Effect of ligands regulation on Al-based metal organic frameworks for selective adsorption of xenon from spent fuel

Abstract

Effective separation of inert gas such as Xe and Kr from used nuclear fuel is significant for maintaining ecological environment safety and recycling nuclear fuel. In this study, Al-CDC and Al-BDC with similar linear ligands were synthesized to reveal the influence of ligand regulation on Xe separation under different pressure conditions. The results displayed that the adsorption capacity of Al-BDC for Xe could reach 2.66 mmol g-1 under normal pressure, which is 1.11 times higher than that of Al-CDC, depending on its higher specific surface area and bigger pore volume. On the contrary, the Xe adsorption capacity of Al-CDC with the feature of narrow micropore structure and saturated C-H or oxygen-containing functional groups reached 1.44 mmol g−1 at 0.1 bar, which was 2.82 times higher than that of Al-BDC, resulting in a remarkable difference in Xe working capacity between Al-CDC (0.43 mmol g−1) and Al-BDC (0.073 mmol g−1) through dynamic breakthrough experiments. Meanwhile, the Henry’s selectivity of Al-CDC for Xe/Kr and Xe/N2 was up to 13.97 and 110.31, Compared with most porous adsorbents in previous reports, Al-CDC exhibits both high adsorption capacity and high selectivity. Innovatively, we analyzed the advantage in capacity and selectivity by the perspective of ligands, and the calculation results of the complete cell also proved that the saturated C-H group and benzene ring center on cyclohexane are the main adsorption sites of Al-CDC and Al-BDC for Xe, respectively. Therefore, a higher polar ligand in Al-CDC could lead to strong static binding energy and single cell binding energy which attribute to a high selective Xe adsorption. These results revealed the key structural characteristics for selective Xe adsorption under different pressure conditions, providing valuable suggestions for the design of separation materials from spent fuel.