4. CONCLUSION
In this study, both NEMD and EMD were utilized to investigate the
transport of He/CH4 through various MXene
(Ti4C3,
Ti3C2,
Ti3C2O2, and
Ti2C) nanopores with different diameters, nanopores’
density and functional groups. Both linear fitting and exponential
fitting were employed to calculate the gas permeance from NEMD
simulation, which yield consistent results withR 2 above 0.97. The gas permeance of all studied
MXene nanopores increases with d , and vary significantly whend <= d gas. It further reveals
that gas molecules pass through the MXene nanopores mainly with two
different mechanisms with d varying: i) when d<= d gas, gas molecules pass through via
molecular sieving, with d and MXene structure (including the
surface functional groups such as -O) strongly affecting the permeance;
ii) when d > d gas, gas
molecules pass through via Knudsen diffusion, with d and MXene
structure affecting the permeance rather weakly. Consequently, MXene
nanopores with d <= d CH4 show
quite high S He/CH4 (57.6 or above), where
CH4 pass through with molecular sieving mechanism, while
those with d > d CH4 showS He/CH4 close to the Knudsen selectivity of 2. In
addition, EMD simulation were used to predict small MXene nanopores’S He/CH4 (with TST for d <= 3 Å),
and gas permeance ratio for the same gas (He or CH4)
passing through different nanopores. Furthermore, increasing the MXene
nanopore’s density was found to increase the gas permeance without
decreasing S He/CH4. Mixture gas
(He&CH4) separation simulations were also performed,
which indicated the exist of one type of gas molecules hardly affect the
permeance of the other gas. All these results could assist in designing
high performance MXene nanopores for He/CH4 separation.