Molecular adsorption and self-diffusion of NO(2), SO(2), and their binary mixture in MIL-47(V) material

The loading dependence of self-diffusion coefficients (D(s)) of NO(2), SO(2), and their equimolar binary mixture in MIL-47(V) have been investigated by using classical molecular dynamics (MD) simulations. The D(s) of NO(2) are found to be two orders of magnitude greater than SO(2) at low loadings and temperatures, and its D(s) decreases monotonically with loading. The D(s) of SO(2) exhibit two diffusion patterns, indicating the specific interaction between the gas molecules and the MIL-47(V) lattice. The maximum activation energy (E(a)) in the pure component and in the mixture for SO(2) are 16.43 and 18.35 kJ mol(−1), and for NO(2) are 2.69 and 1.89 kJ mol(−1), respectively. It is shown that SO(2) requires more amount of energy than NO(2) to increase the diffusion rate. The radial distribution functions (RDFs) of gas–gas and gas–lattice indicate that the Oh of MIL-47(V) are preferential adsorption site for both NO(2) and SO(2) molecules. However, the presence of the hydrogen bonding (HB) interaction between the O of SO(2) and the H of MIL-47(V) and also their binding angle (θ(OHC)) of 120° with the linkers of lattice indicate a stronger binding interaction between the SO(2) and the MIL-47(V), but it does not occur with NO(2). The jump-diffusion of SO(2) between adsorption sites within the lattice has been confirmed by the 2D density distribution plots. Moreover, the extraordinarily high S(diff) for NO(2)/SO(2) of 623.4 shows that NO(2) can diffuse through the MIL-47(V) significantly faster than SO(2), especially at low loading and temperature.