Thiophene-based conjugated ultra-micropore rigid polymers for selective xenon capture

Radioactive isotopes of krypton (Kr) and xenon (Xe) are produced from the fission reaction of nuclear reactors. The separation of Xe/Kr from the nuclear off-gas is important for the spent fuel reprocessing. Compared with the industrial method of cryogenic distillation, physical adsorption is a simple and energy-saving method for Xe/Kr separation. Here, three rigid conjugated micropore polymers, including thiophene containing CMP-PY-BTP, TBTP and fluorine-containing CMP-PY-TFB, were prepared in high yield through direct C-H arylation reac-tion, and their structure-function relationship with Xe/Kr separation was described. CMP-PY-TFB, BTP, and TBTP all possessed rigid micropores with Brunauer-Emmett-Teller specific surface areas of 786.25, 141.64 and 488.30 m2/g, respectively. Among three polymers, CMP-PY-TBTP exhibited the highest Xe/Kr selectivity (11.9 for ideal adsorption solution theory selectivity and 9.3 for Henry selectivity), owing to the combined effect of stronger polarization of its thiophene structural unit and micropore confinement (5.4 angstrom). The density functional theory (DFT) calculation revealed that Xe was more strongly adsorbed in thiophene-containing units than that of fluorine-containing unit which verified the stronger interaction caused by thiophene group's polarization. Though having weaker polarization to Xe, fluorine-containing CMP-PY-TFB exhibited the highest Xe uptake of 43.59 cm3 g-1 due to its largest specific surface area (786.25 m2/g).

Automated summary

This study investigates the role of three conjugated microporous polymer materials in the separation of xenon and krypton. The results show that the CMP-PY-TBTP polymer exhibits the highest selectivity for xenon/krypton separation, while the CMP-PY-TFB polymer exhibits the highest xenon adsorption. These findings have important applications in the separation of xenon and krypton in nuclear waste reprocessing.