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Zhang J.,Tsinghua University | Huang Z.-H.,Tsinghua University | Xu Y.,Beijing Tongfang Puri Technology Co. | Kang F.-Y.,Tsinghua University
Xinxing Tan Cailiao/New Carbon Materials | Year: 2011

Carbon-coated TiO2 was synthesized by mixing TiO2 powders and polyethylene glycol, followed by heat treatment in nitrogen atmosphere. All samples were characterized by powder X-ray diffraction, UV diffuse reflectance spectroscopy, high-resolution transmission electron microscopy, and nitrogen adsorption. The photocatalytic activity of carbon-coated TiO2 for benzene degradation was investigated with a benzene concentration of ~1.2 × 10-5. Results showed that the residual carbon content was influenced greatly by heat treatment temperature (HTT) and the amount of PEG, which decreased and increased with increasing the temperature and the amount of PEG, respectively. The crystallinity of TiO2 was improved when the HTT increased. However, the carbon residue had an inhibition effect on the crystal growth of TiO2. The carbon-coated anatase samples were shown to exhibit higher photocatalytic activities than the pristine TiO2 because of the adsorption enrichment of benzene by carbon around the anatase particles and of the effective charge separation due to the electronic conduction of carbon. Another important factor affecting photocatalytic activity was the crystallinity of the anatase phase. High photocatalytic activity for benzene requires a balance between the carbon content and the anatase crystalline structure. Source


Zhang J.,Tsinghua University | Huang Z.-H.,Tsinghua University | Xu Y.,Beijing Tongfang Puri Technology Co. | Kang F.,Tsinghua University
Journal of the American Ceramic Society | Year: 2013

Graphene/Bi2WO6 composites have been synthesized by hydrothermal reduction at 160°C for 24 h using ethanol as the reducing agent. All as-prepared composites were characterized using X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy, FT-IR spectroscopy, Raman spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, N2 adsorption, and photocatalytic activity evaluation. The effective charge separation of graphene/Bi2WO 6 composites was caused by the electrical conduction of graphene which is the most important factor. The results have proved the formation of interfacial contact between graphene nanosheets and Bi2WO6 nanoplates. The adsorptivity for azo dyes was enhanced greatly with the introduction of graphene. The oxy-functional groups located at the edges of graphene were responsible for the enhanced adsorptivity. As-prepared graphene/Bi2WO6 composites exhibited enhanced light absorption from UV to visible-light region. In addition, the introduction of graphene would also result in smaller crystalline size and lower crystallinity of Bi2WO6. Graphene/Bi2WO6 composites containing an appropriate amount of graphene were proved to exhibit higher adsorptivities and photocatalytic activities for azo dyes. High photocatalytic activities of graphene/Bi2WO6 composites were considered to be the synergetic effects of high adsorption, high light absorption, and high electrical conduction induced by the introduction of graphene. © 2013 The American Ceramic Society. Source


Zhang J.,Tsinghua University | Huang Z.-H.,Tsinghua University | Xu Y.,Beijing Tongfang Puri Technology Co. | Kang F.,Tsinghua University
International Journal of Photoenergy | Year: 2012

The heterostructured TiO 2/N-Bi 2WO 6 composites were prepared by a facile sol-gel-hydrothermal method. The phase structures, morphologies, and optical properties of the samples were characterized by using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive spectroscopy (EDS), and UV-vis diffuse reflectance spectroscopy. The photocatalytic activities for rhodamine B of the as-prepared products were measured under visible and ultraviolet light irradiation at room temperature. The TiO 2/N-Bi 2WO 6 composites exhibited much higher photocatalytic performances than TiO 2 as well as Bi 2WO 6. The enhancement in the visible light photocatalytic performance of the TiO 2/N-Bi 2WO 6 composites could be attributed to the effective electron-hole separations at the interfaces of the two semiconductors, which facilitate the transfer of the photoinduced carriers. Copyright © 2012 Jiang Zhang et al. Source


Zhang J.,Tsinghua University | Huang Z.-H.,Tsinghua University | Xu Y.,Beijing Tongfang Puri Technology Co. | Kang F.,Tsinghua University
International Journal of Photoenergy | Year: 2012

The iodine-doped Bi 2WO 6 (I-BWO) photocatalyst was prepared via a hydrothermal method using potassium iodide as the source of iodine. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. The photocatalytic activity of I-BWO for the degradation of rhodamine B (RhB) was higher than that of pure BWO and I 2-BWO regardless of visible light (>420 nm) or ultraviolet light (400 nm) irradiation. The results of DRS analysis showed that the I-BWO and I 2-BWO catalysts had narrower band gaps. XPS analysis proved that the multivalent iodine species including I 0 and I - were coadsorbed on the defect surface of Bi 2WO 6 in I-BWO. The enhanced PL intensity revealed that a large number of defects of oxygen vacancies were formed by the doping of iodine. The enhanced photocatalytic activity of I-BWO for degradation of RhB was caused by the synergetic effect of a small crystalline size, a narrow band gap, and plenty of oxygen vacancies. © 2012 Jiang Zhang et al. Source

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