Theoretical and experimental study of the influence of cation-Eriochrome complexes on the BDD anodic oxidation of Eriochrome Black T solutions

It has previously been established during the elimination of Eriochrome Black T (EBT) that water hardness is an important condition that limits the efficacy of electrochemical treatments of azo dye effluent by the electrophilic attack of (OH)-O-center dot radicals, due to the possible formation of calcium and magnesium complexes. This outcome was observed when using the Electro-Fenton (EF) approach, where the use of iron as a catalyst is mandatory; however, the synergistic or antagonistic effects of iron were not considered. For this reason, this communication presents important experimental and theoretical insights (using Density Functional Theory (DFT) and Quantum Theory of Atoms in Molecules (QTAIM)) into the influence of different ions (Ca2+, Mg2+ or Fe2+) on the degradation efficiency of EBT solution using anodic oxidation (AO) with boron-doped diamond (BDD) electrodes.