Preparation of 3DG-SnO2 anode for electrochemical oxidation of 2,4,6-trichlorophenol: Theoretical calculation and degradation pathways

Abstract

Novel three-dimensional graphene and SnO2 (3DG-SnO2) composite anode was prepared by a simple pressing process for electrochemical oxidation of 2,4,6-trichlorophenol (2,4,6-TCP). The 3DG-SnO2 material was studied by SEM, TEM, XRD and FTIR to characterize its morphology, crystal structure and functional group. The cyclic voltammetry and linear scan voltammetry were carried out to evaluate electrochemical performance of 3DG-SnO2 samples. The characterization results reveal that the SnO2 were homogeneously distributed in the 3DG, and the composite of 3DG greatly enhanced the oxygen evolution voltage and active sites of SnO2. Active species trapping experiments indicate that the •OH radicals was the most important oxidant species and the •OH generation rate at 3DG-SnO2 material was 2.60 times higher than that of bare SnO2 anode. Therefore, in electrochemical oxidation of 50 mg/L 2,4,6-TCP process, the 3DG-SnO2 anode displayed higher electrochemical activity with degradation efficiency of 100% and COD degradation efficiency of 75.48% after 120 min of electrolysis, and its average current efficiency is 1.47 times than that of SnO2 anode. A quadratic model was also developed by response surface analysis to predict the 2,4,6-TCP removal efficiency. Under optimized conditions (initial 2,4,6-TCP concentration = 200 mg/L, current density = 23.54 mA/cm2, Na2SO4 concentration = 0.19 mol/L, pH = 8.16), the 2,4,6-TCP removal efficiency reached up to 99.77% after 60 min of electrolysis. Moreover, the preferential attack sites of 2,4,6-TCP by OH radicals were also predicted by theoretical calculations and the specific degradation products were identified by GC-MS. Three plausible degradation pathways were proposed accordingly.