3D covalent organic framework for morphologically induced high performance membranes with strong resistance toward physical aging
Abstract The physicochemical properties of filler materials are critical considerations influencing the separation performances of mixed matrix membranes (MMMs) Herein, a three dimensional covalent organic framework (3D COF) with a secondary amine containing backbone was designed to offer large surface area, high porosity and good affinity toward CO2 molecules. Membranes prepared from this 3D COF filler and a 6FDA DAM polyimide matrix demonstrated a more significant enhancement in the CO2/CH4 separation performance, which was unattainable by its 2D COF analogue. Specifically, with 10 and 15 wt% loadings of 3D COF fillers, the MMMs membranes were able to enhance the CO2 permeability by ~57% and 140% respectively, at a comparable, if not better, CO2/CH4 selectivity than the unfilled membrane. Furthermore, glassy polymers of high fractional free volume such as 6FDA DAM tend to suffer from a ubiquitous loss in performance over time due to a physical aging effect. In this regard, the 3D COF was effective in slowing down the aging process by capitalizing on its high surface area and amine functional groups to immobilize and rigidify the 6FDA DAM polymer chains, preventing the collapse of the free volume. This allows 97% of the initial membrane performances to be effectively retained after 240 days of aging. Our findings suggest the potential of morphologically tuned COFs to develop high performance MMMs with strong practical relevance.
Journal of Membrane Science