Metal-Organic Frameworks with Reduced Hydrophilicity for Postcombustion CO₂ Capture from Wet Flue Gas

Postcombustion CO₂ capture from wet flue gas is a daunting challenge that metal-organic-framework-based (MOF-based) adsorbents need to address, because the moisture in the gas stream may not only hydrolyze the coordination bonds of MOFs but also be competitively adsorbed in MOFs leading to compromised CO₂ capture performance. In this study, two isostructural water-stable MOFs decorated with alkyl groups, namely, UiO-66(Zr)-(OAc)₂ and UiO-66(Zr)-(OPr)₂, are synthesized from UiO-66(Zr)-(OH)₂ via a facile postsynthetic esterification strategy and evaluated for their water affinity and CO₂ capture performance. The increased water contact angle and reduced water vapor capacity at 60% relative humidity indicate the positive role of the propionyl group of UiO-66(Zr)-(OPr)₂ in reducing material hydrophilicity. When the adsorbent beds are not fully saturated with water, breakthrough experiments using simulated wet flue gas reveal that UiO-66(Zr)-(OPr)₂ possesses a CO₂/N₂ adsorption selectivity of 76.6, which is 229% that of UiO-66(Zr)-(OH)₂ (33.4). Our study successfully demonstrates a scalable material modification approach to engineer MOF adsorbents toward practical CO₂ capture processes under wet conditions.