Stable Magnetite@La–Fe Oxide Core–Shell Nanostructures Prepared via Lattice Lock for Reusable Extraction of Phosphate Anions

Stable magnetic core-shell nanostructures are developed by lattice locking lanthanide-iron (La-Fe) oxide shells with magnetite cores to prevent the release of La from the surfaces of the magnetite nanostructures. The resulting core-shell nanostructures demonstrate excellent outstanding regeneration performance and high adsorption capacity for phosphate (115 mg P·g^-1). These nanostructures release minimal La from the magnetite core surfaces after adsorbent regeneration, with a La loss of only 20% compared to the control sample, Mag@La(OH)₃. La³⁺ ions were released at concentrations ranging from 1 to 2.3 μg·L^-1 at pH levels of 4 to 8, which is within the metal content range found in natural aquatic environments. These results demonstrate the high stability of the nanostructures after regeneration. Furthermore, the adsorbent exhibits high extraction capacity across a wide pH range of 4 to 10 and performs well even in the presence of interfering anions at phosphate-to-anion molar ratios of 1:5, 1:25, and 1:100. Microscopic and spectroscopic analyses reveal that the primary extraction mechanism of phosphate in the La-containing shells is surface precipitation. This approach not only improves the use of magnetic core-shell nanostructures as adsorbents but also demonstrates the creation of a broad range of stable magnetic functional materials for diverse applications.