| Single crystal TiO2materials have been widely studied and applied in the field of photocatalysis. To date, most studies are focused on the anatase TiO2single crystals in octahedron and decanedron with dominant (001),(101), or (010) facets. Nearly all these TiO2single crystals are used as photocatalysts under UV light irradiation rather than the visible light irradiation due to the large band gap of anatase (3.2eV). To overcome the disadvantages of the single crystal TiO2photocatalysts, this work focuses on the preparation of new single crystal TiO2materials with controllable morphology and pore structure by optimizing the preparation methods and conditions, which are used in photocatalytic reactions concerning dyes degradation, H2production by splitting water, and selective oxidation of alcohols to the corresponding aldehydes. Our research mainly concentrates on the effects of the crystal plane, pore structure, and morphology on the photocatalytic activity. Meanwhile, modification of the single crystal TiO2with CdS quantum dots and Ti3+has also been carried out to achieve highly active visible photocatalysts.The detailed work and the main innovation are divided into the four parts addressed as follows.1. Ordered mesoporous TiO2single crystal with exposed (001) facets as a UV photocatalystSingle-crystal TiO2with2D or3D ordered mesoporous structures and exposed (001) facets were synthesized by SBA-15or KIT-6templated alcoholysis of TiOSO4in the solvent of tert-butyl alcohol under solvothermal conditions. During liquid phase photocatalytic selective oxidation of alcohol to aldehyde under UV-light irradiation, the single-crystal TiO2exhibited much higher activity than the poly-crystal TiO2, since the high crystallization degree favored the transfer of photoelectrons, which might reduce their recombination rate with holes. Besides, the exposed(001) facetsfacets favored the photocatalytic oxidation owing to the high surface energy and the increased oxygen vacancies which reduced the photocharges recombination rate by capturing photoelectrons. Meanwhile, the TiO2with ordered mesoporous structures showed higher activity than that with disordered mesopores, and the3D ordered mesoporous channels were more favalable for photocatalytic oxidation than the2D ordered mesoporous channels, which could be attributed to both the enhanced light harvesting owing to the multiple light reflections in pore channels, and the facilitated diffusion and adsorption of reactant molecules.2. Single crystal TiO2with layered structure and exposed (001) facetsSingle crystal TiO2with layered structure and exposed (001) facets was firstly synthesized by alcoholysis of TiF4in the solvent of benzyl alcohol under solvothermal conditions. The percentage of the (001) facets of the layered single crystal TiO2was about90%. The formation mechanism of the layered single crystal TiO2materials was detailed studied by optimizing the solvothermal conditions. The layered structure was constructed by the self-assembly of the π-π bonding among the benzene rings, and the fluorinion as the stabilizing agent of crystal plane could decrease the surface energy of the (001) high energy facets and stabilize the (001) facets in order to make the layered TiO2with exposed (001) facets. Meanwhile, this synthetic system can be used to prepare the TiO2photonic film, which is assembled by the oriented growth of TiO2nanocrystals. The photonic film with strong plasmonic bands is colored to the naked eye. The layered TiO2photocatalyst displays high photocatalytic activity during the photocatalytic selective oxidation of alcohols to the corresponding aldehydes, due to the high surface area, the high percentage of the (001) facets, and the layered structure enhanced the light harvesting owing to the multiple light reflections between the two adjacent nanosheets.3. TiO2mesocrystal with exposed (001) facets and doped with CdS quantum dots as a visible photocatalyst CdS quantum dots decorated TiO2mesocrystals visible photocatalyst with exposed{001} facets have been firstly prepared by a simple ion-exchange treatment. The Ti O2mesocrystals homogeneously decorated with surface enrichment of CdS quantum dots exhibited significant improvement in photocatalytic selective oxidation of benzyl alcohol and its derivatives under visible light irradiation than pure T1O2mesocages, ascribing to the enhanced light-harvesting capability, the enhanced photosensitizing effect of surface enriched CdS quantum dots and the formation heterojunctions between CdS and TiO2. Meanwhile, the sample prepared by ion-exchange displayed higher photocatalytic activity than those samples prepared by direct-deposited or physically mixed methods, due to the uniform dispersion of CdS quantum dots, the increasing number of heterojunctions, the lower recombination rate of photocharges, and the strong interaction between CdS and TiO2. The mechanism of photocatalytic selective oxidation of alcohols was also investigated by the addition of different scavengers.4. In situ Ti3+-doped TiO2visible photocatalyst in nanosheets with dominant (001) facetsIn situ Ti3+-doped TiO2crystal in mesoporous nanosheets with dominant (001) facets was prepared by supercritical treatment of the precursor obtained from sol-gel hydrolysis of mixed Ti(n-OC4HcH9)4and TiF4. This photocatalyst exhibited high activity in synchronical pollutant degradation and produce H2by water splitting under visible light irradiation owing to synergistic promoting effects. On one hand, the narrowed energy band gap resulted from Ti3+-doping and the high surface area enhanced light harvest and reactant adsorption. On the other hand, the high crystallization degree accelerated electron transfer and thus, inhibited photoelectron-hole recombination. Furthermore, the exposed (001) facets with high surface energy favored the activation of reactant molecules. The photocatalytic degradation of organic pollutants promoted the H2production by consuming photogenerated holes, which inhibited their recombination with photoelectrons used for reducing H+during water splitting. |
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