| Environment pollution and energy shortage are the two major global problems for our human beings to solve in recent years. Semiconductor photocatalytic technology has become an effective solution to environmental pollution and energy crisis in an ideal way, because of it having highly redox ability and using solar energy directly to drive the photocatalytic reaction at ambient temperature. Owing to superior photocatalytic activity, chemical stability, low cost and nontoxicity, etc., TiO2 semiconductor photocatalyst is widely used in the fields of sewage treatment, air purification and splitting water to produce hydrogen. The performance of TiO2 photocatalyst for photocatalytic degradation processes is strongly dependent on its crystal phase, crystallinity, crystallite size, specific surface area and morphology. Therefore, it is very important to enhance photocatalytic performance of TiO2 and their composites for the further studying the relationship between the controllable synthesis, microstructures and the photocatalytic activity. In this study, a large number of investigations have focused on the controllable synthesis and doping modification of TiO2. The main research work is as follows:Anatase titanium dioxide(TiO2) microspheres with high photocatalytic activity were prepared by a novel pyrolysis method using titanium sulfate powders as the precursor. The photocatalytic activity of the as-obtained anatase TiO2 microspheres was evaluated by degrading rhodamine B(RhB, 20 mg/L) and 4-nitrophenol(4-NP, 10 mg/L) under UV-light irradiation at room temperature. A possible mechanism for the formation of TiO2 microspheres was proposed. The effects of calcination temperature and time on the morphologies and photocatalytic activities of the TiO2 microspheres were further studied. It was found that the anatase TiO2 microspheres can be obtained above 600 oC. The nucleation of primary TiO2 particles stemmed from the rapid pyrolysis of titanium sulfate powders, followed by the aggregation and recrystallization, resulting in the formation of anatase TiO2 microspheres. With increasing the calcination temperature from 600 to 900 oC, the crystallinity and pore size of the TiO2 microspheres increased and their specific surface areas decreased. The experimental results indicate that the crystallinity and specific surface area of the TiO2 microspheres have significant effects on their photocatalytic activities. The as-synthesized TiO2 microspheres obtained at 700 oC for 6 h exhibited the highest photocatalytic activity and good stability.The g-C3N4/Ti3+-TiO2 composites were prepared by hydrothermal-ultraphonic method. The photocatalytic activity of the as-obtained composite was evaluated for the degradation of rhodamine B(RhB, 20 mg/L) and reduction of Cr(VI) in aqueous solutions under simulated sunlight irradiation. The composition, element chemical state, microstructures and light adsorption were also characterized. The mechanism of photocatalytic degradation of rhodamine B and the photocatalytic reduction of Cr(VI) was also studied. Compared to the single g-C3N4 and Ti3+-TiO2, the mixed phase g-C3N4/Ti3+-TiO2 had an enhanced photocatalytic property and the sample with g-C3N4/Ti3+-TiO2 mass ratio of 0.06 showed the highest visible-light photocatalytic activity. This might be ascribed to the incorporation of g-C3N4 participating in wide optical adsorption as well as the coexposed(101) and(001) facets of anatase forming a surface heterojunction within single TiO2 particle and a impurity level induced by the Ti3+ exists in the band gap of TiO2, which facilitates the separation and transportation of photo-generated charge carriers, and thus enhancing the photocatalytic property. Moreover, the composites photocatalyst with the nanosheet morphology and dual-mesoporous structure is conducive to increase the reactive sites, and thus improving the efficiency of the photocatalytic reaction. Quenching experimental results showed that both h+ and ?O2– radicals are main reactive oxygen species that responsible for the degradation of RhB. |
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