The First Kr-Selective Carbon Molecular Sieve for Inverse Adsorption of Krypton Over Xenon at Ambient Temperature.

The efficient adsorption-based separation of krypton (Kr) and xenon (Xe) is of paramount importance but is challenged by their similar physicochemical properties. While carbon adsorbents are theoretically promising for Kr/Xe sieving, practical success has remained elusive. Here, a series of ultramicroporous carbon molecular sieves synthesized from sucrose-derived hydrochar is reported. The study employs careful characterization and controlled thermal pyrolysis to tailor ultramicropore formation and elucidate the evolution of the carbon framework. The leading material, C-Suc-750, has an ideal pore size of ≈4.0 Å. In particular, C-Suc-750 has achieved a remarkable Kr/Xe uptake ratio of 39.3 at ambient conditions, setting a new benchmark for selective Kr adsorption and molecular sieving of Kr/Xe. Breakthrough experiments further confirm the superior molecular sieving performance of C-Suc-750, highlighting its potential for Kr recovery in nuclear waste treatment. Moreover, molecular dynamics (MD) simulations demonstrate the critical role of narrow slit-pore of the carbon molecular sieve in molecular sieving separation of Kr/Xe, providing insights into the mechanism driving this selectivity.