Enhanced phosphate adsorption using Zr-Al and Ce-Al binary oxide nanoparticles

Abstract

In addressing eutrophication resulting from phosphate accumulation, multi-metallic oxides often outperform single-metallic oxides in phosphate adsorption capacity. While alumina is abundant, its stability in acidic or alkaline environments is limited. Contrastingly, zirconium and cerium oxides demonstrate superior acid and base resistance, alongside specific phosphate affinity. This study focuses on the synthesis of Zr-Al and Ce-Al binary oxide nanoparticles through a sol-gel approach for phosphate removal from aqueous solutions, evaluating their efficiency through batch experiments. By judiciously adjusting the Zr/Al and Ce/Al ratios, binary oxide nanoparticles with distinct structures, grain sizes, surface characteristics, and phosphate adsorption properties were fabricated. Results indicate that Zr(3)Al(10) and Ce(3)Al(10) nanoparticles exhibit optimal phosphate adsorption properties among Zr-Al binary oxide variants and Ce-Al binary oxide counterparts, respectively. Kinetic data conform to the pseudo-second-order model for phosphate adsorption on Zr(3)Al(10) and Ce(3)Al(10), while equilibrium adsorption isotherms align with the Langmuir model. Phosphate adsorption capacities reached 83 mg/g for Zr(3)Al(10) and 210 mg/g for Ce(3)Al(10), positioning them as potent adsorbents. Coexisting anions minimally influence phosphate adsorption on Zr(3)Al(10) and Ce(3)Al(10) nanoparticles, indicating high selectivity towards phosphate, whereas Ca²⁺ and Mg²⁺ ions notably enhance phosphate adsorption. Mechanistically, phosphate adsorption on both nanoparticles follows electrostatic attraction, ligand exchange, and inner-sphere complexation, with surface-OH groups playing a pivotal role. Leveraging the advantageous properties of their parent materials, Zr-Al and Ce-Al binary oxide adsorbents exhibit synergistic effects, enhancing their potential for phosphate removal.