Cathode Electro-fenton Oxidation Of Azo Dye Methyl Orange Catalyzed By Magnetic Fe₃O₄ Nanoparticles

The rich variety of dyes plays an important role in the colorful daily life and has huge economic potential.But in the production and use of the process also produce a lot of dye wastewater,which itself has a strong pollution,the composition of complex,deep color,high concentration of pollutants,and because of the characteristics of the process,dye wastewater often contains a lot of salt and strong acidity.In addition,the dye molecules also have low reactivity and biodegradability,it is difficult to be degraded in wastewater treatment,easily lead to the pollution of natural water,has been the problem in wastewater treatment.In this paper,a typical azo dye methyl orange(MO)as the target pollutants,the use of magnetic Fe3O4 nanoparticles catalytic cathode Fenton degradation,and carried out a series of studies.First of all,the preparation,characterization and performance analysis of C-PTFE gas diffusion electrode were studied.It was found that the electrode has high porosity after heat treatment,and has a faster H2O2 production rate and a higher H2O2 accumulated concentration.The Fe3O4 catalyst was synthesized by chemical coprecipitation method.The Fe3O4 catalyst was characterized by XRD,SEM and TEM.The synthesized Fe3O4 catalyst had high purity and good crystal morphology,microsphere shape and uniform in size.The average particle size was 30-50nm.Secondly,the degradation characteristics of heterogeneous magnetic Fe3O4 nanoparticles in the process of degradation of azo dye MO in aqueous solution by cathodic electrodeposition were studied.The effects of reaction conditions,such as current density,initial pH of the solution,amount of catalyst,air flow and initial concentration of the solution on the degradation efficiency were discussed.The experimental results showed that under the condition of 10 mA cm-2 current density,1.5 L/min air flow rate,1.0 g/L Fe3O4 catalyst and pH 3,500 mL,50 mg/L MO solution during the reaction time of 90 min,the degradation rate of MO was 86%,the cumulative concentration of H2O2 reached 35.7 mg/L,and the catalyst had good stability,the concentration of dissolved Fe was less than 3.5 mg/L.The degradation rate of MO could be improved by increasing the current density,the amount of catalyst and the air flow rate of the reaction system,and the system had a good pH adaptability,there are still 68.6%of the MO had been degraded when pH was 9.5.Although the degradation rate of MO decreased with the increase of initial concentration of solution,the absolute removal amount was increased.Finally,the changes of H2O2 and·OH concentration,UV-Vis absorption spectra,TOC,NO3-and SO42-concentrations and three-dimensional fluorescence spectra were studied in the process of degradation of MO by Fe3O4 catalyzed cathodic electro-Fenton.The data showed that approximately 50%of the H2O2 is converted to·OH during the course of the reaction,and the accumulated concentration was up to 17.6 mg,/L.The degradation of MO molecules produced many small molecular intermediates,which were stable and difficult to be further oxidized.Only 32%of TOC was removed,and these intermediates had a fluorescence effect,which increased the fluorescence intensity of the solution.In addition,during the degradation process,the sulfonic acid groups in the MO molecules could be oxidized to SO42-,while the oxidation of the nitrogen elements in the azo or amine groups was not mainly mineralization to NO3-At the same time,the geometries of the MO molecules were optimized by the B3LYP method of the density functional theory(DFT)at the 6-311 ++ G(d,p)basis set by Gaussian 09 software,and fully optimized configuration obtained by theoretical calculation.The natural charge and the Wiberg bond order of each atom in the molecule were carried out theoretical calculations and analysis by natural bond orbital theory(NBO),and the possible attack sites and potential breakpoints of the-OH in the process of MO degradation were analyzed theoretically.Based on the theoretical analysis and the results of LC-MS detection,9 main degradation products and degradation mechanism of MO in the cathodic electric-Fenton system were put forward and the possible degradation pathway was deduced.