Electrochemical mineralization of sulfamethoxazole over wide pH range using FeIIFeIII 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 0.2 mM SMT solution at applied current density of 7.5 mA cm−2 using Ti4O7 anode. Comparative electro-Fenton (EF-Fe2+) with 0.2 mM 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.