Gas Separation by Kinked Single-Walled Carbon Nanotubes

A kink model for gas separation is presented. Transport of pure nitrogen, oxygen and their mixture in single walled carbon nanotubes (SWCNTs) with a kink formed by bending is studied using molecular dynamics simulations. The results show that a kinked SWCNT results in transport resistance to nitrogen while allowing oxygen to pass even though the two gases have very similar molecular sizes. The permeability decreases while the selectivity increases with increasing the bending angle of SWCNTs. The tradeoff between permeability and selectivity is evaluated by linear weighting method to attain an optimum bending angle for gas separation. It is also found that the kink model can be used to improve the permeability by changing the diameter of the SWCNTs while keeping a high selectivity in the gas separation process. Both the permeability and purity of oxygen increase with increasing the gas pressure. Interestingly, it is very convenient to obtain the required purity and permeability of the oxygen by adjusting the bending angle of SWCNTs.