Potential parameters for helium adsorption in silicalite

The pore volume of a micro or a nanoporous material is one of the crucial parameters in molecular simulation of gas adsorption. It is necessary to compare the results of the simulations with that of the experiments. In simulations, the pore volume is usually obtained from the configuration integral using the potential parameters of helium-solid interactions. The state of the art in obtaining these helium-solid parameters is through Lorentz-Berthelot mixing rules, used in conjunction with potential parameters of another adsorbing gas. In such an approach, the parameters (and hence helium pore volume) depend on choice of the adsorbing gas. However, true helium pore volume in simulations can only be obtained by mimicking the experimental adsorption behavior of helium itself, without involving any other gas. In this work, we report a consistent method to obtain the potential parameters for helium adsorption on a porous solid from low pressure helium adsorption data. The method is applied to helium-silicalite system and the parameters for He-O interactions in silicalite were obtained to be 3.06 angstrom and 22.9 K. Using these parameters, a helium pore volume of 0.151 cm(3)/g (at 300 K) is obtained for silicalite. The results are further validated by comparing the adsorption isotherms of helium in the high pressure region. (C) 2010 Elsevier Inc. All rights reserved.