Synthesis of Ti/SnO<sub>2</sub>-Sb electrode modified by nitrogen and sulfur co-doped graphene for optimization the electrooxidation of neutral red and methyl orange dyes

Abstract

The degradation of methyl orange (MO) and neutral red (NR) was studied by the direct electrooxidation using nitrogen and sulfur co-doped graphene (NSG) supported antimony doped tin oxide (SnO<sub>2</sub>-Sb). Sol-gel and microwave technics were used to prepare the material (Ti/SnO<sub>2</sub>-Sb-NSG). Raman, XRD, FTIR and TGA/DSC analyses help to confirm the coating of titanium substrate with the SnO<sub>2</sub>-Sb-NSG film. Linear sweet voltammetry results show that Ti/SnO<sub>2</sub>-Sb-NSG material possesses high oxygen overvoltage. Three independent variables including electrolysis time, current density and dye concentration on the performance of the anodic oxidation system was modeled using the Box-Behnken Design. The optimum conditions for MO and NR degradation were for current density 18 mA/cm² and 58 mA/cm², electrolysis time 6 h and 6 h and dye concentration 29 mg/L and 82 mg/L, respectively. However, based on these optimums, MO was degraded at 98.71 % while NR was just degraded at 82.7%. Based on the intermediate compounds, the degradation mechanism of MO at the Ti/SnO<sub>2</sub>-Sb-NSG anode was proposed. Ti/SnO<sub>2</sub>-Sb-NSG electrode showed a higher efficient electrocatalytic performance for NR and MO degradation than that of Ti/Sb-SnO<sub>2</sub> or Ti/Sb-SnO<sub>2</sub>-NG electrodes. Furthermore, the lifetime of Ti/SnO<sub>2</sub>-Sb-NSG was about 31.6 h while Ti/SnO<sub>2</sub>-Sb electrode was 9.0 h.