Based On Supercritical Technology, New Type Of Tio <sub> 2 </ Sub> Preparation And Modification Of Its Photocatalytic Properties

Much attention has been paid for heterogeneous photocatalysis owing to its potential application in many areas, especially in the treatment of environmental pollutants. Among various semiconductor photocatalysts, TiO₂ is most frequently employed because of its non-toxic, low cost, high activity and strong stability in aqueous media. Usually, TiO₂ particles are prepared Sol-Gel method followed by a drying process. However, the direct calcination of the TiO₂ gel usually causes gathering of small particles and more severely, the collapse of pore structure, resulting in the poor photocatalytic activity. The modification of TiO₂ with metal and nonmetal additives is widely used to improve the photocatalytic activity. If the combination between the additives and TiO₂ is not strong enough, these additives may leach off during the photocatalytic reactions. In this thesis, the TiO₂ samples doped with different metal additives were prepared by sol-gel method and the TiO₂ samples doped with non-metal additives were prepared by treating the precursors under supercritical condition with NH₃/ethanol fluid. We also prepared TiO₂ samples with large surface area by surfactant self-assembly method followed by treating under supercritical conditions with either ethanol or CO₂ fluid which may result in the mesoporous TiO₂ samples. The photocatalytic degradation of phenol in aqueous solution is used as a probe to evaluate their photocatalytic activities. XRD, XPS, TEM, SEM, BET, FLS, RAMAN, FTIR, nitrogen adsorption-desorption were used to characterize these photocatalysts. The relationships between photocatalytic performances and structural characteristics or surface electronic states were discussed briefly. The followings are the details:1. The undoped and the La³⁺-doped TiO₂ catalysts obtained from the sol-gel process with or without ultrasonic irradiation followed by supercritical drying have well crystallized anatase phase, higher surface area, larger pore size and pore volume and more oxygen vacancies and/or defects, which were favorable for the photocatalytic degradation of phenol. The modification of La³⁺-dopant could enhance...