Synthesis, Growth Mechanism, and Properties of Open-Hexagonal and Nanoporous-Wall Ceria Nanotubes Fabricated via Alkaline Hydrothermal Route

Abstract

Ce(OH)3 open-hexagonal nanotubes [Ce(OH)3-OH-NT] and Ce(OH)3 nanoporous-wall nanotubes [Ce(OH)3-NW-NT] have been successfully synthesized, for the first time, by a hydrothermal alkaline route and characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, Brunauer−Emmett−Teller method, differential thermal analysis−thermogravimetric analysis, and temperature-programmed reduction. The growth mechanism of Ce(OH)3-OH-NT via a hydrothermal alkaline route has been found to occur by the dissolution and recrystallization of surrounding Ce(OH)3 compounds followed by anisotropical growth of Ce(OH)3-OH-NT gradually along the c-axis of nanotubes. The growth of Ce(OH)3-OH-NT has been observed, for the first time, to occur over two different Ce(OH)3 compound bases: multidirectional growth of Ce(OH)3-OH-NT over a Ce(OH)3 spherical core base to obtain nanotube flowers and vertical growth of Ce(OH)3-OH-NT over a Ce(OH)3 flat base to obtain a nanotube jungle. Ce(OH)3-NW-NT has been successfully fabricated by further treating Ce(OH)3-OH-NT under static alkaline treatment at room temperature. Calcination of Ce(OH)3-OH-NT and Ce(OH)3-NW-NT leads to the formation of CeO2 open-hexagonal nanotubes (CeO2-OH-NT) and CeO2 nanoporous-wall nanotubes (CeO2-NW-NT), respectively. CeO2-OH-NT and CeO2-NW-NT are found to have higher surface area, easier reducibility, and higher mobility of surface oxygen species than CeO2 nanoparticles (CeO2-NP).