Molecular Dynamics Simulations of Carbon Monoxide Self-diffusion in the Nanoporous of the Cu-BTC

Abstract

In this study, the self-diffusion coefficients of carbon monoxide in the Cu-BTC nanoporous have been studied by molecular dynamics simulation. Metal-organic framework (MOF) materials pose an interesting substitute to more traditional nanoporous materials for a variety of separation processes. Separation processes including nanoporous materials can be controlled by two factors: diffusive transport rates and adsorption equilibrium. Adsorption equilibrium has been studied for some of gases in MOFs, but almost nothing is about molecular diffusion rates in MOFs. One of the known MOF is Cu-BTC that is formed of copper as metal center and benzene-1, 3, 5–tricarboxylate as linker molecule. The MD simulations have been carried out in the NVT and NVE ensemble. For simulation equilibration of the system at the desired temperature, an NVT simulation is used and for computing the self-diffusion coefficient, the ensemble is switched to NVE. The simulations have been performed at 100, 150, 200, 250, 298, 350, 400, 450 and 500K with loading of 40 guest molecules per unit cell. The Mean square displacement, self-diffusion coefficient and activation energy have been calculated in total and in the X, Y and Z direction. The calculated MSD for the center of mass of the carbon monoxide molecules in the X, Y and Z-directions shows that the motion of carbon monoxide is homogeneous in the Cu-BTC and there is isotropic translational diffusion for carbon monoxide in the Cu-BTC. The calculated self-diffusion coefficients increase as temperature is increased. We use the Arrhenius equation to calculate the activation energy. The calculated activation energy is 4.43kJ.mole-1.