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Adsorptive removal of an eight-component volatile organic compound mixture by Cu-, Co-, and Zr-metal-organic frameworks: experimental and theoretical studies



To effectively mitigate hazardous volatile organic compounds (VOCs) in air, studies focusing on adsorption techniques for their complex mixtures, rather than individual species, are of great demand in light of the scarcity of relevant data. Four broadly studied Cu- (MOF-199 (also known as HKUST-1)), Co- (Co-CUK-1), and Zr- (UiO-66 (U6) and UiO-66-NH2 (U6N)) metal-organic frameworks (MOFs) were effectively synthesized, characterized, and studied as the adsorbents along with a microporous activated carbon (AC) as a reference adsorbent. Further, a multiple target system was built to include eight VOCs (four aromatics (benzene, toluene, styrene, m-xylene) and four oxygen-containing aliphatic compounds (methyl ethyl ketone (MEK), methyl isobutyl ketone (MiBK), butyl acetate (BuAc), and isobutyl alcohol (iBuAl))) for both single-/multi-component systems. The MOFs adsorbed polar VOCs favorably, with the M199 outperforming the rest. The 10% breakthrough volume (L atm g-1) for M199 was noted to decrease in the following order: MiBK (7,659) > MEK (4,772) > iBuAl (1,954) > styrene (1,775) > m-xylene (316) > BuAc (206) > toluene (50) > benzene (36). In case of U6, the presence of amine groups (U6N) had a positive impact towards the adsorption of all eight analyzed VOCs. The experimental and density functional theory (DFT)-based modelling indicated competition for the surface sorption sites for both individual and mixture system. In case of MOFs, the uncoordinated metal centers (Lewis acidic sites) were found to be primarily involved in the adsorption of polar VOCs, while the π-π interactions and van der Waals forces were the predominant adsorption mechanisms in the case of AC. The theoretical DFT results also supported the enhanced adsorption performance of M199 over other MOFs based on its rigid structure.

K. Vikrant, Ki.H. Kim, V. Kumar, D.A. Giannakoudakis, and D.W. Boukhvalov. Chemical Engineering Journal, 397 (2020) 125391.


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