Papers by Author: Wen Bin Cao

Abstract: The main issues that limit the large-scale application of TiO₂ in photocatalysis is its low utilization of solar energy and high recombination rate of photogenerated charges. To overcome these limitations, a type II WO₃·H₂O/TiO₂ heterojunction has been prepared via a one-step mild hydrothermal method that uses Na₂WO₄·2H₂O and P25 as the starting materials and proceeds at 150°C without requiring any post-heat treatment for crystallization, special solvents or additives. The XRD and HRTEM results show that the prepared powders were composed of orthorhombic WO₃·H₂O and TiO₂, and demonstrate the existence of the WO₃·H₂O/TiO₂ heterojunctions. The photocatalytic activity of the as-prepared WO₃·H₂O/TiO₂ heterojunction powders was investigated by using the degradation of phenol. The WO₃·H₂O/TiO₂ heterojunction powders exhibited the best photocatalytic performance when the nominal W/Ti ratio was 6.57%, and showed better photocatalytic performance than commercial P25 and orthorhombic WO₃·H₂O.

Abstract: With people's increasing demands for the improvement of air quality and quality of life, the demand for new decorative materials with air purification function will be increasing. This study is based on a life cycle assessment (LCA)-based approach to develop a list of resources, energy consumption and pollutant emissions in the life cycle of typical visible light photocatalytic liquid products, to calculate the important environmental impact of visible light photocatalytic liquid products, and to analyze and identify the critical stages affecting environmental performance of product, to guide the selection of green buildings and the development of ecological building materials. The results show that, for the purpose of visible light photocatalytic liquid, the global warming potential is 40.97kgCO₂ equivalent/t, the abiotic depletion potential is 9.34×10^-5kgSb equivalent/t, the respiratory inorganic index is 7.88×10^-2kgPM_2.5 equivalent/t, and the eutrophication is 4.13×10^-2kgPO₄^3-equivalent/t, acidification effect is 0.34kgSO₂ equivalent/t; and the environmental impact in the product life cycle for the purpose of this study are mainly resulted from energy use, and transport process represents the main stage of eutrophication.

Abstract: Stable TiO₂ aqueous dispersion with an averaged secondary particle size of about 10 nm was achieved by using commercially available dispersant Di-7N. The stability of the dispersion was measured by Zeta-potential test. And the results showed that the optimal mass fraction of Di-7N was 12 wt%. The adsorption mechanism examined by FTIR analysis indicates that the carboxylate groups in Di-7N is absorbed on the surface of nano-TiO₂ particles and the adsorbed structure is proposed to be bidentate chelating.

Abstract: TiO₂ thin films were prepared on SiO₂-coated glass substrates using sols deriving from high concentration titanyl sulfate solution by the spin-coating technique. The calcined films were characterized by X-ray diffraction, UV-Vis spectroscopy, scanning electron microscopy. The film exhibited high transmittance in the visible light region and high absorption in the ultraviolet region. The contact angle of SiO₂/TiO₂ decreased to below 5° under 30 min of UV light irradiation and can sustain for 1 weeks.

Abstract: Yellow colored anatase Fe/N co-doped TiO₂ powders have been successfully synthesized by one step hydrothermal method at a lower temperature. The grain size was about 10 nm and the specific surface area of the powders ranged from 160 to 166 m²/g. The light absorption of Fe/N co-doped TiO₂ powders was enhanced in the visible light region of 400~500 nm and a new absorption peak at about 470 nm appeared when the Fe/Ti ratio exceeded 0.5%. The visible light photoactivity of Fe/N co-doped TiO₂ powders has been greatly improved than that of un-doped TiO₂ powders under visible light irradiation.

Abstract: In the field of military communications, the SNR of speech signal is low because of the additive noise,. The two-level Wiener filter is adopted to analysis the noise characteristics. The DSP system architecture solutions are given out in this paper.The algorithms of the PSD mean module, Mel scale filter bank module, voice activity detection module and gain control module are introduced in detail. Finally, the application results are given out, which indicate that two Wiener filter can achieve better results, in short stationary noise environments when face the low SNR.

Abstract: As to the speech signal processing problems under the complex voice environment, the characters of speech harmonic and the structure of voiced harmonic are discussed in this paper. In the third dimension frequency domain, quadratic Fourier transform algorithm based on logarithmic amplitude-frequency characteristics is used to propose the concept of the third dimension spectral harmonic ratio" by the behavior of the quasi-sinusoidal characteristics of the speech short-time Fourier spectrum slicing, which is cosider to be an important basis to discriminate speech activity detection. The concept of third dimension spectral harmonic ratio maks the speech signal as a special signal, and separate from the other noise signal completely. For voice noise outside the speech segment, it is no longer need to discuss its own characteristics and without the need for pre-processing to shield the noise accurately, which bring new ideas for the speech signal detection in the complex noise environment.

Abstract: Nanocrystalline W-doped TiO₂ powders with different initial W/Ti ratio in starting materials have been prepared by hydrothermal method. The phase composition, morphologies, specific surface areas and the photocatalytic activities under visible light irradiation of the synthesized powders have been characterized. XRD identification reveals that the synthesized powders were composed of anatase. No rutile has been detected in the products. The specific surface area of the powders was ranged from 185 to 210 m²/g by BET measurement. The averaged grain size of the powders was calculated as about 12 nm by Scheller's method. Uniform size distribution and good crystallinity have been confirmed by TEM. UV-Vis spectra show that the absorption edges of the synthesized W-doped TiO₂ powders with different nominal doping concentration of W ions have been red-shifted into visible light region, which suggests that the W ions have been doped into the lattice of TiO₂. In our case, W-doped TiO₂ with initial W/Ti atomic ratio of 1% in starting materials has the best photocatalytic activities when decompose the Methylblue in its aqueous solution, which is consistent with that of the theoretical results from our previous work.

Abstract: Silica-sol and activated carbon were used to prepare SiC whiskers by microwave heating. The effect of packing density of raw material powders on the morphologies of SiC whiskers has been investigated. It was argued that by decreasing the packing density of raw material powders, the growing space of the SiC whiskers increases and the morphologies of the whiskers changes from flexural to straight along with the increase in length. When the packing density was lower than 0.26 g/cm³, straight and dispersal SiC whiskers with high slenderness ratio could be obtained.

Abstract: Nanometer-sized β-SiC were synthesized by carbothermal reduction of silica sol with acetylene carbon black at 1600 °C for 2h. Three kinds (straight, bamboo-like, branch-like) of SiC nanowires were deposited on the graphite plate, while SiC particle agglomerates and nanowires were formed in the graphite crucible. All the nanowires were formed via VS mechanism through the reaction between gaseous SiO and CO produced from the process of carbothermal reduction.