Effect of Ligand Functionalization on the Separation of Small Hydrocarbons and CO<sub>2</sub> by a Series of <b>MUF-15</b> Analogues
Omid T. Qazvini, Lauren K. Macreadie, Shane G. Telfer
Abstract
Investigating the impact of ligand functionalization on the gas separation performance of metal–organic frameworks (MOFs) is important because it provides valuable insights into the design and architectures of high-performance materials. Here, we report five new MOFs that are derivatives of MUF-15. They adopt the general formula [Co6(μ3-OH)2(ipa-X)5(H2O)2], where ipa-X is a 5-substituted isophthalate linker with a fluoro, hydroxyl, bromo, nitro, or methyl substituent, and are denoted as MUF-15-X. MUF-15-F and MUF-15-NO2 are isoreticular to MUF-15, while MUF-15-Br and MUF-15-CH3 are closely related isomers of the MUF-15 topology. The frameworks exhibit various degrees of structural stability. The methyl group confers high moisture stability on the framework, while the hydroxyl group results in low stability. The chemical characteristics and dimensions of the framework pores are influenced by the functional group, resulting in distinct differences in gas sorption and separation performance. The nitro-functionalized framework is flexible upon the adsorption of certain gases, notably CO2 and ethane. We examined the effectiveness of these materials for the separations of C2H6/C2H4, C2H4/C2H2, and C2H2/CO2 and found that the functional groups can invert the selectivity of MUF-15 toward these gas pairs.