Metal–Organic Frameworks for the Adsorptive Removal of Gaseous Aliphatic Ketones

Abstract

Recent research endeavors have established metal-organic frameworks (MOFs) as suitable platforms for the adsorptive removal of various environmental pollutants. In this regard, the sorptive performances of four MOFs (MOF-199, UiO-66, UiO-66-NH₂, and Co-CUK-1) were investigated against two gaseous aliphatic ketones (methyl ethyl ketone (MEK) and methyl isobutyl ketone (MiBK)) at a low partial pressure (0.1 Pa). Activated carbon was utilized as a reference commercial sorbent. The 10% breakthrough volume (BTV10) values for MEK decreased in the following order: MOF-199 (4772 L atm g^-1) > activated carbon (224 L atm g^-1) > UiO-66-NH₂ (106 L atm g^-1) > UiO-66 (53 L atm g^-1) > Co-CUK-1 (16 L atm g^-1). In case of MiBK, the relative ordering in BTV10 was consistently maintained while showing noticeable increases in its magnitude: MOF-199 (7659 L atm g^-1) > activated carbon (816 L atm g^-1) > UiO-66-NH₂ (304 L atm g^-1) > UiO-66 (150 L atm g^-1) > Co-CUK-1 (31 L atm g^-1). The superiority of MOF-199 was confirmed toward the adsorptive removal of gaseous aliphatic ketones. For a binary mixture of ketones, the BTV10 values of MOF-199 were reduced considerably for MEK and MiBK (in comparison to single component sorption) such as 1579 and 3969 L atm g^-1, respectively, reflecting competitive inhibition of the adsorption process. Theoretical simulations based on density functional theory (DFT) elucidated the involvement of highly favorable coordination between the carbonyl group present in ketone molecules and the uncoordinated Cu(II) sites in the MOF-199 structure (Lewis acidic centers). Interestingly, MOF-199 maintained appreciable performance toward the mixture of ketones up to 5 cycles to support its practical merit.