The capture performance of An-MOF for fission gases: Insight from DFT and AIMD calculations

Abstract

Radioactive fission gases have numerous negative effects on the biosphere, and the capture of fission gases is a primary issue for environmental safety. The actinide organic framework structures (An-MOFs) have extremely high stability under harsh conditions and are expected to be highly efficient adsorbents. In this work, we have investigated the adsorption behaviors of fission gases in An-MOFs (Th and U) through density functional theory (DFT) and ab initio molecular dynamics (AIMD) calculations. The potential energy surfaces of fission gases (Kr, Xe, and I2) on the non-periodic cluster model, 8-coordinated secondary building units (SBUs) are obtained. The results show that Th-8-SBU exhibits a stronger adsorption capacity for fission gases than U-8-SBU, and all An-gas interactions are primarily governed by electrostatic attraction interaction revealed by electronic density topological analyses. The periodic boundary condition (PBC) model was also utilized to study the adsorption in Th-MOF, the adsorption energy of I2 in periodic Th-MOF is −43.67 kJ/mol, significantly higher than Xe (−20.50 kJ/mol) and Kr (−14.71 kJ/mol). The charge density difference (CDD) and the partial density of states (PDOS) indicate the presence of significant charge accumulation between Th and I atoms, as well as the stronger Th–I bond formed by orbital hybridization, which are the main reasons for the stronger adsorption ability of Th-MOF to I2. Ab initio molecular dynamics simulations conducted at both 300 and 600 K confirm that Th-MOF can effectively capture I2 molecules. Our results highlight the good performance of Th-MOF for the sustainable capture of I2 gases, indicating its promising application in this field.