Morphological engineering of hydrogen organic frameworks to boost CO2 separation in mixed matrix membranes

Hydrogen-bonded organic frameworks (HOFs) have emerged as promising materials for membrane applications due to their well-defined porosity and solution processability. Nevertheless, HOF integration into mixed matrix membranes (MMMs) is constrained by the challenge of transforming bulky HOF particulate fillers into freestanding membranes with excellent polymer matrix compatibility. This study systematically synthesized HOF-ZJU-201 as the fillers in three distinct morphologies—nanocrystals (NC), nanosheets (NS), and nanopolyhedra (NP)—utilizing dimethylformamide as nucleation promoter and monocarboxylic acids (acetic acid/benzoic acid) as growth inhibitors. The morphology of the fillers significantly influenced gas separation performance, with NS-based PIM-1 MMMs showing the most pronounced enhancement. The optimized HOF-ZJU-201 NS/PIM-1 membrane with 5 % HOFs achieved a CO 2 permeability of 8738.4 Barrer and a CO 2 /N 2 ideal selectivity of 31.2 in single-gas permeation tests, representing 99 % higher permeability and 107 % higher selectivity than pristine PIM-1 membrane. In mixed-gas tests, this membrane demonstrated CO 2 permeability ranging from 7108.6 to 8419.6 Barrer and CO 2 /N 2 selectivity of 43.7–50.2, outperforming many state-of-the-art MMMs. Mechanistic investigations revealed that the abundant –NH 2 and –F functional groups formed polarized gas transport channels, enabling preferential CO 2 permeation. Additionally, the horizontal arrangement of nanosheets, coupled with superior interfacial properties, markedly increased the diffusive resistance for N 2 molecules. This research provides essential insights into HOF-based membranes and highlights morphological engineering as an effective strategy to optimize MMM performance for gas separation application. • HOF-ZJU-201 was synthesized with well-defined shapes of nanocrystal, nanosheet and nanopolyhedron. • Continuous mixed matrix membranes were fabricated by blending of HOF-ZJU-201 filler and PIM-1 polymer. • The two-dimensional structure of nanosheets minimized the resistance to CO 2 molecule diffusion. • The optimal membrane demonstrated a CO 2 permeability of 7837.3 Barrer and a gas selectivity of 50.2 for CO 2 /N 2 mixture.