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.