Lattice-gas modeling of adsorption on nanotube bundles at criticality

Adsorption thermodynamics of interacting particles adsorbed on nanotube bundles is studied through a lattice-gas model and Monte Carlo simulations. The adsorbent is modeled as one-dimensional channels of equivalent adsorption sites arranged in a triangular cross-sectional structure. Two kinds of lateral interaction energies have been considered: (1) wL, interaction energy between nearest-neighbor particles adsorbed along a single channel and (2) wT, interaction energy between particles adsorbed across nearest-neighbor channels. We focus on the case of repulsive transversal interactions (wT>0), for which a rich variety of ordered phases are observed in the adlayer, depending on the value of the parameters kBT/wT (kB being the Boltzmann constant) and wL/wT. The influence of each ordered structure on adsorption isotherms and differential heat of adsorption has been analyzed and discussed in the context of the lattice-gas theory.