Study On The Structural Regulation And Photocatalytic Properties Of TiO₂-Based Composites

In this dissertation,anatase titanium dioxide（TiO₂）was selected as the main research object to explore its regulation mechanism of photocatalytic activity by modern material characterization methods,density functional theory calculation and photoelectrochemical research methods.Morphology regulation,crystal plane regulation,heterogeneous interface construction and heterojunction optimization were used as research methods to solve practical problems such as high scattering,poor affinity,easy agglomeration,difficult recovery and low visible absorption of TiO₂in the photocatalytic process.By means of degradation of organic matter,reduction of high-priced toxic ions and decomposition of water to produce hydrogen,efficient and green new energy photocatalytic composite materials were explored and studied.The major conclusions were listed as following.（1）The surface of carbon fiber（CFs）was grown with titanium carbide（Ti C）and titanate as the transition layer to control the microscopic morphology of nano-TiO₂,and a CFs@Ti C/TiO₂composite with good photocatalytic performance was obtained.The immobilization of TiO₂with controllable morphology on the surface of CFs was achieved,which solved the application problems of easy agglomeration and difficult recovery of nano-TiO₂during catalytic use.The feasibility and universality of the method were verified by extended experimental study.The mechanism of catalytic reaction was discussed and put forward,which,as a whole,laid a theoretical foundation for the design of catalyst devices.（2）The effects of different crystal planes on the activation energy,adsorption energy and band gap of TiO₂were systematically studied by theoretical calculation.Results provided a theoretical basis for the improved performance of TiO₂via crystal plane regulation and the improved utilization rate of light by the construction of multicomponent heterojunction to adjust band gap.By regulating the exposure ratio of TiO₂crystal plane with introducing F^-,square TiO₂with highly exposed（001）was obtained,yielding to the formation of the surface heterojunction.A high-quality heterogeneous interface between g-C₃N₄and square TiO₂was constructed by the simple and easily controlled vapor deposition method.A photocatalytic mechanism for the rapid degradation and reduction of organic compounds and hexavalent chromium ions(Cr⁶⁺)in the composites under visible light was proposed under the coupling effect of TiO₂crystal plane regulation and heterojunction.（3）A one-step method was designed to prepare 3D floriform NH₄TiOF₃/TiO₂/g-C₃N₄Z-type photocatalytic composites.The three-dimensional layered structure of the composite and the porous structural properties of NH₄TiOF₃enabled the light to have multiple refractions and reflections within the catalyst,resulting in the improved light utilization efficiency.The introduction of NH₄TiOF₃and TiO₂effectively inhibited the electron-hole pairs（e^--h⁺）recombination in TiO₂.The hydrogen production rate of the composites was 3.6 mmol/g/h,better than that of the same type composites reported before and maintaining good cyclic stability.The formation mechanism of Z-type heterojunction was discussed,and the validity of the proposed material design strategy was verified,which provided a new choice for the development of efficient 3D bionic photocatalyst.（4）Using NH₄TiOF₃/TiO₂/g-C₃N₄as raw material,the one-step assembly of Au NPs and CQDs on the catalyst surface was realized in the hydrolysis process of NH₄TiOF₃to TiO₂,and the quaternary composite of g-C₃N₄/TiO₂/CQDs/Au with effective e^--h⁺separation,good e^-transfer,suitable band gap and good utilization of visible light was prepared.The aforementioned composite showed excellent hydrogen production performance（5.6 mmol/g/h）in the process of simulated solar catalysis pyrolysis of aquatic hydrogen,attributing to the construction of Z-type heterojunction and coupling role of each component.The reaction path and photocatalytic mechanism of the material preparation were discussed and revealed.（5）Nitrogen doped（N-doped）improved the adsorption performance and visible light absorption of TiO₂,thus improved the photocatalytic performance.And the validity of the improved adsorption and catalytic performance of TiO₂via N-doped was verified by the photocatalytic degradation of tetracycline hydrochloride（TC）and the hydrogen evolution from water.Platinum nanocrystals（Pt NCs）were obtained by photoreduction and adsorption of Pt ions by N-doped TiO₂.Combined with theoretical calculation,the role of Pt NCs was discussed.The strong interaction between N-doped TiO₂and Pt NCs in the physical adsorption limit was confirmed by XANES,which happens to overcame the poor catalytic stability of Pt supported on TiO₂.The photocatalytic hydrogen production rate was 22.6 mmol/g/h,112 times that of pure TiO₂and the catalytic activity still remained at the high level after 72 h long cycle test.