Preparation Of Rare Earth Modified PbO₂ Electrode And Its Degradation Of Sulfamethazine

Sulfamethazine(SMZ)is a kind of sulfonamides,which widely exists in the environment and has application prospect.The degradation of SMZ by catalytic oxidation has the advantages of high efficiency and simple operation.For electrochemical oxidation,anode material plays an important role on the organic pollutants degradation.PbO2 has been regarded as an excellent metal oxide electrode due to its easy preparation,low cost,high chemical stability,as well as high overpotential for the oxygen reaction.However,there are some problems,such as the weak mineralization ability and current efficiency,limited service life and so on.Therefore,in the present work,the following investigation have been carried out for the development of PbO2 electrodes with excellent electrochemical properties and strong electrocatalytic oxidation ability by doping rare earth elements,which were applied to the electrochemical degradation.We selected SMZ as a representative organic pollutant,and the mechanism of degradation of SMZ in aqueous solutions was discussed.The main research contents and results were summarized as follows:A novel PbO2 electrode modified with rare earth elements(Ce,Er,Gd and La)doping(named as R-PbO2)was prepared by electrodeposition in the present study.In this paper,the microstructure and electrocatalytic oxidation ability of R-PbO2 electrode were characterized,respectively.Then the R-PbO2 electrode with the best performance was obtained.Moreover,quantitative analysis of the effects of doping rare earth elements to electrocatalytic oxidation was investigated.(1)The micro-morphologies and crystal structure of R-PbO2 were characterized by SEM,EDS,XRD and XPS techniques,respectively.Compared with the traditional PbO2 electrode,R-PbO2 electrode had smaller grain size and higher the proportion of adsorbed oxygen(such as OH).The adsorbed oxygen content of Er modified PbO2 electrode was increased by 17%.(2)Their electrochemical properties were determined by CV,polarization curve and accelerated life test.The OEP and voltammetric charge quantity of R-PbO2 electrode were higher than unmodified PbO2 electrode.The reactive active sites and the service life were increased.(3)Compared with the unmodified PbO2 electrode,the-OH formation ability and utilization ratio of the R-PbO2 electrode were improved.The Er-Pb02 electrode was 1.49 times higher than that of the unmodified PbO2 electrode.(4)We selected p-NP as the target organic pollutant,and the electrocatalytic oxidation of p-NP was studied in aqueous solutions to characterize electrocatalytic oxidation ability of the modified electrodes.The results show that the electrochemical degradation of p-NP followed pseudo-first-order kinetics.The degradation rate followed the order:Er-PbO2>Gd-PbO2>La-PbO2>Ce-PbO2>PbO2,which is consistent with the order of the relative content of adsorbed oxygen.Especially for Er-PbO2 electrode,the pseudo-first order kinetic for p-NP degradation was 0.41,which was only 0.19 for un-doped PbO2.(5)Given all that,Er-PbO2 electrode has the best performance,which was used to study the degradation of pollutants.(6)By calculating the Lewis values of rare earth elements,it is found that there is a positive correlation between the effect of rare earth elements on electrocatalytic oxidation and its own relative Lewis acid value.The electrocatalytic degradation of SMZ in aqueous solution and the mechanism of degradation were investigated.BDD electrode,Er-PbO2 electrode(PbO2 electrode)and SnO2 electrode were used as anode.The effects of current density on the SMZ degradation and the general degradation pathway for the’electrochemical degradation of SMZ were examined in this study.(1)The electrochemical degradation of SMZ followed pseudo-first-order kinetics.The degradation rate of BDD electrode was the highest and the residual rate of COD was lowest at 40 mA/cm2 current density.At 20 mA/cm2 current density,PbO2 electrode has the best removal rate on SMZ.At 30 mA/cm2 current density,SnO2 electrode has the best removal rate on SMZ,COD removal rate is the highest.(2)In the process of electrocatalytic oxidation,the utilization ratio of OH at BDD electrode is 100%,the utilization ratio of OH at PbO2 electrode is 97.59%,and the utilization ratio of-OH at SnO2 electrode is 83.57%.(3)Based on the reaction products identified,it is speculated that the degradation process is mainly nitrification,the breaking of S-N bond of sulfonamide,the oxidation of phenylamine group and so on.