Formation of CeO2 nanotubes from Ce(OH)CO3 nanorods through Kirkendall diffusion.

In this paper, CeO(2) nanotubes based on the Kirkendall effect (for simplicity, this type of nanotubes is denoted as K-type CeO(2) nanotubes) are fabricated through a solid-liquid interface reaction between Ce(OH)CO(3) nanorods and NaOH solutions. Our studies indicate the formation mechanism of K-type CeO(2) nanotubes is quite different from those of CeO(2) nanotubes subjected to template (T-type CeO(2) nanotubes) and lamellar rolling (L-type CeO(2) nanotubes) reported previously by our group. The K-type CeO(2) 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)CO(3) nanorods to form K-type CeO(2) nanotubes. In contrast, the interior space in T-type CeO(2) nanotubes decreases with reaction time. XRD is applied to study the phase transformation in the formation process of K-type CeO(2) nanotubes. Our study also indicates NaOH and reaction temperature are two key factors responsible for formation of K-type CeO(2) nanotubes. Combined with the T- and L-type nanotubes, three types of CeO(2) nanotubes with different formation mechanisms are successfully synthesized in one reaction system, which might afford some guidance for the synthesis of other inorganic nanotubes.