Pore-Structure Regulation of Hybrid Carbon Molecular Sieve Membranes by Hypercrosslinked Porous Nanofillers for High-Performance CO2 and H2 Separation

Abstract

Hybrid carbon molecular sieve (HCMS) membranes are attractive materials for low-energy gas separation, as their stiff ultramicroporous carbon networks provide strong molecular-sieving capability. In this study, hypercrosslinked polystyrene nanoparticles prepared using formaldehyde dimethyl acetal, denoted as PS-FDA, were introduced as porous structure-regulating fillers to tune the microstructural evolution of polyimide-derived CMS membranes. By adjusting the filler loading and pyrolysis temperature, the resulting HCMS membranes achieved excellent gas separation performance. The optimized 5-PS-FDA/PI-600 HCMS membrane exhibited the best overall performance, giving CO2 and H2 permeabilities of 16,050.92 and 18,810.15 Barrer, corresponding to approximately 152% and 139% increases over the pristine PI-600 HCMS membrane, respectively. At the same time, this membrane retained CO2/N2, CO2/CH4, H2/N2, and H2/CH4 selectivities of 28.15, 37.40, 32.99, and 43.85, respectively, surpassing the 2019 and 2015 Robeson upper bounds. Diffusivity/solubility analysis further indicated that the permeability enhancement was mainly associated with improved diffusional transport rather than increased gas sorption. Pressure-dependent permeation measurements and a 7-day physical aging test further showed that the optimized HCMS membrane preserved its molecular-sieving characteristics under the tested conditions. These results demonstrate that hypercrosslinked porous nanofillers can effectively regulate the pore-structure evolution of PI-derived HCMS membranes and offer a feasible approach for developing stable, highly permeable carbon membranes.