Unveiling the Enhancement of Sulfidation for Fe(IV) Production in a Sulfidated Microscale Zero-Valent Iron Activated Peroxydisulfate Process

Ferryl ion species (Fe(IV)) is considered as an important reactive species in zero-valent iron activated perox-ydisulfate (PDS) process that has great potential for decontamination due to its merits. Sulfidation is an effective chemical reaction process to improve the activity of microscale zero-valent iron (mZVI). In this subject, the effect of sulfidation on the production of Fe(IV), and the key reaction pathways of Fe(IV) generation in sulfidated mZVI (S-mZVI)/PDS system are still unclear. In this work, by using methyl phenol sulfoxide as a probe, we found that sulfidation could greatly change the pathway of Fe(IV) generation, in which the heterogeneous process was proposed to play an important role in activating PDS to produce Fe(IV). In comparison, the production of Fe(IV) in mZVI/PDS system was dependent on aqueous Fe(II) released from mZVI corrosion. Further analysis indicated that the improvement of Fe(IV) production caused by sulfidation could be ascribed to the acceleration of Fe(II) release as well as electron transfer. Sulfur species especially S(-II) could participate in the Fe(II)/Fe(III) cycle for Fe(II) regeneration, and underwent oxidation according to X-ray photoelectron spectroscopy analysis. In addi-tion, we investigated the influence of key parameters (initial pH, PDS dosage, S-mZVI dosage) and coexisting anions (Cl-, SO42-, HCO3-) on Fe(IV) production in S-mZVI/PDS system. This study not only distinguishes the interface activation of PDS for Fe(IV) production from the homogeneous process, but also provides a new insight for the sulfidation to enhance the performance of iron-based materials on advanced oxidation processes.