Selective krypton uptake through trap confinement, formation of Kr2 dimer, and light response in a photochromic and radiation-resistant thorium-diarylethene-framework

Capturing trace krypton (Kr) from used nuclear fuel (UNF) off-gas remains a big challenge, because of low Kr uptake and poor Kr/N₂ selectivity for current available adsorbents. Herein, we demonstrate a photochromic and radiation-resistant thorium-diarylethene-framework (DMOF-Th-1o). The pristine DMOF-Th-1o renders ultrahigh Kr uptake up to 7.5 cm³/g at 0.1 bar and record Kr/N₂ selectivity (>100) at low pressure. This is mainly because of, as unveiled by theoretical calculation, the trap-type pore (3.8 Å) in DMOF-Th-1o that perfectly matches with the kinetic diameter (3.7 Å) of Kr to exactly fix one Kr atom, while forms a unique Kr₂ dimer with short Kr-Kr contact (4.18 Å). More impressively, we further observed record Kr uptake (13 cm³/g) at 0.1 bar in the color-changed counterpart of DMOF-Th-1c, exceeding all reported adsorbents under the same condition. Correspondingly, the Kr/N₂ selectivity is further boosted by more than twofold. Moreover, breakthrough test from a simulated off-gas containing 40 ppm Kr was used to confirm the real Kr/N₂ separation performance, indicative of benchmark Kr/N₂ separation.