Preparation Of Tungsten Oxide-based Semiconductor Heterojunction Photocatalysts And Their Photocatalytic Properties

In recent years,energy shortage and environmental pollution have become increasingly serious issues and the focus of attention in the world.As one of the most promising solutions to solve these problems,semiconductor photocatalysis has aroused people’s great attention because it is an energy-saving,clean and pollution-free‘green’technology.However,a single semiconductor photocatalyst always has a series of problems such as low mass transfer efficiency and fast photogenerated electron-hole pairs recombination.Therefore,finding an effective way to solve such problems has far-reaching significance for the improvement of photocatalytic performance.Studies have found that when a semiconductor is combined with other materials（such as other semiconductors,metals,or carbon materials,etc）to form heterostructures,the composites can rapidly transfer photo-generated carriers,reduce the recombination of photo-generated electron-hole pairs,and effectively improve the mass transfer efficiency,thus enhance the photocatalytic performance of the semiconductors.This study focuses on the tungsten trioxide（WO₃）-based semiconductor composite photocatalysts.Through simple room temperature precipitation method,calcination method and hydrothermal method,two kinds of semiconductor-semiconductor heterojunction photocatalysts are designed and synthesized,and XRD,XPS,TEM,SEM,HRTEM,PL,UV-vis DRS and other characterization methods are used to examine the phase structure,morphology and light absorption of the photocatalysts.Through the degradation of pollutants in aqueous solution under the visible light irradiation,the photocatalytic performances of the photocatalysts are investigated.The specific results are as follows:（1）Ag₂WO₄/WO₃ heterojunction photocatalyst is prepared by combining simple hydrothermal method and room temperature precipitation method,and its phase structure,morphology and light absorption are characterized.The results show that we have successfully synthesized Ag₂WO₄/WO₃ heterojunction photocatalyst without any impurities.The Ag₂WO₄ nanoparticles are evenly distributed on the surface of WO₃naosheets,and the catalyst has good light absorption in the visible region.Through the degradation of pollutants RhB and MO in aqueous solution under visible light irradiation we study the performance of Ag₂WO₄/WO₃ heterojunction photocatalyst.The photocatalytic mechanism and cyclic stability of the photocatalysts are also investigated.The results show that the Ag₂WO₄/WO₃ heterojunction photocatalyst shows good photocatalytic performance and cycle stability.The main active species in the photocatalytic degradation process are h⁺and·OH.（2）The WO₃/g-C₃N₄ heterojunction photocatalyst is prepared by combining simple calcination method and hydrothermal method,and its phase structure,morphology and light absorption are characterized.The results show that we have successfully synthesized WO₃/g-C₃N₄ heterojunction photocatalyst with good morphology.The WO₃ nanosheets are contacted with the g-C₃N₄ nanosheets to form an effective heterojunction,and the catalyst has good absorption in the visible light region.Based on the model of photocatalytic degradation of pollutants RhB under visible light irradiation,we study the properties of WO₃/g-C₃N₄ heterojunction photocatalyst,and discuss the photocatalytic mechanism and cycling stability.The results show that the WO₃/g-C₃N₄ heterojunction photocatalyst shows good photocatalytic performance and cycle stability.The photocatalytic degradation of pollutants is a Z-scheme heterojunction transition and the active species·O₂^-and·OH play important roles in the photocatalytic degradation.