Molecular adsorption and self-diffusion of NO2, SO2, and their binary mixture in MIL-47(V) material

The loading dependence of self-diffusion coefficients (D-s) of NO2, SO2, and their equimolar binary mixture in MIL-47(V) have been investigated by using classical molecular dynamics (MD) simulations. The D-s of NO2 are found to be two orders of magnitude greater than SO2 at low loadings and temperatures, and its D-s decreases monotonically with loading. The D-s of SO2 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 SO2 are 16.43 and 18.35 kJ mol(-1), and for NO2 are 2.69 and 1.89 kJ mol(-1), respectively. It is shown that SO2 requires more amount of energy than NO2 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 NO2 and SO2 molecules. However, the presence of the hydrogen bonding (HB) interaction between the O of SO2 and the H of MIL-47(V) and also their binding angle (& theta;(OHC)) of 120 & DEG; with the linkers of lattice indicate a stronger binding interaction between the SO2 and the MIL-47(V), but it does not occur with NO2. The jump-diffusion of SO2 between adsorption sites within the lattice has been confirmed by the 2D density distribution plots. Moreover, the extraordinarily high S-diff for NO2/SO2 of 623.4 shows that NO2 can diffuse through the MIL-47(V) significantly faster than SO2, especially at low loading and temperature.