Active Species Modulation On Metal Oxide For Removal Of Refractory Organic Pollutants In Water

With the rapid development of social economy,industry,and agriculture,the types and number of refractory organic pollutants in water are increasing,and the problem of water pollution is becoming increasingly serious.The long-term accumulation of refractory organic pollutants in water bodies,such as polycyclic aromatic hydrocarbons（PAHs）and antibiotics,can seriously harm ecosystems and human health.Therefore,it is important to develop technologies for efficiently degrading refractory organic pollutants in water bodies.Advanced oxidation technology is commonly used for the degradation of refractory organic pollutants in water due to its advantages of high reactivity and low cost.Currently,common advanced oxidation technologies include photocatalytic oxidation technology and oxidant oxidation technology,which mainly degrade organic pollutants by reacting with light,catalysts,oxidants,etc.to produce highly active species（such as·OH,·Cl）.Therefore,regulation and promotion of active species formation and in-depth study of the mechanism of active species formation and action mechanisms contribute to better degradation of refractory organic pollutants in water.There are many methods to promote the formation of active species,such as adding catalysts,complexing agents,and so on.Based on this,this paper selects two metal oxides,γ-Fe OOH（photocatalytic oxidation system）and Mn₂O₃（ClO₂ catalytic oxidation system）,were used as catalysts to investigate the formation and mechanism of active species in the system,as well as the kinetic characteristics of photocatalytic oxidation degradation of sulfamethazine（SM2）and ClO₂ catalytic oxidation degradation of benzo[a]pyrene（Bap）.The specific research work is as follows:1.Oxalic acid（OA）was added to improve the ability of lepidocrocite to produce reactive oxygen species in photochemical systems.Firstly,experimental results of SM2degradation under different conditions show that the degradation effect of SM2 by the lepidocrocite oxalic acid photochemical system was the best（64%）,with a degradation rate of 442 times that of the lepidocrocite photochemical system.Secondly,the adsorption coordination configuration of oxalic acid on the surface of lepidocrocite,the method of oxalic acid induced iron ion leaching on the surface of lepidocrocite,and the production pathway of reactive oxygen species were investigated through free radical inhibition experiments,iron dissolution experiments under different wavelengths of monochromatic light,in situ ATR-IR,and surface enhanced Raman spectroscopy.The experimental results confirm that oxalic acid was adsorbed on the surface of Lepidocrocite in the form of a double toothed mononuclear and induced the dissolution of iron from the surface of lepidocrocite in a non reducing form,The dissolved Fe（C₂O₄）₃^3-photoreduction produces Fe（II）,which then reacts with·O₂^-in one step to produce·OH（no H₂O₂ is produced in this process）.Finally,comparing the XPS,SEM,and TEM of lepidocrocite before and after the reaction,we found that the Fe（II）content on the surface of lepidocrocite increased from37%to 53.1%after the reaction,and there was a lattice stripe spacing（which can be attributed to the（020）crystal surface of goethite）in the TEM after the reaction,indicating that there was a transition from Lepidocrocite to goethite during the reaction process.2.Mn₂O₃ was used to promote the activation of ClO₂ and improve the ability of ClO₂to produce active species.First of all,the experimental results of Bap degradation under different conditions indicate that Mn₂O₃has the best catalytic effect on ClO₂ degradation of Bap,with a reaction rate 7.17 times that of ClO₂.Secondly,the quenching experiment of active species and the quantitative experiment of active species confirmed that Mn₂O₃mainly activated ClO₂ to degrade Bap by producing high valent manganese and promoting the formation of active oxygen species and active chlorine species in the system.Finally,GC-MS was used to investigate the pathway of Mn₂O₃ catalyzed ClO₂ degradation of Bap,which can be roughly divided into three stages:The first stage is the oxidation of Bap to produce diketone intermediates;In the second stage,the generated intermediate is further oxidized and ring-opened to generate ditridecyl phthalate/trans-13-octadecenoic acid;In the third stage,the intermediate produced in the first two processes further opens the ring,and the free radicals formed are recombined with themselves and other intermediate products to form n-heptane.