Enhancing CO2 separation performance of mixed matrix membranes by incorporation of L-cysteine-functionalized MoS2

The incorporation of lamellar materials into polymer matrix can improve the gas separation performance of mixed matrix membranes (MMMs), which have great potential in chemical separation process. However, few intrinsic selectivity sites on MoS2 sheets suppress further employment in the membrane separation. In this work, the vacancies and defects-containing MoS2 sheets were prepared by high temperature oxidation and hydrothermal reaction in NaOH solution, and then L-cysteine-functionalized MoS2 (Cys-MoS2) was synthesized by a thiol-click chemistry reaction between S vacancies and thiol groups as confirmed by transmission electron microscope (TEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and N2 absorption. After blending with polyether-block-amide (Pebax), the as-prepared MMMs showed outstanding mechanical properties as a result of the homogeneous dispersion of Cys-MoS2 and hydrogen bonding between two phases as evidenced by attenuated total reflectance-FTIR, scanning electron microscope (SEM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The highest permeability of 297 Barrer accompanied with a CO2/N2 selectivity of 120 was obtained for MMMs loaded with 1.5 wt% Cys-MoS2, which were enhanced by 206.2 % and 124.7 % over the pristine Pebax membrane, respectively. Meanwhile, this value was superior to that of the previously reported Pebax-based MMMs, transcending 2019 upper bound. The enhanced gas separation performance is due to the improved CO2 adsorption selectivity by the vacancies and defects of Cys-MoS2, while the amine groups carrier enhanced CO2 reactivity selectivity.