Modulation Of Bi₂WO₆ By Ethylene Glycol And Photocatalytic Performance Study

Photocatalysis is an effective means to address environmental pollution,energy crisis and health threats.The research on performance-efficient photocatalytic semiconductor materials has become a hot research topic.Bi₂WO₆（BWO）is a layered chalcogenide structure with a narrow band gap that gives it better photoresponsiveness,and the built-in electric field between the[Bi₂O₂]²⁺and[WO₄]^2-layers facilitates the migration and separation of photogenerated charges.This makes BWO one of the most widely studied photocatalytic materials today.In this thesis,the modulation of BWO morphology by EG was investigated by adjusting the EG content and preparation process.When the volume ratio of EG to glacial acetic acid was 1:3 and the solvent heat temperature was 120℃,the 120℃BWO samples were stacked in the form of discus-like agglomerates.The fine round cake particles possess a large specific surface area,short charge transfer path and suitable stacking pore structure,which will be beneficial to the photocatalytic reaction efficiency.In contrast,the excess EG increased the viscosity of the solution and reduced the synthesis reaction rate,and the sample particles existed as biconcave cake agglomerates of larger volume,which inhibited the photocatalytic activity instead.In this thesis,primary and secondary solvothermal reactions were designed to investigate the modification of BWO structure by EG.Combined with XRD,XPS,HRTEM and EPR tests,it was determined that the metal Bi produced by EG reduction was located in the interior of the BWO crystal and on the surface of the nanosheet,respectively.The internal metallic Bi will become a new charge trapping center,and it is difficult for the charge to migrate to the catalyst surface to participate in the reaction,and the photocatalytic activity of the sample is inhibited.The surface metallic Bi modified Bi-BWO samples have the best photocatalytic performance.This is attributed to the oxygen vacancies etched out on the surface and the metallic Bi,the electrostatic field and SPR effects together promote the carrier transfer and separation efficiency.Meanwhile,the altered energy band structure also enhances the reduction of photogenerated electrons.In this thesis,the inhibitory effect of internal defects on photocatalytic activity was verified using Fe elements.Comprehensive tests show that the introduced Fe element does not change the crystal structure of BWO by replacing Bi³⁺or W⁶⁺ions,but is reduced to a lower valence state by EG in the form of Fe WO₄ iron-oxygen compounds.The photocatalytic activity of Fe-BWO samples is inhibited by the Fe WO₄ phase induced to produce more grain boundary defects;occupy the potentially optically active volume of BWO;cover the surface active sites of the catalyst.This experiment further demonstrates that the modification of the internal structure of BWO by EG is negative and has implications for the modification studies of transition group metals.