On the water stability of ionic liquids/Cu-BTC composites: an experimental study

Ionic liquids/metal-organic framework composites are recognized as promising adsorbents for CO₂ capture due to the outstanding adsorption performance, whereas their water stability, which is critical for the real application of ILs/MOF composites, has not been taken into consideration. In this work, the water stability of two ILs/Cu-BTC composites, i.e., 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF₄]) /Cu-BTC and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆]) /Cu-BTC, were investigated. We found that the loading of ILs does not impose remarkable impacts on the crystalline structure of Cu-BTC upon water exposure; whereas the thermal stability and surface area of Cu-BTC were decreased by the incorporation of ILs, thereby leading to the reduced CO₂ uptake in spite of the enhanced CO₂ heat of adsorption. Furthermore, it was revealed that the decomposition of Cu-BTC occurred within the first hour of water exposure. Nevertheless, the loading of ILs retarded the decomposition of Cu-BTC according to the variations in BET surface area upon water exposure.

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