Enhanced electrocatalytic removal of tetracycline using dual carbon material combined particle electrodes in a three-dimensional electrochemical system: Degradation pathway and mechanism

In order to assemble low cost and high performance electrochemical oxidation system for wastewater treatment, biochar was decorated by graphene to synthesize carbon composite graphene/biochar (GBC) as particle electrode filled into a three-dimensional electrochemical reactor. The GBC particle electrodes demonstrated better electrochemical reaction activity than biochar (BC) particle electrodes. The GBC three-dimensional electrochemical reactor achieved 99.48% removal of tetracycline (5 mg/L) under an input voltage of 10 V. The electrochemical oxidation performance of GBC electrode system was competitive to some metal/metal oxides or metal/carbon material electrode system reported. The removal efficiency of tetracycline was less sensitive to the initial pH of solution from 3.0 to 11.0. The GBC electrode had higher oxygen evolution potential (OEP) (1.76 V), and lower Tafel slope (0.013 V dec−1) than that of the BC. Coated graphene improved electrical conductivity to prompt electron aggregation on surface of the biochar resulting in more reactive oxygen species (ROS) generation. The indirect electrochemical degradation of tetracycline was dominated by non-radicals pathway that singlet oxygen (1O2) rather than free radicals (·OH, O2·-) played the main role. This study proposed a new strategy to develop non-metallic particle electrodes using carbon-based materials for high efficient electrocatalytic oxidation in the electrochemical treatment system.