Thermally annealed polyimide-based mixed matrix membrane containing ZIF-67 decorated porous graphene oxide nanosheets with enhanced propylene/propane selectivity

Abstract

This work presents a new type of thermally annealed 6FDA-DAM-based mixed matrix membranes (MMMs) containing two-dimensional (2D) ZIF-67-decorated porous graphene oxide nanosheets (ZPGO67) with promising C3H6/C3H8 transport properties. Different characterization techniques, including XRD, DSC, FTIR, and fluorescence spectroscopy, were used to elucidate possible changes in physicochemical properties and structure of MMMs through thermal annealing. C3H6/C3H8 sorption isotherms for pristine 6FDA-DAM and MMM containing ZPGO67 were also measured at different temperatures. Single-gas permeation data indicated that embedding a 20 wt% ZPGO67 filler in the polyimide matrix increased C3H6 permeability from 19.5 Barrer to 58.8 Barrer at 2 bar and 35 °C. The corresponding thermally annealed MMMs showed not only high C3H6/C3H8 permselectivity also excellent resistance to plasticization. For instance, MMM thermally annealed at 400 °C presented C3H6/C3H8 permselectivity of 17.8, at 2 bar and 35 °C, considerably higher than that obtained for the non-annealed MMM. This membrane also showed stable C3H6 permeability of 18.2 Barrer and C3H6/C3H8 permselectivity of 11.3 at 5 bar and 50 °C for 24 h. The high C3H6/C3H8 permselectivity and good anti-plasticization behavior of thermally annealed membranes were mainly attributed to the formation of charge-transfer complexes (CTCs), as evidenced by fluorescence spectroscopy analysis and Tg measurement.