Search

The fabrication of two kinds of Ce[O.sub.2] nanotubes with unique structures and morphologies by using Ce(OH)C[O.sub.3] nanorods as precursors is demonstrated.

In this paper, CeO2 nanotubes based on the Kirkendall effect (for simplicity, this type of nanotubes is denoted as K-type CeO2 nanotubes) are fabricated through a solid—liquid interface reaction between Ce(OH)CO3 nanorods and NaOH solutions, Our studies indicate the formation mechanism of K-type CeO2 nanotubes is quite different from those of CeO2 nanotubes subjected to template (T-type CeO2 nanotubes) and lamellar rolling (L-type CeO2 nanotubes) reported previously by our group. The K-type CeO2 nanotubes are prepared by congregating Kirkendall voids and subsequent calcinations. The time evolution processes are imaged by TEM, and the results show that as the reaction processes, interior spaces are formed and enlarged in Ce(OH)CO3 nanorods to form K-type CeO2 nanotubes. In contrast, the intenor space in T-type CeO2 nanotubes decreases with reaction time. XRD is applied to study the phase transformation in the formation process of K-type CeO2 nanotubes. Our study also indicates NaOH and reaction temperature are two key factors responsible for formation of K-type CeO2 nanotubes. Combined with the T- and L-type nanotubes, three types of CeO2 nanotubes with different formation mechanisms are successfully synthesized in one reaction system, which might afford some guidance for the synthesis of other inorganic nanotubes. [ABSTRACT FROM AUTHOR]

CeO2 nanotubes have been synthesized with a simple solid-liquid interface reaction route in the absence of any surfactants. Although the basic reaction principles are similar, two kinds of nanotubes with completely different morphologies and structures can be generated by slightly tuning the postprocessing conditions. The first formation involves employing Ce(OH)CO3 nanorods as both the physical and chemical templates, and the other requires layered Ce(OH)3 as an anisotropic intermediate species. During this process, NaOH and reaction temperature were demonstrated as the key factors responsible for the formation of Ce(OH)3 intermediate and final CeO2 nanotubes with well-defined structures. The structural details were provided by a combination of XRD, SEM, TEM, and HRTEM investigations. Catalytic measurement shows that both nanotubes are very active for CO oxidation, and at 250 °C, the conversion rates of CeO2 nanotubes are 3 times higher than that of the bulk counterpart. [ABSTRACT FROM AUTHOR]