The diffusion of binary mixtures of CO2 and N2 in a series of functionalized MCM-41 materials was studied using molecular dynamics (MD) simulations. Transport diffusion coefficients were obtained in order to assess the effect of surface functionalization with organic groups. Unmodified MCM-41 was found to be transport selective for N2. The spatial distribution of the two coadsorbed species showed that N2 molecules permeated faster and occupied the central pore region to a greater extent than CO2 molecules. CO2 was found to have a much lower permeability than N2 due to stronger interactions with the surface of MCM-41 and a tendency to become trapped in nooks in the amorphous pore wall. This effect was not reproduced when using a more simplistic model pore with a smooth surface demonstrating the importance of using a realistic pore model. Larger aminophenyl surface groups were found to significantly reduce the N 2 selectivity due to a decrease in the flux of N2 and an increase in the flux of CO2. We explain this effect in terms of the marked difference in the transport mechanisms of CO2 and N 2 in functionalized MCM-41 materials. Lastly, we remark on the importance of calculating the cross-term diffusion coefficients for this series of materials.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Electronic, Optical and Magnetic Materials
- Surfaces, Coatings and Films