Carbon nanotubes (CNTs) show exceptional properties which make them extremely attractive for many applications. The electronic structure of potassium adsorbed single-walled carbon nanotubes (SWCNTs) is investigated by x-ray near edge structure (XANES) spectroscopy. Gas molecules (H 2 O, O 2 , CO 2 , CO) and potassium (K) adsorbates showed non negligible sensitivity to the geometry, thermal annealing treatment, and hybridization. The SWCNT type is shown by transmission electron microscopy (TEM) whereas an aleatory arrangement of SWCNTs and the spherical iron particles along carbon nanotubes are observed by scanning electron microscopy (SEM). XANES shows that the charge transfer effect in K-doping SWCNTs increases the conductivity to 62.7%. The adsorption study demonstrates that the adsorption mechanism to remove potassium from aqueous solutions using SWCNTs is assimilated to the ion exchange process. The functional groups OH − , C=O and C≡C are involved in the adsorption process. They are correlated to the assignment of the adsorbates given by XANES.

The multi-walled carbon nanotubes (MWCNTs) studied in this work were synthesized by the catalytic chemical vapor deposition (CCVD) process, and were thermally annealed by the hot filament plasma enhanced (HF PE) method at 550 °C for two hours. The x-ray absorption near edge structure (XANES) technique was used to investigate the adsorption and desorption phenomena of the MWCNTs at normal and grazing incidence angles. The adsorbates were found to have different sensitivities to the thermal annealing. The geometry of the incident beam consistently gave information about the adsorption and desorption phenomena. In addition, the adsorption of non-intrinsic potassium quantitatively affected the intrinsic adsorbates and contributed to increase the conductivity of the MWCNTs. The desorption of potassium was almost 70% greater after the thermal annealing. The potassium non-intrinsic adsorbates are from a physisorption mechanism whereas the intrinsic adsorbates result from chemisorption.