Study On The Synthesis Of WO₃ And Its Photocatalytic Performance After CuCrO₂ Composite

Photocatalytic water splitting for H₂ production is one of the ideal ways to clean hydrogen production.n-p composite catalysts is a type of photocatalyst with good application prospects.WO₃can absorb visible light,has better stability,and its valence band top potential is more corrected than E_H2O/O2.It is a more promising n-type semiconductor material.Among them,the preparation method and preparation conditions of composite catalyst will affect the combination between the composite monomers and the number of effective composite units,and then affect its photocatalytic performance.The thesis uses sodium tungstate and ammonium tungstate as raw materials,when the molar ratio of inorganic acidifying agent nitric acid to tungsten was 2.8:1.0,WO₃was synthesized by hydrothermal method.By means of X-ray diffraction,scanning electron microscopy and ultraviolet-visible diffuse reflectance,and raman spectroscopy,etc.The effect of types and dosage of auxiliary reagents for organic acids,types of tungsten sources,hydrothermal reaction time,hydrothermal reaction temperature and heat treatment of hydrothermal sampleson crystal phases and morphologies of WO₃were investigated in detail.Further investigation,for the corresponding WO₃and the same batch of CuCrO₂synthesized by the combustion method,the effect of photocatalytic performance of WO₃-CuCrO₂composite catalyst prepared by the same method and conditions.Determined:In the experimental range of this paper,the suitable hydrothermal preparation conditions of WO₃are as follows:Malic acid was used as auxiliary reagent,sodium tungstate as tungsten source,molar ratio of malic acid to tungsten source was 0.8∶1.0,hydrothermal reaction temperature was 200℃,hydrothermal reaction time was 16 h.It is found that the crystallization integrity of WO₃obtained by hydrothermal reaction needs to be improved by heat treatment,so as to improve the photocatalytic hydrogen production activity of WO₃-CuCrO₂.In this paper,the conversion mechanism of WO₃in hydrothermal reaction assisted by malic acid has been discussed,which has not been reported in literature.The paper investigated the effects of the preparation method and preparation conditions of WO₃-CuCrO₂on the performance of the composite catalysts for photocatalytic decomposition of water to produce hydrogen.The suitable conditions for preparing WO₃-CuCrO₂composite catalyst by mechanical grinding method were determined as follows:WO₃solid powder was first treated with an alcoholic solution of nitric acid at p H=6,CuCrO₂solid powder was first treated with an alcoholic solution of ammonia at p H=12,and then,according to the molar ratio of WO₃to CuCrO₂was 1.2∶1.0,the two solid powders were mixed,ground and dried,and then calcined at 500℃for 1.5 h in an air atmosphere.The paper further explores the promotion effect of Ag loading on the WO₃-CuCrO₂photocatalyst,and the effect of Ag loading method and amount on the photocatalytic hydrogen production performance of the composite catalysts were investigated in detail.It was found that Ag has a significant promotion effect on WO₃-CuCrO₂.The suitable Ag loading method and amount are as follows:Respectively on the surface of WO₃and CuCrO₂,loading metal Ag with equivalent to 0.2 wt%of the total mass of WO₃^（6）-CuCrO₂^（12）,and respectively before the final heat treatment of WO₃and CuCrO₂,The corresponding amount of silver nitrate solution was loaded on the surface of WO₃and CuCrO₂by equal volume dipping method.Such loading methods are rarely reported.After loading the WO₃and CuCrO₂,the composite catalyst was prepared according to the aforementioned suitable conditions,and it was recorded as:0.2 wt%Ag/（500℃-2h-WO₃）-0.2 wt%Ag/（800℃-3 h-CuCrO₂）.Finally,the hydrogen production performance of 0.2 wt%Ag/（500℃-2 h-WO₃）-0.2wt%Ag/（800℃-3 h-CuCrO₂）was investigated at the irradiation of 300 W xenon lamp and250 W high pressure mercury lamp.The results showed that the samples have good photocatalytic stability.