Unprecedented gas separation performance of ITTB/CNT nanocomposite membranes at low temperature by strong interfacial interaction enhanced rigidity

Abstract

One of the biggest challenges in mixed matrix membranes (MMM) for gas separation applications is how to achieve homogeneous nanocomposite membranes with excellent separation performance. Here, for the first time, this goal can be achieved by novel MMMs fabricated from a highly microporous Tröger's base (TB) ladder polymer matrix (ITTB) containing triptycene as contortion center, and COOH functionalized single wall carbon nanotubes (CNT) as filler ranging from 0.6 to 2.0 wt%. By the strong acid-base interaction between COOH (from CNT) and tertiary-amine (from TB) as well as π-π interaction between the triptycene unit and CNT skeleton, the resulting MMMs with good compatibility were confirmed by Raman spectroscopy and SEM image analysis. The MMMs with 1.0 wt% CNT loading (P-CNT-1.0) exhibited both higher O2 permeability (701 vs 504 Barrer) and O2/N2 selectivity (5.79 vs 5.54) than the pristine ITTB, and the aO2/N2 further increased to 7.28 after 100 days aging. Additionally, the P-CNT-1.0 also showed an unprecedented pure-gas aO2/N2 of 11.7 combined with a PO2 of 129 Barrer at −20 °C. An exceptional high mixed-gas O2/N2 selectivity of 10.1 was also observed for P-CNT-1.0 at −20 °C and 20 bar upstream pressure, whereas the pristine ITTB plasticized at 2 bar. The higher performance of P-CNT-1.0 is due to the strong interaction between the CNT and ITTB further enhanced the rigidity of ITTB main chain. The 1.0 wt% CNT loading into ITTB simultaneously enhanced the permeability, selectivity and stability, which provides great potential for PIM-based MMMs in air separation applications.