The Preparation And Property Of Ti-perovskite Photocatalytic Materials

With the development of global industrialization process, environmental pollution is becoming more and more serious. Environmental problem have become an important issue which influence human survival and development in the 21 st century. Because of the simple reaction process, easily operating conditions, low energy consumption, degradation of pollutants completely and no secondary pollution, photocatalytic reaction has become a kind of ideal environment pollution controlling technology and clean energy production technology. Perovskite-based photocatalysts, with general formula of ABO3, are promising candidates for active photocatalytic materials not only due to its non-toxic, the low cost and stability, but also because of the occupancy of both the A and B sites being tailored by a wide range of cations and valences. In this paper, we aimed at producing active catalysts in the visible light, and studying the relationship between synthetic process of active photocatalysts and their mechanism of photocatalytic activity by various characterization methods of materials. The contents of the research are as follow:（1） The CaCu3Ti4O12（CCTO） samples were synthesized by the molten salt method. We have described the molten salt method for synthesizing CCTO samples of the different morphologies which be a good candidate in photocatalytic reduction of CO2 into CH4 and CO by varying the molten salt proportions, calcining temperatures, and calcination time under visible light irradiation. The different morphologies include nanowires, cuboid twenty, hexahedron and polyhedron doped nanowires The crystal structure of the sample was analyzed by XRD, SEM, Uv-vis and TEM. The photocatalytic experiment of the CCTO sample for the reduction of CO2 was carried out in a closed gas-circulating system with top irradiation. The reason that the various total activity of reduction of CO2 in different morphologies is probably attributed to different morphologies with different crystal faces, the different content of surface defect sites（Cu+）, specific surface area and band gap. The CCTO sample synthesized by a solid-state method was proved to be an effective photocatalyst for CO2 reduction. Especially, the nanowires have a lower recombination rate of photogenerated electron-hole pairs and enhanced CO2 photoreduction rates due to the hole trapping by Cu+. The formation rates of CO and CH4 are 14.4 μmol·g-1·h-1 and 24 μmol·g-1·h-1, respectively.（2） The Pb₂Bi₂Ti₄O₁₁（PBTO） samples were synthesized by hydrothermal method and molten salt method. The crystal structure of the sample was analyzed by XRD, SEM and BET. The photocatalytic activity of the as-prepared samples has been evaluated by degradation of RhB and MO solution under Vis-light irradiation. Among them, the degradation rates of RhB and MO in sample which was prepared by hydrothermal method（H-PBTO） were 64 % and 68 % in 100 minutes, respectively, and that of the M-PBTO sample which was prepared by molten salt method（M-PBTO） were 100 % within 1 h and 92 % in 100 minutes, respectively. This can be explained by the different morphologies of M-PBTO and H-PBTO samples. The activities of the photocatalysts are especially dependent on the exposed facets of the particles and the formed internal electric field along the direction of high-energy crystal face in M-PBTO sample can promote the separation of photoinduced charges. Thus its catalytic performance is significantly higher than that of H-PBTO sample.（3） The Bi₁₂TiO₂₀（BTO） samples were synthesized by molten salt method and the traditional solid phase method. The crystal structure of the sample was analyzed by XRD, SEM. The photocatalytic activity of the as-prepared samples has been evaluated by degradation of RhB solution under Vis-light irradiation. This can be explained by the sample which was prepared by molten salt method having relatively higher specific surface area and providing more active sites, and including the mixed phase being easily to form the heterojunction structure. So it has higher photocatalytic activity that the degradation rates of its was 100 % in 1 h, due to improving the quantum number of interfacial charge, and making electronic light easier to reach the surface of the catalyst.