Understanding how pore surface fluorination influences light hydrocarbon separation in metal–organic frameworks

Abstract

The designability and tunability of the pore structure are the advantage of metal–organic frameworks (MOFs) for adsorptive separation applications. However, it is still challenging to design MOF adsorbent rationally according to industrial demands, because of the complexity in the separation processes and the relative lack of structure-separation relationship information. Herein, we established a contrastive model ingeniously via structural modification at the atom level in three Cu(II)-MOFs constructed from isonicotinic acid (HINA) and its fluorinated analogue 3-fluoro-isonicotinic acid (HFINA), targeting on controlling pore surface fluorination for studying light hydrocarbon separation. Both the fluorinated MOFs (Cu-FINA-1 and 2) show notably enhanced C2H2/C2H4 and C3H4/C3H6 selectivity compared with Cu-INA without increasing regeneration energy consumption. Especially, Cu-FINA-2 exhibits a considerable IAST selectivity (6.3–9.3) for C3H4/C3H6, while Cu-FINA-1 achieves a C3H6 process productivity of 31.6 cm3/g in column breakthrough experiments. Molecular simulations reveal that the polar F sites within the confined pores can interact with gas adsorbates through C-H···F hydrogen bonds, and the tailored pore size and optimal diffusion kinetics mainly contribute to the excellent separation selectivity for Cu-FINA-1. This work highlights how pore surface fluorination and related structural evolution can influence light hydrocarbon adsorption/separation properties in MOFs, and thus promotes the rational design and precise optimization of new adsorbents for alkynes/alkenes separations, even at the atom level.