Breaking the Fe3+ regeneration bottleneck in aerated electro-Fenton systems through reductive pyrite activation

H 2 O 2 supply alone did not determine electro-Fenton efficiency. • Pyrite outperformed soluble Fe 2+ by sustaining Fe 3+ reduction. • Cathodic activation generated reactive Fe-S/sulfur mediators. • ·OH contributed to BPA oxidation and toxicity attenuation. Electro-Fenton systems are limited not only by H 2 O 2 production but also by the slow regeneration of Fe 2+ from Fe 3+ , which restricts continuous hydroxyl radical formation. Here, we developed an aerated electro-Fenton system coupled with natural pyrite and show that its high activity originates from matched H 2 O 2 supply and pyrite-sustained iron cycling. The aEF-pyrite system achieved nearly complete bisphenol A removal within 60 min, with an apparent rate constant of 0.052 min −1 , which was 26.0, 13.0 and 6.5 times higher than those of the electrochemical system, aerated electrochemical system and conventional aEF-Fe 2+ system, respectively. Cathodic aeration promoted in situ H 2 O 2 accumulation, whereas pyrite maintained a higher Fe 2+ concentration and suppressed Fe 3+ accumulation, enabling continuous conversion of H 2 O 2 into ·OH. Surface and solution analyses showed that pyrite participated in Fe and S redox transformation rather than acting only as a passive iron source. DFT-based electronic-structure analyses further indicate that electron injection into pyrite preferentially weakens S S antibonding states, providing a basis for reductive sulfur activation and the formation of reactive Fe-S/sulfur intermediates. These intermediates can serve as a mobile electron-transfer pool for Fe 3+ reduction, bypassing the sluggish H 2 O 2 -mediated regeneration pathway. The system also showed broad pH adaptability, reduced iron precipitation, effective toxicity attenuation and good performance in complex water matrices. This work identifies reductive pyrite activation as a mechanism for sustaining Fe cycling in aerated electro-Fenton chemistry and provides a practical route for improving Fenton oxidation through mineral-mediated Fe 3+ regeneration. Download: Download high-res image (153KB) Download: Download full-size image