Advanced Oxidation System Based On Carbon Nitride Supported MnCo₂O₄ For Degradation Of Phenyl Pollutants And Its Mechanism

Sulfate radical-based advanced oxidation technology（SR-AOPs）is a popular technology that uses radical to degrade and mineralize pollutants.The strong oxidizing components(SO₄^·-,OH^·and ¹O₂,etc.)formed by the activation of oxidants（PMS,PS）by metal catalysts or external energy sources have high efficiency of degrade organic pollutants.At present,in a large number of studies on SR-AOPs,synthetic materials based on metal oxi des as catalysts have received extensive attention.Metal oxides and metal oxide composites are favored by researchers due t o their stable and effective catalytic capabilities.In this paper,cobalt nitrate hexahydrate（Co（NO₃）₂·6H₂O）,manganese acetate（Mn Ac）and dicyandiamide（DCD）are used as raw materials to synthesize a new catalyst CMCN by high-temperature calcination.The catalyst CMCN2 composed of cobalt manganese tetroxide（MnCo ₂O₄）and carbon nitride（g-C₃N₄）has the best catalytic effect.This article mainly includes the following four parts:1)the structural characterization and characteristics of the catalyst CMCN2.2)Degradation performance of benzene ring compounds with nitrobenzene（NB）as the main target pollutant inCMCN2/PMS system.3)The conversion process and synergy of active componetes(high-valent metal-oxo species,SO₄^·-and OH^·)during the degradation of nitrobenzene.4)Practical application of CMCN2/PMS todegrade petrochemical wastewater.Firstly,the XRD,EDS and XPS characterization methods proved that the experiment successfully synthesized CMCN2 with MnCo₂O₄/g-C₃N₄ as a component,and CMCN2 contains a special covalent bond N-M=O.By changing the composition and ratio of the original material,MnCo₂O₄/g-C₃N₄ has the best degradation efficiency,and the removal rate of nitrobenzene can reach 96.3%after 240 minutes.At the same time,the experiment took nitrobenzene,phenol,2,4-DCP and bisphenol A as the target pollutants,and explored the ability of CMCN2/PM S system to degrade benzene ring compounds.The results show that MnCo₂O₄/g-C₃N₄ has a higher mineralization capacity for benzene ring compounds.Subsequently,the experiment selected nitrobenzene as the target pollutant.The p H experiment confirmed that the CMCN2/PMS system has the most efficient degradation ability at p H=9.More importantly,MnCo₂O₄/g-C₃N₄ has good p H adaptability to p H changesin the p H range of 3-10.By changing the amount of catalyst and PMS added,it is determined that the optimal catalytic conditions for the CMCN2/PMS system were CMCN2=0.2g/L,PMS=0.4g/L and p H=9.Unlike the traditional SR-AOP,in addition to radical quenching experiments and ESR verification that SO₄^·-and OH^·are the active factors inCMCN2/PMS,the special oxidation pathway of DMSO to DMSO2 indicates that high-valent metal-oxo species(M^V（O）/M^IV（O）)is another active factor inCMCN2/PMS.CMCN2/PMS completes the degradation of pollutants through the synergy of three active components M^V（O）/M^IV（O）,SO₄^·-and OH^·.The study found that in the process of CMCN2activation of PMS,the formation of SO₄^·-and OH^·originates from the activation of metal ions to break the O-O bond in PMS to form SO₄^·-,which reacts with H₂O to form OH^·.The reason for the formation of M^V（O）/M^IV（O）is that the special covalent bond oxygen=metal-nitrogen（O=M-N）undergoes sacrificial oxidation,and metal atoms continuously lose electrons.In the continuous electron transfer process,M=O breaks,the valence state of Mⁿ increases,and free O atoms in the metal trapping system form unstable intermediate product Mⁿ⁺¹-O-H.As the O-H bond breaks,O and M atoms combine again to form M^V（O）/M^IV（O）(X-Mⁿ⁺¹=O,X represents a macromolecular heterocycle).M^V（O）/M^IV（O）,SO₄^·-and OH^·jointly degrade organic pollutants in the aqueous system.This article explores the performance of CMCN2/PMS in degrading petrochemical wastewater.After 240 minutes of catalytic treatment,the removal rate of COD in petrochemical wastewater containing nitrobenzene derivatives was 60.5%,and the removal rate of TOC was 42.2%.The three-dimensional fluorescence spectrum shows that after 240 minutes,the area of the fluorescence peak of the organic matter distributed in the area B is significantly reduced,and the organic matter component is effectively mineralized.This study introduced the formation process of M^V（O）/M^IV（O）,SO₄^·-and OH^·in detail from the perspective of metal electron transfer,which provided a reference for the application of advanced oxidation methods in the subsequent research to degrade phenyl pollutants.