Water-enhanced CO capture in metal-organic frameworks.

CO capture from post-combustion flue gas originating from coal or natural gas power plants, or even from the ambient atmosphere, is a promising strategy to reduce the atmospheric CO concentration and achieve global decarbonization goals. However, the co-existence of water vapor in these sources presents a significant challenge, as water often competes with CO for adsorption sites, thereby diminishing the performance of adsorbent materials. Selectively capturing CO in the presence of moisture is a key goal, as there is a growing demand for materials capable of selectively adsorbing CO under humid conditions. Among these, metal-organic frameworks (MOFs), a class of porous, highly tunable materials, have attracted extensive interest for gas capture, storage, and separation applications. The numerous combinations of secondary building units and organic linkers offer abundant opportunities for designing systems with enhanced CO selectivity. Interestingly, some recent studies have demonstrated that interactions between water and CO within the confined pore space of MOFs can enhance CO uptake, flipping the traditionally detrimental role of moisture into a beneficial one. These findings introduce a new paradigm: water-enhanced CO capture in MOFs. In this review, we summarize these recent discoveries, highlighting examples of MOFs that exhibit enhanced CO adsorption under humid conditions compared to dry conditions. We discuss the underlying mechanisms, design strategies, and structural features that enable this behavior. Finally, we offer a brief perspective on future directions for MOF development in the context of water-enhanced CO capture.