Nonaqueous Sol-Gel Synthesized Hierarchical CeO2 Nanocrystal Microspheres as Novel Adsorbents for Wastewater Treatment

Hierarchical CeO2 nanocrystal microspheres were synthesized with a nonaqueous sol-gel method at a low temperature of 120 degrees C. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and nitrogen sorption measurements. The adsorption performances of hierarchical CeO2 nanocrystal microspheres were tested with the batch removals of typical pollutants of Cr(VI) and rhodamine B from simulated wastewater. It was found that the nanostructured CeO2 could effectively remove Cr(VI) without pH preadjustment. The Freundlich adsorption isotherm was applicable to describe the removal processes. Kinetics of the Cr(VI) removal was found to follow pseudosecond-order rate equation. Furthermore, the as-prepared and Cr(VI)-adsorbed hierarchical CeO2 nanocrystal microspheres were carefully analyzed by X-ray photoelectron spectroscopy (XPS). On the basis of the XPS results, a possible mechanism of Cr(VI) removal with hierarchical CeO2 nanocrystal microspheres was proposed. Moreover, these nonaqueous sol-gel synthesized hierarchical CeO2 nanocrystal microspheres also exhibited remarkable ability to remove rhodamine B, suggesting they are promising absorbents for wastewater treatment.