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

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 CeO 2 open-hexagonal nanotubes (CeO 2 -OH-NT) and CeO 2 nanoporous-wall nanotubes (CeO 2 -NW-NT), respectively. CeO 2 -OH-NT and CeO 2 -NW-NT are found to have higher surface area, easier reducibility, and higher mobility of surface oxygen species than CeO 2 nanoparticles (CeO 2 -NP).