The overlooked role of electrostatic repulsion between nanoparticle catalysts in ligand-enhanced heterogeneous Fenton-like reactions

Chelating agents are now frequently used to facilitate Fenton and Fenton-like reactions by building complexes with iron. A series of advantages can be exemplified, such as fast circulation of Fe(III)/Fe(II), enhanced catalytic performance of Fe-ligand, and iron precipitation inhibition, etc. However, few studies explored whether elec-trostatic repulsion between nanoparticle catalysts had an influence on catalytic performance in ligand-enhanced Fenton-like reactions. In this study, we discovered that the coexistence of 0.1 mM EDTA and 10 mM phosphate dramatically accelerated diclofenac (DCF) degradation by Fe3O4/Air (similar to 95% within 20 h). In-depth explorations demonstrated the enhanced electrostatic repulsion between Fe3O4 caused by the addition of EDTA and phosphate played a key role in the promoted DCF degradation. The enhanced electrostatic repulsion between Fe3O4 led to a notable increase in the percentage of Fe-EDTA, which benefited O2 activation and DCF degradation. Reactive oxygen species (ROS) were mainly generated through one-electron activation mechanism of O-2 and center dot OH were confirmed to be predominant active species responsible for DCF degradation. Fe(II)-EDTA on Fe3O4 surface was evidenced to be served as main sites for O-2 and H2O2 activation. During the degradation reaction, sufficient surface Fe(II) on Fe3O4 was maintained with the assistance of EDTA. Toxicity analysis showed that DCF was transformed into less toxic intermediates, demonstrating the feasibility of this technology in practical applica-tions. This work for the first time reveals the importance of electrostatic repulsion between nanoparticle catalysts in ligand-enhanced Fenton-like reactions, providing a low-cost and effective advanced oxidation process for contaminants degradation.