Physisorption of N2 on Single Walled Carbon Nanotubes: A Comparison of Computer Simulation and Experimental Results

摘要

Nitrogen physical adsorption on single-walled carbon nanotube (SWNT) bundles was studied with Grand Canonical Ensemble Monte Carlo computer simulations in a wide temperature range. The results were compared with experimental data obtained in our laboratory and with those published in the literature. The sample employed in this work was also characterized by TG-DTA, XRD, SEM-EDX and AFM/STM. The nanotubes were modeled by grouping them in bundles forming a hexagonal array. Local adsorption isotherms were calculated. The simulations reported here reproduced the experimental adsorption isotherms on SWNT of different diameters; the coincidence between experiments and simulations at low pressures was remarkably good. The adsorption potential was analyzed and the results were employed to interpret several distributions obtained from the simulations. The location of the expected adsorption sites is confirmed. Finally, the adsorbed phase within the tubes was characterized. The excellent agreement between the simulations and experiments suggests that the impurities present in real samples do not greatly affect the isotherms in the low-pressure limit. Nevertheless, they could be altering the experimental isotherms at moderate and high pressures. In favor of this argument is the fact that there is a large dispersion in the experimental data obtained on different samples, which is not found for other systems, and the evidences offered by the STM/AFM images presented in this work.