Surface structure regulation of sulfidated zero-valent iron by H2O2 for efficient pH self-regulation and proton cycle to boost heterogeneous Fenton-like reaction for pollutant control

Sulfidated zero-valent iron (SZVI) has been widely used in controlling organic pollutants. However, the significant decrease in catalytic activity of SZVI-based Fenton-like systems under neutral and alkaline conditions remains a large problem. Herein, it was found that surface structure regulation of SZVI with H₂O₂ (HT-SZVI) greatly enhanced its reactivity and efficiently activated H₂O₂ to oxidize various organics in a wide pH range. The HT-SZVI/H₂O₂ system exhibited a pH self-regulation capability that stabilized the eventual solution pH at ∼3.5 at the initial pH of 3.0–9.0. The excellent oxidation performance was primarily attributed to surface-bound ^•OH produced from H₂O₂ activation by surface Fe(II) sites on HT-SZVI. Additionally, dissolved Fe(II) converted from surface Fe(II) induced proton generation to self-regulate pH. Newly formed high proton-conductive FeS and Fe₃O₄ shells accelerated the transfer of accumulated protons in solution to iron core to produce Fe(II), enabling efficient proton consumption-regeneration cycle and enhancing ^•OH production.