Hydrothermal Fabrication Of BiVO₄/Diatomite Composite Photocatalysts And Their Photocatalytic Performance

Current industrial development has led to serious energy and environmental crises,and photocatalysis has provided an effective solution to this problem.In practical application,traditional oxide TiO2 photocatalyst has been widely studied.However,the wide band gap limits its absorption of visible light,and so the study on narrow band gap photocatalysts has become a research hotspot.Catalysts containing bismuth,such as Bi2O3,Bi2S3,Bi2Ti2O7,Bi2WO6 and BiOCl,generally have narrow band gaps and respond to visible light.Monoclinic BiVO4 is a good visible light photocatalyst with a band gap of 2.4eV,and diatomite has a porous structure which is considered as a good catalyst carrier.To the best of our knowledge,there have been few studies on a BiVO4/diatomite composite photocatalyst.In this thesis,the research work is mainly focused on their hydrothermal preparation and photodegration performance.The results and conclusions are as follows:(1)EDTA-assisted hydrothermal process was used to prepare BiVO4 visible light photocatalyst.The effects of pH value of precursor solutions on the crystallization,morphology and photocatalytic performance of the as-prepared samples were investigated.The results show that BiVO4 obtained under moderate acidic conditions has better photodegradation performance,while BiVO4 produced under strong acidic and neutral conditions has worse photodegradation performance.Therefore,when the hydrothermal temperature is 180℃ and the holding time is 5h,the pH ranging from 3 to 5 is the optimal process conditions for EDTA-assisted hydrothermal preparation of BiVO4 photocatalyst.(2)BiVO4/diatomite visible light photocatalyst was prepared by EDTA-assisted hydrothermal method.The influence of the content of diatomite in the composite photocatalysts on their photocatalytic performance was studied in detail.The results show that their photocatalytic performance increases first and then decreases with the increase of diatomite content.At 15wt%diatomite content,BiVO4/diatomite composite photocatalyst exhibits the best photocatalytic performance.(3)Deposition of metal Ag on BiVO4/diatomite composite photocatalysts was also studied.The effects of different Ag-loaded amounts on their photocatalytic performance were revealed.The results show that the photodegradation efficiency can be improved by the deposition of Ag to a certain extent,but the overuse of Ag would also decrease the photodegradation efficiency.