Highly permeable thermally rearranged polymer composite membranes with a graphene oxide scaffold for gas separation

Abstract

Thermally rearranged (TR) polymers are an important class of microporous polymers with remarkable gas transport performance, particularly suitable for CO₂ permeation and separation over large gas molecules. The fabrication of TR polymers into ultrathin membranes is highly desirable for practical application, but it is very challenging. In this work, a 2D scaffold of graphene oxide (GO) nanosheets was formed inside a TR polymer to assist the fabrication of a defect-free and ultrathin (less than 40 nm) selective layer of thermally rearranged polybenzoxazole-co-imide (TR-PBOI) membranes for energy-efficient CO₂ separation. The GO scaffold inside the polymer phase not only enabled the formation of the ultrathin selective layer of TR-PBOI, but also provided mechanical robustness. The resulting membrane showed remarkable gas permeance, while maintaining the gas selectivity of the pristine polymer. In particular, it had a CO₂ permeance of 1784 GPU and a CO₂/CH₄ selectivity of 32, whereas the freestanding TR-PBOI membrane only exhibited a CO₂ permeance of 3.7 GPU with a CO₂/CH₄ selectivity of 35. In other words, the rGO–PBOI (TR-PBOI with reduced GO) membrane has 482 times higher CO₂ permeance than the TR-PBOI freestanding membrane at a similar CO₂/CH₄ selectivity.