Visible-light-driven activation of micro-concentration H2O2 by Fe(III)-fulvic acid complexes for efficient pollutant degradation

Abstract

The inherent inefficiency associated with the utilization of micro-concentration hydrogen peroxide (H₂O₂) in conventional Fenton systems arises from the sluggish cycling between Fe(III) and Fe(II). To address this fundamental limitation, the present study demonstrates that complexes formed between Fe(III) and fulvic acid (FA) can effectively harness visible-light-driven ligand-to-metal charge transfer (LMCT). This photochemical process facilitates a synergistic dual-pathway activation of H₂O₂: 1) Fe(II) generated through intramolecular electron transfer reduction of the Fe(III)-FA complex directly activated H₂O₂; 2) In the photoexcited ∗Fe(III)-FA complex, the reduction of the key intermediate ∗OOH lowered the activation energy barrier, facilitating the formation of ∙OH and O₂^·- radicals. Moreover, at a stoichiometric molar ratio of H₂O₂ to contaminant set at 1:1, contaminant removal efficiency achieves an impressive 95%. This light-enhanced mechanism establishes a new paradigm for efficient micro-concentration -level oxidation using H₂O₂, demonstrating exceptional effectiveness in eliminating trace pollutants.