Hybrid Cu/Zn-BDC@MA-BTC Structures as Synergistic Fillers for High-Performance Mixed Matrix Gas Separation Membrane

Abstract

Achieving an optimal balance between permeability and selectivity, along with enhancing CO2 separation performance, is a key challenge in the development of mixed-matrix membranes. In this study, a binary Cu2+/Zn2+ MOF based on the H2BDC ligand was employed due to the presence of unsaturated metal sites and hydroxyl groups, which exhibit a strong affinity for interacting with polar gases such as CO2. To further improve the performance of Cu-BDC/Zn-BDC, an MA-BTC-based HOF was utilized, where the amine (NH−) and carboxylate (COO–) functional groups facilitate hydrogen bonding and enhance CO2 interactions. The HOF was grown in situ on the MOF surface, resulting in the formation of the hybrid Cu-BDC/Zn-BDC@MA-BTC structure as a MOF/HOF system. The successful synthesis and formation of the hybrid structure were confirmed through BET, SEM, XRD, and FTIR analyses. The Cu-BDC/Zn-BDC@MA-BTC composite was incorporated into a Pebax-1657 polymer matrix at various weight fractions (0.1, 0.15, 0.2, 0.25, and 0.3 wt %), among which the Pebax/MOF/HOF (0.3 wt %) membrane exhibited the best performance. At 30 °C and 10 bar, this membrane showed a CO2 permeability of 196.68 Barrer and CO2/N2 and CO2/CH4 selectivities of 63.85 and 23.84, respectively, representing enhancements of 60.1%, 13.7%, and 37.7% compared to the pristine membrane. Surface modification of Cu-BDC/Zn-BDC through the in situ growth of MA-BTC resulted in a more stable structure with higher specific surface area and flexibility, as well as improved compatibility between the hybrid structure and the polymer matrix, ultimately leading to enhanced separation performance of the mixed-matrix membranes.