Exploring divergent gas separation behavior in MXene-PDMS asymmetric composite and symmetric dense membranes with a quaternary gas mixture (H2/CO2/N2/CH4): Effect of MXene alignment

Abstract

Membrane-based separation is expected to offer competitive advantages in the separation and purification of H2-based gas streams due to its high energy efficiency and simple fabrication. However, polymer-based membrane suffers from a Robeson-related permeability/selectivity trade-off, which requires the incorporation of advanced filler materials (a.k.a. mixed-matrix membranes, MMM) to increase the separation performance. However, conventional fabrication of MMMs typically produces a thick selective layer that limits the membrane flux. Hence, in this work, we aim to create an asymmetric composite membrane with the polymer matrix developed with Polydimethylsiloxane (PDMS)/MXene as the selective layer to investigate the separation performance under H2/CO2/N2/CH4 quaternary gas mixture. First, the performance was validated with dense symmetric MMMs to determine the optimal loading for Single-Layer (SL) MXene and Multi-Layer (ML) MXene, which 1.0 wt% SL-MXene and 3.0 wt% ML-MXene were optimized for the fabrication of asymmetric composite membrane as the performance surpasses the Robeson upper bound. The conversion of dense symmetric MMMs into asymmetric composite membranes increases the mixed-gas selectivity, albeit with a slight dip in H2 permeability, indicating the good membrane integrity of the developed membrane. With the support of molecular dynamics simulation, the decrease in H2 permeability has been identified by the preferential interaction of MXene with the porous support as compared to PDMS. Nevertheless, the performance of our membrane is comparable, if not better, than most of the reported performance in the literature, together with the stable H2-based separation performance of the SL1-AC membrane after a 120-hour duration. © 2025