Structure and Bonding of Trace Ni Catalyst in Carbon Nanotube Studied by Ni K-Edge XANES

We carry out Ni K-edge X-ray Absorption Near Edge Structure (XANES) analyses to study local electronic and geometric structure around Ni impurities after HCl treatment in carbon nanotubes (CNTs) by applying full multiple scattering calculations. For the trace Ni species in CNT after the treatment, we consider possible models consistent with Ni-C distance and coordination number estimated by previous Extended X-ray Absorption Fine Structure (EXAFS) analyses. The present analyses allow us to distinguish between two defect models for the Ni location; a crack-like defect and Stone-Wales defect. We also find that the curvature of CNTs affects the calculated XANES spectra, which can provide useful information about outer or inner adsorption on CNT walls. Ab initio density functional calculation supports the presence of Ni atoms at the outside of the nanotube. [DOI: 10.1380/ejssnt.2005.427]