Electrochemical mineralization of sulfamethoxazole over wide pH range using Fe II Fe III LDH modified carbon felt cathode: Degradation pathway, toxicity and reusability of the modified cathode

Hierarchical three-dimensional (3D) porous architecture FeIIFeIII layered double hydroxide (LDH) multiwall was grown on carbon-felt (CF) substrate via solvothermal process. The as-deposited FeIIFeIII LDH/CF cathode was composed of highly oriented and well crystallized interconnected nanowalls with high electrical conductivity and excellent catalytic activity over a wide pH range (pH 3–9) for heterogeneous electro-Fenton (HEF) degradation of antibiotic sulfamethoxazole (SMT) in aqueous medium. Mineralization efficiencies (in terms of TOC removal) of ∼97%, 93% and 90% was achieved at pH 3, 6 and 9 respectively for FeIIFeIII cathode during HEF treatment of 0.2mM SMT solution at applied current density of 7.5 mA cm−2 using Ti4O7 anode. Comparative electro-Fenton (EF-Fe2+) with 0.2mM Fe2+ or electrooxidation with H2O2 production (EO-H2O2) studies using raw CF cathode at similar experimental conditions showed relatively lower mineralization with highest TOC removal efficiency of 77% and 64% obtained at pH 3 for EF-Fe2+ and EO-H2O2 respectively. Oxidative degradation of SMT in HEF system was by (i) Ti4O7(%OH) generated at anode surface at all pH studied, (ii) surface catalyzed process and (iii) contribution from homogeneous catalyzed process at pH 3 due to leached iron ions. The prepared FeIIFeIII LDH/CF exhibited excellent catalytic stability with good reusability up to 10 cycles of 4 h treatment at pH 6. Initial SMT solution showed relatively high toxicity but total detoxification of the solution was attained after 8 h of treatment by HEF with FeIIFeIIILDH/CF cathode. HEF with FeIIFeIII LDH/CF cathode is an exciting technique for remediation of organic contaminated wastewater.