| Environmental pollution and energy crisis are the two major issues that couldaffect the survival and development of human society. TiO2shows unique advantagein the field of photocatalytic due to its excellent optical properties, chemical stability,as well as low cost. However, the application of TiO2is limited by its high band gapenergy (3.0and3.2eV for the rutile and anatase phases, respectively), high carrierrecombination probability and poor adsorbing affinity toward organic molecules.In-situ preparation of anodized TiO2nanotube arrays (TiO2NTs) on titanium substratewas proposed in this project. To improve its quantum efficiency and photocatalyticproperties, TiO2NTs were modified with narrow bandgap semiconductor, preciousmetal, and graphene, respectively. The composite photocatalysts played an importantrole in the photocatalytic oxidation of organic pollutant, photocatalytic reduction ofheavy metal as well as photocatalytic conversion of carbon dioxide (CO2). The detailsare listed as follows:(1) TiO2NTs with highly ordered structure were prepared by anodizing processand crystallized by calcination treatment. Three dimensional (3D) Bi2S3crystals wereprepared onto the TiO2NTs in ethylene glycol (EG) solvent by pulsedelectrodeposition technique. The optimal preparation conditions of well-crystallizedBi2S3nanomaterials with ideal morphology were investigate by alterring parameterssuch as temperature, voltage and time.3D Bi2S3nanomaterials with uniquemorphology could be achieved when the deposition voltage was-1V or-2V and thetemperature ranged from120℃to125℃. However, in a certain range, thedeposition time had little impact on the morphology of Bi2S3and it mainly influencedthe deposit amount of Bi2S3crystals.(2) Single crystalline, three dimensional white fungus-like mesoporous Bi2S3crystals were modified onto the TiO2NTs in dimethyl sulfoxide (DMSO) solvent bypulsed electrodeposition technique which constructs a unique heterojunctionphotocatalyst bearing large surface area and high adsorbility. The Bi2S3/TiO2catalystshows intense absorption in the visible range due to the narrow bandgap of Bi2S3.Under irradiation of solar light, a high efficiency in simultaneously photocatalyticpurification of2,4-dichlorophenoxyacetic acid (2,4-D)/Cr(VI) contaminated waterwas obtained by employing the Bi2S3/TiO2NTs as photocatalysts.2,4-D, a stable andtoxic aromatic compound, can be effectively decomposed by the hydroxyl radicals initiated by photogenerated holes on the Bi2S3/TiO2whilst highly poisonous Cr(VI)can be reduced to Cr(III) by accepting the electrons and reacting with the byproductsfrom2,4-D degradation.(3) Graphite oxide was initially prepared from graphite powder according to themodified Hummer’s method and was exfoliated to form a homogeneous grapheneoxide (GO) colloidal dispersion. Graphene film was formed on the surface of TiO2NTs (EG-TiO2NTs)through in-situ electrochemical reduction of the graphene oxidedispersion by cyclic voltammetry. Then a stable Pd-EG-TiO2NTs compositephotocatalyst was prepared by successive pulse electrodeposition of the preciousmetal palladium (Pd) onto the surface of graphene film. Due to the excellent electrontransport properties of Pd and graphene as well as the strong adsorption ability ofgraphene film, the new catalyst exhibited significant photocatalytic activity inconversion of carbon dioxide (CO2) to methanol, which made it possible tosimultaneously solve the energy and environmental issues and realized a efficientreuse of CO2. |
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