Efficient removal arsenate from water by biochar-loaded Ce3+-enriched ultra-fine ceria nanoparticles through adsorption-precipitation

Highlights: • Ce-BC exhibited excellent performance for As(V) removal. • The formation of CeAsO₄ via adsorption-precipitation was the main sorption mechanism. • The maximum As(V) sorption capacity of Ce-BC was 227.0 mg g⁻¹. • Ce³⁺ of ceria was demonstrated playing the vital role on As(V) removal. Biochar-loaded Ce³⁺-enriched ultra-fine ceria nanoparticles (Ce-BC) were used as a novel nanostructured adsorbent for the removal of arsenate (As(V)) from aqueous solutions. The effect of cerium valence on As(V) adsorption and the mechanism of As(V) adsorption onto Ce-BC were investigated using batch experiments and a series of spectroscopy detection technologies. The adsorption isotherm data fitted with the Langmuir model, with maximum As(V) sorption capacity of 219.8 mg g⁻¹ at pH 5.0 and 25 °C. The adsorption kinetics fitted well with the pseudo-second-order model. Ce³⁺ on the surface of Ce-BC plays an important role in the adsorption of As(V). The decrease in Ce³⁺ concentration from 60.1% to 48.9% on the Ce-BC surface, significantly decreased the adsorption of As(V) on Ce-BC. Furthermore, a strong affinity between As(V) and Ce³⁺-enriched Ce-BC was revealed, resulting in irreversible adsorption. Most importantly, the adsorbed As(V) could further react with Ce³⁺ of the ultra-fine cerium oxide nanoparticles in Ce-BC to form rod-like CeAsO₄ precipitates. Through the novel adsorption-precipitation process, Ce-BC can be used to remove trace As(V).