Modulating the iron (hydr)oxides/sulfides by H₂O₂ for a high-performance sulfidated zero-valent iron

Sulfidation of zero-valent iron (SZVI) can enhance the reactivity of ZVI to contaminants removal. The composition and structure of ZVI surface have a significant impact on the sulfidation efficiency. Pre-corrosion of ZVI with oxidizing substances has emerged as a promising means to modulate the ZVI surface composition. In this work, we introduce hydrogen peroxide (H₂O₂) for pre-corrosion of ZVI during sulfidation, resulting in a high-performance SZVI_H2O2. The kinetic constant (k_obs) for the removal of Cr(VI) by SZVI_H2O2 is 2.046 min^-1, which is 5.25 times higher than that of SZVI. The H₂O₂ pre-corrosion of ZVI causes the surface iron (hydr)oxide reconfigure and the produced FeOOH benefits the sulfidizing reaction. The resulting SZVI_H2O2 forms a multi-layer shell on the SZVI_H2O2 surface, consisting of a Fe₃O₄ outer layer encapsulating a FeS_x sublayer. FeS_x and Fe₃O₄ work together to facilitate electron transfer from internal Fe⁰ to contaminants. Additionally, the unique Fe₃O₄ shell can protect the inner FeS_x from oxidation, thereby increasing the reaction durability of SZVI_H2O2. The current work reveals the mechanism of oxidant pre-corrosion of ZVI, enhancing its reactivity, which represents a significant step forward in interfacial modulation of ZVI for efficient contaminant removal.