MOFs with Open Metal(III) Sites for the Environmental Capture of Polar Volatile Organic Compounds

Abstract

Metal-Organic Frameworks (MOFs) with open metal sites (OMS) interact strongly with a range of polar gases/vapors. However, under ambient conditions, their selective adsorption is generally impaired due to a high OMS affinity to water. This led previously to the privilege selection of hydrophobic MOFs for the selective capture/detection of volatile organic compounds (VOCs). Herein, we show that this paradigm is challenged by metal(III) polycarboxylates MOFs, bearing a high concentration of OMS, as MIL-100(Fe), enabling the selective capture of polar VOCs even in the presence of water. With experimental and computational tools, including single-component gravimetric and dynamic mixture adsorption measurements, in situ infrared (IR) spectroscopy and Density Functional Theory calculations we reveal that this adsorption mechanism involves a direct coordination of the VOC on the OMS, associated with an interaction energy that exceeds that of water. Hence, MOFs with OMS are demonstrated to be of interest for air purification purposes.

Metal–organic frameworks for the capture of α-pinene traces

“…They have been identified as promising candidates over the traditional porous materials for the sorption of a wide range of indoor and outdoor contaminants (CO x , NO x , SO x ) 23,24 as well as diverse VOCs (aldehydes, ketones, acids, alcohols, and aromatics). [25][26][27][28] Their attractiveness for VOCs capture, even at trace levels, relies on their unique richness in terms of structural and chemical features that can be modulated to favour a strong affinity for the target VOC via electrostatic interactions, p-complex formation, hydrogen bonding or even throughout geometric confinement. [25][26][27] In addition, MOF materials containing high-valence metal ions have been demonstrated to be highly chemically stable which is of crucial interest for their long-term use under working conditions.…”