Visible-light Ag₃PO₄-based Z-scheme Composites:Controllable Synthesis,characterization And Properties

Solar-driven semiconductor photocatalytic is considered to be an effective technique to handle the shortage of non-renewable energy and the pollute of environmental,which brings hope to handle the problem of sustainable development of modern society.The current research of photocatalysts found that the Ag₃PO₄ material has visible light absorption and strong photo-redox ability,especially in the photocatalytic applications of oxygen generation and organic degradation.However,the single semiconductor cannot effectively realize the conversion and utilization of light energy because of the contradiction between high activity and stability in Ag₃PO₄.Therefore,it is urgently to improve the stability and redox ability of photocatalyst in this field.Many previous researches have shown that the rapid separation of photo-generated charges can be achieved through the construction of heterojunctions by coupling two semiconductors,which is an important measure to solve the defects of single photocatalysts.Herein,based on the Z-scheme mechanism,the composite systems of Ag₃PO₄/WO₃ or Ag₃PO₄/g-C₃N₄ were designed and synthesized,and the combine of modified g-C₃N₄ and Ag₃PO₄was further explored.It was found that the photocorrosion of Ag₃PO₄ can be inhibited and the strong redox ability of the Ag₃PO₄ can be reserved,the specific research details are as follows:（1）The WO₃ nanosheets with uniform morphology were synthesized through hydrothermal method,and further used mechanical exfoliation to obtain the highly dispersed lamellar structure.To synthesize the Ag₃PO₄/WO₃ composites system,coupling between semiconductors was realized by chemical precipitation method.The photocatalysis performance of the heterojunction were assessed by investigating the photocatalytic oxygen production and organic degradation.The morphology,structure and charges transfer pathway of the composites material were analyzed according to various characterization.The results show that the surface of Ag₃PO₄ was wrapped with WO₃,and the lamellar structure increases photocatalytic active sites.The favorate contact interfacial accelerate the charges transfer,thus the highest oxygen production of this system has reached to 306.6μmol·L^-1·h^-1in unit of time.（2）The precursor of g-C₃N₄ was prepared by thermal polymerization,and the Ag₃PO₄/g-C₃N₄composite material was prepared by using electrostatically driven self-assembly and chemical precipitation.The one-dimensional（1D）structure of g-C₃N₄ was favor for the effective transfer of photogenerated charges,and the thin-walled porous tube structure provides more reactive sites.The photocatalytic oxygen evolution reaction of composite materials has been studied under visible light,the highest yield rate was 370.2μmol·L^-1·h^-1 in per hour.Using a series of characterization to analyze the molecular structure,optical properties and explore the mechanism of oxygen generation,and the reason of photocatalytic oxygen generation increased was revealed.（3）The 2D g-C₃N₄ was modified by P-doped and then coupled with Ag₃PO₄ to construct Z-scheme Ag₃PO₄/P-CN visible light photocatalytic system.The recombination ratio and lifetime of photo-generated carriers were analyzed via steady-state transient fluorescence characterization.Based on the Z-scheme system,Ag₃PO₄/P-CN exhibited max O₂ generation of 357.1μmol·L^-1·h^-1,the produce oxygen rate of P-doped composites sample was 1.5 times exceeds than that undoped material.Based on the speedy separation of photogenerated charges,the combination of high stability and high activity of the composite system were realized.