Adsorption of phosphate ions from aqueous solutions by a CeO₂ functionalized Fe₃O₄@SiO₂ core-shell magnetic nanomaterial

Abstract

Phosphate is generally considered to be one of the nutrients for plants which may cause eutrophication of the aquatic environment. In this study, a CeO₂-functionalized Fe₃O₄@SiO₂ core-shell magnetic nanomaterial (denoted as Fe₃O₄@SiO₂-CeO₂) was prepared and used as the adsorbent to remove phosphate from water. The adsorbents were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and N₂ adsorption/desorption isotherms. Characterization results show that the particle size is around 8.63 nm, Brunauer–Emmett–Teller (BET) surface area is 179.7 m² · g⁻¹ and the pore volume is 0.39 cm³ · g⁻¹ for magnetite Fe₃O₄@SiO₂-CeO₂. The adsorbents could be rapidly separated under an external magnetic field. Batch adsorption tests show that the Fe₃O₄@SiO₂-CeO₂ adsorbent exhibited high adsorption affinity for phosphate. Additionally, phosphate adsorption isotherms over the adsorbents could be well described by the Langmuir model, suggesting monolayer adsorption, and phosphate adsorption kinetics followed the pseudo-second-order kinetics. Moreover, increasing pH led to suppressed phosphate adsorption, and phosphate adsorption slightly increased with ionic strength.