Preparation Of FeOOH/BiOBr With Light-switchable Oxygen Vacancies And Performance For Photocatalytic Oxygen Evolution

Photocatalytic water splitting utilizing solar energy to obtain hydrogen and oxygen is an effective way to solve global environmental problems and energy crises.Overall water splitting consists of two half reactions:oxygen reduction reaction（OER）by photogenerated holes and hydrogen evolution reaction（HER）by photogenerated electron.Among them,OER involves complex four electron-transfer processes with sluggish kinetics,thus it has been regarded as the rate-limiting step and has an important factor affecting the development of water splitting technology.Therefore,researchers are committed to developing a low-cost and high-efficiency oxygen evolution photocatalyst for promoting the efficient and rapid process of photocatalytic water splitting.Bi OBr photocatalysts has attracted much attention for photocatalytic oxygen evolution reaction due to its unique layered structure,favorable price,non-toxic and friendly to environment.Meanwhile,it has excellent oxygen evolution activity and stability because of its valence band location satisfy the requirements of oxygen evolution.However,the activity of pure Bi OBr photocatalysts is still limited by the weak light response ability and low separation efficiency of photogenerated carriers,so finding a simple and effective regulatory strategy to prepare highly active Bi OBr basal photocatalysts has become the focus of research in this field.（1）Preparation and photocatalytic oxygen evolution performance of light-switchable oxygen vacancies Bi OBrA series of Bi OBr photocatalysts were prepared by a simple one-step alcoholysis method through adjusting synthesis temperature（20、40、60、80℃）using bismuth nitrate pentahydrate as bismuth source and sodium bromate as bromine source.The oxygen evolution activity of different Bi OBr had been evaluated under simulated sunlight.The formation,recovery and content of oxygen vacancies on the surface of the catalysts were analyzed by UV-vis diffuse reflection spectroscopy（UV-vis DRS）and Electron paramagnetic resonance（EPR）.The results show that in the process of photocatalytic water splitting,the prepared catalyst could produce oxygen vacancies under light conditions,and the content of oxygen vacancies gradually increases with the decrease of the preparation temperature;when the light was turned off,oxygen vacancies on the surface of the catalysts will disappear in the presence of water and air,so that the catalyst can be restored.The formation of oxygen vacancies not only can effectively improve the light response ability of Bi OBr,but also form defective states on the surface of Bi OBr,thereby capturing part of the photogenerated electrons and inhibiting the direct recombination of electrons and holes,ultimately resulting in higher oxygen evolution performance.However,excessive OVs will become the recombination centers of carriers,thus reducing the photocatalytic performance.Therefore,the oxygen evolution performance of samples reached the highest value of 166.2μmol g^-1 h^-1 at 60^oC.（2）Preparation of Fe OOH/Bi OBr with light-switchable oxygen vacancies and performance for photocatalytic oxygen evolutionIn order to further improve the photogenerated electron-hole pairs separation efficiency of Bi OBr catalyst with light-switchable oxygen vacancies,the cocatalysts Fe OOH as the hole transport layer was used to form Fe OOH deposited on Bi OBr with light-switchable oxygen vacancies by a simple chemical deposition method.The oxygen evolution activity of samples had been evaluated under simulated sunlight.The results show that amorphous Fe OOH was successfully loaded on Bi OBr with light-switchable oxygen vacancies,and a strong intimate interface contact between Fe OOH and Bi OBr was formed.As a result,in the process of photocatalytic water splitting,the photogenerated electrons generated by Bi OBr were captured by the light-induced oxygen vacancies and then react with the sacrificial agent;while,the photogenerated holes of Bi OBr was transmitted to Fe OOH to participate in oxygen evolution reaction from water.Therefore,the separation efficiency of photogenerated electron-hole pairs and the oxygen evolution performance of samples was increased with the addition of Fe OOH.The maximum OER rate was 252.34μmol g^-1 h^-1,which was 1.52 times that of the pure Bi OBr.