New Insights into the Role of Crystalline Fe3P in Phosphatized Zerovalent Iron for Enhancing Advanced Oxidation Processes and Storage Stability

Zerovalent iron (ZVI) is a widely utilized remediation agent for contaminated soil and groundwater; however, it has consistently faced the challenge of balancing catalytic activity with storage stability. Herein, submicron ZVI particles were phosphatized to produce phosphatized ZVI (P-ZVI), which was employed to activate peroxydisulfate (PDS) for phenol degradation. As anticipated, phosphatization significantly enhanced both the storage stability (>10 months vs 1 d) and catalytic activity (4.37 vs 0.12 L m^-2 h^-1) of ZVI compared to unphosphatized counterparts attributed to the formation of a crystalline Fe₃P shell on P-ZVI. This Fe₃P shell selectively interacts with H₂O/O₂/PDS, maintaining the stability of P-ZVI under high humidity and oxygen conditions while creating mass transfer channels that enhance reactivity in the presence of PDS. Characterization results from the reaction process demonstrated that the Fe₃P shell activated PDS through both direct (via Fe cations) and indirect pathways (through a phosphorus anion-mediated Fe³⁺/Fe²⁺ cycle), generating reactive species and facilitating mass transfer between core Fe⁰ and external PDS for efficient PDS activation and phenol degradation. This study elucidates how constructing an Fe₃P shell can realize selective activation of PDS while simultaneously enhancing both the storage and catalytic stabilities of ZVI, thereby boosting the practical application of PDS-based advanced oxidation processes in various environmental remediation.