Formation mechanism and size control of ceria nanocubes

Abstract

Well-crystallized CeO₂ cubes of 10–20 nm, which predominantly exposed the polar {100} facet, were fabricated under hydrothermal conditions. The growth mechanism of the nanocubes was investigated by analyzing the structures of the intermediate products at different intervals, and found that the formation route of the nanocubes involved both oriented attachment at the early stage and the Ostwald ripening over the entire process. Ce(OH)₃ nanorods were readily formed at the initial stage, while their dissolution, recrystallization and oxidation, under hydrothermal conditions, yielded CeO₂ polyhedra, which were further transformed into CeO₂ nanocubes. During this growth process, the nucleation and epitaxial growth of CeO₂ nanocubes occurred on the Ce(OH)₃ nanorods. Moreover, the OH⁻/Ce³⁺ ratio in synthetic solution played a decisive role in tuning the size of ceria nanocubes; increasing the OH⁻/Ce³⁺ ratio lowered the size of ceria nanocubes. The catalytic properties of the CeO₂ nanocubes for CO oxidation showed a prominent size effect; the conversion of CO increased as the size of the nanocubes reduced.