Nm Of Tio <sub> 2 </ Sub> Surface Structure On The Photoinduced Charge Separation And Photocatalytic Properties

Nanosized TiO₂ has received widely attention in the photocatalysis and photoelectric conversion fields due to its cheapness, nontoxicity, no secondary pollution and strong oxidation capacity. However, the practical applications have been limited greatly because of the low efficiency for utilizing solar light and the easy recombination of photoinduced charges in itself. In this paper, we have carried out four mothods, including surface modification with surfactant, morphology control, post-treatment by phosphorous acid and co-doping of metal ions to modify nanosized TiO₂ photocatalyst, trying to enhance the photocatalytic activity, by changing its surface structure and morphology, so as to further improve the separation status of photoinduced charges.During the process of surface modification, Sodium dodecylbenzenesulfonate groups (DBS) as an anion surfactant was mainly used to modify TiO₂, the effects of DBS modification on photocatalytic performance, including mainly activity and lifetime, of nanosized TiO₂ in the degradation of gaseous n-C₅H₁₂ were studied, together with the mechanism of DBS modification mainly by means of surface photovoltage spectroscopy (SPS) and photoluminescence (PL). The results show that the modification with DBS molecule groups can inhibit crystallite growth, improve particle dispersibility, enhance the capability for adsorbing organic substances, and increase separation rate of photoinduced charges, which are responsible for the increase in the photocatalytic activity. Compared with that of unmodified sample, the lifetime of the surface-modified photocatalyst does not decrease, demonstrating that DBS groups are relatively stable. Moreover, in our experiment, the kinetic study suggests that, the photocatalytic reaction of gaseous n-C₅H₁₂ on TiO₂ follows a Langmuir-Hinshelwood model,with a pseudo-first order process.On the low-temperature and acid thermal conditions, Cetyltrimethylammonium bromides (CTAB), a cation surfactant, acting as structure-directing agent, was used to control the morphology of TiO₂. The effects of the sol-hydrothermal conditions, including mainly reactive temperature, pH value and CTAB concentration, on the preferential growth of TiO₂ crystallites were primarily investigated. The results show that appropriate amount of CTAB can induce preferred growth of nanocrystalline TiO₂ along <001> direction at a low temperature, which is shifted to the kinetic growth regime. Compared with the as-prepared spherical TiO₂ in the absence of CTAB, the preferred grown TiO₂ exhibits high photocatalytic activity, which is attributed to its high photoinduced charges separation rate, as well as to strong oxidizing capability of photoinduced holes and to large surface area. Moreover, the resulting TiO₂ nanoparticles can be directly dispersed in the organic system because of CTAB modification, which could further expand its application field.The modification of nanosized TiO₂ with phosphorous acid has been completed by an impregnation process. The effects of phosphorous acid modification on the thermal stability and photocatalytic activity of anatase TiO₂ were mainly investigated. The results show that the phosphorous acid modification obviously enhances the thermal stability of nanosized anatase TiO₂, even still having a principal anatase phase composition after thermal treatment at 800℃. Photocatalytic tests show that the as-prepared TiO₂ modified with appropriate amount of phosphorous acid by thermal treatment at high temperature exhibits high activity, even superior to P-25 TiO₂, which is attributed to the enhanced crystallinity so that promote photoinduced charges separation and to the large surface area.Nanosized TiO₂ was modified by co-doping La (Rare Earth) and Zn (Transition Metal) as the representative of the metal elements. The effect of introduction of metalions on the process of phase transformation was primarily studied. The results show the introduction of La and Zn ions can hinder the process of phase transformation, and the former inhibition is stronger than the later. In the anatase TiO₂ samples with a small amount of rutile, the higher is the crystallinity, the higher is the photocatalytic activity, which is mainly attributed to the decreasing of surface defect so that promote photoinduced charges separation.The above systematic studies shows that the surface structure, morphology and phase composition of nanosized TiO₂ can be comprehensively influence the separation status of photoinduced charges, further affecting the photocatalytic activity. Thereby, the effective modification of TiO₂ can be achieved by modulating the above factors. Moreover, it can be suggested that the SPS is an effective tool to reveal the status of photoinduced charges, so as to provide an solid support on the development of high performance of the semiconductor photocatalyst.