  CO2/CH4 separation using ionic liquids (ILs) encapsulated metal-organic
frameworks (MOFs), especially ZIF-8, has shown promise as a new technique for
separating CO2 from CH4. However, the mechanisms behind the high CO2/CH4
selectivity of the method remains indistinct. Here we report the progress of
understanding the mechanisms from examining the ZIF-8 aperture configuration
variation using DFT and MD simulations. The results indicate that the pristine
aperture configuration exhibits the best separation performance, and the
addition of ILs prevents the apertures from large swing (i.e. configuration
variation). Subsequently, the effect of IL viscosity on the layout variation
was investigated. MD simulations also show that the pristine aperture
configuration is more stabilized by ILs with large viscosity (0-87Cp). Further
increase of IL viscosity above 87Cp did not result in noticeable changes in the
aperture stability.
