Construction Of Defect-Engineered TiO₂ And WO₃ For Photocatalytic Water Splitting

Photocatalysis is a potential technology to solve environmental pollution and energy shortage,but the low solar conversion efficiency limits its further application.Construction of unique architectures can result in the improved light absorbability,and rational construction of defects(such as oxygen vacancies)can enhance the charge transport efficiency.In this work,construction of unique architectures and defects are systematically researched to improve the solar conversion efficiency,which is significant to the development of human society and scientific research.Firstly,the author designed the defect-engineered cage-like TiO₂ hollow spheres by hydrogenation.After the hydrogenation treatment,the cage-like pores and disordered surface layer were in situ generated on the shell of the hollow spheres.Both the multiple reflection improved by the cage-like hollow structures and the narrowed band gap induced by defect engineering can enhance the ultraviolet and visible light absorption.Additionally,the high concentration of oxygen vacancies,as well as the defect-engineered disordered surface layer,can improve the efficiency for migration and separation of generated charge carries.The defect-engineered cage-like hollow spheres exhibit a high hydrogen evolution rate,which are?12 times higher than the hydrogenated TiO₂ solid spheres,?9 times higher than the original TiO₂ hollow spheres.The high activity profits from the unique architectures and defect engineering.Furthermore,the author tailored the quantity and distribution of oxygen vacancies on surface or bulk by tuning the concentration of H₂ during the thermal treatment of WO₃,and clearly demonstrated the function of oxygen vacancies on photocatalytic oxygen evolution in water splitting.Both surface and bulk oxygen vacancies on the catalysts can promote the photocatalytic activity,however,they work in different ways.By narrowing band gap,bulk oxygen vacancies mainly promote absorption of visible light;by lowering the valence band edge,surface oxygen vacancies are efficient to increase charge separation efficiency.Compared with the light absorption,the charge separation is more critical in this photocatalytic process,and thus surface oxygen vacancies play a more decisive role.On the basis of above work,the author synthesized the defect-engineered WO₃ photonic crystals with three-dimensional ordered microporous(3DOM)structure.The red edge of the photonic stop band was easily tuned to match with the WO₃ absorption band.The matched slow photon effect of the photonic crystals enhances the light harvesting.The high concentration of surface oxygen vacancies introduced by H₂/N₂ thermal treatment are favorable to accelerate the generation,migration and separation of charge carriers.The defect-engineered 3DOM WO₃ PCs exhibit a much higher oxygen evolution rate than the defect-engineered WO₃ nanoparticles.Construction of unique architectures and defect is a promising strategy to enhance charge separation and light absorption of photocatalytic system.The author anticipates this strategy may provide new insights or references for designing other efficient photocatalysts.