Study On Charge Transfer Process And Surface Reaction Regulation In Photocatalysis

With the rapid development of human society,the energy and environmental issues have attracted increasing attentions and gradually become the two main challenges during sustainable development of human beings.As a renewable and clean energy,the efficient utilization of solar energy is an important guarantee for the sustainable development of society.Photocatalysis is one of the effective ways to directly convert solar energy into chemical energy.However,semiconductor photocatalysis still faces great challenges in inadequate catalytic active site,high recombination rate of photogenerated charges and sluggish surface reaction kinetics etc.Therefore,the efficiency of photocatalysis needs to be improved urgently.In this thesis,by taking charge transfer process and surface reaction regulation in photocatalysis as the main study content,three kinds of photocatalysts with excellent performance were prepared by surface modification strategies such as co-catalyst modulation and Cl^-modification.On the basis of systematic characterization and in-depth study,the mechanism of the improved photocatalytic performance was explored.The specific study contents are as follows:（1）Pt nanoclusters were loaded on the surface of plasma Mo O₂ by impregnation method,which realized the efficient transfer and utilization of hot carriers generated by Mo O₂ to Pt nanoclusters under irradiation.The results show that the composite nano-materials exhibit significantly enhanced plasma effect under illumination,can realize the total conversion of CO at low temperature,and maintain a wide temperature range of the total conversion of CO.Optical studies and in-situ infrared spectroscopy show that upon illumination,the pathway of plasmon-energy decay in Mo O₂ was clarified to selectively dissipate through catalytically active Pt sites in the form of hot carriers,thereby inducing efficient photo-induced CO-PROX reaction.This work provides a useful reference for the design of plasma photocatalytic material system with efficient hot carrier transfer.（2）The effective separation and transport of photo-generated carriers in C₃N₄semiconductor was achieved through the modification of melamine precursor.The results demonstrate that the two-coordinated nitrogen vacancy concentration in C₃N₄can be continuously regulated by Cl^-modification concentration,which remarkably promotes photocatalytic overall water splitting.Over the optimal C₃N₄-Cl4 sample,photocatalytic H₂ evolution and O₂ evolution rates reach 48.2 and 21.8μmol h^-1respectively,which is about 21 times enhancement relative to pristine C₃N₄,and the photocatalyst possesses a good stability.A combination study reveals that the C-Cl bond formed by Cl^-modification of precursor remarkably reduces the formation energy of two-coordinated nitrogen vacancy,realizes the regulation of the selectivity of nitrogen vacancy in C₃N₄,thereby significantly improving the efficiency of separation and transport of photo-generated carriers in C₃N₄.（3）Highly efficient Bi VO₄ semiconductor was prepared by Cl^-surface modification strategy,and the mechanism of Cl^-surface modification in significantly improving the photocatalytic performance was explored.The results show that Cl^-modification not only enhances charge carrier separation,but also remarkably reduces the photocatalytic water oxidation energy barrier and accelerates the kinetics of water oxidation reaction.More importantly,Cl^-modification can act as a cocatalyst to accelerate the surface reaction of photogenerated holes,thereby promoting the photocatalytic water oxidation efficiency.A O₂ evolution rate of 195μmol h^-1 is obtained over the optimal Cl^--modified Bi VO₄（BV-Cl1）under visible-light illumination with AQE reaching 34.6%at 420 nm,which achieves 3.2 orders enhancement as compared with unmodified Bi VO₄（BV）.In addition,the Cl^-modification strategy has good universality and can be applied to other halogen modification and WO₃ semiconductors.This work breaks the traditional Cl poisoning concept in catalysis,and provides a novel viewpoint for designing highly efficient photocatalysts to achieve effective water oxidation.