Surface Modification Of BiOBr And Its Effect On Photocatalytic CO₂ Reduction Performance

The overuse of fossil fuels and excessive carbon dioxide emissions cause serious en-ergy problems and environmental crises.Photocatalytic technology is considered to be an ideal technology for carbon dioxide resource utilization,which can convert carbon dioxide into renewable hydrocarbons by using sunlight and photocatalytic materials.The improve-ment of solar energy utilization and photocatalytic efficiency is the primary task of photo-catalytic technology research.V-VI-VII ternary oxide semiconductors BiOX?X=Cl,Br,I?with special lamellar structure are considered as a novel and efficient photocatalyst.Among them,BiOBr materials have attracted much attention due to their advantages of suitable band gap energy and visible light responsiveness.In this thesis,the research progress of bismuth oxyhalide photocatalysis materials is reviewed firstly.Then,semiconductor modi-fication,defect and co-catalyst strategies are used to modify BiOBr photocatalysts to im-prove its photo catalytic activity and selectivity in carbon dioxide photocatalytic reduction reaction.The formation process of modified sites and its mechanism in photocatalytic proc-ess were studied.The main works can be summarized as follows:1)Simultaneous phosphorylation and Bi modification are successfully introduced into BiOBr hierarchical spheres via a solvothermal reaction using red phosphorus as the additive.Remarkably,the synchronous phosphorylation and Bi modification of BiOBr lead to an im-provement of CO₂ conversion efficiencies.Different characterization techniques were per-formed to explore the existence form of P and Bi modification,the essence behind such an enhancement.The results showed that the nonmetal phosphorus promoted the formation of bismuth metal as reducing agent in the hydrothermal process,and at the same time,bismuth phosphate was formed by the reaction of phosphate and bismuth ion.The metal Bi modifica-tion could enhance the light harvesting,meanwhile,it could change the reaction path of CO₂photocatalytic reduction reaction and improve the selectivity of CH₄.Furthermore,the exis-tence of BiPO₄ could improve the separation efficiency of photogenerated carriers.Under the synchronous BiPO₄ and Bi modification,the activity and hydrocarbon selectivity of BiOBr in photocatalytic CO₂ reduction reaction were effectively improved.2)Based on the perspectives of enhancing the adsorption of reactants and the electron density of photocatalyst,surface oxygen vacancies and metal bismuth synchronously modi-fied BiOBr photocatalyst was synthesized via the surface reduction of NaBH₄ solution.The existence of oxygen vacancies and metal bismuth was confirmed by solid-state electron spin resonance and X-ray diffraction;photochemical and electrochemical characterization tests showed that modification of oxygen vacancies and metal bismuth could effectively improve the absorption of visible light and the separation of photo-generated electrons and holes of BiOBr.CO₂ adsorption-desorption experiments showed that this dual-modification method could effectively enhance adsorption of the CO₂ and increase the active site during the photo catalytic reaction.Thus,the photocatalytic activity and conversion of CH₄ was improved effectively.