Preparation of a novel hafnium-loaded Fe₃ o₄ @SiO₂ superparamagnetic nanoparticles and its adsorption performance for phosphate in water

Phosphorus is an essential element of life but can lead to eutrophication if present above limit in waterways. Hydrous metallic oxides-based magnetic nanoparticle is considered as an easily separable adsorbent for efficient separation of phosphate from sewage. In this paper, superparamag-netic particles consisting of hafnium-modified hydroxides loading on Fe₃ O₄ multicores embedded in SiO₂ matrix were synthesized (MgFeHf-NPs/MgAlHf-NPs) and the performance of capturing phosphate was investigated. The obtained nano-composites showed well-defined crystal struc-ture and sufficient saturation magnetization. High phosphate adsorption capacity was observed with these NPs from solution as well as digested sludge liquor and dewatered sludge wastewater. These NPs also showed high selectivity with other co-existing ions and organics. The enhancement of phosphate adsorption capacity by doping with Hf should be explained by the stronger ligand complexation built by the pair of the hard acid Hf ion and the hard base phosphate that matched up the bonding preferences. MgAlHf-NPs and MgFeHf-NPs exhibited regeneration rates after five adsorption–desorption cycles compared with ordinary MgAl-NPs and MgFe-NPs. This paper attempts to provide a promising nano-sorbent for phosphate recovery.