Controllable Synthesis And Photocatalytic Activities Research Of Bi₂WO₆

Bi₂WO₆is one of the simplest members （when n=1） of the Aurivillius oxidefamily of layered perovskites with the general formula Bi₂A_n-1B_nO_3n+3（A=Ca, Sr,Ba, Pb, Na, K; B=Ti, Nb, Ta, Mo, W, Fe; and n=number of perovskite-likelayers），and it has many excellent intrinsic physical and chemical properties suchas ferroelectric piezoelectricity, pyroelectricity, catalytic behavior, nonlineardielectric susceptibility, and luminescent properties. It has been recognized as aphotocatalyst for water splitting and pollutant degradation under visible lightirradiation.In the experiments, the different morphologies of Bi₂WO₆samples, thedifferent RMo/Wvalue of Bi₂Mo_xW_1-xO₆solid solutions and the different F-dopedBi₂WO₆-xF2xsamples were synthesized through the template-free approachemploying a hydrothermal process. We studied the influences of the differentsynthesis conditions, the additive concentrations, the doping concentrations onthe morphologies, band gap and the photocatalytic properties, meanwhile,various test methods and analytic tools were applied to analysize themicrostructure and phase composition.（1） Hydrothermal/micro-hydrothermal synthesis of Bi₂WO₆samples. The effectsof surfactants, pH values, the additive concentrations and hydrothermal timeon the morphologies and the photocatalytic properties of the Bi₂WO₆samplesare investigated. The experimental results show that the different surfactantsmay synthesize different morphologies of Bi₂WO₆samples, for example,nest-like structure, flabellate structure, broom-like structure, nanoplates,columnar structure. The change of pH value and the additive concentrationsmay affect the morphologies, crystallite size and uniformity of finalsynthesized samples. There is no evidence of significant change with thedifferent hydrothermal time. The phase composition, the morphologies,structure and the photocatalytic properties are investigated based on of XRD analysis, SEM and TEM observation, FI-IR, UV-vis diffuse reflectancespectrum. The results indicate that the whole samples exhibit absorptionbands in the ultraviolet light region and the visible light region, theas-synthesized nest-like Bi₂WO₆microspheres by the same process of theexperiment exhibit better photocatalytic activity in the degradation of30mlRhodamine-B （RhB） under500W Xe lamp light irradiation.（2） Hydrothermal synthesis of the different RMo/Wvalue of Bi₂Mo_xW_1-xO₆solidsolutions. The morphologies and the photocatalytic properties of the differentRMo/Wvalue of Bi₂WxMo1-xO6solid solutions （RMo/W=0,0.25,0.5,0.75, and1,respectively） are investigated. The phase composition, the morphologies,structure and the photocatalytic properties of Bi₂Mo_xW_1-xO₆solid solutionsare investigated by XRD analysis, SEM, TEM, UV-vis spectrum. The resultsreveal that the morphologies of the as-prepared Bi₂WxMo1-xO6solid solutionstransformed from three-dimensional nest-like microspherical superstructureto two-dimensional nanoplates with the increase of the RMo/Wvalue,meanwhile, it causes significant red shifts of the absorbance band and changethe photocatalytic properties.（3） Hydrothermal synthesis of F-doped of Bi₂WO₆-xF2xsamples. The effects ofadditive concentrations of NaF in the process of hydrothermal synthesisBi₂WO₆microspheres and after as-obtained nest-like Bi₂WO₆microsphereson the morphologies, band gap and the photocatalytic properties of theBi₂WO₆samples are investigated. The phase composition, the morphologies,structure and the photocatalytic properties of Bi₂WO₆-xF2xsamples areinvestigated by XRD, XPS, SEM, FI-IR, UV-vis spectrum. The resultsindicate that the morphology of NaF-doped Bi₂WO₆-xF2xsamples changesignificantly via one step hydrothermal process; the morphology of nest-likeBi₂WO₆microspheres has been destroyed with the increase of NaF-dopedconcentrations. Meanwhile, the band gap occur blue shifts of the absorbanceband and the photocatalytic properties get worse. The morphology ofnest-like Bi₂WO₆microspheres has change hardly via two step hydrothermalprocess, however, the band gap will be narrower and the photocatalyticproperties enhanced with the concentration of NaF.