One-pot fabrication of a novel urchin-like Fe3O4/α-FeOOH/Al(OH)3 magnetic nanocomposite for phosphate removal and recovery: adsorption performance and mechanism

Abstract

Driven by the dual crises of global phosphorus depletion and severe aquatic eutrophication, developing sustainable technologies for phosphorus recovery is of paramount importance. Herein, we report a facile one-pot synthesis of a novel magnetic adsorbent Fe₃O₄/α-FeOOH/Al(OH)₃ (MGA) nanocomposite, wherein amorphous aluminum hydroxide is uniformly coated onto an urchin-like magnetite/goethite carrier. Systematic optimization of the Al(OH)₃ loading demonstrated that the optimal composite delivered a maximum phosphate adsorption capacity of 94.9 mg-P g⁻¹ with a partition coefficient of 0.53 mg g⁻¹ µM⁻¹ at pH 7.0. MGA exhibited favorable adsorption performance across a pH range from 6.0 to 10.0, and was virtually unaffected by ubiquitous competing anions (Cl⁻, NO₃⁻, SO₄²⁻, HCO₃⁻, and CH₃COO⁻). Comparative spectroscopic investigations (XPS and FTIR) of the pristine and spent materials elucidated that this exceptional affinity primarily stems from a combination of electrostatic attractions and ligand exchange, leading to the formation of inner-sphere complexes. Desorption tests revealed that MGA sustained a competitive adsorption capacity over five regeneration cycles. Overall, MGA represents an economically viable and highly efficient candidate for the remediation of phosphorus-polluted waters and subsequent resource recovery.