Adsorption Characteristics of Linear Alkanes Adsorbed on Purified HiPco Single-Walled Carbon Nanotubes

We present the results of adsorption isotherm measurements for propane films on single-walled carbon nanotubes, for coverages limited to the first layer. Isotherms were measured at six different temperatures between 190 and 280 K. The results obtained are compared to our previous findings for ethane and butane on the same substrate. This comparison allows us to explore the evolution of the characteristics of adsorbed films as a function of alkane chain length. We found that the same groups of binding sites are available for all three molecules. We also found that there is a gradual smearing of the high-pressure substep in the monolayer data that occurs as the isotherm temperature is increased. This smearing becomes more pronounced as the length of the adsorbed molecule increases. In addition, for each value of the fractional coverage, we observed an increase in the value of the isosteric heat of adsorption as the length of the adsorbate increases.