Enhanced removal of Cu-EDTA in a three-dimensional electrolysis system with highly graphitic activated biochar produced via acidic and K2FeO4 treatment

Herein, we report a novel strategy for the fabrication of almond shell biochar-based materials containing highly dispersed graphene nanosheet structures by sequential treatment with hydrochloric acid and potassium ferrate. The resulting material serving as particle electrodes endowed the three-dimensional electrolysis system with excellent and stable Cu-ethylene diamine tetraacetic acid (Cu-EDTA) decomplexation and mineralization ability, along with Cu(Ⅱ), chemical oxygen demand, and dissolved total organic carbon removal efficiencies of 96.8%, 92.5%, and 86.2%, respectively. In contrast to excess Cu(Ⅱ) or EDTA, the complete complexation between Cu(Ⅱ) and EDTA facilitated EDTA degradation. During the reaction, the adsorption toward Cu(Ⅱ), rather than EDTA, in the complexing system, alleviated the burden of electrochemical oxidation for Cu-EDTA decomplexation. This, together with direct and indirect electrocatalytic oxidation mediated by adsorbed hydroxyl radicals on the particle electrode surface, contributed to the enhanced removal of Cu-EDTA. Density functional theory calculations further demonstrated the main types of active sites and the importance of the graphene nanosheet structure of the particle electrodes. This work provides different perspectives on the electrocatalytic removal of heavy metal complexes.