Effects of Protonation, Hydroxylamination, and Hydrazination of g-C₃N₄ on the Performance of Matrimid^®/g-C₃N₄ Membranes

One of the challenges to continue improving polymeric membranes properties involves the development of novel chemically modified fillers, such as nitrogen-rich 2-D nanomaterials. Graphitic carbon nitride (g-C₃N₄) has attracted significant interest as a new class of these fillers. Protonation is known to afford it desirable functionalities to form unique architectures for various applications. In the work presented herein, doping of Matrimid^® with protonated g-C₃N₄ to yield Matrimid^®/g-C₃N₄ mixed matrix membranes was found to improve gas separation by enhancing the selectivity for CO₂/CH₄ by up to 36.9% at 0.5 wt % filler doping. With a view to further enhancing the contribution of g-C₃N₄ to the performance of the composite membrane, oxygen plasma and hydrazine monohydrate treatments were also assayed as alternatives to protonation. Hydroxylamination by oxygen plasma treatment increased the selectivity for CO₂/CH₄ by up to 52.2% (at 2 wt % doping) and that for O₂/N₂ by up to 26.3% (at 0.5 wt % doping). Hydrazination led to lower enhancements in CO₂/CH₄ separation, by up to 11.4%. This study suggests that chemically-modified g-C₃N₄ may hold promise as an additive for modifying the surface of Matrimid^® and other membranes.