Fe(Ⅱ)/Fe(Ⅲ) cycle enhanced the Electro-Fenton degradation of methylene blue with Fe3O4@C as three-dimensional electrode

Abstract

The cycling rate of iron ions has been reported to limit the Fenton reaction rate. It is, therefore, vital to enhance the cycling rate of iron ions. A composite three-dimensional electrode (FOC) was synthesized using glucose, ammonium carbonate, and FeCl3 through a combination of hydrothermal synthesis and calcination. The electrode’s conditions were subsequently optimized for the applicable pH range and the concentration of methylene blue (MB) that could be effectively degraded. At an FOC-800 dosage of 0.5 g/L, a supply voltage of 4 V, and an initial pH of 4, a degradation rate of 98 % for 10 mg/L MB was achieved, with a 67.5 % reduction in total organic carbon using 2 g/L Na2S2O3 as the electrolyte. The material also demonstrated efficacy in degrading both chemical and pharmaceutical wastewater. A comparative analysis using Na2SO4 as the electrolyte confirmed that Na2S2O3 effectively promoted the cycling of iron ions, enhancing the degradation performance of FOC and expanding its effective pH range. High-performance liquid chromatography (HPLC) was employed to monitor the concentration changes of S2O32- and SO42- during the reaction, while LC-MS was used to identify the degradation products of MB, and ECOSAR was utilized to assess the toxicity of these products. Burst experiments and EPR analysis identified ●OH as the primary active species responsible for degradation, with O2∙- playing a supporting but not dominant role.