Toward Sustainable and Scalable CO ₂ Capture: Functionalized Bentonite Nanocomposite in Polydimethylsiloxane/Polysulfone Membranes for Enhanced Gas Separation

Efficient CO2/CH4 separation is vital for reducing greenhouse gas emissions and upgrading natural gas. This study reports a cost-effective mixed-matrix membrane (MMM) incorporating acid-activated, dopamine-functionalized bentonite clay (D-Clay) into a PDMS-coated polysulfone support. Dopamine modification enhances the clay surface area and introduces amine-rich sites that promote CO2-selective sorption and transport. The optimized membrane containing 0.5 wt % D-Clay exhibits a CO2 permeance of 37.54 GPU and a CO2/CH4 selectivity of 27 representing nearly a 2-fold improvement over the pristine PDMS/PSf (M0) membrane and outperforming several reported nanocomposite systems. The enhanced performance arises from synergistic contributions of facilitated transport, surface diffusion, and molecular sieving. Under mixed-gas testing, membranes M2 and M3 showed CO2/CH4 selectivity losses of 44.59% and 54.8%, respectively, relative to single-gas data, yet maintained performance levels relevant for industrial operation. Overall, the results establish D-Clay as a scalable, low-cost filler that enables robust, high-performance MMMs for natural gas purification and CO2 mitigation.