Surface Engineering of Zr BDC Nanoparticles via Conjugation with Lysine to Enhance the CO2/N2 Separation Performance of Chitosan Mixed Matrix Membranes under Dry and Humid Conditions

Abstract

Mixed matrix membranes (MMMs) incorporated with rigid porous metal–organic framework (MOF) nanoparticles (NPs) are well known for their increased carbon dioxide (CO2) separation performance. For successful separation of CO2 from the flue gas, CO2-philic zirconium-based MOF NPs (Zr BDC or UIO-66) were synthesized and decorated with l-lysine amino acids to incorporate into a chitosan (CS) polymer matrix. The high porosity and surface area of the MOF NPs aided in the CO2 separation permeance, while the selectivity was addressed by the amine functional groups present in l-lysine. The covalently bonded l-lysine onto Zr BDC NPs has a greater CO2 affinity due to the dangling amine groups. Additionally, the amine conjugation strengthened the hydrogen bonds between the MOF and the CS matrix, thereby improving the dispersibility of MOF in the polymer matrix. After successful characterization studies, it was discovered that fabricated MMMs with a 7 wt % loading of lysine-conjugated Zr BDC (lys-c-Zr BDC) NPs with a 4 μm active layer thickness demonstrated better results than the pristine CS and the Zr BDC-embedded CS MMM. The composite lys-c-Zr BDC incorporated CS MMM showed a CO2 permeance of 34.9 GPU and a steady CO2/N2 separation factor of 29.4 under dry conditions and a CO2 permeance of 135.2 GPU and a steady CO2/N2 separation factor of 71.5 under swollen conditions at 85 °C and 0.221 MPa feed pressure. It has also been shown that, under optimum conditions, the fabricated membrane has successfully surpassed the Robeson upper bound curve, which makes it suitable for commercial applications.