Facilitated Transport of CO₂ Through the Transparent and Flexible Cellulose Membrane Promoted by Fixed-Site Carrier

Facilitated transport cellulose membranes with different zinc ion loadings are fabricated via a facile and green solvent system (zinc chloride/calcium chloride solution). Zn2+ ions lower the pristine hydrogen bonds that normally reinforce the cellulose chains, and Ca2+ ions facilitate interactions among the Zn–cellulose chains to form nanofibrils. The strategy provides an effective route to immobilize zinc species into membrane matrix and constructs facilitated transport pathway for CO2 molecules. The self-standing membranes are transparent, flexible and demonstrate ultraselective CO2 permeation. The optimum separation performance is achieved over CM-0 with the highest zinc content (22.2%), and it exhibits a CO2 permeability of 155.0 Barrer, with selectivity ratios of 27.2 (CO2/N2) and 100.6 (CO2/O2). The excellent separation performance is assigned to the π complexation mechanism between Zn2+ and CO2.