Adsorptive separation process based on porous materials is widely employed in various separation scenarios owing to its mild operating conditions and energy-efficient characteristics.

In a study published in Chem, Prof. WU Mingyan's group from the Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences proposed a bottom-up, self-assembly approach to synthesize a novel pillar-cage fluorinated hybrid porous framework (TIFSIX-Cu-J), which exhibits a rare crystalline quasi-Johnson solid J₂₈ structure.

Researchers synthesized TIFSIX-Cu-J by a bottom-up, self-assembly approach with geometrical elements of quadrangular and isosceles triangles. TIFSIX-Cu-J underwent heat-triggered structural transformation, during which the J₂₈ cage was restructured to form a new distorted square orthobicupola structure. The structural changes were elucidated through detailed analysis of the single-crystal-to-single-crystal (SC-SC) transformation and bulk crystalline powder X-ray diffraction.

This self-assembly approach can be applied to synthesize isomorphic crystals such as SIFSIX-Cu-J and ZrFSIX-Cu-J, and can also exhibit in-situ SC-SC structural transformations.

Researchers found that the adsorption capacity of TIFSIX-Cu-J1 for C₃H₄ reached 140.5 cm³∙g^-1, and the adsorption amount differences between C₃H₄ and C₃H₆ increased from 19.6 to 34.8 cm³∙g^-1. TIFSIX-Cu-J1 exhibited a higher C₃H₄/C₃H₆ IAST selectivity than that of TIFSIX-Cu-J. In-situ breakthrough experiments showed that TIFSIX-Cu-J1 packed column can directly yield in a high C₃H₆ productivity, which is about twenty times as high as that of TIFSIX-Cu-J.

Theoretical calculations demonstrated that the more suitable pore surface in the quasi-Johnson solid J₂₈ cavity of TIFSIX-Cu-J1 is beneficial to preferentially capture C₃H₄ rather than C₃H₆ and thus boosts the selective separation of C₃H₄/C₃H₆.

This study provides new insights into systematically designing and synthesizing novel pillar-cage fluorinated hybrid porous frameworks. Also, it highlights the bottom-up, self-assembly approach as an effective one for constructing artificial cage-like three dimensional architectures with selective separation properties in energy-saving gas purification.