Study On The Efficiency And Mechanism Of PPCPs Controlled By Visible LED Synergies With Ferrate In Water

Ferrate（Fe（Ⅵ））is a new type of green oxidizer which integrates oxidation,disinfection,coagulation and adsorption functions.It has been widely concerned in the research of water treatment.However,the oxidation property of Fe（Ⅵ）is easily affected by the pH of solution,and it is easy to self-decomposition and other shortcomings limit the wide application of Fe（Ⅵ）.Compared with the traditional chemical reagent strengthening method and carbon material strengthening method,the light radiation strengthening method has more advantages.It does not need to add additional chemicals to the water,and it is a very efficient,high economic and practical method.Therefore,two processes of Vis-LED/Fe（Ⅵ）enhanced ferrate（Vis-LED/Fe（Ⅵ））and Vis-LED/Fe（Ⅵ）-BPY mediated by 2,2-bipyridine（BPY）were studied for degradation of pharmaceuticals and personal care products（PPCPs）.This study provides a new perspective for understanding Fe（Ⅵ）system and is expected to be the best choice to effectively remove PPCPs.The main conclusions of this study are as follows:（1）Vis-LED co-ferrate system can efficiently degrade PPCPs in water,and the reaction process conforms to pseudo-first-order reaction kinetics.Vis-LED alone has no significant degradation effect on PPCPs,while Vis-LED/Fe（Ⅵ）system degrades PPCPs 2.6-7.8 times faster than Fe（Ⅵ）alone.In the wavelength range of 440 nm-525 nm,the apparent quantum yield of Fe（Ⅵ）decreases with the increase of visible light wavelength,and the degradation rate of diclofenac（DCF）decreases linearly with the increase of visible light wavelength.With the increase of light intensity,Fe（Ⅵ）photolysis produced more active species,which accelerated the degradation of DCF.The increase of Fe（Ⅵ）concentration can also promote the degradation of DCF in this system.However,with the increase of pH,the protonation form of Fe（Ⅵ）in solution changes from HFeO₄^-,which has strong oxidation capacity,to FeO₄^2-,which has relatively weak oxidation capacity.Therefore,the degradation of DCF in this system will be inhibited in alkaline solution.Free radical quenching experiments show that intermediate iron（Fe（Ⅴ）/Fe（Ⅳ））is the main active species for DCF degradation in this system.Model fitting analysis results show that Fe（Ⅴ）is the main active species in the Fe（Ⅵ）system alone,and the oxidation contribution of Fe（Ⅴ）accounts for 59.95%.Fe（Ⅳ）was the main active species in Vis-LED/Fe（Ⅵ）system,and the oxidation contribution of Fe（Ⅳ）was59.18%at 440 nm.In the presence of anions（Cl^-,HCO₃^-and Br^-）in water,DCF can still be effectively removed in Vis-LED/Fe（Ⅵ）system.Finally,the study on the degradation paths of DCF products found that DCF in Vis-LED/Fe（Ⅵ）system mainly includes three degradation paths:hydroxylation,decarboxylation and C-N bond breaking reaction.（2）BPY can effectively mediate and promote the efficient degradation of PPCPs in Vis-LED/Fe（Ⅵ）system,and the degradation rate is 2.7-3.7 times faster than that in Vis-LED/Fe（Ⅵ）system.In pH8 borax buffer solution at room temperature,it only takes 3min.5μM sulfamethoxazole（SMX）can be completely degraded by Vis-LED/Fe（Ⅵ）-BPY system,with the pseudo-primary degradation rate constant of 1.4124 min^-1.The protonation form of Fe（Ⅵ）in solution changes from HFeO₄^-,which has strong oxidation capacity,to FeO₄^2-,which has relatively weak oxidation capacity,so the degradation of DCF in this system will be inhibited in alkaline solution.In the wavelength range of 440 nm-525 nm,the apparent quantum yield of Fe（Ⅵ）decreases with the increase of visible light wavelength,and the degradation rate of sulfamethoxazole（SMX）decreases linearly with the increase of visible light wavelength.With the increase of light intensity,Fe（Ⅵ）photolysis produced more active species,which accelerated the degradation of DCF.In addition,the increase of Fe（Ⅵ）concentration also promoted the degradation of SMX by the system.The results of free radical quenching experiment and competitive kinetics experiment showed that Fe（Ⅴ）/Fe（Ⅳ）was the main oxidizing substance for SMX degradation.The results of model fitting analysis showed that Fe（Ⅴ）was the main active species in Vis-LED/Fe（Ⅵ）-BPY system,the oxidation contribution was 58.59%,and the steady-state concentration of iron in the intermediate state was higher than that in Vis-LED/Fe（Ⅵ）system.The red color of Vis-LED/Fe（Ⅵ）-BPY system solution is due to the presence of Fe（Ⅱ）-BPY complex in the system.According to the model fitting experiment and UV sweeping experiment,the role of BPY in Vis-LED/Fe（Ⅵ）-BPY system is to complex Fe（Ⅱ）and intermediate iron.The stability of intermediate iron in water was improved,the steady-state concentration of intermediate iron was increased,and the degradation effect of SMX was enhanced.In the presence of anions（Cl^-,HCO₃^-and Br^-）in water,SMX can still be effectively removed in Vis-LED/Fe（Ⅵ）-BPY system.In conclusion,Vis-LED/Fe（Ⅵ）system and Vis-LED/Fe（Ⅵ）-BPY system can efficiently remove water PPCPs.In addition,Fe（Ⅳ）and Fe（Ⅴ）have been identified as the main active species in the oxidation process of Vis-LED/Fe（Ⅵ）and Vis-LED/Fe（Ⅵ）-BPY systems,which will provide a new research idea for advanced oxidation technology based on ferrates,and is expected to promote the application of Fe（Ⅵ）in future water treatment field.