Kr Adsorption in Porous Carbons: Temperature-Dependent Experimental and Computational Studies

The temperature dependence of the adsorption energy of krypton adsorption on activated carbon materials was studied by experiment and simulation. Adsorption isotherms were measured at temperatures from 250 to 330 K and analyzed with Henry's law. The adsorption energy determined from these measurements was found to weaken by more than 10% in this range. Slit pore widths for simulations in this work were modeled by the removal of integral numbers of planes in graphite. Vibrational dynamics of the krypton adsorbate and the carbon atom adsorbent were calculated with the stochastic temperature-dependent effective potential (sTDEP) method, using energetics from density functional theory (DFT) with the many-body dispersion energy method (MBD). Thermal displacements of carbon atoms had a negligible effect on the adsorption energy. The width of the slit pore had the greatest effect on the surface dynamics and the energies of the adsorbate atoms at different temperatures. Assuming a distribution of pore widths, the Boltzmann distribution of site occupancies causes a large weakening of the thermally averaged adsorption energy at higher temperatures.