Photocatalytic Performance And Structure-Activity Relation Of TiO₂-based Composite Photocatalysts Synthesized Employing H-titanate Precursors

Engineering TiO2-based composite photocatalysts with surface phase-junctions and heterojunctions is an effective strategy for efficient photocatalysts. In this thesis, TiO2-based composite photocatalysts with various types of surface phase-junctions and heterojunctions have been synthesized by the controlled conversion of H-titanate precursors, and their photocatalytic activity and structure-activity relations in the photocatalytic H2production from water have been comprehensively studied. The main results are:1. A series of heterojunction nanofiber structures were successfully synthesized by a hydrothermal treatment of H-titanate nanofibers and Sr(OH)2in a mixture of ethanol and water. With the Sr(OH)2/H-titanate ratio increasing, the heterojunction nanofiber structures vary from binary TiO2/H-titanate nanofibers to ternary SrTiO3/TiO2/H-titanate nanofibers and eventually binary SrTiO3/H-titanate nanofiber. The selective growth of SrTiO3nanoparticles on the TiO2surface of binary TiO2/H-titanate nanofibers rather than on the H-titanate surface, forming ternary SrTiO3/TiO2/H-titanate nanofibers with a unique sandwich structure. The interfacial charge transfer processes and photocatalytic H2production of various heterojunction nanofibers were studied. The photo excited electrons on the conduction band of both SrTiO3and H-titanate of the sandwich ternary SrTiO3/TiO2/H-titanate nanofibers can efficiently transfer to the conduction of active TiO2in-between and participate the photocatalytic reduction of water to H2, thus the sandwich ternary SrTiO3/TiO2/H-titanate nanofibers are much more photocatalytically active than the binary TiO2/H-titanate and SrTiO3/H-titanate nanofibers. These results reveal that efficient ternary heterojunction photocatalysts require not only appropriate band structures of the components facilitate the interfacial charge transfer but also appropriate geometric structures to facilitate the participation of transferred charges into the surface reactions.2. A series of TiO2photocatalysts with different phase compositions were successfully prepared by varying the HNO3concentration during the hydrothermal treatment of H-titanate precursors. With the HNO3concentration increasing, the phase composition of acquired TiO2varies from pure anatase to anatase-brookite-rutile mixture, brookite-rutile mixture, and eventually pure rutile. The presence of surface phase-junction in TiO2with a mixed phase composition can effectively suppress the charge recombination process and thus significantly enhance the photocatalytic activity. Under the same condition the photocatalytic activity of TiO2photocatalyst consisting of72.9wt%anatase,24.6wt%brookite and2.5wt%rutile is four times as high as that of the commercial P25.3. CuOx/TiO2nanorod composite photocatalysts were successfully prepared employing Cu2+-exchanged H-titanate nanotubes as precursors. The oxygen vacancies formed during the high-temperature transformation of H-titanate into TiO2can reduce Cu2+into Gu2O, forming Cu2O nanoparticles supported on TiO2nanorod; TiO2/Cu2O core/shell nanorod structure can be formed at an appropriate Cu2+loading, and the further increase of Cu2+loading results in the formation of CuO nanoparticles supported on TiO2/Cu2O core/shell nanorod. Among all samples TiO2/Cu2O core/shell nanorods exhibit the highest photocatalytic activity and are very stable. These results demonstrate that CU2O thin film stabilized by the strong TIO2-CU2O interfacial interaction itself can act as an efficient photocatalyst to catalyze the photocatalytic H2production from water.4. NiO/Tio2and Ag0-Ag+/TiO2nanorods composite photocatalyst were successfully prepared employing Ag+-exchanged and Ni2+-exchanged H-titanate nanotubes as the precursors, respectively. The photo-induced reduction of Ag+of Ag0-Ag+/TiO2and Ni2+of NiO/TiO2were observed during the photocatalytic H2production reaction. The promotion effect of Ag SPR effect on the photocatalytic activity of Ag0-Ag+/TiO2were demonstrated by comprehensively comparing their photocatalytic activity under simulated sun light irradiation and the UV light irradiation.