Cation-Exchanged Zeolitic Chalcogenides for CO Adsorption.

We report here the intrinsic advantages of a special family of porous chalcogenides for CO adsorption in terms of high selectivity of CO/N, 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 CO 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 CO adsorption. Samples were prepared through a sequential ion-exchange strategy, and Cs-, Rb-, and K-exchanged samples demonstrated excellent CO adsorption performance. Particularly, K@RWY has the superior CO/N selectivity with the N adsorption even undetected at either 298 or 273 K. It also has the large uptake of 6.3 mmol/g (141 cm/g) at 273 K and 1 atm with an isosteric heat of 35-41 kJ mol, 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.