Synthesis of quantum-size cerium oxide nanocrystallites by a novel homogeneous precipitation method

Mainly by changing the cerium species to be homogeneously precipitated from cerous ion to colloidal cerianite, a special sol-gel process was arranged to synthesize nanocrystalline cerium oxide. The specimen powder was characterized with XRD, SEM, HRTEM, ICP-OES, and UV-vis spectrophotometry. HRTEM detected monodispersed cerianite crystallites with typical size of 3-5 nm, which is a favorable characteristic for many applications. The direct optical band gap estimated from ultraviolet absorption spectrum of the ceria powder is 3.56 eV, which is blue-shifted evidently with respect to the bulk material (Eg = 3.19 eV) and may indicate quantum-size confinement effect in the crystallites. The results show that forced hydrolysis of urea can be used to destabilize the nanocrystal sol, leading to the formation of loosely bound cerianite aggregate.