Removal Of Azo Dyes And Bisphenol A By Activation Of Persulfate With Fe-Mn Bimetallic Catalyst

In this study,two Fe-Mn bimetallic catalysts were prepared by two-step hydrothermal method and co-precipitation method to active persulfate?PS?for the treatment of azo dyes Reactive Black 5?RBK5?and endocrine disruptors bisphenol A?BPA?,respectively.The optimal degradation conditions of two kinds of refractory organic pollutants in two different Fe-Mn bimetallic catalysts activated PS systems were determined by factor experiments.The catalytic mechanism of the system was studied under optimal degradation conditions.Fe₃O₄ nanoparticles were prepared by hydrothermal method.Fe₃O₄-?-MnO₂ was synthesized by hydrothermal method in the second step.HRTEM,XRD,XPS were used to characterize Fe₃O₄-?-MnO₂.The morphology of the catalyst is nanoflower-like,with high crystallinity and high purity.The degradation efficiency of RBK5 and BPA in Fe₃O₄-?-MnO₂/PS system was studied.The concentration of pollutants was 30 mg/L,and the dosage of Fe₃O₄-?-MnO₂ was 1.2 g/L,the concentration of PS was 4.0 mmol/L and initial pH was 7.0,the degradation efficiency of RBK5 in 60 min could reach 91.0%;moreover,the concentration of PS is 3.0 mmol/L,the degradation efficiency of BPA in90 min could reach 92.0%.The quenching experiments results demonstrate that SO₄^·-was the active free radical that plays a major role in Fe₃O₄-?-MnO₂/PS system.The existence of the surface-OH groups and Fe³⁺could be reduced to Fe²⁺by Mn³⁺,which promoted the activation of persulfate.Therefore,Fe₃O₄-?-MnO₂ exhibits excellent catalytic activity.The intermediates in the degradation process of BPA were determined by GC-MS,and the possible degradation pathway of BPA was proposed.Mn-substituted magnetite(Fe_xMn_3-xO₄)with different metal ratios was prepared by co-precipitation method.Among them,Fe_2.10Mn_0.90O₄ showed the highest catalytic activity in PS activation.Fe_2.10Mn_0.90O₄ was characterized by FESEM,XRD,and XPS.The size of the catalyst was about 200-400 nm.The degradation efficiency of RBK5and BPA in Fe_2.10Mn_0.90O₄/PS system was studied.The dosage of Fe_2.10Mn_0.90O₄ was1.2 g/L,the concentration of PS was 0.4 mmol/L and initial pH was 7.0,the degradation efficiency of RBK5 in 40 min could reach 92.5%;moreover,the concentration of PS was 0.5 mmol/L,the degradation efficiency of BPA in 40 min could reach 93.3%.The quenching experiments results demonstrate that SO₄^·-played a major role in the degradation of RBK5 and BPA.The XPS result showed that Mn³⁺could not only activate PS,but also promoted the reduction of Fe³⁺to Fe²⁺.Moreover,Mn³⁺could be reduced to Mn²⁺due to the presence of Fe²⁺,which promoted the cycle of Fe²⁺/Fe³⁺,Mn²⁺/Mn³⁺/Mn⁴⁺,thereby improving the efficiency of PS activation.The intermediates in the degradation process of BPA in Fe_2.10Mn_0.90O₄/PS system were determined by GC-MS,and the possible degradation pathway was determined.These two systems have good degradation efficiency for organic matter of two different structures,and the degradation efficiency of organic matter with asymmol/Letric structure is slightly better than that of symmol/Letric structure.Because of the extra Mn²⁺/Mn³⁺/Mn⁴⁺cycle,The degradation efficiency of RBK5 and BPA in Fe_2.10Mn_0.90O₄/PS system is better than that in Fe₃O₄-?-MnO₂/PS system,and the amount of oxidant required is small and the reaction time is shorter.