Construction Of Single Atomic Metal Sites And Persulfate-driven Dissolved Oxygen Conversion For Aqueous Organic Pollutant Oxidation

With the continuous development of economy and society,the pollution of water environment is becoming more and more serious,and human society is pursuing high speed development while threatening the ecological safety.Wastewater with poor biochemical properties is difficult to remove the organic pollutants by traditional biological organic wastewater treatment methods,and under this condition,advanced oxidation processes（AOPs）come into being.As the research on advanced oxidation technology continues to intensify,scientists have found that peroxide compounds,which also contain peroxygen bonds similar to H₂O₂,can also generate ROS under appropriate catalytic conditions can generate sulfate radicals(SO₄^●-)with higher redox potentials（2.60-3.10 V）and longer half-lives（30-45μs）for the oxidative degradation of pollutants for the oxidative degradation of pollutants.But the use of persulfates introduces high concentrations of SO₄^2-in aqueous solutions,which causes secondary pollution and becomes one of the bottlenecks limiting the development of persulfate oxidation technology.In the heterogeneous catalysis of persulfate,transition metals are the main species of heterogeneous catalysts.Metal-based catalysts based on transition metals have higher activation efficiency for persulfate than non-metallic catalysts.As the research on metal-based heterogeneous catalysts continues to deepen,the single atom catalysts（SACs）catalyzed by metal nanoparticles,which are supported by single metal atoms as the catalytic active site,have gradually come into the view of researchers.This novel catalytic material,which has the advantages of both homogeneous and heterogeneous catalysts,is widely used in the activation of persulfates,and the model of active sites formed by coordination of metal atom centers with surrounding atoms also lays the foundation for exploring the interaction between reactants and catalysts.Dissolved oxygen（DO）,which exists in molecular form in water,is an important reactant species involved in the complex activation process of persulfate.The contribution of DO to the degradation of organic pollutants is very limited.In persulfate oxidation technology,the following problems still exist:（1）the activation mechanism of persulfate is complex,especially the reaction mechanism involving DO is not clear;（2）the actual involvement of single-atom catalytic sites in the activation process of persulfate is not clear;（3）the large amount of SO₄^2-after the reaction is not conducive to resource-saving development.Based on this,this thesis proposes to construct metal single-atom catalysts possessing electron polarization distribution active sites through the modulation of ligand atoms to activate persulfate while driving the conversion of DO as electron acceptor to ROS for the synergistic degradation of organic pollutants in water.The specific study is as follows:Single-atom Fe-N₃O₁ site construction with persulfate driven dissolved oxygen oxidation of organic pollutants.Achieving satisfactory organic pollutant oxidation with a low concentration of peroxymonosulfate（PMS）is vital for persulfate-involved advanced oxidation processes to reduce resource consumption and avoid excessive sulfate anion(SO₄^2-)production.Herein,efficient conversion of dissolved oxygen（DO）over single-atomic Fe-N₃O₁ sites anchored on carbon nitride for efficient contaminant degradation is fulfilled,triggered by a low concentration of PMS（0.2 m M）.Experimental and theoretical results reveal that the preferentially adsorbed PMS onto atomic Fe-N₃O₁ center can deliver electrons toward the single Fe atom to increase its electron density to trigger DO reduction into superoxide radical(O₂^●-)and successive transformation into singlet oxygen（¹O₂）,which is quite different from the conventional PMS activation process mostly depending on PMS itself function for reactive oxygen species generation.This work elucidates the triggering role of low-concentration PMS in DO conversion over a single-atom Fe catalyst,which can inspire the development of resource-saving and environmentally-friendly catalytic oxidation systems for environment.Construction of monatomic Zn-N₄ site and persulfate triger dissolved oxygen for organic pollutants oxidation.Amongst various Fenton-like（SACs）,zinc（Zn）-related SACs have been barely reported due to the fully occupied 3d¹⁰ configuration of Zn²⁺being inactive for the Fenton-like reaction.Herein,the inert element Zn is turned into an active single-atom catalyst（SA-Zn-NC）for the Fenton-like chemistry by forming the atomic Zn-N₄ coordination structure.The SA-Zn-NC shows admirable Fenton-like activity in organic pollutant remediation including self-oxidation and catalytic degradation by O₂^●-and ¹O₂.Experimental and theoretical results unveiled that the single-atomic Zn-N₄ site with electron acquisition can transfer electrons donating from electron-rich pollutants and low-concentration PMS toward dissolved oxygen to actuate DO reduction into O₂^●-and successive conversion into ¹O₂.Thanks to that,under ambient air conditions,only 0.2 m M PMS concentration can achieve rapid and effective degradation of pollutants on the surface of SA-Zn-NC,significantly reducing the amount of PMS,and alleviating the problem of SO₄^2-residue after the reaction.In addition,SA-Zn-NC catalyst has good stability and can treat organic pollutants in water and actual kitchen wastewater in a long time.The research results expand the variety of Fenton-like single atom catalyst and provide a new idea for the development of low consumption and high efficiency water treatment technology.