Nanopore structure and sorption properties of Cu-BTC metal-organic framework

Grand canonical Monte Carlo simulations in conjunction with high-resolution low-pressure argon adsorption experiments were employed to study adsorption mechanisms on the copper(II) benzene-1,3,5-tricarboxylate metal-organic framework (Cu-BTC). We constructed a molecular structural model of Cu-BTC. The pore network of Cu-BTC has a simple cubic symmetry. It consists of main channels of a square cross-section of ca. 0.9 nm diameter and tetrahedral side pockets of ca. 0.5 nm, which are connected to the main channels by triangular windows of ca. 0.35 nm diameter. Using a parameterized united-atom force field, we have determined the preferential adsorption sites and the sequence of adsorption mechanisms from a gradual filling of the side pockets to a stepwise adsorption and condensation in the main channels. The simulation results agree quantitatively with the experimental isotherm of argon up to almost complete filling of the pore network.