Hydroxypyridinone functionalized self-assembled monolayers on nanoporous silica for sequestering lanthanide cations

1,2-Hydroxypyridinone (1,2-HOPO) ligands were installed as self-assembled monolayers on nanoporous silica (MCM-41) to create a superior class of sorbent materials for lanthanide cations. Lanthanides were used as a model system for the radioactive, expensive, and highly hazardous actinides in preliminary screening studies. The ligand properties of the 1,2-HOPO ligand field and the extremely large surface area of MCM-41, coupled with the dense monolayer coating, contribute to the extremely high lanthanide binding capacity of the 1,2-HOPO nanoporous sorbent. At pH 4-5.9, the mass-weighted partition coefficients (K _d) for La, Nd, Eu, and Lu were 354000, 344000, 210800, and 419800, respectively. The rigid, open pore structure of the silica also allows for very rapid sorption. Being silica-based, the sorbent is compatible with vitrification processing into a final glasseous waste form, for subsequent disposition in a deep geological repository.