Hydrogen Bonds Defined Pore Windows Enable Sieving Separation of Propylene from Propane in an Ultramicroporous Metal–Organic Framework

Abstract

Tailoring a MOF with suitable pore windows for the sieving C 3 H 6 /C 3 H 8 separation is attractive but challenging, where controlling the local framework flexibility by introducing functionality provides a solution. In this work, four isoreticular ultramicroporous Zn−triazolate−dicarboxylate frameworks, Zn-ATZ-IP(R) (R = −F, −OH, −NH 2 , and −CH 3 ) (HATZ = 3-amino-1,2,4-triazole; H 2 IP-R = R group functionalized isophthalic acid) with variable pore apertures, were targeted as platforms to study the effect of functional groups on their separation performance. Single-component adsorption isotherms uncovered the potential of Zn-ATZ-IP(OH)-a with hydroxyl groups as a sieving adsorbent. Single X-ray diffraction (SXRD) measurements revealed that strong intraframework hydrogen bonds hinder the free torsion of ATZ − ligand in Zn-ATZ-IP(OH)-a, defining rigid pore windows that admit C 3 H 6 while exclude C 3 H 8 , whereas other groups give adaptive larger pores that allow both C 3 H 6 and C 3 H 8 in. Further, in situ XRD measurements suggested that temperature alters the strength of hydrogen bonds, making Zn-ATZ-IP(OH)-a ideal for roomtemperature sieving of C 3 H 6 /C 3 H 8 . This work highlights the superiority of customizing sieving pores sustained by hydrogen bonds, which advances the rational design of smart adsorbents for energy-efficient light hydrocarbon separations.