Direct Observation of Xe and Kr Adsorption in a Xe-Selective Microporous Metal–Organic Framework

• Published in: Journal of the American Chemical Society 2015-06, Vol.137 (22), p.7007-7010
• Main Authors: Chen, Xianyin, Plonka, Anna M, Banerjee, Debasis, Krishna, Rajamani, Schaef, Herbert T, Ghose, Sanjit, Thallapally, Praveen K, Parise, John B
• Format: Article
• Language: English
• Subjects: MATERIALS SCIENCE
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.5b02556

The cryogenic separation of noble gases is energy-intensive and expensive, especially when low concentrations are involved. Metal–organic frameworks (MOFs) containing polarizing groups within their pore spaces are predicted to be efficient Xe/Kr solid-state adsorbents, but no experimental insights into the nature of the Xe–network interaction are available to date. Here we report a new microporous MOF (designated SBMOF-2) that is selective toward Xe over Kr under ambient conditions, with a Xe/Kr selectivity of about 10 and a Xe capacity of 27.07 wt % at 298 K. Single-crystal diffraction results show that the Xe selectivity may be attributed to the specific geometry of the pores, forming cages built with phenyl rings and enriched with polar −OH groups, both of which serve as strong adsorption sites for polarizable Xe gas. The Xe/Kr separation in SBMOF-2 was investigated with experimental and computational breakthrough methods. These experiments showed that Kr broke through the column first, followed by Xe, which confirmed that SBMOF-2 has a real practical potential for separating Xe from Kr. Calculations showed that the capacity and adsorption selectivity of SBMOF-2 are comparable to those of the best-performing unmodified MOFs such as NiMOF-74 or Co formate.