The Preparation Of Photocatalysts Based On Ag₂CrO₄ And Discussion The Mechanism Of Photocatalytic Degradation Of Organic Pollutants

A large amount of organic pollutants are discharged into the environment every year,such as wastewater containing pesticides and medical household waste.It is essential to remove them effectively in the environment.2,4-dichlorophenol（2,4-DCP）is a typical phenolic organic pollutant,commonly used as pesticide and pharmaceutical intermediates.So far,various methods of removing 2,4-DCP have been explored,including adsorption,photocatalysis,biodegradation,etc.Among them,photocatalysis is considered to be an effective method for 2,4-DCP treatment,because it has extremely high oxidation capacity for organic pollutants,and even completely mineralizes most toxic compounds.As an important number of the photocatalyst family,Ag-based semiconductors have good photosensitivity and high charge transfer rate,therefore attracting more and more attention.Silver chromate（Ag₂CrO₄）based semiconductor photocatalysis have been widely investigated for environmental purification because of its low band gap（～1.8 e V）,excellent photosensitive and unique electronic structure.It exhibits prominent photocatalytic activity in water oxidation and the degradation of organic pollutants.However,the main problems of silver chromate（Ag₂CrO₄）based photocatalysts are that their poor photostability and low photoactivity hinder their widespread applications.In this paper,a composite material based on Ag₂CrO₄ was prepared,and the mechanism of photocatalytic degradation of 2,4-DCP was explored.By constructing a Z-scheme heterojunction and organic material coupling strategy,a composite material based on Ag₂CrO₄was synthesized,which further improved the photocatalytic performance and stability of Ag₂CrO₄.Under visible light irradiation,the photocatalytic performance of the synthesized Ag₂CrO₄-based composite material to2,4-DCP was tested.Based on the experimental and characterization results,the possible mechanism of the photocatalytic degradation reaction is discussed.The specific experimental results are as follows:The Z-scheme Ag₂CrO₄-Polyaniline（Ag₂CrO₄-PANI）composites are synthesized by in situ self-assembly strategy.The obtained Ag₂CrO₄-PANI composites exhibited good photocatalytic performance and stability for the degradation of2,4-dichlorophenol（2,4-DCP）in aqueous solution under visible-light irradiation.The best composite with PANI content of 6.0 wt%showed the highest photocatalytic activity for the degradation of 2,4-DCP,and its apparent rate constant was 0.0312min^-1,which was 1.6 times and 13.9 times that of Ag₂CrO₄ and PANI.The photocatalytic activity of Ag₂CrO₄-PANI toward 2,4-DCP still kept 33%after four reuses,while pure Ag₂CrO₄ only kept 12%.The enhanced photocatalytic degradation activity is mainly attributed to the formation of Ag₂CrO₄-PANI Z-type heterojunction,which not only can realize the effective spatial separation of photogenerated charge carriers,but also retains strong oxidation and reduction capabilities.The high photocatalytic stability is due to the successful suppression of photocorrosion of Ag₂CrO_4-PANI composite by transferring the photogenerated electrons of Ag₂CrO₄ to PANI.