The Preparation Of Visible-light Driven Semiconductor Photocatalysts And The Study Of Photodegradation Properties And Mechanism With Organic Pollutants

Global Environmental pollution and fossilenergy shortage are becoming serious problems that are restricting the development of human and affecting people’s daily life.To solve these problems,many approaches have been developed by investigators and relevant department over the years.Semiconductor photocatalytic technology,one kind of advanced oxidation method,is a novel environmental treatment technology that can efficiently use solar energy.It cannot only efficiently photodegrade organic pollutants,but also alleviate the problem of energy shortage.The key of photocatalytic technology is to develop stable and efficient photocatalyst.At present,the most widely used photocatalyst is TiO₂ which can be driven by ultraviolet light.As ultraviolet light accounts for less than 4%of energy in sunlight,the utilization rate of TiO₂ on sunlight is extremely low.Therefore,the development of semiconductor materials with Visible-Light Driven（VLD）has become a priority in the in-depth study of photocatalytic technology.Up to date,researchers have developed many semiconductor materials with visible-light-driven,such as simple oxides（WO₃ and Bi₂O₃）,complex oxides（Ag₃PO₄,Bi₂MoO₆,Ag₂MoO₄）,sulfide（MoS₂ and CdS）and nitride（C₃N₄ and Ta₃N₅）.Among these semoconductors,Ag₃PO₄ and WO₃ were proved to be a novel VLD semiconductor photocatalysts with extensive potential application in photodegrading organic pollutants.However,the shortages of the low individual photocatalytic efficiency and poor stability of photocatalytic activity that limit their application in practical production.In this study,this several VLD photocatalysts were modified reasonably via facile precipitation method and their photocatalytic performance have been greatly improved.At the same time,the influence of the reaction parament such as the initial concentration of dye,the typle of photocatalysts and contaminants has also investigated.The results are as follows:1.The Ag₃PO₄ modified with graphene quantum dots composites（GQDs-Ag₃PO₄）have been synthesized via a facile precipitation method to further improve the photocatalytic performance of Ag₃PO₄.In this study,the composition,structure and optical property of as-prepared photocatalysts were characterized and we found the diameter of the composite catalyst shrunk much smaller than pure Ag₃PO₄ while thesurface area of GQDs-Ag₃PO₄ composites increased than pure Ag₃PO₄microsphere.GQDs-Ag₃PO₄ composite displays a better absorption property,and the absorption edge located at⁷00 nm.Meanwhile,the test result of photocatalystic activity showed as follows:Interestingly,these GQDs-Ag₃PO₄ exhibited improved visible light photocatalytic performance for the degradation of rhodamine B（RhB）than pure Ag₃PO₄.The composite with GQDs weight percentage of 0.48 showed the most excellent performance,which was completely almost 11.25 times than that of pure Ag₃PO₄.Furthermore,this composite also showed excellent photocatalytic performance for the photodegradation of para-chlorophenol（4-CP）,Levofloxacin（LEVO）and negatively charged aromatic dye methyl orange（MO）.The remarkable enhancement of photocatalytic performance should be attributed to the larger surface area,the enhanced light absorption property and the effective suppression of electron-hole recombination.2.A novel WO₃ decorated with Ag₂MoO₄ heterojunction have been synthesized through a facile precipitation method.Ag₂MoO₄ particles were firmly deposited on the surface of WO₃ nanoplates,forming“particles-on-plates”heterojunction structures.These heterojunction structures exhibited improved photocatalytic activities for the degradation of rhodamine B（RhB）,4 chlorophenol（4-CP）and tetracycline hydrochloride（TC）than pure Ag₂MoO₄ and WO₃ under visible-light irradiation.In addition,the heterojunction with Ag₂MoO₄ weight percentage of 10%showed the best photocatalytic performance,which was almost 2 and 1.9 times than that of pure WO₃or Ag₂MoO₄ with the same weight respectively.Furthermore,the photocatalytic efficiency of the Ag₂MoO₄-WO₃ heterojunction is extremely higher than that of the mixture of two individual photocatalysts with the same weight of components（Ag₂MoO₄ and WO₃）.In addition,this heterojunction also exhibited prominent photocatalytic performance for photodegrading TC.The TC degradation rate reached up to 99%under visible-light irradiation.This remarkable enhanced photocatalytic performance results from the staggered bandgap between Ag₂MoO₄ and WO₃,which can suppress the recombination of electron-hole pairs efficiently.Moreover,based on the radical trapping experiment,the superoxide radical anions（·OH）and photogenerated holes（h⁺）were the crucial active oxidizing species.In summary,the research in this paper has important reference value for the deep development of VLD semiconductor photocatalytic materials,and it provides technical support for the photocatalytic technology in the photodegradation of organic pollutants,which is of significance in the field of environmental pollution control and energy saving.