Cation-Exchanged Zeolitic Chalcogenides for CO₂ Adsorption

We report here the intrinsic advantages of a special family of porous chalcogenides for CO₂ adsorption in terms of high selectivity of CO₂/N₂, large uptake capacity, and robust structure due to their first-ever unique integration of the chalcogen-soft surface, high porosity, all-inorganic crystalline framework, and the tunable charge-to-volume ratio of exchangeable cations. Although tuning the CO₂ adsorption properties via the type of exchangeable cations has been well-studied in oxides and MOFs, little is known about the effects of inorganic exchangeable cations in porous chalcogenides, in part because ion exchange in chalcogenides can be very sluggish and incomplete due to their soft character. We have demonstrated that, through a methodological change to progressively tune the host-guest interactions, both facile and nearly complete ion exchange can be accomplished. Herein, a series of cation-exchanged zeolitic chalcogenides (denoted as M@RWY) were studied for the first time for CO₂ adsorption. Samples were prepared through a sequential ion-exchange strategy, and Cs⁺-, Rb⁺-, and K⁺-exchanged samples demonstrated excellent CO₂ adsorption performance. Particularly, K@RWY has the superior CO₂/N₂ selectivity with the N₂ adsorption even undetected at either 298 or 273 K. It also has the large uptake of 6.3 mmol/g (141 cm³/g) at 273 K and 1 atm with an isosteric heat of 35-41 kJ mol^-1, the best among known porous chalcogenides. Moreover, it permits a facile regeneration and exhibits an excellent recyclability, as shown by the multicycling adsorption experiments. Notably, K@RWY also demonstrates a strong tolerance toward water.