Figure 2. The number of permeated molecules NP versus timet through various MXenes with different nanopores. (a) ~4 Å Ti4C3 nanopores, (b) 2.92 Å Ti4C3 nanopores, (c) enlarged drawing of (b), (d) ~2 Å nanopores of four kinds of MXenes. The NP ~t relationship for other kinds of MXenes with 2~4 Å nanopores are shown in Figures S1-S2 . The black dashed line represents the fitted curve.
Currently, there are two prevailing fitting methods for calculating gas permeance from NEMD simulations of relaxation process: exponential fitting11, 26, 31, 52-54 and linear fitting,55-58 see supplementary information (SI) gas permeance calculation methods for details, yet there has been seldom studies on whether these two methods could yield consistent results.Figure 3 shows that, the simulated permeance of He and CH4 cross the four studied MXene nanopores with varyingd , calculated with both fitting methods well agree with each other, with correlation coefficient (R 2) above 0.97. Further theoretical derivations (Equations S7-S8 in SI) show the results calculated with these two methods should agree with each other if the calculations are performed correctly. Thus, following discussions would focus on gas permeance calculated from the linear fitting method.