Synthesis Of Highly Active Facets Exposed TiO₂and Photo-Electrochemical Properties

As the development of human, society and economic, environment pollution and shortage of clean, reliable energies become seriously global problems, which have attracted much attentions in past decades, ecologically clean chemical techniques, materials and technologies are desired to solve the above problems. TiO2, one of the most important semiconductor metal oxide, attracted much attentions again, due to its potential applications in photocatalysis, electrocatalysis, sensors, hydrogen production, lithium batteries, and dye-sensitized solar cells.Highly active facets, as an important research direction of TiO2photocatalysis, the engineering of highly active facets has also attracted much researchers recently. Owing to the minimization of surface energy, highly active facets will diminish rapidly during the crystalline growth process, leaving less active {101} facets as the main facets on the surface. Recently, Yang et al have successfully synthesized {001} facets exposed anatase TiO2nanosheet, using hydrofluoric acid as the surfactant. Comparing with commercial P25,{001} facets exposed anatase TiO2nanosheet exhibited5times higher photocatalysis efficiency. However, most of the engineered highly active facets are {010} facets and {001} facets, few works has been done on other highly active facets. The engineering of other highly active facets and highly active facets exposed nanostructure are still challenging. In this dissertation, we take TiO2as study subject, engineer highly active facets and highly active facets exposed nanostructure, develop photocatalyst and photoelectrode with high efficiency.This dissemination focuses on the engineering of highly active facets and corresponding nanostructure, mainly concerns with the following five aspects:Firstly, TiOF2ball-flowers were successfully synthesized, which consist of both hexagonal and cubic single crystal TiOF2sheets. After an annealing treatment, the hexagonal and cubic single crystal TiOF2sheets were converted to single crystal anatase TiO2sheets dominated with {116} and {001} facets respectively.Secondly, a facile process to synthesize anatase TNSA directly on an FTO substrate, each nanosheet of which was self-organized via the "Oriented Attachment"(OA) mechanism by {116} facet-oriented nanocrystallites. Furthermore, the facets paralleled to the nanosheet surface can be changed from {116} to {001} by varying the precursor. By this scheme, we showed definitely that the {116} facet-oriented TNSA shows50%higher photocatalytic activity than {001} facet-oriented TNSA in the degradation of MB under UV light irradiation.Thirdly, hierarchical TiO2ball-flower structure was synthesized through a facile hydrothermal route. The hierarchical structure was dominated by {116} facets. Furthermore, comparing with P25and {001} facets exposed TiO2nanosheets, the {116} facets dominated hierarchical structure exhibited enhanced both ultraviolet and visible photocatalytic activity.Fourthly, an improved one-step route, in which ethanol was taken as the solvent, while hydrofluoric acid with high relative concentration acted as a hydrolysis monitor and capping agent, was taken to synthesize TiO2on the FTO substrate. The large-area ’nanofishnet’ film self-assembled by single crystalline anatase nanosheets are exposed with {116} facets. The prepared ’nanofishnet’ films showed both enhanced anti-reflection performance and electrochemical properties, which originate from the light-trapping nature and from the high-index exposed facets.Finally, the effect of growth parameters (growth time, growth temperature, precursor concentration, surfactant, etl.) on the light trapping’nanofishnet’ were examined in detail. The electrochemical properties of different light trapping ’nanofishnet’ were also investigated.Based on the above mentioned highly facets engineering and nanostructure constructing of anatase TiO2, highly active {116} facets and corresponding ball-flower/nanosheet array structure were successfully synthesized. The samples exhibited enhanced anti-reflection performance, photocatalysis performance and electrochemical performance respectively. These achievements provide new alternative strategies to engineer highly active facets and design highly efficient photocatalysts/photoelectrodes.