A new nanoporous alucone-amine hybrid membrane with extremely high CO₂/CH₄ selectivity

Fabricating membranes that can remove CO₂ from a gaseous mixture has eluded scientists for a long time. The problem is highly important in view of global warming, with CO₂ being the main culprit. Novel alucone-amine hybrid (AAH) membranes with extremely high selectivity of CO₂ from its mixture with CH₄ were fabricated using 1,6 hexane diamine (HDA) and triethyl aluminum (TEA). This was accomplished by, first, engineering the mesopores of a porous support alumina disk to small and uniform nanopores by boehmite sol spin coatings and, then, functionalizing the membranes with an alucone-amine hybrid. To obtain the optimal morphology, the number of boehmite sol coatings and the ratio of HDA to TEA were varied. The optimal morphology was fabricated with fifteen cycles of boehmite sol spin coating and HDA/TEA ratio of 2. The morphology of the resulting optimal membranes, their surface area, and pore-size distribution were characterized by several complementary techniques. Multiple analytical techniques confirmed probably two structures of hexagonal and tetragonal for the fabricated AAH, although its XRD pattern is absent from the HighScore Xpert reference library. The functional membranes have a nanoflake morphology, with their CO₂ permeance being 7.72 × 10 ^-6 mol. m^-2. S^-1. Pa^-1, CO₂ selectivity of 2.85 × 10⁵ and 48-days stability. To further test the alucone-amine powder, sorption measurements were carried out. AAH exhibited an exceptionally high CO₂ adsorption capacity of 57.8 mmol g^-1, while showing only a minor amount of CH₄ adsorption, resulting in extremely high CO₂/CH₄ selectivity.