Enhanced generation of H2O2 and radicals on Co9S8/partly-graphitized carbon cathode for degradation of bio-refractory organic wastewater

In electrochemical advanced oxidation processes (EAOPs), the hydrogen peroxide (H2O2) could be in-situ generated from the two-electron (2e) oxygen reduction reaction (ORR), which was then converted to (OH)-O-center dot radicals in the role of cathode catalyst. To improve the efficiency of H2O2 generation, cobalt sulfide/partly-graphitized carbon (Co9S8/PGC) composites as EAOPs cathodes were synthesized via a simple simultaneous carbonization method. The structural and electrochemical properties of Co9S8/PGC were investigated. Results demonstrated that Co9S8 with coexistence of Co2+/Co3+ was tightly embedded into the PGC skeleton. Abundant oxygen-containing groups on the PGC surface could improve the wettability and hydrophilicity of the Co9S8/PGC (800 degrees C), contributing to the formation of more catalytic active sites in the porous structure. Synergistic effect between Co9S8 and PGC could improve the electron transfer efficiency and O-2 mass transfer by increasing the contact interface area between electrode and electrolyte, inducing the high selectivity for 2e ORR. The mixed-valence nature of Co9S8 (Co2+/Co3+) exhibited high catalytic activity for promoting the (OH)-O-center dot generation from H2O2. Degradation rates of phenol and TOC removal rate of ceftazidime reached approximately 89.1 and 84.3% at 120 and 480 min, respectively, indicating that Co9S8/PGC cathode had promise for further application. (C) 2016 Elsevier Ltd. All rights reserved.