Adsorption and desorption phenomena on thermally annealed multi-walled carbon nanotubes by XANES study

Abstract

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.