Investigation Upon Design, Preparation And Photocatalytic Properties Of Bismuth Vanadate Based Photocatalysts

China is a major country of vanadium industry in the world.Both the reserves of vanadium bearing minerals and the output of vanadium products of China rank the toppest in the world.However,manufacture and application of the vanadium products mainly focus on the bulk products in China at present.In order to satisfy the important requirement of sustainable development of China vanadium industry,the vanadium bearing products with high value-added should be exploited as well as the application field of these vanadium products also need to be expanded.Photocatalysis is a procedure where light and catalysts are concurrently used to support or speed up a chemical reaction,which can be used for the degradation of pollutions and water splitting.Bismuth vanadate?BiVO₄?can be active in visible light irradiation,so this vanadium bearing compound is selected as a photocatalyst candidate in present work.The microstructure is designed as well as the preparation process are studied in order to improve the photocatalytic and recycling performance under visible light irradiation for application in the photocatalytic field.Under visible light irradiation,monoclinic bismuth vanadate?m-BiVO₄?sphere and nanoribbon express outstanding photocatalytic activities for the degradation of methylene blue?MB?among the synthesized BiVO₄ samples with different crystal structures,crystal sizes and morphologies.Graphitic carbon nitride?g-C₃N₄?and reduced graphene oxide?rGO?are added in BiVO₄ to form heterostructure systems,respectively.The BiVO₄/g-C₃N₄ and BiVO₄/rGO composite demonstrate faster charge transfer and improved separation of photogenerated charge carriers.Consequently,the photocatalytic activities including degradation rate,degradation speed and durability are enhanced.For the practical application,the reusability problem of BiVO₄ based photocatalysts is solved by introduction of carbon fiber and carbon fiber cloth as supporting materials.The main achievements and innovative progresses are exhibited as follow:?1?BiVO₄ samples are synthesized through the co-precipitation method,sol-gel method and solvothermal/hydrothermal method?with and without surfactants?,respectively.In three methods,only the m-BiVO₄ hollow microspheres?1.5?2 ?m in diameter?fabricated by hydrothermal method achieve high photocatalytic degradation activity of?84%.Localized Ostwald ripening and chemically induced self-transformation mechanism are the main driving force for the formation of hollow spheres.The average crystallite size,specific surface area,hollow interior structure and photocatalytic degradation activity of these BiVO₄ hollow spheres could be tuned by altering the amount of urea.?2?Two different types of m-BiVO₄ are synthesized via hydrothermal method under different experimental parameters including solvent,pH value,precursor,temperature,et al.By using water as a solvent,the m-BiVO₄ spheres consisted of nano-particles were synthesized in the condition of pH=2 at 180 ? after 12 hour,which yield an efficient photocatalytic activity as up to 96%in 4 hours against the degradation of MB under visible light irradiation.However,the degradation rate decreased to 89%after 3 cycles.By using water and ethanol as a mixture solvent?H2O:C₂H₅OH?3:1?,the uniform m-BiVO₄ nanoribbons possessing well-defined 1-D architectures were further synthesized under pH=2 at 180 ? after 24 hours.The obtained m-BiVO₄ nanoribbons show efficient photocatalytic activities up to 97%in 30 minutes against the degradation of MB under visible light irradiation.The photocatalytic activities of m-BiVO₄ nanoribbons also remains stable up to 95%after 3 cycles illustrating a good recyclability,which might be attributed to the higher surface area and better crystallinity.?3?g-C₃N₄ nanosheets are grafted on the surface of m-BiVO₄,in order to further improve the photocatalytic and recyclable performance.Employing the water as solvent,g-C₃N₄ nanosheets are well dispersed on the nanoplates surface of m-BiVO₄ at 100 0C after 12 hours.The photocatalytic activities of the BiVO₄/g-C₃N₄ composite against the degradation of MB under visible light is 98%within 25 min,which is about 2.4 and 1.2 times of the pure g-C₃N₄ and m-BiVO₄,respectively.This BiVO₄/g-C₃N₄ heterostructure material also shows outstanding durability that is?95%degradation efficiency of MB even after eight consecutive cycles.?4?By using solvent of C₂H₅OH:H2O:CH3COOH?3:1:1?,new type core shell heterostructure materials of BiVO₄/g-C₃N₄ and BiVO₄/rGO are synthesized at 180 ?after 10 hours.Due to the incompletely binding between BiVO₄ and g-C₃N₄,BiVO₄/g-C₃N₄ composite shows a lower photocatalytic activities of 84%against the degradation of MB.Comparatively speaking,the photoactivity of BiVO₄/rGO composite upon visible light irradiation is enhanced by yielding superior electronic coupling because of the electron conductivity of rGO.In the BiVO₄/rGO composite,the enhanced separation of photogenerated charge carriers in 3D networks results in superior photocatalytic activities of MB decomposition up to 98%with great reusability.?5?In order to solve the drainage problem during washing after each photodegradation cycle,carbon fiber and carbon fiber cloth are introduced as supporting materials for photocatalysts.After coating on carbon fiber cloth,the obtained samples?BiVO₄/rGO@carbon fiber cloth?show stable degradation efficiency of?95%for MB after two cycles.But BiVO₄/rGO composites start to separate from the surface of carbon fiber cloth after the third cycle.To solve this problem,m-BiVO₄@carbon fiber material is obtained by a new hydrothermal condition with usage of urea as binder and ethylenediaminetetraacetic acid?EDTA?as surfactant.The immobilization of m-BiVO₄ hollow microspheres photocatalyst on the surface of carbon cloth do not reduce the visible light absorption capability with comparison to that of pure m-BiVO₄.Moreover,the m-BiVO₄@carbon fiber composite shows an enhanced reusability up to 92%after three consecutive cycles.Because of the strong mobility of BiVO₄ with carbon fiber,the BiVO₄@carbon fiber with high activity and reusability can be a good solution for the drainage problem.