Ligand-assisted heterogeneous catalytic H2O2 activation for pollutant degradation: The trade-off between coordination site passivation and adjacent site activation

Ligand modification is an effective and universal strategy to enhance the sluggish surface reaction kinetic in the heterogeneous Fenton system. However, the mechanistic for the promotion effect concerning the complex surface adsorption/activation processes remains unrevealed. Herein, we find that the catalytic H2O2 activation ability of BiFeO3 can be significantly enhanced by EDTA and other polycarboxylate ligands. The complexing effect of EDTA enhances the activation rate of H2O2 via decreasing the redox potential of the FeIII/FeII pair, also remarkably improves the utilization efficiency of H2O2 via preserving the electron-rich FeII under the attack of O2•/HO2•. More importantly, based on kinetic analyses and theoretical calculations, we reveal that the active site for H2O2 activation on the EDTA-adsorbed BiFeO3 surface is the adjacent free FeIII, rather than the EDTA complexing FeIII and the non-adjacent free FeIII. A unique dual effect mechanism of EDTA on the heterogeneous Fenton reaction via the coordination site passivation and adjacent site activation is elucidated. This work clarifies the microcosmic role of ligands in governing the catalytic activity of the surface active site, also provide a significant guidance to rationally develop efficient ligand-assisted heterogeneous reaction system for pollutant degradation.