Tunable Robust pacs-MOFs: a Platform for Systematic Enhancement of the C₂H₂ Uptake and C₂H₂/C₂H₄ Separation Performance

Abstract

As a modulatable class of porous crystalline materials, metal-organic frameworks (MOFs) have gained intensive research attention in the domain of gas storage and separation. In this study, we report on the synthesis and gas adsorption properties of two robust MOFs with the general formula [Co₃(μ₃-OH)(cpt)₃Co₃(μ₃-OH)(L)₃(H₂O)₉](NO₃)₄(guests) _n [L = 3-amino-1,2,4-triazole (1) and 3,5-diamino-1,2,4-triazole (2); Hcpt = 4-(4-carboxyphenyl)-1,2,4-triazole], which show the same pacs topology. Both MOFs are isostructural to each other and show MIL-88-type frameworks whose pore spaces are partitioned by different functionlized trinuclear 1,2,4-triazolate-based clusters. The similar framework components with different amounts of functional groups make them an ideal platform to permit a systematic gas sorption/separation study to evaluate the effects of distinctive parameters on the C₂H₂ uptake and separation performance. Because of the presence of additional amido groups, the MOF 2 equipped with a datz-based cluster (Hdatz = 3,5-diamino-1,2,4-triazole) shows a much improved C₂H₂ uptake capacity and separation performance over that of the MOF 1 equipped with atz-based clusters (Hatz = 3-amino-1,2,4-triazole), although the surface area of the MOF 1 is almost twice than that of the MOF 2. Moreover, the high density of open metal sites, abundant free amido groups, and charged framework give the MOF 2 an excellent C₂H₂ separation performance, with ideal adsorbed solution theory selectivity values reaching up to 11.5 and 13 for C₂H₂/C₂H₄ (1:99) and C₂H₂/CO₂ (50:50) at 298 K and 1 bar, showing potential for use in natural gas purification.