Topotactical Route to Multiwalled Cerium Oxide Nanotubes from MWCNTs

Abstract The development of new strategies for synthesizing 1D cerium oxide (CeO 2 ) hollow nanostructures has attracted much attention in recent years due to the importance of their superior properties and highly anisotropic geometry. This study reports an unpublished route of fabricating novel multiwalled CeO 2‐δ nanotubes (CeO 2‐δ NTs) in which the entire volume of functionalized multiwalled carbon nanotubes ( f ‐MWCNTs) is converted into the CeO 2‐δ pseudomorph through oxidation and dehydration topotactic reactions. The stable CeO 2‐δ (111) planes are topotactically grown on the curved C (002) planes, preferentially exposed along the nanotube axis. In their initial condition, the novel nanotubes consist of Ce oxyhydroxide (CeO 2‐x (OH) x ) with residual carbon. When heating the air up to 500 °C, CeO 2‐x (OH) x transforms gradually by dehydration into CeO 2‐δ , while the residual carbon is oxidized. Despite compositional changes, nanotubes maintain their multiwalled structural integrity up to ≈550 °C. The CeO 2‐δ NTs exhibit an unusually high presence of Ce 3+ ions and surface O vacancies, contributing to a low direct band gap ranging from 2.67 to 2.32 eV compared to their NPs counterparts (3.2 eV).