Visible Light Degradation Of Bisphenol A By CQD/Ag₃PO₄ Composites

As a"green"technology,it has great potential in environmental governance.Photocatalysis is the complete decomposition of organic pollutants into carbon dioxide,water and inorganic water molecules under the action of photocatalyst.The research and development of catalyst is the key point of photocatalysis technology.Silver phosphate（Ag₃PO₄）has been favored by researchers for its excellent visible light catalytic performance in organic wastewater treatment.However,Ag₃PO₄ has unstable chemical properties,and is prone to photocorrosion,which reduces its catalytic performance.Therefore,the application of Ag₃PO₄ in the environmental field is limited.Carbon quantum dots（CQD）can improve the photocatalytic activity of silver phosphate due to their excellent up-conversion fluorescence properties and good electron acceptor.Firstly,Ag₃PO₄ was modified by modifying the morphology,the efficiency and reuse rate of Ag₃PO₄ for bisphenol A degradation in visible light were improved.On this basis,CQD and Ag₃PO₄ were combined,the preparation conditions of CQD/Ag₃PO₄ catalyst were optimized.Its photocatalytic performance and mechanism under visible light were discussed.The results are as follows:（1）Ag₃PO₄ was successfully prepared by coprecipitation.The morphology and structure of the catalyst were characterized by means of XRD,BET,SEM,TEM,XPS,uv-vis and PL.The results showed that the prepared flake Ag₃PO₄ had higher photocatalytic activity than pure Ag₃PO_4.The new Ag₃PO₄ material has flaky structure with side length of 1¹0 m and thickness of 50⁶00 nm.Having more（111）crystal faces,the ratio of（111）to（110）was increased from 1.23 to 1.87,it’s one times the surface area.It can effectively enhance the absorption of visible light and lower electron-hole recombination rate.The Ag₃PO₄-2 had the best photocatalytic performance,and the degradation rate of bisphenol A was up to 97%after 20 min.The main active substance in the photocatalytic reaction of pure Ag₃PO₄ is h⁺,however,flake Ag₃PO₄ improved the oxidation capacity of the active substance·O₂-.（2）CQD with high fluorescence performance was successfully prepared by hydrothermal synthesis.The role of CQD in Ag₃PO₄ photocatalytic degradation of BPA was investigated.Fluorescence spectrum,ultraviolet absorption spectrum,particle size and infrared spectrum were used for characterization.Results show that when the reaction temperature is 180℃,holding time for 10 h,CQD fluorescence properties is strongest.Under these conditions,CQD/Ag₃PO₄ photocatalyst has better photocatalytic activity.The effects of CQD incorporation on the photocatalytic performance of CQD/Ag₃PO₄ were further investigated.It was found that the kinetic constant of CQD/Ag₃PO₄ composite catalyst reached a maximum of 0.0769 min^-1when the addition amount was 3 mL,which was 2.84 times of pure Ag₃PO₄.（3）The optimized CQD/Ag₃PO₄ catalyst was characterized by XRD,SEM,XPS and uv-vis,and the photocatalytic mechanism was discussed.The results show that the external morphology of Ag₃PO₄ is changed by CQDs.The surface of CQD/Ag₃PO₄ composite catalyst was short and protruded,and the edges and corners became smooth.The band gap width of Ag₃PO₄ is slightly larger than that of CQD/Ag₃PO₄ composite material.CQD/Ag₃PO₄ has a strong light absorption ability of composite catalyst,CQD can effectively inhibit Ag₃PO₄ generated electron hole composite,thus effectively improving the catalytic efficiency.Inhibition experiments on active species showed that the main active species in the photocatalytic degradation of BPA were h⁺and·O₂-.