Study On TiO₂ Photocatalytic Oxidation Performance Based On Oxygen Vacancy

TiO2 is one of the most widely studied and most mature photocatalysts in photocatalysis research. The intrinsic parameters of TiO2, such as the electron transport properties of different crystallographic planes, the composition of crystal defects, and the state of adsorbed oxygen, are the key factors that determine its photocatalytic performance. Oxygen vacancy is the core element influencing the transfer pathway of photoexcited electron and the activation type of surface adsorbed oxygen. It has been proved that oxygen vacancy on the surface of photocatalyst can significantly influence the catalytic performance, because oxygen vacancy can not only widen the light response range, but also promote the capture of photogenerated electrons by the surface adsorbed oxygen molecules and thus accelerating the formation of surface active oxygen species. As an important part of surface chemical micro-environment, acid sites can remarkably affect the photocatalytic performance by enhancing the chemisorption capability and promoting the dissociation of intermediates. This thesis is trying to create oxygen vacancies and acid sites on the surface of TiO2, study the influences on photocatalytic performance, and explore the mechanism of photocatalytic reaction.We provided a controllable strategy for creating oxygen vacancies with different distributions and Br(?)nsted acid sites on the surface of anatase TiO2 by a facile immersing and annealing process. The photocatalytic activity was evaluated using the gas phase degradation of toluene as the model reaction. XPS, FT-IR, ESR, TPD and other measurements were used to study the elemental distribution, surface acid sites distribution, surface active species and oxygen adsorption capability. We discussed the influences of the surface chemical micro-environment on photocatalytic activity, and proposed the most possible photocatalytic mechanism.The following conclusions may be drawn from the present work:(1) The modifications of anatase TiO2 by hydrochloric acid and thermal treatments created oxygen vacancies and Br(?)nsted acid sites on the photocatalyst surface, which effectively adjusted of the surface chemical micro-environment, broadened the light response range, and promoted the photocatalytic efficiency. (2) The photocatalytic activity for the gas phase degradation of toluene of modified TiO2 had been remarkably enhanced. The highest degradation rate of toluene was about 60% for 5 hours irradiation, which was 3 times higher than that of unmodified TiO2. (3) By studying the effect of the surface chemical micro-environment of modified TiO2 on photocatalytic activity, a photoexcited mechanism based on the oxygen vacancies of the modified TiO2 was proposed. A synergetic effect of oxygen vacancies and Br(?)nsted acid sites on TiO2 contributes to the great enhancement of visible light photocatalytic activity.The characteristics and innovations of this study are as follows:Providing a controllable strategy to create oxygen vacancies with different distribution and Br(?)nsted acid sites on the surface of anatase TiO2 by a facile immersing and annealing process. We revealed the oxygen vacancies based photocatalytic oxidation mechanism by using the oxidation of organic molecules as the model reaction, and provided a novel idea to elucidate the essence of photocatalytic reaction.