3D ultra-micropore organic polymers with fixed group and thieno[3,2-b] thiophene to enhance adsorption and separation of Xe/Kr

The reduction of environmental pollution and the exploration of economic values require the efficient separation and purification of xenon (Xe) and krypton (Kr) from radioactive gases generated during nuclear fission processes. To address this issue, we have synthesized three thieno[3,2-b]thiophene-based porous organic polymers (POP-ch-ET, POP-ch-SP and POP-ch-ME) via high yield C-H direct arylation reaction, all of which exhibited excellent thermal and acid-base stability. Notably, the three-dimensional (3D) structures of POP-ch-SP and POPch-ME allowed higher Xe capacity compared to the two-dimensional (2D) structure of POP-ch-ET. Density functional theory (DFT) calculations confirmed that thieno[3,2-b]thiophene moieties contributed to a more negative adsorption energy for Xe than benzene. Among them, POP-ch-SP with fixed group showed superior Xe capacity (2.37 mmol/g) at 298 K and 1.0 bar and the highest ideal adsorption solution theory (IAST) selectivity (11.5). This superior performance is attributed to its 3D ultra-micropore structure, which enables closer proximity between aromatic rings, thereby enhancing Xe interaction. The DFT calculation further revealed that the adsorption energy of Xe in POP-ch-SP was more negative compared to other POPs, indicating a stronger interaction. In addition, POP-ch-SP exhibited the largest Delta Qst (14.2 kJ/mol) between Xe and Kr, highlighting a marked affinity difference. In dynamic breakthrough experiments, POP-ch-SP demonstrated robust Xe/Kr separation efficiency under both low (400 ppm Xe and 40 ppm Kr in dry air) and high concentration scenarios (Xe/ Kr, v/v, 20/80), underscoring its promising potential for practical applications in radioactive gas management.