Strategies For Improving The Separation Efficiency Of Photogenerated Carriers Of Photocatalysts And Study Of The Photocatalysis Application

The demand for energy increased with the economic development and the improvement of human living standards.At present,the over exploitation and consumption of fossil energy has caused increasingly serious energy and ecological environment problems.The development and use of green and clean energy is conducive to the sustainable development of human society.Solar energy is an inexhaustible and widely distributed clean and renewable energy,which can be converted to chemical energy using the semiconductor materials for storage.This is expected to solve the current problems of environmental pollution and energy shortage and achieve sustainable development.However,the key scientific issue of low quantum efficiency of converting solar energy into chemical energy limits its practical use.The development of photocatalysts with high activity,high stability and low cost has become the research focus in the field of green energy.The process of converting solar energy into chemical energy catalyzed by semiconductor photocatalysts mainly includes the generation,transport,recombination and reaction of photogenerated carriers.Therefore,the utilization efficiency of photogenerated carriers is crucial to improve the overall efficiency of semiconductor photocatalysts.The main methods to improve the carrier utilization efficiency of semiconductor photocatalysts are:broadening the wavelength range of light absorption,improving the charge conduction performance,reducing the recombination center of electrons and holes,and accelerating the surface catalytic reaction rate.Since the recombination rate of photogenerated carriers(～10^-9 s)is usually much faster than the reaction rate(～10^-3-10^-8 s),it is crucial to improve the separation efficiency of photogenerated carriers.From the perspective to enhance the separation efficiency of photogenerated carriers,the photocatalytic activity of semiconductor photocatalysts can be improved by using supported cocatalysts,coupling strategies of doping,defect engineering and constructing heterojunctions,as well as external pyroelectric field assistance strategy to improve the separation efficiency of photogenerated carriers.The main contents of the paper include:（1）Aiming at the problems of low separation efficiency of photogenerated carriers and slow kinetic rate of oxygen evolution reaction when Zn_xCd_1-xS used as a photocatalyst for overwater splitting,Ho₂Ru₂O₇/Zn_0.5Cd_0.5S loaded oxygen evolution cocatalyst was prepared.The experimental results show that Ho₂Ru₂O₇has higher oxygen evolution ability than that of Ru O₂.When used as a cocatalyst to prepare the photocatalyst,the generated photogenerated holes can be transferred to the cocatalyst,thereby significantly improving the seperation efficiency of photogenerated carrier and the oxygen evolution abiltiy.When used as photocatalyst for overwater splitting,after 5h of illumination,the hydrogen production and oxygen production achieved as high as194.22 and 96.93μmol·g^-1,respectively.This work provides a new idea for improving the catalytic activity of photocatalysts for overwater splitting.（2）Using the coupling strategy of B doping,S vacancies,and Schottky junctions to parepare B-ZCS_v/Cd-T,the seperation efficiency of the photogenerated carriers is improved.When used dye degradation reaction to replace the water oxidation reaction,the photocatalytic ability of the photocatalyst is further improved.The experimental results show that this coupling strategy tunes the band structure of B-ZCS_v/Cd-T and improves the separation efficiency of photogenerated charges.When coupled with the oxidative of Rh B,its photocatalytic activity can be further enhanced.When the optimized catalyst B-ZCS_v/Cd-400 was used for overall dye wastewater splitting,an enhanced photocatalytic abilty with 204.22μmol·g^-1of hydrogen evolution ratte and87.48%of dye degradation efficiency can be obtained.This work provides an adaptable and efficient approach for improving photoactivity through a combined strategy of vacancy engineering,B doping and Schottky junction structures,and by coupling more favorable thermodynamic reactions.（3）In view of the problem that photogenerated carriers are easy to recombine when Bi₂WO₆ is used for CO₂ photoreduction,the strategy of external pyroelectric field is adopted,and the built-in electric field can be generated under the condition of temperature difference due to the pyroelectric field,so as to improve the separation efficiency of photogenerated carriers of Bi₂WO₆,thereby improving its photocatalytic CO₂ reduction performance.The experimental results show that the external pyroelectric field can improve the photogenerated carrier separation efficiency of Bi₂WO₆.Under the synergistic effect of the pyroelectric field and the optical external field,a methanol yield of 115.02μmol·g^-1can be obtained for Bi₂WO₆,which is much higher than that of under a single pyroelectric field(23.63μmol·g^-1)and an optical field(11.39μmol·g^-1).This work provides a new idea for improving the separation efficiency of photogenerated charge carriers in semiconductor catalysts.