Performance Regulation Of Single-Atom Fe Catalys And Its Mechanism Analysis Over Organic Pollutants Degradation

Emerging organic pollutants（EOPs）（mainly including antibiotics/drug resistance genes,persistent organic pollutants,endocrine disruptors,pharmaceuticals and personal care products,etc.）are commonly present in water bodies,which pose a serious threat to the ecological environment and human health.Since it is difficult to effectively remove EOPs by traditional biochemical treatment processes,Eops can still be detected in secondary treatment or even tertiary effluent,so the depth treatment is crucial.At present,advanced oxidation process（AOPs）is widely used in the depth treatment.Due to its ease of operation,diversity of active species and activation pathways,and applicability over a wide p H range,peroxymonosulfate-based advanced oxidation process（PMS-AOPs）is promising in the treatment application of EOPs among them.In addition,single-atom catalysts have attracted much attention in the study of PMS-AOPs for their excellent catalytic activity,stability and clear chemical environment of active centers.However,there are still challenges in precisely regulating the activity of Fenton-like single-atom catalysts.Based on this,this article adjusts the metal-supports interaction from the perspectives of metal single-atom loading,support,and coordination configuration,thereby achieving efficient activation of PMS by single-atom catalysts and generating selective Fe^IV═O,significantly improving their degradation efficiency for EOPs,and providing a new theoretical basis for designing high-performance Fenton-like single-atom catalysts.The main contents of this study are as follows:（1）The mechanism of activation of PMS by nitrogen-doped carbon supported Fe single atom catalyst was explored.A simple,economical and efficient synthesis method of Fenton-like Fe single atom catalyst was developed.Fe0.4-NC can activate PMS and quickly remove 0.1 m M BPA within 1 min,and has good resistance to natural organic matter and mineral ions.The Fe N4 configuration of Fe single atom catalyst was confirmed by XAS analysis,and the leading role of Fe^IV═O in the oxidation and degradation of pollutants was revealed by quenching experiment,¹⁸O isotope labeling experiment and EPR technique.（2）The promotion mechanism of Fe single atom catalyzed activity mediated by CN support regulation and the mechanism of PMS activation were explored.A two-step regulation strategy was developed to regulate the Fe³⁺loading first and then the CN carrier,which realized the twice improvement of the degradation ability of PMS activated by Fe single atom catalyst.Fe1.0-CN-TA2.0,which has the highest activity,can efficiently activation PMS and degrade0.4 m M BPA within 2.0 min,and has good water matrix adaptability and stability,and can run continuously for 124 h in fixed bed reactor.XAS analysis confirmed the Fe-N4 configuration of Fe1.0-CN-TA2.0,and revealed that the increase in the proportion of carbon in the CN support changed the electronic structure of CN and increased the valence of the single-atom Fe site.The enhanced PMS activation ability,quenching experiment,¹⁸O isotope labeling experiment,EPR technology and DFT combined revealed that Fe^IV═O was the main active species causing the oxidative degradation of pollutants.（3）The mechanism of improving the activity of Fe single atom catalyst and the mechanism of PMS activation caused by the change of the electronic structure of CN support regulated by Benzene-1,4-diamine（BDA）was explored.The activity of Fe1-CN-BDA0.75 is 5.1 times that of Fe1-CN after the introduction of BDA,which can rapidly activate PMS and degrade0.1m M BPA within 1 min,and has a good ability to resist the interference factors of actual water.XAS analysis confirmed the Fe-N4 configuration of Fe1-CN-BDA0.75,and revealed that the carbon-rich characteristics of CN support changed the electronic structure of CN and reduced the electron density of single-atom Fe sites.The synthesis of quenching experiments,EPR technology and DFT revealed that the generation of Fe^IV═O in the reaction system was the key to the degradation of pollutants.（4）The mechanism of promoting the activity of Fe single atom catalysts and activating PMS due to the difference of the hybridization orbits of carbon atoms in precursors on the electronic structure of CN support were investigated.By introducing tricarboxylic acid1,3,5-cyclohexane tricarboxylic acid（Ch TA）with sp³ hybrid and 1,3,5-phenyltricarboxylic acid（BTA）with sp² hybrid with similar configuration but different carbon atom hybridization orbits into the precursors,Fe single atom catalysts Fe1-CN-Ch TA and Fe1-CN-BTA were prepared accordingly.Fe1-CN-Ch TA achieves the catalytic degradation of 0.1m M 4-CP within 2.5 min in the presence of PMS,and the activity is 10.4 times and 12.0 times that of Fe1-CN and Fe1-CN-BTA,respectively.Meanwhile,Fe1-CN-Ch TA has excellent resistance to natural organic matter and inorganic salt ions in water and broad p H adaptation ability.The running time of 244 h in the fixed bed flow reaction shows its good stability.XAS analysis confirmed the Fe-N4 configuration of Fe1-CN,Fe-N5 and Fe-N4C configuration of Fe1-CN-Ch TA and Fe1-CN-BTA,respectively.The changed the configuration finally affected the catalytic performance based on MSI.The active species that plays a dominant role is Fe IV═O.Quenching experiment and EPR technology show that Fe^IV═O plays a dominant role in the reaction system.