Maximizing Lanthanum Atomic Utilization via Surface-Confined Lattice Substitution in Magnetite Core–Shell Structures for Superior Phosphate Removal

Lanthanum (La)-based materials are superior candidates for phosphate sequestration; however, conventional surface-coating strategies on magnetic scaffolds often suffer from active site shielding and require energy-intensive synthesis, resulting in suboptimal rare-earth utilization and poor interfacial stability. Herein, we propose a surface-confined lattice engineering strategy to fabricate a La-substituted magnetite shell (Fe 3- x La x O 4 ) on a magnetite core (LaL/Mag) via a facile 50 °C coprecipitation route. By integrating La 3+ directly into the spinel lattice rather than physical loading, we achieved atomic-level dispersion that maximizes the exposure of near-surface active sites. This configuration achieves nearly double the La utilization efficiency (1020 vs 564 mg P/g La) compared to benchmark La(OH) 3 -coated analogues, enabling high-efficiency phosphate capture with a minimal La loading of ∼2.3 wt %. HR-TEM and XPS analyses demonstrate that the lattice-substitution induces local strain and optimized coordination environments, facilitating rapid phosphate immobilization via inner-sphere complexation and LaPO 4 precipitation. Furthermore, the magnetically recoverable LaL/Mag maintains 74% of its initial capacity after five regeneration cycles, demonstrating superior structural robustness. This study provides a sustainable paradigm for designing rare-earth-economical adsorbents, offering an energy-efficient pathway for advanced phosphorus recovery and eutrophication management in complex water matrices.