Design And Photo/Electro-catalytic Performance Study Of Bismuth Vanadates Based Catalysts

Employing solar energy-driven photocatalytic reactions to purify water and using solar/electric energy for nitrogen fixation have emerged as green and high-efficiency approach to tackle with the environmental issues.The fabrication of high-performance catalysts plays the key role in the photo/electrocatalytic reaction.As a mixed metal oxide,bismuth vanadates which possess unique crystalline/band structure and good chemical stability,has been investigated widely.This thesis mainly designs bismuth vanadates based materials with hollow structure,heterojunctions and homojunctions by a simple electrospinning method.The effects of its nanostructure,band alignment,and defects on the photocatalytic activity of as-fabricated bismuth are further investigated.Moreover,amorphous bismuth vanadates and polymeric carbon nitride are designed for the application in photocatalytic Cr?VI?reduction and electrocatalytic nitrogen fixationBiVO₄ nanotubes with hollow interior and mesopores,which endow the nanotubes with enhanced surface areas,are fabricated through an organic salt induced electrospinning gradient method.In contrast with BiVO₄ nanofibers which are fabricated by using inorganic salt,the formation mechanism of nanotubes is determined.When the ratio,composition and amount are changed,the nanotubes still could be obtained,manifesting the universality of as-proposed formation mechanism.The BiVO₄ nanotubes are capable of havesting more light due to the multiple specular reflections of incident light in the interior of the nanotubes.When evaluated as photocatalysts for photocatalytic Cr?VI?reduction,BiVO₄ nanotubes exhibit much better performance compared with BiVO₄ nanofibers,which could be ascribed to the enhanced surface areas and strengthened light havesting ability.By tuning the ratios of solvents and salts during electrospinning process,Bi₂O₃quantum dots?QDs?decorated BiVO₄ nanofibers and Bi₄V₂O₁₁ nanocrystals embedded BiVO₄ nanofibers are fabricated,respectively.The Bi₂O₃ QDs decoration and Bi₄V₂O₁₁ nanocrystals embedding achieve the construction of nanosized heterojunctions.The formation mechanisms of Bi₂O₃ QDs decoration and Bi₄V₂O₁₁nanocrystals embedding are further investigated.The Bi₂O₃ QDs decoration and Bi₄V₂O₁₁ nanocrystals embedding could effectively boost the interfacial charge transfer in as-constructed nanosized heterojunctions,thus realizing rapid separation of photoinduced electrons and holes.Therefore,as-obtained Bi₂O₃ QDs decorated BiVO₄ nanofibers and Bi₄V₂O₁₁ nanocrystals embedded BiVO₄ nanofibers display enhanced visible-light-driven photocatalytic activity for RhB degradation and Cr?VI?reduction than BiVO₄ nanofibers.Through controlling the atmosphere and temperature during the calcination treatment of electrospinning fibers,Bi⁵⁺self-doped Bi₄V₂O₁₁ p-n homojunction and?-?Bi₄V₂O₁₁ homojunction?phase junction?are fabricated,respectively.The Bi⁵⁺self-doped Bi₄V₂O₁₁ p-n homojunction could be obtained when calcined with abundant oxygen.Moreover,abundant oxygen could induce salt migration towards the shell region,hence resulting in nanofibers,which is a new mechanism rather than salt gradient effect for the formation of hollow structure.The?-?Bi₄V₂O₁₁homojunction could be obtained under a suitable calcination temperature.As-fabricated Bi₄V₂O₁₁ based homojunction photocatalysts exhibit remarkably facilitated photogenerated charge carriers separation and transport in contrast with Bi₄V₂O₁₁ without homojunction.Under visible light irradiation,Bi⁵⁺self-doped Bi₄V₂O₁₁ p-n homojunction and?-?Bi₄V₂O₁₁ homojunction photocatalysts achieve superior photocatalytic performance for Cr?VI?reduction.Besides,?-?Bi₄V₂O₁₁phase junction photocatalyst also shows promoted photocatalytic nitrogen fixation performance.The salts with different solubility are employed during the electrospinning process to induce partial salt gradient effect,which is further utilized to fabricate Bi₄V₂O₁₁/CeO₂ heterojunction nanotube photocatalyst with amorphous structure.The amorphous Bi₄V₂O₁₁ possesses multiple defects,leading to effective separation of photoinduced charge carriers in as-constructed heterojunction.In sharp contrast with the counterpart with crystalline structure,the heterojunction photocatalyst with amorphous structure displays much more outstanding photocatalytic properties for Cr?VI?reduction.Furthermore,the multiple defects endow Bi₄V₂O₁₁/CeO₂ nanotube catalyst with adsorption sites for N₂.As a result,Bi₄V₂O₁₁/CeO₂ catalyst with amorphous structure also achieves enhanced electrocatalytic nitrogen fixation performance.When modified by amorphization method,polymeric carbon nitride can own nitrogen vacancies,which leads to the enhanced photocatalytic Cr?VI?reduction and electrocatalytic nitrogen reduction reaction activity.