The Effect Of Catalyst Surface Properties And Pollutant Molecular Structure On The Activation Mechanism Of Peroxymonosulfate

With the development of human activities,the threat to ecological environment is becoming more and more serious.Organic pollutants from water not only damage the ecology,but also affect human health.Persulfate（PS）activation is a new and efficient pollutant control technology developed rapidly in recent decades.Activated PS molecules can produce a variety of highly active substances to degrade and mineralize different types of organic pollutants.In recent years,although PS activation technology has made great progress,it is also faced with challenges.In the activation system,it mainly includes catalyst,PS molecule,pollutant and solvent.Among them,the catalyst is an important medium for PS activation,but the effect of its surface properties on the activation mechanism of PS is still unclear.In addition,previous studies focused on the design of catalysts,but ignored the effect of pollutants on the activation mechanism of PS.Based on this,we explored the influence of catalyst surface properties and pollutant molecular structure on the activation mechanism of PS,explained why catalyst surface properties improve the activation performance of PS,and confirmed that pollutant molecular structure can affect the activation mechanism of PS.Through the study of the above issues,the main conclusions are as follows:（1）.Oxygen vacancy can be established on the surface of PrBa_0.5Sr_0.5Co_1.5Fe_0.5O_5+d（PBSCF）by calcination at high temperature with hydrogen,and the PBSCF catalysts with different oxygen vacancy concentrations can be obtained by adjusting the calcination time.Oxygen vacancies can promote the peroxymonosulfate（PMS）activation,and this promotion increased with the concentration of oxygen vacancies increased.XRD and EPR spectra show that the crystal structure and oxygen vacancy remain stable before and after the reaction.The quenching experiment,EPR spectroscopy,PMS decomposition rate test and electrochemical analysis show that oxygen vacancy can promote the generation of radical and singlet oxygen,and transform the nonradical activation mechanism of PMS from PBSCF-mediated electron transfer process to singlet oxygen.Based on DFT theory,the transformation of the nonradical activation mechanism is attributed to the regulation of the surface properties by oxygen vacancy.The introduction of oxygen vacancy redistributes the surface charge of the catalyst,reduces the adsorption energy of PMS and changes the adsorption configuration of PMS.This effect leads to the decomposition of PMS,which is originally adsorbable on the surface of the material,into superoxide free radicals and then into singlet oxygen.（2）.Manganese dioxide octahedral molecular sieve（Mn-OMS）was prepared by one-step hydrothermal method to investigate the effect of pollutant types on the activation mechanism of PMS.Studies have shown that the degradation of different types of pollutants in Mn-OMS/PMS system is significantly different due to the influence of pollutant types on the activation mechanism of PMS.Combined with quenching experiments,EPR spectroscopy,PMS decomposition rate tests,solvent exchange,and electrochemical analysis,we demonstrated that pollutant types can alter the activation path of PMS.In Mn-OMS/PMS systems,the electron-rich pollutants are degraded by a catalyst-mediated electron transfer process,while the electron-poor pollutants are degraded by radicals and singlet oxygen.In addition,H₂O molecules have been proved to be involved in singlet oxygen generation,so we propose a singlet oxygen generation pathway involving H₂O molecules.By comparing the pathways of different activation mechanisms,the ability of low-valent manganese ions on the catalyst surface,contaminants,or H₂O molecules transfer electrons to O-O bonds was identified as a key step in the influence of contaminants on the PMS activation mechanism.（3）Metal-organic coordination compound Fe-OEC（OEC is an oxygen releasing complex） was prepared by simple complexation principle for homogeneous PMS activation.SEM/TEM showed that Fe-OEC was a lamellar amorphous catalyst.XPS spectra confirmed the presence of Fe（II）and Fe（III）in Fe-OEC,and UV-vis spectra further showed that Fe（III）-OEC in solution tended to be the low spin Fe（II）-OEC.Compared with other catalysts,Fe（II）-OEC has excellent PMS activation ability.The 2 mg/L Fe-OEC（Fe content less than 0.3 mg/L）can activate PMS to degrade different types of pollutants with ultra-high efficiency.Usually,the degradation rate of pollutants can reach 100%in 10 min,and the mineralization rate of different pollutants is more than 50%.The quenching experiments and UV-vis spectra showed that the electron-rich pollutants were mainly degraded by Fe（IV）,while the electron-poor pollutants were mainly degraded by radicals.