Interfacial electron redistribution allows advanced phosphate adsorption in Zn/La-loaded magnetic mesoporous nanospheres

Abstract

A core-shell structured Zn/La magnetic mesoporous silica (denoted as Zn/La-MMS) composite we successfully constructed via etching and co-deposition techniques, achieving exceptionally efficient adsorption of phosphate. At an optimized Zn/La ratio of 0.5 (i.e., Zn/La-0.5 MMS), the composite exhibited an ordered mesoporous structure and superior adsorption performance with a maximum phosphate adsorption capacity of 140.9 mg P/g (15-fold higher than the pristine MMS). High adsorption performance was achieved across a broad pH range of 3 to 11 and in the presence of substantial amounts of co-existing ions/substances (Cl⁻, NO₃⁻, SO₄²⁻, HCO₃⁻, and humic acid at concentrations 20–50 times that of the PO₄³⁻-P concentration). After five adsorption-regeneration cycles, 79 % adsorption capacity remained with material recovery rates >95 % via magnetic separation. A bimetallic synergistic mechanism was revealed via X-ray absorption fine-structure characterizations and density functional theory (DFT) calculations. The electronegativity difference between La and Zn induces interfacial electron redistribution, driving electron back-donation from the La/Zn-O hybridized orbitals to the O 2p antibonding orbitals of HPO₄²⁻, forming stable covalent coordination bonds (La-O-P/Zn-O-P), which allowed the exceptionally high and efficient adsorption of phosphate. This phenomenon is expected to have important implications for the development of novel adsorption materials for advanced removal of phosphate.