| The use of BiVO4 as a photoelectrode catalyst for photoelectric conversion and photocatalytic hydrogen was limited due to small light absorption range, low photoelectric conversion efficiency. The most effective way to solve the problems is using composite semiconductors with heterojunction.CuWO4 film, BiVO4 film and CuWO4/BiVO4 composite film were prepared by sol-gel method. The effect of preparation process on sol viscosity, the film surface structure, morphology was researched by using viscometer, optical microscopy, X-ray diffraction, scanning electron microscopy, UV-visible spectrometer and other testing methods.1. CuWO4 film is prepared by sol-gel, a detailed study in the influence of process parameters, the following conclusions:(conclusions are as following)1) high-quality surface film can be obtained by Spin Coating Method at 2000r/min.CuWO4 precursor film was disposed for 60 mins and then dried, the drying process can increase the effect of the removal of organic matter; the optimal fiim was obtained with the rate of rising temperature at 1℃/min～2℃/min.2) the effect of heat treatment time was compared with the temperature rising to 550℃ at 1℃/min the intensity of CuWO4 phase diffraction peaks significantly increased with insulation for 3h, which indicated better crystallization of CUWO4 phase rapid cooling method goes against crystallization of CuWO4 phase as the diffraction peak intensity is lower; the structure and morphology of CuWO4 film coated on three different substrates (FTO conductive glass, quartz glass, ordinary glass) were comparative analysis; which shows the best crystallization on FTO substrate with larger grains and presence of (111) preferred orientation.3) A high-quality CuWO4 film can be obtained by following procedures:coated on FTO substrate by spin coating method at 2000r/min, dried for 120mins at 100℃ after stilled for 60mins, heating to 550oC at 1℃/min～2℃/min, annealed for 3h then cooled down with the furnace temperature2. In this paper, BiVO4 film are prepared with Sol-Gel method. The influence of the preparation process parameters are studied. The main conclusions are as follows:1) When the sol precursor of BiVO4 added CMC-Na, and the ratio is 1:100, the viscosity increases to 2.3891×10-3 Pa·s, at this time, the sol can be uniformly spread on the substrate, thus get the best results; After BiVO4 film been heat treated, uniformity of the film are improved with the method of dipping tyra, with the increase of immersion time of the sol, the grain of BiVO4 film gradually increases,and the intensity of the diffraction peaks are significantly increased, the best re-impregnation growth time range from 3h to 5h; Rapid cooling is not conducive to crystallization and grain growth of the BiVO4 film.2) With the method of spin coating, when the spin coater speed is 2000r/min, and added CMC-Na sol solution with the ratio of 1:100 to the FTO substrate, dried at the conditions of 60℃ 120 min, then heat up to 550℃ with the speed of 1℃/min～2℃/ min,and preservation 3 hours, then been furnace cooling, and then put into the sol solution, dipping 5h, it can get good quality of BiVO4 film after heat treatment3.Using "layer by layer" prepared with different structures and multilayer composite film composition, and its constituent units in basic research XRD patterns and surface topography on the study of UV-Vis spectra of composite films, the following results:1) Compared with the single BiVO4 film grown on the FTO substrate, the film grown on CuWO4 presenting higher peak intensity in the (121),which has evident preferred orientation, on the FTO substrate, the monolayer CuWO4 film has good crystallinity, and presents substantially hexahedral shape.Besides, BiVO4 film grain predominantly in olive-shaped, appears very small amount,almost no hexahedral shape grains, and with worse crystallinity than the former.However,the CuWO4 grains grown on BiVO4 presents more regularly hexahedron shapes and much higher degree of density, which is compleletiy different from that grown on FTO.2) The absorption of Single CuWO4 film in visible light ranges from 493nm to 530nm.If CuWO4 films are increased to five layers, which will appeares slightly red-shifted absorption range.Single BiVO4 effective absorption in visible light ranges from 485nm to 570nm, when increased to 5 BiVO4 layer, the absorption range of obvious red shift3) Both BiVO4 and CuWO4 different combinations films influence the absorption spectrum. BiVO4 layer composited on CuWO4 film will make absorption edge red-shifted obviously. BiVO4 continue to increase the number of layers to four, while continuing to absorbred shift, but the absorption coefficient decreased;4) In general, five BiV04 films make the absorption edge redshift most obviously, but four BiVO4 layers+1 CuWO4 layer composite film has the highest absorption coefficient in the range of 420～700nm. |
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