybdophosphoric acid and spinning voltage, the size of the distance. Surface morphology of the nanofibers was characterized by scanning electron microscopy (SEM). The fibers generated from the solutions were more homogeneous in sizes, especially when more THF was added. With the phosphomolybdate amount of increase in untreated, cold pressing, hot pressing modulus showed a trend to decrease. The infrared results show that the composite membrane contains four phosphomolybdate absorption peaks, which is consistent with the predicted results.

Abstract: In this experiment, nanotitanium dioxide photocatalyst are prepared by treatment of a mixed solution of TiCl₄ and NH₃·H₂O. The conditions of synthesis catalyst are studied according to drying methods and roasting temperatures. The crystal phase of prepared powders is studied by XRD and FT-IR. At last we discussed photocatalysis activity of TiO₂. The results show that the best roasting temperature is 500 °C and the optimal drying method is microwave drying.

Abstract: TiO₂ nanotube arrays have attracted remarkable attention in recent years for diverse applications including water splitting photocatalysis, gas sensors, lithium-ion batteries and dye-sensitized solar cells, etc due to its semiconductor properties ,large surface area and nanotublar structures. Compared with TiO₂ nanotube, free-standing and through-hole TiO₂ nanotube membranes with optimized microstructure, direct electrons transfer,stability to mechanical vibrations,have a broader applied potential. This report presents several preparation methods of free-standing and through-hole nanotube membranes, and explains the mechanism of detachment process. These methods can be classified into two types: one is an in-situ method and the other is an ex-situ.

Abstract: Cellulose acetate (CA) nanofibers were electrospun in trifluoroacetic acid (TFA) under various conditions of concentration, voltage and dope flow rate while tip to collector distance (TCD) kept constant. Results showed that concentrations lower than 8 wt. % could only be electrospun at low flow rates. Bead free fibers were easily electrospun from higher CA concentrations 13 wt. % to 15 wt. %. Concentrations greater than 15 wt. % formed a viscous solution that could not be uniformly dispersed, thus impeding electrospinning. Medium voltage 20KV was found to produce good fibers while flow rates of 0.5ml/h and above, produced non-uniform fibers with a wide range. Average fiber diameters of 104nm and 129nm were formed at 13 wt. % and 15 wt. % (0.4ml/h, 20KV) respectively.

Abstract: Dielectrophoresis (DEP) has been verified to be an efficient means of assembling carbon nanotubes (CNTs) for various applications. This paper simulates the electric field distribution of the quadruple electrode structure when the external AC voltage is applied between a pair of opposite electrodes. There exist induced electric potentials between high voltage electrodes and floating electrodes and thus floating electrodes seriously change the field distribution. For a pair of wide parallel electrodes, the deposition of one CNT bridging the electrode pair will greatly alter the local electric field and repel the further deposition of CNTs in the vicinity. The screening distance is relevant with the width of the electrode gap, which provides a way to estimate the density of assembled CNTs between the electrode pair.

Abstract: In this work, a series of multi-walled carbon nanotube (MWNT)/polycarbonate (PC) composites were prepared. A combined experimental of transmission electron microscope (TEM) and dynamic mechanical analysis (DMA) were used to study on the morphology and thermo-mechanical properties of MWNT/PC composites as a function of MWNT aspect ratio. The results showed that smaller aspect ratio nanotubes lead to greater broadening of the loss modulus peak in frequency space, however, there was no effect of aspect ratio on the glass transition temperature. The breadth of the loss modulus peak was found to correlate with the free space parameter, a measure of the spacing between the MWNTs. These results shed light on the separate impacts of aspect ratio, dispersion, and interface modification on the viscoelastic behavior of prepared MWNT/PC composites.

Abstract: In this work, CaCO₃ nanoparticles have been synthesized via heat-treatment of a new precursor. Effect of calcinations temperature on particle size has been investigated. The products were characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). nanoCaCO₃ was modified using chloroform as solvent and fatty acid as modifier atroom temperature. The advantage of this modification is that it can be proceed at room temperature and it can reduce energy consumption.