Preparation Of Silver Carbonate Composite Photocatalytic Materials And Its Degradation Mechanism Of Pollutants In Water Under Visible Light

Recently,due to the rapid progress of industries,more and more emerging contaminants,including pharmaceutical antibiotics,flame retardants,personal care products（PPCPs）and secretion of interferon,etc.,have been detected in the natural water environment,which causes serious environmental pollution and damages the biological health.As for antibiotics,even if the content in the water environment is low,it still leads to the production of resistance genes in microorganisms,and produces the super antibiotic-resistant bacteria.Hence,it is imperative to explore a suitable and effective method to solve residual antibiotics in the environment.Compared with traditional treatment technology,photocatalysis based on semiconductor materials has the characteristics of low cost,friendly environment,energy saving and excellent effect for the removal of refractory pollutants.In the present paper,Bi₅O₇I/Bi₂O₂CO₃/Ag₂CO₃ and In₂O₃/Ag₂CO₃nanocomposites were prepared by a facile hydrothermal calcination and one-step in-situ growth technology.Then their photocatalytic performance were measured by degrading Levofloxacin（LEV）under visible light.Finally,a possible degradation mechanism was proposed through characterization and theoretical calculation.In this paper,based on the research of Z-scheme heterojunction composite Bi₅O₇I/Bi₂O₂CO₃/Ag₂CO₃,a novel S-scheme heterojunction（a special Z-scheme heterojunction）composite In₂O₃/Ag₂CO₃ was further studied,and the photodegradation of antibiotic pollutants in water by Z-scheme heterojunction silver carbonate composites were deeply studied and analyzed.（1）In the present work,a novel dual Z-scheme heterojunction of Bi₅O₇I/Bi₂O₂CO₃/Ag₂CO₃（BBA）was fabricated using a facile hydrothermal calcination and one-step in-situ growth technology,which performs well in the degradation（86.9%）for Levofloxacin within 60 min under visible light irradiation.Optimistically,the degradation rate is about 1.5,4.1,1.3 and 1.4 times than that of pure Bi₅O₇I,Bi₂O₂CO₃,Ag₂CO₃ and binary Bi₅O₇I/Bi₂O₂CO₃,respectively.The enhanced photocatalytic performance can be conductive to improve the division efficiency of electron-hole pairs（e^–/h⁺）and generation of various free radicals in the dual Z-scheme system.Besides,the generation of hydroxyl radicals（·OH）,superoxide radicals（·O₂^–）and holes（h⁺）species were certified directly by Electron Spin Resonance（ESR）test.The contribution of active species on degradation of Levofloxacin follows the order of h⁺>·OH>·O₂^–.Additionally,Levofloxacin and the intermediate products were detected and their toxicity are also analyzed with Quantitative Structure-Activity Relationship prediction.Finally,combined with some experimental characterizations such as ESR test,the electron transfer degradation mechanism of double Z-scheme heterojunction was proposed.（2）In the present work,a novel S-scheme heterojunction of In₂O₃/Ag₂CO₃（InAg）was synthesized with in-situ hydrothermal precipitation methods.The characteristics and Density Functional Theory（DFT）calculation prove that the transfer of photogenerated electrons in the In₂O₃/Ag₂CO₃ system follows the mechanism of S-scheme heterojunction.And the Internal Electric Field（IEF）resulted from the S-scheme heterojunction of In₂O₃/Ag₂CO₃ drives the direct transferring of photogenerated electrons from the conduction band（CB）of the Ag₂CO₃ to valence band（VB）of the In₂O₃,resulted in an efficient separation of photogenerated electron-hole pairs and great accumulation of e^–and h⁺on the CB of In₂O₃ and VB of Ag₂CO₃,respectively.The photoluminescence lifetime of InAg is greatly extended from 4.21 ns to 8.42 ns,and h⁺and·OH are the most important active radicals.As-prepared S-scheme heterojunction of InAg show the highest photodegradation rate（86.1%）and mineralization ability（46.2%）toward Levofloxacin under visible light.Finally,combined with DFT calculation and in-situ experimental characterization,both probable degradation pathways and mechanism were presented.