Double coaxial structure and dual physicochemical properties of carbon nanotubes composed of stacked nitrogen-doped and undoped multiwalls

Carbon nanotubes with a double coaxial structure of nitrogen-doped and undoped multiwalls were successfully prepared by the template technique using porous anodic aluminum oxide film as a template. The inner carbon layer (or the outer carbon layer) of the double coaxial carbon nanotubes is free from N, while the outer carbon layer (or the inner carbon layer) is uniformly doped with N. Transmission electron microscopy cannot differentiate between the outer and inner layers, but all the results by Raman, X-ray diffraction, and X-ray photoelectron spectroscopy provide evidence that the N-doped layer is less crystallized than the undoped one. Furthermore, the N-doped layer has apparently higher chemical reactivity toward oxygen than the undoped one due to more edge-active sites resulting from the introduction of nitrogen species. Electrical conductance measurement indicates that despite poorer crystallinity the N-doped layer has higher conductivity than undoped one. The resulting multiwalled carbon nanotubes thus have not only double-stack coaxial structure but also dual physicochemical properties.