Efficient recovery of phosphate by Fe3O4/La-MOF: An insight of adsorption performance and mechanism from electrochemical properties

Phosphorus (P) is known as a valuable resource, and recycling it from wastewater can avoid environmental pollution and resource waste. Herein, a regenerable magnetic Fe 3 O 4 and La-based metal–organic framework functional material (Fe 3 O 4 /La-MOF) was synthesized by solvent thermal method and its adsorption performances of phosphate were evaluated. The as-prepared magnetic Fe 3 O 4 /La-MOF exhibited magnetic separation efficiency of 97.9% and it could maintain the high adsorption capacity over a wide pH range from 3 to 10, as well as showed an excellent P adsorption selectivity in presence of Cl - , NO 3 – , HCO 3 – , CO 3 2– and SO 4 2- . The isotherm data were consistent with the Langmuir model, and the adsorption kinetic data conformed to the pseudo-second-order model, revealing that there was chemical adsorption between Fe 3 O 4 /La-MOF and phosphate. The electrochemical behavior of Fe 3 O 4 /La-MOF before and after phosphate adsorption showed that the band gap energy of LUMO (Lowest Unoccupied Molecular Orbital) and HOMO (Highest Occupied Molecular Orbital) of P adsorbed Fe 3 O 4 /La-MOF was lower than that of the material itself, which indicated the successful adsorption of phosphate on Fe 3 O 4 /La-MOF and the forming of a perfect hybrid structure. The characterization analysis of FT-IR and XPS illustrated that intra-sphere complex (La O P) formed between Fe 3 O 4 /La-MOF and phosphate by ligand exchange, which might be the dominant mechanism, followed by electrostatic attraction and precipitation. This study highlighted the great promise of magnetic reusable Fe 3 O 4 /La-MOF composite for application in phosphate removal and recovery.