Carbon nanotubes and graphene oxide-based solvent-free hybrid nanofluids functionalized mixed-matrix membranes for efficient CO₂/N₂ separation

In this study, two kinds of novel mixed-matrix membranes (MMMs) were fabricated by incorporating covalently grafted polyetheramine (M2070)-carbon nanotubes (CNTs) or graphene oxide (GO) solvent-free hybrid nanofluids (denoted as CNTs NF and GO NF) into Pebax-1657 polymeric matrix to improve separation performance of CO₂/N₂, respectively. The pure gas and mixed gases permeabilities of MMMs were investigated, respectively. In addition, the effects of feed pressure and operating temperature on separation performance were discussed systematically. Excellent interfacial compatibility is obtained due to the potential advantage of high dispersion property of solvent-free hybrid nanofluids. Moreover, specific functional groups (ethylene oxide (EO) unit and [sbnd]NH[sbnd]) of polyetheramine canopy M2070 were confirmed to improve CO₂ permeability and CO₂/N₂ selectivity. Particularly, an optimal CO₂/N₂ separation factor of 72 with a CO₂ permeability of 332 Barrer was obtained, indicating an increase of 442% in CO₂ permeability and an increase of 77% in CO₂/N₂ selectivity compared with those of pristine Pebax membrane at 1.0 bar, 25 °C and dry mixed gases state, surpassing the 2008 Robeson upper bound. Finally, phase transition model of CO₂ selective separation was proposed according to more detailed gas permeability measurements to further explore the CO₂ selective separation mechanism.