Molecular dynamics simulation of small gas molecule permeation through CAU-1 membrane

CAU-1 is one of aluminum-based amine-functionalized Metal–Organic Frameworks (MOFs). Gas perme-ation and separation behaviors through CAU-1 membrane were simulated by the dual-control plane nonequilibrium molecular dynamics (DCP-NEMD) method. The thickness of membrane was 3.55 nm. Gases CO2, N2, CH4, H2, He, Kr and Xe were chosen for the calculation in both single component and bin-ary mixtures. The permeation process was calculated in grand canonical (lVT) ensemble with periodic boundary conditions (PBC) in x- and y-directions at different temperatures. The calculated permeance of H2, CH4, N2, CO2 and Kr decreased with increasing temperature in both single and binary system, while that of Xe with kinetic molecule of 0.41 nm increased with increasing temperature. It shows Xe perme-ation is governed by activated diffusion. The simulated separation factors of CO2/N2 and CO2/CH4 of 4.2 and 1.3 respectively were lower than the experimental ones when only considering van der Waals inter-action. Further consideration of electrostatic potential leads to improved calculation CO2/N2 and CO2/CH4 separation factor of 23.0 and 12.9 respectively that were consistent with the experimental ones of 26.2 and 14.8. It suggests the necessity of considering the Coulomb interactions between CO2 and NH2-on the pore wall of CAU-1 for permeation of CO2. For H2/N2 and H2/CH4 the ideal selectivities also keep consis-tent with our experimental results. Interestingly, the simulated separation factor for noble Kr/Xe reaches infinite, predicting that CAU-1 membrane possesses potential separation properties for radioactive Kr/Xe.