Preparation Of A Visible Light Driven Bi₂o₃-tio₂ Composite Photocatalyst And Used For Photocatalytic Degradation Of Organic Pollutants

Among various oxide semiconductor photocatalysts, TiO₂ was proved to be one of the most effective and suitable photocatalyst for degradation of organic pollutants because of its biological and chemical inertness, stability against photocorrosion, non-toxicity, high redox ability and less cost. But its relatively wide band gap (3.2 eV for anntase) and the fast recombination rate of photogenerated electron-hole pairs limit its further application in the visible light region (400nm<λ<700nm), which accounts for 43% of the incoming solar energy. To overcome the above two drawbacks, one of the most promising ideas is coupling TiO₂ with other narrow band gap semiconductors with matching band potentials, which can construct a heterojunction structure. In a coupled semiconductor system, the narrow band gap semiconductor can be excited by visible light irradiation and some of the photogenerated electrons or holes will then be transferred to TiO₂ vis heterojunction interface, lending to efficient charge separation. In this dissertation, we are motivated to work in this direction and prepare Bi₂O₃-TiO₂ composite by new synthesis method. Their crystalline phase, morphology, physical property and chemical property and optical absorption have been systemic investigated as well as their photocatalytic activities and photocatalytic mechanism. Finally we find some interesting and useful results. This dissertation consists of following contents.A series of Bi₂O₃-TiO₂ composite photocatalysts were prepared with a facile nonaqueous sol-gel method through varying the Bi-Ti atomic ratio and calcination temperature, where CTAB were used as the surface solubilizer. The catalyst structures had been extensively characterized by using X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), UV-visible diffuse reflectance spectroscopy (UV-vis DRS). The characterization results revealed that all of the Bi₂O₃-TiO₂ composite exhibited smaller crystallite size, higher thermal stability and stronger absorbance in visible light range than pure TiO₂. The photocatalytic activities of as-prepared catalysts were evaluated by the degradation of methyl orange (MO), the results showed that the Bi-Ti atomic ratio of 0.0175 was optimal in the photocatalytic activities under visible light irradiation, and the calcination temperature affected both the physicochemical properties and photocatalytic activities of the catalysts. XPS and XRD were further used to test stability of the photocatalyst, which maintained a high activity without obvious deactivation after five recycles of the degradation.Visible light driven mesoporous Bi₂O₃-TiO₂ composite photocatalyst was prepared via an ethylene glycol complex polycondensation route, where ethylene glycol acted as a polycondensation agent to capture the metal irons through a complex polycondensation mechanism. The obtained photocatalyst was characterized by XPS, XRD, HRTEM, BET and UV-vis DRS, and the characterization results revealed that the Bi₂O₃-TiO₂ composite exhibited smaller size of crystallite, higher specific surface area and stronger absorbance in visible light range than pure TiO₂. It was also found that the resulting composite showed higher photocatalytic activity than TiO₂ on the degradation of Rhodamine B (RhB) in water under visible light irradiation (λ>400nm). Bi₂O₃-TiO₂ composite exhibited 83% degradation of RhB. Whereas, pure TiO₂ only had 18% decolorrization of RhB due to the photosensitization pathway.