Study On The Catalytic Synergistic Mechanism Of Bismuthbased Catalyst Activate Persulfate To Generate Active Species Population

A large number of difficult-to-treat pesticide wastewater will be produced with the increase of the agricultural modernization process in our country,which will harm the environment.New advanced oxidation processes based on semiconductor photocatalysis advanced oxidation process and persulfate?PS?advanced oxidation process have been tried to treat pesticide wastewater.However,semiconductor photocatalysis advanced oxidation process mainly relies on the band structure of the semiconductor photocatalytic material to generate active species dominated by·O₂^-and·OH to degrade pollutants.This treatment method has the disadvantages of long degradation time and inability to fully mineralize when facing organic pollutants with stable and complex structures such as pesticides.Constructing surface defect can be used to regulate the performance of the catalyst to solve the above problems.In the heterogeneous catalytic reactions,the surface defect oxygen vacancies of the catalyst can provide a large number of the dangling bonds for adsorbing reactants.And the local electrons accumulated on the oxygen vacancies can activate the adsorbed reactants through electronic feedback,thereby affecting the catalytic reaction process.In addition,constructing semiconductor heterojunction is also a common method to effectively regulate the catalytic activity of catalysts.Heterojunctions can be constructed by selecting semiconductor materials with matching band structures to effectively control the separation and transfer efficiency of photogenerated electron-hole pairs,thereby improving their catalytic performance.The persulfate advanced oxidation process that generates·SO₄^-with strong oxidization by activating PS has a certain degradation effect on pesticide wastewater.However,the activation process of PS is uncontrolled.And a large number of active species will self-quench without utilization,resulting in the waste of PS.Based on the above,regulating the properties of semiconductor photocatalytic material by constructing oxygen vacancies and heterojunctions,and combining with persulfate advanced oxidation process,will become an effective way to treat difficult-to-degrade pollutants such as pesticide wastewater.Therefore,bismuth-based semiconductor photocatalytic materials such as Bi OCl,Bi₂O₃,Bi₂S₃ are selected to construct oxygen vacancies and heterojunctions in this paper.The purpose is to study the catalytic performance of the catalyst and the reaction mechanism in the reaction system of adding PS and visible light.Finally,it provides theoretical support for establishing a catalytic reaction system,which is semiconductor photocatalytic materials efficiently activate PS to generate active species population to degrade pollutants.The specific research content is summarized as follows:?1?Study on the catalytic synergistic mechanism of Bi O_1-xCl microsphere activating PMS to generate active species populationUsing bismuth nitrate pentahydrate,potassium chloride and L?+?-Ascorbic acid as raw materials,Bi O_1-xCl microsphere with suitable oxygen vacancy concentration and maximum specific surface area were successfully synthesized by microwave-assisted under adding 0.2mmol L?+?-Ascorbic acid.In the reaction system with 0.025 g PMS and visible light,the catalyst can degrade 2.5 mg/L acetamiprid over 65%in 360 min.The research results show that the special microsphere structure of Bi O_1-xCl creates a large specific surface area,which can provide more active sites for adsorption reactions,and effectively adsorb HSO₅^-produced by PMS for chain reaction of subsequent active species transformation,thereby improving the utilization rate and conversion rate of HSO₅^-.Meanwhile,oxygen vacancy with suitable concentration can effectively activate HSO₅^-adsorbed at the oxygen vacancy by regulating the electronic feedback efficiency of the photogenerated electrons.The chain reaction of the conversion of active species is promoted to form the active species population through the synergistic effect of microstructure and oxygen vacancy,which improves the catalytic degradation effect.?2?Study on the catalytic synergistic mechanism of Z-scheme Bi₂O₃/Bi O_1-xCl heterojunction activating PMS to generate active species populationUsing bismuth nitrate pentahydrate,potassium chloride and sodium hypochlorite as raw materials,Z-scheme Bi₂O₃/Bi O_1-xCl heterojunction with suitable oxygen vacancy concentration were successfully in-situ oxidation synthesized under adding 0.5 m L sodium hypochlorite.In the reaction system with 0.01 g PMS and visible light,the catalyst can degrade 2.5 mg/L imidacloprid over 99%in 360 min.Characterization and experimental results show that the synthesized Z-scheme Bi₂O₃/Bi O_1-xCl heterojunction has a suitable interface electric field direction,which can effectively drive the separation and transfer of photo-generated electrons and holes,thereby increasing the probability of redox reaction happen.Meanwhile,the oxygen vacancies on the Z-scheme Bi₂O₃/Bi O_1-xCl heterojunction can effectively adsorb HSO₅^-produced by PMS to form shielding protection,which can effectively reduce the direct light decomposition of HSO₅^-under visible light and reduce the self-quenching reactions of unused active species,thereby improving the utilization of PMS.Therefore,the Z-scheme Bi₂O₃/Bi O_1-xCl heterojunction can perform a stepwise controllable adsorption activation reaction of PMS under visible light through the synergistic effect of oxygen vacancy and the interfacial electric field,which effectively improves the conversion rate and utilization rate of active species,thereby helping improve the catalytic effect.?3?Study on the catalytic synergistic mechanism of Bi₂S₃/Bi O_1-xCl heterojunction activating PDS to optimize the rate of active species population generationUsing bismuth nitrate pentahydrate,potassium chloride and thiourea as raw materials,Bi₂S₃/Bi O_1-xCl heterojunction with suitable oxygen vacancy concentration were successfully in-situ ion exchange synthesized under adding 0.083 mmol thiourea.In the reaction system with0.1 g PDS and visible light,the catalyst can degrade 2.5 mg/L dinotefuran over 95%in 300 min.First-principles calculation,characterization and experimental results show that the Bi₂S₃/Bi O_1-xCl heterojunction can form an interface electric field with a suitable electric field direction at the interface of the heterojunction,which effectively improves the transfer efficiency of photogenerated electrons and holes,and help subsequent generation and transformation of active species.Meanwhile,through theoretical calculations,it was found that the oxygen vacancies on the exposed?001?crystal plane of Bi O_1-xCl in the Bi₂S₃/Bi O_1-xCl heterojunction are conducive to the adsorption and activation of S₂O₈^2-produced by PDS,and make it complete dissociation adsorption to produces·SO₄^-.Therefore,the Bi₂S₃/Bi O_1-xCl heterojunction performs a stepwise controllable adsorption activation reaction of PDS under visible light through the synergistic effect of oxygen vacancy and the interfacial electric field,which optimizes the generation and conversion rate of active species,thereby effectively improving the utilization rate of the active species,which promotes the chain reaction of the conversion of active species to form the active species population,and finally improving the catalytic effect.