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

The inherent inefficiency associated with the utilization of micro-concentration hydrogen peroxide (H 2 O 2 ) 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 H 2 O 2 : 1) Fe(II) generated through intramolecular electron transfer reduction of the Fe(III)-FA complex directly activated H 2 O 2 ; 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 O 2 ·- radicals. Moreover, at a stoichiometric molar ratio of H 2 O 2 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 H 2 O 2 , demonstrating exceptional effectiveness in eliminating trace pollutants. • Achieved >90% BPA degradation at ultra-low H 2 O 2 :pollutant molar ratio of 1:1 • Revealed dual H 2 O 2 activation pathways via Fe(III)-fulvic acid(FA) LMCT process • Identified key *OOH intermediate and reaction routes using in-situ Raman spectroscopy • Demonstrated effective operation across a wide pH range from 3 to 9