Facile One-Step Synthesis of Double-Shelled CeO2 Hollow Spheres and Their Optical and Catalytic Properties

Abstract

Abstract Double-shelled CeO2 hollow microspheres (4–5 µm) were synthesized through a facile one-step hydrothermal treatment of Ce(NO3)3·6H2O in the presence of citric acid and hexamethylenetetramine (HMTA), and scanning and transmission electron microscopies demonstrated the samples are hollow spheres with litchi-like surfaces. The assembly of the hollow spheres was contributed to coordination effect of additives employed in the reaction system and the ripening growth in the process. Meanwhile, two other spherical structures including polyhedron-constituted and porous microspheres assembled with nanocrystals were also synthesized by varying the experimental parameters in the synthetic route. The UV–vis spectroscopic investigation demonstrated that the absorption edge of the three samples was blue shifted accordingly with their constituted primary crystallite sizes. In addition, investigation showed that the catalytic activities for CO oxidation of the three spheres types were considerably higher than those of commercial CeO2 powders, and their activities were in the order of porous > litchi-like double-shelled hollow > polyhedron-constituted, consistent with their BET surface area of 33, 22, and 10 m2 g−1. Specially, the litchi-like double-shelled hollow spheres showed much better catalytic properties per unit weight catalyst.