Preparation Of Oxygen-vacancy Metal Oxide Photocatalyst By Catalytic Combustion Method And Its Hydrogen Production Performance

It is of great significance to design and synthesize semiconductor photocatalyst with controllable defect structure and to reveal the essential role of defects in charge transfer and chemical reaction process.The introduction of oxygen vacancy defects(VO)is one of the most important methods for the effective modification of oxide semiconductor photocatalysts.The reaction conditions for VO formation are often harsh and the formation mechanism is difficult to be clearly revealed,which result in poor universal applicability for constructing VO on general metal oxides.Moreover,it is difficult to control the concentration of VO and the ratio of surface VO to bulk VO.Therefore,it is of great significance to develop a simple method for the controllable introduction of VO into titanium dioxide(TiO2)and other semiconductors for the preparation of defective photocatalysts and clear understanding of the role of VO in the photocatalytic process.The major contents are summarized as follows:(1)We developed a facile anaerobic catalytic combustion method using dichloromethane(CH2CI2)as a reactant to prepare a crystalline TiO2/amorphous TiO2 composite photocatalyst by constructing VO in TiO2 and changing its surface crystal structure.The concentration of VO and the ratio of surface VO to bulk VO were controlled by changing the reaction temperature.The formation of VO,the concentration of VO and the change of the ratio of surface to bulk VO in TiO2 were confirmed by various structural characterizations.The results suggested that the surface VO are first generated on TiO2 at lower temperature and increase gradually with the increase of reaction temperature.Then,the higher temperature activation results in the bulk VO formation in TiO2 and it concentration also increases along with reaction temperature,leading to gradual decrease in the relative concentration ratio of surface/bulk VO in TiO2.The results of activity test and characterization indicated that VO on TiO2 plays a very important role in the photocatalytic process,and the relative concentration ratio of surface VO to bulk VO also has a great influence on the photocatalytic hydrogen production activity.The surface VO on TiO2 induces visible light photocatalytic H2 production activity because it enhances the visible light harvesting capability of TiO2 and provides more adsorption sites for H2 evolution.Besides,the surface VO as the charge carrier trap can facilitate the separation process of photogenerated charges from intrinsic excitation with UV light irradiation,which leads to enhanced UV light photocatalytic activity.However,the bulk VO as the recombination center for the photogenerated electrons and holes can hamper the photogennerated charge separation process,which causes significantly decreased visble light and solar light photocatalytic activities.Furthermore,this strategy has the general applicability for the preparation of VO enriched metal oxides including MoO3,ZnO,and WO3.(2)The Pt/amorphous TiO2/anatase TiO2 composite photocatalyst was prepared by loading Pt cocatalyst on the VO containing TiO2.The photocatalytic hydrogen production activities of the samples under visible light and simulated sunlight were tested,the interaction between Pt cocatalyst and VO defect was studed,and the possible mechanism of photocatalytic hydrogen production of platinized VO containing TiO2 under sunlight irradaiton was proposed.We found that all of the platinized samples show significant enhanced H2 production as compared to their parent samples without platinization.It indicated that there was a synergistic effect between Pt and VO,which further enhanced the solar hydrogen energy conversion of TiO2.Under light irradiation,the core of anatase single crystal can be excited by ultraviolet light to produce photogenerated electrons,which flows to the amorphous shell through the interface of crystalline core/amorphous shell and can be captured by the VO on the TiO2 surface,thus greatly improving the separation efficiency of photogenerated charges.These photogenerated electrons then migrate to the Pt cocatalyst.Meanwhile,the surface VO on amorphous shell induces the visible light harvesting(>400 nm)to produce free electrons and provides adsorption sites for H2 evolution.This study provides a reference strategy for the construction of VO on various metal oxide semiconductors.