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.