Synergistic Enhancement of CO ₂ Separation Performance in Pebax 1657 Membranes via Carboxylated Nanocellulose and Glycine Incorporation

The advancement of membrane materials exhibiting both high CO2 permeability and enhanced CO2/N2 selectivity remains essential, while simultaneously enhancing the sustainability of membrane fabrication processes is equally important. In this work, a series of mixed matrix membranes (MMMs) were constructed by introducing carboxylated nanocellulose fibers (CNF) into Pebax 1657, followed by further functionalization with amino acid glycine (Gly) to construct facilitated transport pathways under humid conditions. Gas separation results revealed that a moderate CNF loading significantly enhanced both CO2 permeability and CO2/N2 selectivity, with the optimal 5 wt % CNF membranes exhibiting a CO2 permeability of 167.7 Barrer and a CO2/N2 selectivity of 63.5 under dry conditions. Upon the introduction of Gly and operation under humid mixed-gas conditions, the membranes exhibited facilitated transport behavior, leading to further improvements in CO2 permeability while maintaining stable selectivity. Stability tests confirmed that the membranes retained stable gas separation performance during the testing period. The resulting membranes approach the Robeson upper bound, demonstrating the effectiveness of combining rigid nanocellulose frameworks with amino acid carriers for efficient and stable CO2 separation.