Study On The Degradation Of Metronidazole And Cinnmic Aicd By Electrochemical Oxidation

With the rapid development of China’s economy, the problem of water pollution becomes more serious. The pharmaceutical wastewater is a kind of refractory and toxic wastewater with the complex components, high concentration of pollutants and bio-refractory. In this paper, metronidazole(MNZ) and cinnamon acid(CA) were selected as model compounds. The pure PbO2 electrode and transition metals modified Pb O2 electrodes were prepared by the method of electrodeposition and used to study for the degradation of pollutants in aqueous with the method of electrochemical oxidation.The pure PbO2 electrode was chosen as anode to study the removal of metronidazole with the method of electrochemical oxidation under different experimental parameters. The results were shown that the decay of metronidazole followed the pseudo-first-order kinetics(R2 > 0.98) and the removal of metronidazole, COD and EE/O were 78.09%, 21.77% and 7.98 kWh/m3, respectively, under the optimal conditions that the concentration of supporting electrolyte, the initial concentration of metronidazole, p H and current density were 0.1mol/L, 100mg/L, 6.4, 10 m A/cm2, respectively. The main degradation pathway of MNZ was speculated based on the intermediated products which generated during the process of electrochemical oxidation degrade MNZ were detected by IC and GC/MS.Different transitiom metals(M= Co, Mo, Zr) modified Pb O2 electrodes which the molar ratios were 0.5%, 1%, 2% were prepared and used as anodes to degrade metronidazole at the optimal conditions. Compared with pure PbO2 electrode, the 1.0% M-doped PbO2 electrodes showed the best performance for the removal of metronidazole and COD which all higher than that of pure Pb O2 electrode.Different modified Pb O2 electrodes and PbO2 electrode were characterized by SEM, XRD, LSV and CV. From the SEM images we could see that the electrode surfaces of modified PbO2 electrodes become so dense that improve the electrode performances of corrosion resistance and service life. The XRD patterns showed that smaller crystalline grains were found after doping and the crystallinity of the electrode surface was improved, which increased the surface area and active sites of electrodes. The LSV test indicated that modified PbO2 electrodes had higher oxygen evolution overpotential, which could inhibited the oxyge n evolution reaction and improve the current efficiency effectively. The CV test showed that modified Pb O2 electrodes had greater current of reduction and oxidation peaks compared with pure Pb O2 electrode, which increased the electrochemical activity so that more active groups would be produced in the process of degradation of organic compounds.The 1.0% M-doped Pb O2 electrodes were selected as anodes to study the electrochemical oxidation of cinnamon acid in aqueous solution and the results shown that the Mo-Pb O2 electrode had the best removal of CA and COD. The experimental parameters which influenced the electrochemical degradation of CA over Mo-PbO2 electrode were studied. The results revealed that the electrochemical degradation of CA followed the pseudo-first-order kinetics and the optimal removal of CA, COD and EE/O were 85.51%, 25.79% and 7.48 kWh/m3 under the optimal conditions that the electrolyte concentration, initial concentration of CA, current density and initial value of p H were 0.1 mol/L, 300 mg/L, 10 mA/cm2 and 3.34, respectively. The main degradation pathway of CA was speculated based on the intermediated products which generated during the process of electrochemical oxidation degrade CA identified by IC and GC/MS.