Metallic Oxides Activate Persulfate For The Degradation Of Organic Pollutants Via Non-radical Pathways

Advanced oxidation technology based on the metal heterogeneous catalytic activation of persulfate（PS）has received significant attention in the field of wastewater treatment owing to its benefits of strong oxidation capability,quick reaction time,mild reaction conditions,and straightforward operation.Nevertheless,metal oxide catalysts encounter some issues,such as low selectivity for target pollutants,poor stability,and difficulties in separating and recovering powder materials.To address these challenges,new metallic oxide catalysts were designed and fabricated.PS was activated to degrade organic pollutants via non-radical pathway,thus improving the selective degradation of pollutants.By optimizing the spatial structure,constructing oxygen vacancy defects,and applying immobilized substrate,the catalytic activity and cyclic stability of the catalyst were enhanced,and rapid separation and recovery of the catalyst was realized.The findings provide both theoretical and technical guidance for the design of efficient catalysts in PS activation and advance the application of PS-based advanced oxidation processes in wastewater treatment.The following are the primary findings of this study:（1）The confinement effect of nanomaterials associated with their hollow shell structure has been shown to consequently accelerate the rate of PS activation.In this study,Co₃O₄/Ni Co₂O₄DSNCs with double-shell hollow structure were synthesized using ZIF-67 as a template and a metal ion etching then precipitation method.Their performance in activating peroxydisulfate（PDS）was evaluated by degrading the organic pollutant bisphenol A（BPA）.The results demonstrate that the Co₃O₄/Ni Co₂O₄DSNCs with a double-shell structure removed 76.7%of BPA within 18 minutes,which is higher than the single-shell structure Co₃O₄ NCs（13.4%）,Ni Co₂O₄ NCs（59.2%）and heterojunction metal oxide Co₃O₄-Ni Co₂O₄（51.3%）.PDS can combine with the Co₃O₄inner shell and the Ni Co₂O₄ outer shell to form surface-activated complexes that oxidize and degrade BPA by electron-withdrawing,which is a typical non-radical activation process.Additionally,the Co₃O₄/Ni Co₂O₄DSNCs activated PDS system exhibited good selectivity for BPA degradation and effectively resisted the interference of halogen and background organic matter in water environments.This study proposes an effective strategy for regulating the spatial structure of metal oxide materials and developing a PS activation system to degrade organic pollutants via non-radical pathways.（2）Oxygen vacancy defects with abundant localized electrons can enhance the combination of the catalytic material and PS,thus improving the PS activation processes.In order to further optimize the catalytic performance of Co₃O₄ derived from ZIF-67,a ZIF-67@ZIF-8 precursor was constructed using an epitaxial growth method.Hollow Co-Zn metal oxide nanocages enriched with oxygen vacancies（OVs-Zn Co₂O₄HNCs）were synthesized,which were applied to PDS activation for the degradation of organic pollutants.The results show that the incorporation of Zn into the Co₃O₄ lattice significantly increases the number of OVs in the catalyst while maintaining the spatial configuration of the Co₃O₄ NCs.The reaction rate constant for PDS activation to degrade BPA,catalyzed by OVs-Zn Co₂O₄ HNCs catalysts(0.2021 min^-1),is approximately 20 times higher than that of Co₃O₄ NCs catalysts(0.0108 min^-1),which is linearly correlated with the OVs content in catalysts.OVs promote the binding of PDS molecules to the surface of the catalyst,forming surface-activated complexes that oxidize and degrade BPA by withdrawing electrons.This system is suitable for the selective degradation of organic pollutants with low ionic potential.This study provides an effective strategy for regulating the defects sites of metal oxide materials and developing a PS activation system to degrade organic pollutants via non-radical pathways.（3）Powder metal oxide catalysts are often difficult to separate and recover during PS activation,which can be effectively addressed by growing them in-situ on immobilized substrates.Multimetallic Cu Co Ni oxide nanowires（Cu Co Ni–NF）were grown in-situ on a nickel foam（NF）substrate using a hydrothermal method,and the immobilized catalyst was used to activate PDS for the degradation of organic pollutants.The results indicate that NF not only acts as a substrate support but also participates in the formation of catalyst as an internal slow-release Ni source.Cu Co Ni-NF exhibited high catalytic activity and stability during PDS activation,and its immobilized form effectively resolved the problem of catalyst separation and recovery.Cu Co Ni–NF first donates electrons to PDS to arrive at an oxidized state and subsequently deprives electrons from BPA to return to its initial state,thus mediating the electron transfer process from BPA to PDS.Cu Co Ni–NF demonstrated high catalytic activity in the p H range of 5.2–9.2,and resistance to background HCO₃^–and humic acid.This study provides an effective strategy for the immobilization of metal oxide materials and developing a PS activation system to degrade organic pollutants via non-radical pathways.（4）To further improve the biocompatibility and stability of the immobilized substrate catalyst,the metal components were optimized by selecting environmentally friendly Ni and Mn elements.The bimetallic oxide（Ni Mn-NF）was grown in-situ on NF as the substrate using the hydrothermal method and the synthesis conditions were optimized to improve the catalytic performance and cyclic stability.The results showed that Ni Mn-NF completely removed BPA within 20 minutes under the optimized preparation conditions.This was higher than monometal catalyst Ni-NF（47.5%）and Mn-NF（72.3%）.During the ten-cycle degradation process,Ni Mn-NF system showed excellent stability and achieved complete removal of BPA within 30 minutes.The high-valence metal species Mn（IV）was the main active species.Additionally,Ni Mn-NF maintain high catalytic activity in the p H range of 2.2-11.8,and showed good anti-interference performance against most anions,cations,and humic acids in water environments.The biotoxicity of BPA wastewater decreased obviously after treatment,and the relative luminosity intensity of bacterium increased from 7.8%to 53.7%.This study presents an effective strategy for constructing stable and biocompatible metal oxide catalysts.