Facet-Dependent Phosphate Adsorption of CeO2

Cerium-based adsorbents are effective for the removal of phosphate from water, with the reactivity of cerium dioxide (CeO2) being highly dependent on the exposed crystal facets. However, molecular-level interactions that control the facet-dependent reactivity toward phosphate adsorption remain elusive. In this study, we synthesized CeO2 nanostructures with distinct morphologies─rods (CeO2-R), octahedrons (CeO2-O), and cubes (CeO2-C)─that predominantly expose the (110), (111), and (100) crystal facets, respectively. Phosphate adsorption on various CeO2 facets was systematically investigated through a series of batch adsorption experiments, complemented by Fourier transform infrared (FTIR) spectroscopy and density functional theory (DFT) calculations. The phosphate adsorption follows second-order kinetics and aligns with the Langmuir isotherm model. This process is facilitated by the formation of inner-sphere complexes between the Ce–OH groups on the CeO2 surface and the phosphate ions. The adsorption performance is significantly influenced by the geometric configuration of the exposed CeO2 facets, with the normalized phosphate adsorption capacity to surface area following the trend of CeO2-R > CeO2-C > CeO2-O. These results may have strong implications for prediction of the fate of contaminants at the solid–liquid interface and optimization of advanced adsorbent materials for water treatment applications.