Electrochemical Removal of Ni–EDTA Mediated by Chlorine and Hydroxyl Radicals on BDD Anodes

As a highly reactive oxidative species, chlorine radicals ( E Cl • 0 = 2.47 V vs standard hydrogen electrode, SHE) could react with carboxylic and amino group-containing organic matter efficiently. To this end, mechanistic insights into the reactive species (Cl • and • OH)-mediated Ni–EDTA decomposition were examined in depth. The used boron-doped diamond (BDD) anode could achieve remarkably enhanced decomposition of Ni–EDTA in NaCl electrolyte, indicated by the apparent reaction kinetics constant being 2.7 and 4 times that in the presence of Na 2 SO 4 and NaClO 4, respectively. The experimental results and theoretical simulations revealed that the chlorine evolution reaction (CER) was thermodynamically favorable on the BDD anode, which facilitated the electro-generation of Cl • . Competitive kinetics and quenching experiments proved that the second-order rate constant of Cl • with Ni–EDTA is ∼1.38 × 10 10 M –1 s –1, which is higher than that of • OH with Ni–EDTA (∼2.68 × 10 9 M –1 s –1 ). Furthermore, the experimental results and density functional theory (DFT) calculations show that the molecular changes of Ni–EDTA are mediated by Cl • and • OH through the H-abstraction and electron-transfer pathway in EDTA 4– . This study demonstrates positive implications in the electrochemical decomplexation of wastewater containing chlorine, which makes water treatment more effective, more economical, and much easier.