Controllable Preparation And Photocatalytic Properties Of Novel Types Of Semiconductor Photocatalysts

This dissertation was committed to study preparation, characterization andphotocatalytic properties of novel types of semiconductor photocatalyticmaterials. The main research work is listed as follows:（1） The octahedrons-, cubes-and nanoplates-shaped single-crystalNaY（MoO₄）₂were successfully synthesized through tuning amounts ofNa₂MoO₄under hydrothermal conditions at180^<sup>oC for20h, free of organicadditives, seeds and templates. The as-synthesized single-crystal NaY（MoO₄）₂were characterized by field-emission scanning electron microscope （FE-SEM）,energy-dispersive X-ray （EDX）spectroscopy, X-ray diffraction （XRD）, trans-mission electron microscopy （TEM）, Brunauer-Emmett-Teller （BET） specificsurface area and UV-vis diffuse reflectance spectroscopy in detail. Theformation process of nanoplates single-crystal NaY （MoO₄）₂was investigatedthrough XRD analysis and SEM observations of the intermediate products atdifferent reaction stages. The photocatalytic properties of the as-obtainedoctahedrons、cubes、nanoplates and P25were compared. The results indicatedthat the as-obtained products showed a morphology-dependent photocatalyticactivity on degradation of Rhodamine B under visible-light irradiation and thesingle-crystal NaY （MoO₄）₂nanoplates with93%of {001} facets exhibitedeven much higher photocatalytic activities than commercial P25. To the best ofour knowledge, this is the first time double alkaline rare-earth molybdatehasbeen used as a photocatalyst for dye degradation under visible-light irradiation.The photocatalytic mechanism of single-crystal NaY （MoO₄）₂was proposed onthe basis of crystal structure analysis, theoretical calculation, and the result ofphotocatalytic experiment as well. （2） The nanoscale NaBi（MoO₄）₂and AgBi（WO₄）₂were successfully synthe-sized under simple hydrothermal conditions at200^<sup>oC for20h. The as-obtainedNaBi（MoO₄）₂and AgBi（WO₄）₂products were characterized by XRD, FE-SEM,EDX spectra and UV-vis diffuse reflectance spectroscopy in detail. It was foundthat the pH values of aqueous solution have important influences on themorphologies of the resultant products. We researched the water splittingactivity of the nanostructured NaBi （MoO₄）₂and AgBi（WO₄）₂under Xe lamplight irradiation. Combined with theoretical calculations of energy band-edgepositions of the two semiconductors, the mechanism of photocatalytic splittingwater was proposed.（3） The BiOI nanoplates dominated by high-energy {001} facets weresuccessfully synthesized under simple microwave reaction conditions. Then,BiOI/AgI and BiOI/Ag2O composite photocatalysts were synthesized underphotoreduction and ultrasonic chemistry conditions, respectively, using as-prepared BiOI as supports. The as-obtained BiOI/AgI and BiOI/Ag2O productswere characterized by FE-SEM, EDX spectra, XRD, and UV-vis diffusereflectance spectroscopy in detail. The photocatalytic properties of the as-obtained BiOI, BiOI/AgI and BiOI/Ag2O were studied. The results indicatedthat the as-obtained composite photocatalysts products exhibited much higherphotocatalytic activities than pure BiOI on the degradation kinds of dyes andeven phenol. The mechanisms of enhanced photocatalytic activity of BiOI/AgIand BiOI/Ag2O were proposed on the basis of theoretical calculation.