Molybdate And Modified Composite Materials Activated Persulfate For The Degradation Of BPAF:Performance And Mechanism

Advanced persulfate oxidation technology based on sulfate radical(SO₄^·-)has high treatment efficiency,short reaction period and wide application range,and has been developed as an optimal method to remove refractory organic pollutants in water treatment process.The heterogeneous persulfate activation system based on molybdate and its modified composites can not only efficiently remove refractory organic pollutants,but also can reduce the dissolution of metal ions by immobilization of catalytic active components.Therefore,it is a reliable alternative method of homogeneous PS and PMS activation system.Based on this,this paper focused on the preparation of FeMoO₄,Cu@FeMoO₄ and CNTs@FeMoO₄ heterogeneous catalysts,and systematically studied the efficacy and mechanism of activating PMS or PS to degrade endocrine disruptor BPAF in water.The specific research contents and main research conclusions are as follows:1)FeMoO₄ was successfully synthesized by a simple hydrothermal synthesis,and was used as heterogeneous catalyst to activate PMS for the degradation of BPAF.The morphology,microstructure,crystal morphology,surface element valence state and bonding energy of the synthetic material were analyzed in detail through SEM,HR-TEM,XRD,XPS and FTIR characterization analysis,which fully demonstrated the successful preparation of FeMoO₄.Experimental results showed that FeMoO₄ had a well catalytic for activating PMS.The influence of internal factors of the system,such as initial dosage of FeMoO₄ and PMS,reaction temperature,p H of initial reaction solution,etc.on the degradation efficiency of BPAF were investigated.When the initial dosage of FeMoO₄,PMS and BPAF were 200 mg/L,1 m M,5 mg/L,respectively,the removal rate of BPAF could reach 95.2%and k_obs was 0.012 min^-1.In addition,the degradation rate of BPAF was positively correlated with the concentration of catalyst and PMS,and negatively correlated with the initial solution p H.The effects of common anions(SO₄^2-,HCO₃^-,NO₃^-and Cl^-)on the degradation of BPAF were also evaluated.The results showed that FeMoO₄ powder had good stability and good catalytic activity after repeated use for 8 times.Moreover,the XRD and FTIR characterization of FeMoO₄ powder showed that the material had little change before and after the reaction,which further indicated that the material had good stability.Through quenching experiment and EPR test results,the main active substances produced in the system were analyzed as^·OH,SO₄^·-and ¹O₂.At the same time,the content of^·OH and SO₄^·-produced in the system was semi-quantitatively analyzed by data simulation calculation and indirect experiment.In addition,based on electrochemical and XPS characterization analysis,the reaction mechanism was proposed,which was mainly through the REDOX of Fe（Ⅲ）/Fe（Ⅱ）and Mo（Ⅳ）/Mo（Ⅵ）to generate^·OH and SO₄^·-.2)In order to further explore more efficient catalyst,this study adopted a simple one-step hydrothermal synthesis method to synthesize the complex bimetallic molybdate Cu@FeMoO₄,which was used as a heterogeneous catalyst for PS to achieve efficient degradation of BPAF.The activity of the composites prepared by different material ratio,different reaction temperature and different surfactant dosage was studied.The composite Cu@FeMoO₄ powder was characterized by SEM,EDS,XPS and FTIR.The morphology,composition,surface element valence state and bonding energy of the composite were analyzed in detail.In order to clarify the feasibility of Cu@FeMoO₄ as a novel heterogeneous catalytic material,the oxidative degradation of BPAF by activated PS system was systematically evaluated,the main active oxygen species were identified.Compared with FeMoO₄/PS and Cu Mo O₄/PS systems,the Cu@FeMoO₄/PS system had the best degradation performance of BPAF.When the initial dosage Cu@FeMoO₄ was 150 mg/L,PS was 1 m M,BPAF was 5mg/L,the removal rate of BPAF could reach 93.3%,and k_obs was 0.149 min^-1.By quenching experiment and EPR test,^·OH,SO₄^·-and ¹O₂ were verified as the main active substances in the system.The content of^·OH and SO₄^·-produced in the system was semi-quantitatively analyzed by characteristic product method.In addition,based on XPS and FTIR characterization analysis,the mechanism of synergistic promotion of the oxidative decomposition of organic pollutants BPAF in Cu@FeMoO₄/PS system by SO₄^·-,^·OH,O₂^·-and ¹O₂ was proposed.Among them,SO₄^·-,^·OH and ¹O₂ play a key role in the effective degradation of BPAF,while O₂^·-plays a role in promoting the catalytic oxidation process mainly as the precursor of ¹O₂ and the intermediate mass transfer to promote the REDOX cycle of low-price metals.3)In view of the low catalytic efficiency of FeMoO₄ and the poor stability of Cu@FeMoO₄,the CNTs@FeMoO₄ composite was proposed to activate PS for the degradation of BPAF.The influence of different loading/doping content of CNTs was investigated.The morphology,composition,crystal form,surface element valence state and bonding energy of the synthesized material were analyzed in detail by SEM,HR-TEM,XRD,XPS,FTIR and Raman characterization.In order to explore the feasibility of CNTs@FeMoO₄ activated PS,the oxidative degradation of BPAF in the CNTs@FeMoO₄/PS system was systematically evaluated,and the catalytic mechanism was discussed.Compared with FeMoO₄/PMS,FeMoO₄/PS and Cu@FeMoO₄/PS systems,the CNTs@FeMoO₄/PS system had the best catalytic performance for BPAF degradation.When the initial dosage of CNTs@FeMoO₄ was100 mg/L,PS was 0.25 m M,BPAF was 5 mg/L,and the reaction time was 30 min,the removal rate of BPAF could reach 86.9%,and the k_obs was 0.064 min^-1.The main active substances were^·OH,SO₄^·-,O₂^·-and ¹O₂,which were identified by quenching test and EPR test.Based on the electrochemical analysis,XPS,FTIR and Raman characterization analysis,three mechanisms were proposed,which were the free radical,non-free radical mechanism and electron transfer mechanism.The free radical mechanism was mainly through Fe（Ⅲ）/Fe（Ⅱ）and Mo（Ⅳ）/Mo（Ⅵ）REDOX to produce^·OH and SO₄^·-.At the same time,¹O₂ was mainly generated by non-free radicals between CNTs and PS through electron transfer mechanism.In addition,O₂^·-was also produced as an intermediate during the catalytic process,which was then recombined to form ¹O₂.The main factors affecting the degradation efficiency of BPAF were investigated,such as the initial dosage of CNTs@FeMoO₄,the initial dosage of PS,the p H of the initial reaction solution,the reaction temperature and other factors.The experimental results showed that the reaction system was less sensitive to the initial p H of the solution and the degradation rate of BPAF changed little when the initial p H of the solution was in the range of 3.0～9.0.The effect of common anions(HCO₃^-,Cl^-,NO₃^-and SO₄^2-)on the removal of BPAF in CNTs@FeMoO₄/PS system was also observed.The experimental results showed that HCO₃^-had an obvious inhibitory effect on the removal of BPAF in the system,while the presence of Cl^-had both promoting and inhibiting effects on the removal of BPAF in the system.CNTs@FeMoO₄ had a certain stability and reusability,and the CNTs@FeMoO₄/PS system had a certain universal applicability,which could effectively degrade a variety of organic pollutants.4)Finally,the main degradation pathways of BPAF were analyzed.In FeMoO₄/PMS system,the mineralization rate of BPAF was as high as 66.4%.There were two main degradation mechanisms of BPAF:one was the common free radical(^·OH and SO₄^·-)degradation mechanism,and the other was the non-free radical（¹O₂）degradation mechanism.Compared with the above three catalytic systems,CNTs@FeMoO₄/PS had high efficiency,good catalyst stability,and showed good degradation performance for a variety of organic pollutants,which may be the best catalyst to activate PS.