Growth mechanism of ceria nanorods by precipitation at room temperature and morphology-dependent photocatalytic performance

Abstract

Ceria (CeO₂) nanorods have been prepared by simple short-term precipitation at room temperature for the first time using aqueous solutions based on Ce(NO₃)₃·6H₂O and NaOH. TEM showed that (a) the two solutions alone yielded nanooctahedra of cross section ∼10 nm and (b) selective surface modification by isopropanol (IPA) played a significant role in the morphological development of approximately square nanorods of dimensions 4–5 nm width, 15–25 nm length, and [110] growth direction. DFT was used to assess surface energies and the interactions of the H₂O and IPA molecules with the {111}, {110}, and {100} ceria surfaces. A growth mechanism on the basis of these adsorption energies and orientations is proposed and it depends on the favorable IPA adsorption energy. Its effect is twofold. First, it facilitates the formation of a {110} prism that alters the morphology from octahedral to spheroidal and then cuboidal. Second, the anisotropic electrostatic field in the electrical double layer, which is established by the oriented adsorption of the IPA molecule, is considered to facilitate the growth of the nanorod morphology. XPS data show that nanorods exhibit a greater concentration of Ce³⁺ (and associated oxygen vacancies) than do the nanooctahedra. The parameters determining the development of nanoparticle morphology are ranked in the order: packing density ≈ lattice spacing > IPA adsorption > H₂O adsorption > surface energy. The present work suggests the applicability of crystallography considerations and DFT modeling to direct the crystal growth of specific morphologies.