Figure 1. (a) Side views of four MXenes (Ti2C, Ti3C2, Ti3C2O2, Ti4C3). The atoms of carbon, oxygen, and titanium are represented by cyan, red, and pink balls, respectively. (b) Four MXene nanopores with diameters of ~3 Å. (c) The different diameters of various MXene nanopores, ranging from ~2 Å to 9 Å. (d) Snap shot of the NVT NEMD simulation system with single-layer MXene nanopore at simulation time, t , of 0 ps. Cyan balls refer to the randomly distributed gas molecules (He or CH4).