Highly porous and stable metal–organic frameworks for uranium extraction

Three metal–organic frameworks (MOFs) of the UiO-68 network topology were prepared using the amino-TPDC or TPDC bridging ligands containing orthogonal phosphorylurea groups (TPDC is p,p′-terphenyldicarboxylic acid), and investigated for sorption of uranium from water and artificial seawater. The stable and porous phosphorylurea-derived MOFs were shown to be highly efficient in sorbing uranyl ions, with saturation sorption capacities as high as 217 mg U g−1 which is equivalent to binding one uranyl ion for every two sorbent groups. Coordination modes between uranyl groups and simplified phosphorylurea motifs were investigated by DFT calculations, revealing a thermodynamically favorable monodentate binding of two phosphorylurea ligands to one uranyl ion. Convergent orientation of phosphorylurea groups at appropriate distances inside the MOF cavities is believed to facilitate their cooperative binding with uranyl ions. This work represents the first application of MOFs as novel sorbents to extract actinide elements from aqueous media.