Abstract
Monte Carlo computer simulation in simple pore models was used to investigate the pore filling mechanism proposed by Dubinin for adsorption in activated carbon. The first argument; that adsorption into micropores is primarily due to the potential field exerted by the solid is valid only for small micropores, and the second argument; that molecules fill the space and that the degree of filling depends on the adsorption potential (RT ln (p 0/p)) is partly true. We check the validity of the characteristic curve where isotherms plotted as the logarithm of the density versus the square of the adsorption potential collapse onto a single straight line. We find that linearity is never observed for pores of uniform size, but a single curve is observed, as indicated by the Polanyi theory. For a given characteristic energy, the Dubinin equation corresponds to a solid with a specific pore size distribution. Plots of the adsorption heat versus loading follow a complex pattern: initially, they increase or decrease for sufficiently homogeneous or heterogeneous surfaces, respectively; at higher loadings, there is a sharp increase because of the increase of neighbouring molecules and then a sharp decrease because of the increasing importance of repulsion when the adsorbate is very dense.
Acknowledgements
Support from the Australian Research Council is appreciated.