Mixed Matrix Membranes with Ionic Liquid-Grafted Layered Double Hydroxides: Characterizations and CO2 Separation Properties

Carbon dioxide (CO2) separation plays a vital role in environmental protection and resource reuse. A potential approach to achieving satisfactory CO2 separation is combining the benefits of ionic liquids (ILs) and membranes. In this work, the IL-LDH nanosheets were obtained by functionalized IL modifying layered double hydroxides (LDH) and used to construct the Pebax/IL-LDH mixed matrix membranes (MMMs). The X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) spectra analysis displayed that the IL was successfully grafted to the LDH nanosheets. The characterizations of MMMs showed that the introduction of IL-LDH reduces the crystallinity of the Pebax membrane, and there are hydrogen bond interactions between fillers and Pebax. The IL modification strengthens the membranes with better CO2 affinity and improves the interfacial compatibility between Pebax and LDH. Meanwhile, the CO2-philic nanochannels formed by the slits of IL-LDH nanosheets facilitate CO2 transport in MMMs. Such inherent properties of the IL and LDH conjunctly contribute to the improvement of the CO2 separation performance of membranes. The optimum Pebax/IL(20)-LDH MMM has a high CO2 permeability of ∼388 barrer at 30 °C, which is approximately 2.9 times that of pure Pebax, and the CO2/CH4 selectivity does not change significantly. Besides, the Pebax/IL(20)-LDH MMM exhibited a notable increase in CO2 permeability as the working temperature increased, ultimately attaining ∼576 barrer at 50 °C.