Mechanism Study On Fenton-like Advanced Oxidation To Remove Isoprothiolane Mediated By Graphene-based Materials

Isoprothiolane（IPT）is a carcinogenic and toxic pesticide.As a new pollutant,it has been gradually detected in water bodies all over the world.The latest Hygienic Standard for Drinking Water（GB 5749-2022）has added it as a new water quality index,with a limit of 0.3 mg/L.Fe（Ⅲ）-rGO,as a catalyst,was successfully prepared by bonding Fe（Ⅲ）on the surface of reduced reduced graphene oxide（rGO）by hydrothermal method.By means of scanning electron microscope,specific surface area analyzer,fourier infrared spectrometer and X-ray diffraction,it is proved that Fe is uniformly distributed on the catalyst surface（Fe content is 8.8%）in the form ofβ-Fe OOH by forming Fe-O bond.In order to effectively remove IPT from drinking water,the Fe（Ⅲ）-rGO/H₂O₂/PMS and Fe（Ⅲ）-rGO/H₂O₂/PAA system were constructed by introducing H₂O₂,peroxymonosulfate（PMS）,and peracetic acid（PAA）,respectively,which can be activated by Fe（Ⅲ）-rGO.The experimental results showed that these two systems can effectively remove IPT.In Fe（Ⅲ）-rGO/H₂O₂/PMS system,adsorption stage is 0～10min,Fenton-like AOP is the reaction between Fe（Ⅲ）and H₂O₂ in 10～70min,and PMS-AOP is the reaction between Fe（II）and PMS in 70～130min.Fe（Ⅲ）-rGO performed as an excellent catalyst to activate H₂O₂ and PMS for IPT degradation.IPT removal efficiency was proven to be better in the Fe（Ⅲ）-rGO/H₂O₂/PMS system（96.2%）than in the Fenton-like AOP（72.6%）and PMS-AOP（80.0%）individually.The analysis results of X-ray photoelectron spectroscopy（XPS）confirmed that 49.1%of Fe（Ⅲ）was effectively reduced to Fe（II）in the Fenton-like AOP,and 6.6%of Fe（II）played a crucial role in the following PMS-AOP.The synergistic process of Fenton-like AOP and PMS-AOP mediated by Fe（Ⅲ）-rGO involved the valence state conversion of Fe,which consequently improved the utilization efficiency of Fe（Ⅲ）-rGO and the removal efficiency of IPT.Fe（Ⅲ）-rGO significantly accelerated the Fe（Ⅲ）/Fe（II）cycle,and generated superoxide radical（O₂^-·）and singlet oxygen（¹O₂）in the Fe（Ⅲ）-rGO/H₂O₂/PMS system.The quenching experiment proved that ¹O₂ and O₂^-·played a leading role in the degradation of IPT.Fe（Ⅲ）-rGO acts as the electron transfer mediator,thus,promoting electron transfer from IPT to H₂O₂ and PMS,and accelerating the generation of active species.In addition,the probe experiment proved that Fe（IV）with high oxidation performance was produced in PMS-AOP and efficiently removed some of the IPT.Similar to Fe（Ⅲ）-rGO/H₂O₂/PMS system,In Fe（Ⅲ）-rGO/H₂O₂/PAA system,adsorption stage is 0～10min,Fenton-like AOP is the reaction between Fe（Ⅲ）and H₂O₂in 10～70min,and PAA-AOP is the reaction between Fe（II）and PAA in 70～130min.The removal efficiency of IPT in Fe（Ⅲ）-rGO/H₂O₂/PAA system was 92.4%,which was higher than that in PAA-AOP（86.4%）.XPS results showed that the Fe（Ⅲ）/Fe（II）cycle also occurred during the degradation of IPT.There was 49.7%of Fe（Ⅲ）was reduced to Fe（II）in Fenton-like AOP,and 4.3%of generated Fe（II）was oxidized to Fe（Ⅲ）in PAA-AOP.The quenching experiment proved that ¹O₂ and O₂^-·played a major role in the degradation of IPT,and the probe experiment proved that a certain concentration of Fe（IV）was produced in PAA-AOP stage,which promoted the degradation of IPT.The result of experiments showed that the removal efficiency of IPT can be maintained above 50%even after five consecutive degradation experiments of Fe（Ⅲ）-rGO,which showed that Fe（Ⅲ）-rGO has excellent stability and reusability.Additionally,IPT removal efficiency was always above 90%when the initial p H ranges from 3 to 11,and iron sludge formation was greatly reduced because of the stable chemical bonding of Fe（Ⅲ）to the rGO surface,which effectively overcame the two inherent defects of traditional Fenton reaction:limited by p H and a large amount of iron sludge.The synergetic system of Fenton-like AOP and PMS-AOP,PAA-AOP mediated by Fe（Ⅲ）-rGO was successfully realized.Therefore,this study provides a new multisystem and synergistic approach for the efficient removal of organic micro-pollutants from water.