Activation Of Peroxymonosulfate By Delafossite Oxide For The Degradation Of Organic Contaminants

Advanced oxidation process based on peroxymonosulfate（PMS）can effectively degrade various organic pollutants and be used for environmental pollution control such as groundwater or soil ecological restoration.Among them,the heterogeneous catalytic PMS system using solid catalysts can generate a variety of active oxygen species with strong oxidizing ability.It shows high efficiency and wide application prospects in the degradation of pollutants in water.However,the current oxidation systems still have problems such as low catalytic activity and unclear microstructure-efficiency-mechanism relationships.Therefore,this work aims to develop a new type of high-performance and stable water treatment material and to clarify the effect mechanism of its microstructure and micro-interface characteristics on the performance of catalytic PMS to remove refractory organics in water.This work is based on the heterogeneous advanced oxidation system of PMS catalyzed by delafossite oxide.It focuses on the design of catalysts with different microstructures,the regulation of active oxygen species and yield,and the exploration of the mechanism of PMS catalytic decomposition.The main research work is as follows:The ratio of 2H and 3R types in silver-based delafossite（AgFeO₂）was regulated by controlling different calcination temperatures（300 ^oC,400 ^oC,500 ^oC）.AgFeO₂ with different2H-AgFeO₂ content exhibited excellent performance for catalytic PMS removal of Orange I（OI）.In the PMS activation process,the surface hydroxyl groups were regarded as the catalytic active sites of AgFeO₂.This study found that the catalytic performance of AgFeO₂was found to be significantly enhanced with the increasing content of 2H-AgFeO₂.Through linear regression of experimental data and DFT calculations,it is confirmed that the higher2H-AgFeO₂ content in AgFeO₂ promoted the concentration of surface hydroxyl groups and the reactivity of AgFeO₂ for PMS activation.The in-situ ESR showed that ¹O₂,O₂^·-,SO₄^·-and·OH were the dominating reactive oxygen species（ROSs）that participated in the catalytic process.Additionally,the electron transfer of Ag⁰/Ag⁺and Fe²⁺/Fe³⁺cycles facilitated the decomposition of PMS to generate ROSs.The g-C₃N₄/AgFeO₂ composite catalyst was prepared by a two-step calcination method.After a small number of g-C₃N₄ combining with AgFeO₂,it exhibited higher catalytic activity than AgFeO₂ alone in activating PMS to degrade OI.Under the best reaction parameters,the degradation rate of OI was increased to 91%within 30 min.The enhanced activity of g-C₃N₄/AgFeO₂ catalyzed by PMS could be attributed to the increased relative content of low-valent metal species(Ag⁰,Fe²⁺)on the catalyst surface and improved the electron transfer ability after the addition of g-C₃N₄,thereby promoting the effective decomposition of PMS.Moreover,the leaching of metal ions in the g-C₃N₄/AgFeO₂/PMS catalytic system was significantly lower than that of the AgFeO₂/PMS system,and it showed good stability and reusability in continuous cycles.It was identified that ¹O₂,O₂^·-,SO₄^·-and·OH were the main ROSs in the degradation process of OI.The concentration of oxygen vacancies（OVs）on AgFe_1-xNi_xO₂ surface was regulated by varying the ratio of Ni dopant.The AgFe_1-xNi_xO₂ catalyst with abundant OVs has excellent catalytic activity for the degradation of BPA in the presence of PMS.In-situ ESR witnessed that the yield of O₂^·-and ¹O₂ in the catalytic system increased significantly with the increase of the OVs content on the catalyst surface,while the production of SO₄^·-and·OH showed a relatively decreasing trend.It was mainly attributed to the preferential dissociation of PMS into O₂ on the OVs,additionally,OVs facilitated the superior surface oxygen mobility and electrical conductivity,which also gave rise to a significant enhancement in O₂^·-and ¹O₂generation,thereby accelerating the degradation of pollutants.Mechanism studies have shown that the synergistic of Mⁿ⁺/M^（n+1）+and active oxygen(_OV^··/O_O^?,O²-/O2)ensured continuous active oxygen formation and excellent catalytic activity.The copper-based delafossite（Cu Co O₂ and Cu Cr O₂）catalysts with different B-site elements were synthesized by hydrothermal method.both of which showed excellent catalytic performance of PMS to degrade OI in water,and the OI degradation rate reached 98%and93%,respectively.Furthermore,the effects of various parameters and background substances on the two catalytic systems were systematically studied.Combining a series of tests such as ESR,electrochemistry,FT-IR and XPS,two different potential structure-dependent PMS catalytic mechanisms were proposed.In the Cu Co O₂/PMS system,PMS was catalytically decomposed to produce SO₄^·-,O₂^·-and ¹O₂,which were the main ROSs responsible for the degradation of organic matter.In the Cu Cr O₂/PMS system,the degradation of OI did not depend on radicals or ¹O₂,nor a direct electron transfer mechanism.Instead,the interaction between the outer sphere of PMS and Cu Cr O₂ formed a surface-limited metastable intermediate,which directly attacked organic substrate.