Pore Modulation of Hydrogen-Bonded Organic Frameworks for Efficient Separation of Propylene

Developing hydrogen-bonded organic frameworks (HOFs) that combine functional sites, size control, and storage capability for targeting gas molecule capture is a novel and challenging venture. However, there is a lack of effective strategies to tune the hydrogen-bonded network to achieve high-performance HOFs. Here, a series of HOFs termed as HOF-ZSTU-M (M=1, 2, and 3) with different pore structures are obtained by introducing structure-directing agents (SDAs) into the hydrogen-bonding network of tetrakis (4-carboxyphenyl) porphyrin (TCPP). These HOFs have distinct space configurations with pore channels ranging from discrete to continuous multi-dimensional. Single-crystal X-ray diffraction (SCXRD) analysis reveals a rare diversity of hydrogen-bonding models dominated by SDAs. HOF-ZSTU-2, which forms a strong layered hydrogen-bonding network with ammonium (NH₄ ⁺ ) through multiple carboxyl groups, has a suitable 1D "pearl-chain" channel for the selective capture of propylene (C₃ H₆ ). At 298 K and 1 bar, the C₃ H₆ storage density of HOF-ZSTU-2 reaches 0.6 kg L^-1 , representing one of the best C₃ H₆ storage materials, while offering a propylene/propane (C₃ H₆ /C₃ H₈ ) selectivity of 12.2. Theoretical calculations and in situ SCXRD provide a detailed analysis of the binding strength of C₃ H₆ at different locations in the pearl-chain channel. Dynamic breakthrough tests confirm that HOF-ZSTU-2 can effectively separate C₃ H₆ from multi-mixtures.