Combination of aluminum molecular rings with chemical reduction centers for iodine capture and aggregation

Abstract

The sustainable development of nuclear energy urgently needs to focus on developing stable, efficient and low-cost adsorbent materials to tackle nuclear waste. We herein report a designed assembly of aluminum molecular rings (Al₈) for effective iodine capture and aggregation. Instead of using expensive and rigid tetrapodand ligands, we succeeded in assembling Al₈ with flexible pseudo-tetracarboxylic acid ligands (PT ligands, combining cheap and small ligands with transition metal centers) by the coordination-driven self-assembly strategy. Based on such an approach, we isolated a broad range of stable porous materials by regulating the PT ligands and achieved framework topology regulation (transformation from scu to ftw). Notably, this is the first time a porous assembly of Al₈ with tetrapodand ligands is realized. The annular cavities in Al₈ and a variety of pores created by PT ligands endow these materials with notable adsorption capacity towards iodine vapor molecules (73 wt% for AlOC-151 and 86 wt% for AlOC-155). As revealed by single-crystal X-ray diffraction studies, these annular cavities and pores act as reactors to induce the shape-matching formation of polyiodides with different aggregation states. Interestingly, the presence of Fe metal centers promotes the partial chemical reduction of iodine from I₂ to I_x⁻ (x = 3, 5), which is evidenced by the combination of bond valence sum (BVS) calculations, charge balancing, X-ray photoelectron spectroscopy (XPS) and conductivity measurements. This work has developed a synthetic approach for the preparation of porous frameworks and provides a reference for the designed synthesis of advanced radioactive capture adsorbent materials.