Biochar-loaded Ce³⁺-enriched ultra-fine ceria nanoparticles for phosphate adsorption

Biochar-loaded Ce³⁺-enriched ultra-fine ceria nanoparticles (Ce-BC) was prepared by a facile impregnation-precipitation-pyrolysis process and applied as adsorbents to adsorb phosphate from water. The crystal size of ceria nanoparticles in the Ce-BC was as small as 2-5 nm and the concentration of Ce³⁺ was high to 59.6 %, which was benefited from the rapid precipitation, N₂ pyrolysis atmosphere and the presence of the biochar during preparation. Ce-BC exhibited a fast adsorption kinetics for phosphate and the adsorption equilibrium could be reached within 10 min. The maximum phosphate adsorption capacity was up to 77.7 mg P g^-1 at pH 3.0. Based on Fourier transform infrared (FTIR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) analysis, Ce³⁺ of ceria was demonstrated playing the vital role on phosphate removal and the formation of CePO₄ nanocrystals was the main adsorption mechanism. This work provides a facile strategy for preparing high Ce³⁺ contenting materials and shows a great potential application for the phosphate removal for its high-effective and high stability.