Construction Of Oxygen Vacancy And Metal Site On Two Dimensional Bismuth Oxybromide Semiconductor For Photocatalytic Molecular Oxygen Activation

Molecular oxygen（O₂）,an environmental friendly and cost effective oxidant,plays a significant role in various organic oxidation reactions.Sunlight-driven activation of O₂ on semiconductors provides an appealing strategy to reduce the consumption of fossil fuels and carbon dioxide emission via capturing solar energy into chemicals.However,there are a number of problems for traditional semiconductors（for exampe,BiOBr）,such as poor light absorption,severe recombination and low migration rate of photogenerated carriers,and insufficient adsorption of O₂.These shortages hinder the wide application of the semicondutors in photocatalytic oxidations.To address the above issues,oxygen vacancy and metallic active site are successfully constructed on the surface of BiOBr for regulating the band structure,photogenerated charge kinetics,and the charge/energy transfer during the activation of O₂.As a result,highly efficient and selective O₂ activation is achieved for enhanced photocatalytic organic oxidations.The main contents are as follows:1.BiOBr nanosheets with/without oxygen vacancies(BiOBr _OV/BiOBr)are fabricated for photocatalytic aerobic oxidative coupling of amines.It turns out that oxygen vacancies can effectively promote the separation of photogenerated electron-hole pairs and the adsorption of O₂,thereby facilitating the activation of O₂and enhancing the catalytic performance.2.By virtue of the strong O-bonding capacity,Fe sites are anchored on the BiOBr _OV(BiOBr _OV-Fe)for promoted activation of O₂.Notably,the reactive oxygen species（ROS）are altered from both superoxide anion radical and singlet oxygen to singlet oxygen only with increased production rate after the introduction of Fe sites.As revealed by the photo/electrochemical characterizations,the Fe sites can not only accelerate the separation and migration of photogenerated carriers,but also promote the adsorption of O₂.As a step further,low-temperature time-resolved phosphorescence spectra and X-ray photoelectron spectra/electron paramagnetic resonance spectra under illumination are employed to gain in-depth understanding on the enhanced singlet oxygen production.The results indicate that the Fe species can boost the quantum yield of excited triplet state and accelerate the energy transfer from excited triplet state to adsorbed O₂ via a chemical loop of Fe³⁺/Fe²⁺,thereby achieving highly efficient and selective generation of ¹O₂.As a result,the versatile iron sites on defective BiOBr nanosheets contributes to near-unity conversion rate and selectivity in both aerobic oxidative coupling of amines to imines and sulfoxidation of organic sulfides.