Surface defects were created on carbon nanotubes by catalytic steam gasification or catalytic etching with iron as catalysts. The structure and morphology of the etched carbon nanotubes were studied by transmission electron microscopy and scanning tunneling microscopy. The electronic structure of the etched carbon nanotubes was investigated by ultra-violet photo-electron spectroscopy. The etched carbon nanotubes were treated with nitric acid to obtain oxygen-containing functional groups. The amount and the thermal stability of these groups were studied using temperature-resolved X-ray photo-electron spectroscopy. Temperature-programmed desorption with ammonia as a probe molecule was used to investigate the interaction of the surface defects with foreign molecules in the gas phase. Transmission electron microscopy and scanning tunneling microscopic studies revealed the presence of surface defects, especially edge planes, on the etched carbon nanotubes. Etching of carbon nanotubes led to a less pronounced p-π band than in as-is carbon nanotubes, as revealed by ultra-violet photo-electron spectroscopy studies. The X-ray photo-electron spectroscopy and NH3- temperature-programmed desorption studies demonstrated that the defects on the carbon nanotubes enhanced the reactivity of the exposed surfaces, permitting a higher degree of oxygen functionalization and more active adsorption sites.

Visualization and Functions of Surface Defects on Carbon Nanotubes Created by Catalytic Etching. W.Xia, X.Yin, S.Kundu, M.Sánchez, A.Birkner, C.Wöll, M.Muhler: Carbon, 2011, 49[1], 299-305