Optimizing Propylene/Propane Sieving Separation through Gate-Pressure Control within a Flexible Organic Framework

The separation of propylene (C3H6) and propane (C3H8) is of great significance in the chemical industry, which poses a challenge due to their almost identical kinetic diameters and similar physical properties. In this work, we synthesized an ultramicroporous flexible hydrogen-bonded organic framework (named HOF-FJU-106) by using molecule 2,3,6,7-tetra (4-cyanophenyl) tetrathiafulvalene (TTF-4CN). The formation of the dimer causes the TTF-4CN molecular to bend and weaken pi-stacked interactions, coupled with the flexibility of C equivalent to N & ctdot;H-C hydrogen bonds, which leads to reversible conversion between open and closed frameworks through the mutual slip of adjacent layers/columns under activation and stimulation of gas molecules. Through gas adsorption isotherms and adsorption enthalpy, HOF-FJU-106a exhibited adaptive adsorption and stronger binding affinity for C3H6, and presented a recorded gas uptake ratio of C3H6/C3H8 (23.77) among presentative HOF materials at room temperature to date. Importantly, the flexible HOF-FJU-106a shows an interesting phenomenon about the reversible gate pressure control under variable temperature, which realized the gas adsorption and separation performance enhancement for the binary C3H6/C3H8 mixtures. This strategy through designing HOFs with thermoregulatory gating effect is a powerful way to maximize the performance of materials.