Preparation of Mixed Matrix Membranes Using Graphitic Carbon Nitride as Solid Cross-Linking Agent for CO2 Separation

Abstract The development of efficient carbon capture technologies, such as membrane separation technology, is of vital importance for achieving carbon neutrality. Mixed matrix membranes (MMMs) integrate the advantages of polymer matrices and inorganic fillers, making them promising materials for high-performance carbon capture. However, their practical separation performance is often severely limited by poor interfacial compatibility. To address this challenge, we designed and fabricated a series of chemically bonded MMMs. Graphitic carbon nitride (g-C3N4) served as a solid-state cross-linker, with its amino groups reacting with the benzyl bromide moieties of the brominated polyimide (PI-Br) matrix through nucleophilic substitution. This interfacial chemical bonding improved polymer–filler compatibility and introduced interfacial cross-linking constraints, thereby regulating polymer chain packing. Comprehensive characterization Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) indicated that the organic–inorganic interfacial interactions effectively minimized nonselective interfacial defects and promoted efficient gas transport. Among the investigated membranes, PI-Br-4-3% demonstrated the most favorable separation capability, with CO2 permeability and CO2/CH4 selectivity reaching 335.38 Barrer and 47.03, respectively. Furthermore, the cross-linked MMM demonstrated remarkable stability under varying pressure and temperature conditions, providing solid empirical evidence for its potential application in industrial natural gas purification.