Tuning Pore Polarization to Boost Ethane/Ethylene Separation Performance in Hydrogen-Bonded Organic Frameworks.

Hydrogen-bonded organic frameworks (HOFs) show great potential in energy-saving C H /C H separation, but there are few examples of one-step acquisition of C H from C H /C H because it is still difficult to achieve the reverse-order adsorption of C H and C H . In this work, we boost the C H /C H separation performance in two graphene-sheet-like HOFs by tuning pore polarization. Upon heating, an in situ solid phase transformation can be observed from HOF-NBDA(DMA) (DMA=dimethylamine cation) to HOF-NBDA, accompanied with transformation of the electronegative skeleton into neutral one. As a result, the pore surface of HOF-NBDA has become nonpolar, which is beneficial to selectively adsorbing C H . The difference in the capacities for C H and C H is 23.4 cm  g for HOF-NBDA, and the C H /C H uptake ratio is 136 %, which are much higher than those for HOF-NBDA(DMA) (5.0 cm  g and 108 % respectively). Practical breakthrough experiments demonstrate HOF-NBDA could produce polymer-grade C H from C H /C H (1/99, v/v) mixture with a high productivity of 29.2 L kg at 298 K, which is about five times as high as HOF-NBDA(DMA) (5.4 L kg ). In addition, in situ breakthrough experiments and theoretical calculations indicate the pore surface of HOF-NBDA is beneficial to preferentially capture C H and thus boosts selective separation of C H /C H .