Boosting Xe/Kr separation by a Mixed-linker strategy in Radiation-Resistant Aluminum-Based Metal − Organic frameworks

Capturing and separating radioactive isotopes of Xenon (Xe) and Krypton (Kr) from off-gas streams in the reprocessing of used nuclear fuel (UNF) gaseous radioactive nuclides emerges as a major concern to meet the rapid growth and sustainable development of nuclear energy. Owing to the inert atomic gases (Xe and Kr) nature without dipole or quadruple moments and their existing extremely low concentrations in radioactive off-gas mixture, it is a grand challenge to design radiation-resistant porous adsorbents for efficient Xe capture and Xe/Kr separation at dilute conditions. Herein, we report a mixed-linker strategy to realize a confined aliphatic pore environment in high radioactive stable CAU-10 type Aluminum-based MOFs using isophthalate and 5-methylisophthalate as mixed linkers for Xe/Kr separation at low concentration. By systematically tune the ratio of the two linkers, the precise and appropriate amount of aliphatic methyl groups could be immobilized on the framework to achieve delicate regulation of pore structure (pore shape and pore size), which significantly increase Xe binding affinity. Mixed-linker CAU-10-H-CH3-0.21–0.79 shows significantly enhanced Xe capture and separation performance at dilute conditions compared to pristine CAU-10-H and fully methyl functionalized CAU-10-CH3, demonstrated by adsorption isotherms and breakthrough curves. The high radioactive stability of CAU-10 type Al-MOFs was also identified by gamma-ray irradiation experiments, suggesting a great potential for practical application.