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 (Kd) for La, Nd, Eu, and Lu were 354,000, 344,000, 210,800, and 419,800, 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.