Redox Oscillations Regenerate Inactivated Zerovalent Iron Particles

Zero-valent iron (ZVI) is among the most widely applied micro-nano materials for environmental remediation. Despite its high efficacy toward pollutant removal, the long-term performance of ZVI is often hindered by surface passivation, which diminishes reactivity and necessitates regeneration. Here, we present a redox oscillation strategy for regenerating inactivated ZVI via cyclic microbial reduction and ambient oxidation. The regenerated ZVI exhibited substantially enhanced surface electron-donating capacity (2.5 × 10–2 mmol e– g–1) compared to inactivated ZVI (5.3 × 10–3 mmol e– g–1), along with recovered electron transfer kinetics (4.0 × 10–3 s–1) compared to inactivated ZVI (6.2 × 10–4 s–1). Consequently, regenerated ZVI achieved a 7.2-fold higher Cr(VI) reduction efficiency, together with improved removal of nitrate and p-nitrophenol. Mechanistic analyses revealed that regeneration was driven by the synergistic disruption and transformation of the passivating oxide layer: physical alteration increased surface area and porosity, while chemical transformation yielded low-crystalline iron oxides with enhanced surface redox activity. These modifications created additional surface reactive sites, thereby facilitating pollutant sorption and transformation. This study demonstrates redox oscillation as a promising approach to sustain the reactivity and durability of ZVI in remediation applications.