Characterization of nanopores by standard enthalpy and entropy of adsorption of probe molecules

Numerous theories have been developed for the determination of pore size distribution in adsorbent materials. The calculated pore size distribution is sensitive to the model selected for adsorption in slits, spheres, or cylinders and cannot be independently verified by experimental methods. Physical constants which are independent of theory can be determined from equilibrium thermodynamic experiments. Given an adsorbent material and a probe molecule, these constants are: (1) pore volume; (2) standard molar enthalpy of adsorption at the limit of zero pressure; (3) standard molar entropy of adsorption at finite pressure. The standard enthalpy and entropy changes are from the initial state of a perfect gas to the final state of a hypothetical adsorbed gas that obeys Henry’s law. These standard thermodynamic properties characterize the interaction of a single probe molecule with the surface of the nanopores.