Effect of Different Nanofillers in Mixed Matrix Membranes for CO₂ Separation

The latest innovations in gas separation technologies reveal that including amine-functionalized carriers with embedding two-dimensional (2D) nanosheets in polymer membranes substantially augments the efficacy of CO2 separation. This study presents an approach wherein UiO-66 (a Zr terephthalate) is modified with Cloisite Na-MMT, an organically modified montmorillonite (MMT) clay, via a postsynthesis modification (PSM) process. The MMT-modified UiO-66 (Cloisite@UiO-66), along with the amino-functionalized UiO-66 (UiO-66-NH2) blended with graphene oxide (GO) with filler loading between 2.5–5.0 wt %, are then subsequently integrated into the polysulfone (PSf) polymer matrix to fabricate mixed matrix membranes (MMMs) for applications in gas separation. Fourier-transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and field emission scanning electron microscopy (FE-SEM) analysis were employed to analyze chemical interactions and surface morphology of synthesized nanofillers and the prepared membranes. Gas separation experiments were performed using a CO2:N2 and CO2:CH4 mixture (10:90 vol %) under the absolute temperature of 25 ± 2 °C and 2 bar pressure. Incorporating the blending of GO with UiO-66-NH2 and hybrid Cloisite@UiO-66 into the MMM led to substantial improvements in CO2 permeance and significantly increased the CO2/N2 and CO2/CH4 selectivity of the fabricated membranes. The Cloisite@UiO-66@MMM exhibited a remarkable CO2 permeance of 89.02 GPU and optimal selectivity of 76.09 for CO2/N2 and 50.86 for CO2/CH4 among all the tested MMMs. These findings suggest that composite fillers, which combine the functionalities of MOFs, GO, and MMT-modified MOFs, hold considerable potential for tuning and improving the performance characteristics of polymer-based membranes. Such membranes have significant potential for the efficient separation of CO2 from industrial emissions, natural gas, and various complex gas mixtures, thereby facilitating the development of more efficient and sustainable solutions for gas capture and purification in various applications in the future.