Functionalized Graphene/PAN Hollow Fiber Mixed Matrix Membranes: Effects of Surface Functionality and Loading on CO2/N2 Separation

Abstract The development of high-performance hollow fiber mixed matrix membranes (HFMMMs) for post-combustion carbon capture requires rational design of nanofillers that simultaneously enhance CO2 transport, molecular selectivity, and operational stability. In this study, polyacrylonitrile (PAN) HFMMMs incorporating pristine, hydroxyl-, amine-, and carboxyl-functionalized graphene nanosheets were first systematically investigated to elucidate the influence of graphene surface functionality on membrane morphology, physicochemical properties, and CO2/N2 separation performance. Hydroxyl-functionalized graphene exhibited the best overall performance owing to its superior polymer−filler compatibility and enhanced affinity for CO2 molecules. The loading of the hydroxyl-functionalized graphene was subsequently optimized, with 0.1 wt % yielding the highest separation performance, whereas higher loadings promoted graphene agglomeration, resulting in structural defects and deteriorated gas separation performance. Furthermore, the influence of the PDMS coating solvent was evaluated, and cyclohexane produced a more uniform defect-sealing layer than n-hexane, leading to improved membrane selectivity. Under the optimized fabrication conditions, the membrane exhibited a CO2 permeance of 272 GPU and an ideal CO2/N2 selectivity of 11.3 at 4 Barg during single-gas permeation. More importantly, under simulated flue gas conditions, the optimized membrane achieved a CO2 permeance of 35.3 GPU with a CO2/N2 selectivity of 15.1 at 5 Barg, while maintaining stable separation performance over sixty days of continuous operation. These findings demonstrate that systematic optimization of graphene surface functionality, filler loading, and PDMS coating conditions provides an effective strategy for developing PAN HFMMMs for post-combustion CO2 capture under realistic operating conditions.