Integrating surface phosphate modification and lattice nitrogen doping for synergistic removal of Cr(VI)

A microscale zero-valent iron (mZVI) composite integrating surface phosphate (P) modification and lattice nitrogen (N) doping (NP-mZVI) was successfully fabricated by one-step mechanochemical method in aim to establish synergistic adsorption-reduction pathways for enhanced Cr(VI) removal. NP-mZVI demonstrated superior reactivity for Cr(VI) removal with 100% of both removal efficiency and conversion rate, which significantly outperform the pristine ball-milled mZVI bm and P-modified mZVI bm . Furthermore, NP-mZVI also exhibited excellent removal performance for a range of heavy metals (e.g., Ni(II), Pb(II), Cu(II), and Cd(II)), and was also demonstrated to be pH-universal, long-term stability, and environmental applicability. The strategic integration of lattice N doping and surface P coordination in NP-mZVI establishes a dual-path optimization mechanism for enhanced Cr(VI) removal. Surface P groups enable bidentate Cr(VI) complexation through ligand-specific recognition, reducing adsorption energy barriers while creating Fe-O-P mediate directional charge transfer. Concurrently, interstitial N doping induces lattice tensile strain via Fe Fe bond elongation, weakening metallic bonding networks to amplify electron liberation from the Fe 0 core. N facilitates electron release through strain engineering while P directs interfacial electron utilization. This synergistic coupling of core activation and surface mediation resolves the kinetic mismatch between electron supply and interfacial demand, achieving superior Cr(VI) removal efficiency through adsorption-reduction pathway integration. This study highlighting the synergistic effects of surface P modification and lattice N doping for mZVI in enhancing the reduction and removal of Cr(VI), and provides a new insight into rational design of modified mZVI with high reactivity.