Ideal two-dimensional molecular sieves for gas separation: Metal trihalides MX3 with precise atomic pores

Abstract

Membrane technology has been widely applied in gas separation field. In this work, a series of two-dimensional (2D) metal trihalides MX3 (AsI3, ScI3, SbI3, YI3, BiI3, ScCl3, ScBr3 and YBr3) are expected to be served as realistic 2D molecular sieves in gas separation applications due to their intrinsically and uniformly well-defined atomic pores. The gas separation performance of these 2D MX3 molecular sieves has been systematically explored by using first-principles calculations. Different from the conventional membranes, the atomic pores of 2D MX3 molecular sieves behave like breathing mode via flexible change of M-X bond during the gas molecules transport process. These 2D MX3 molecular sieves exhibit excellent H2/CO and O2/N2 separation performance, which surpasses the state-of-the-art upper bound. Remarkably, the O2/N2 selectivity of YBr3, SbI3, YI3 and BiI3 molecular sieves is within the range of 102-103 under superior permeance, which exceeds that of common membranes (~101) to a large extent. The extremely high selectivity and superior permeance indicate that these 2D MX3 molecular sieves possess great potentials in gas separation applications.