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

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 Ix− (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.