Phosphate Supply-Driven Interfacial Coordination Microenvironment Dictates the Electronic Structure and Reactivity of Zero-Valent Iron

The environmental remediation performance of zero-valent iron (ZVI) fundamentally relies on physicochemical processes at its solid–liquid interface. Although phosphorus modification is widely employed to regulate the interfacial behavior of ZVI, the evolution of iron–phosphorus interfacial species and the impact on the electronic structure and reactivity remain insufficiently understood. This work systematically investigated the evolution of the ZVI interfacial structure and behavior by controlling the phosphate supply. Phosphorus species are predominantly monodispersed on the ZVI surface via inner-sphere coordination under a moderate phosphate supply, forming an amorphous structure characterized by Fe–O–P. Dynamic reconstruction of the Fe–O–P microstructure upshifted the d -band center of ZVI, thereby enhancing electron transport and boosting the apparent rate constant for Cr(VI) removal by up to 158-fold. The interfacial reaction gradually shifted from surface-restricted coordination to structural reconstruction involving near-surface iron species as the phosphate supply increased. Consequently, the Fe–O–P coordination units undergo spatial expansion and structural rearrangement within the interfacial region, ultimately forming crystalline Fe 3 (PO 4 ) 2, which severely suppresses electron migration and reactivity. This work reveals a systematic volcano-type structure–activity relationship in which microstructurally evolving phosphate species regulate the electronic structure of ZVI, providing a critical theoretical foundation for the rational design of next-generation iron-based materials.