Probing the interaction of U(vi) with phosphonate-functionalized mesoporous silica using solid-state NMR spectroscopy

Eva C Uribe; Harris E Mason; Jennifer A Shusterman; Anthony Bruchet; Heino Nitsche

doi:10.1039/c6dt01200k

Probing the interaction of U(vi) with phosphonate-functionalized mesoporous silica using solid-state NMR spectroscopy

Dalton Trans. 2016 Jun 21;45(25):10447-58. doi: 10.1039/c6dt01200k.

Authors

Eva C Uribe¹, Harris E Mason², Jennifer A Shusterman³, Anthony Bruchet¹, Heino Nitsche¹

Affiliations

¹ Department of Chemistry, University of California, Berkeley, Berkeley, California 94720, USA. [email protected].
² Glenn T. Seaborg Institute, Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, L-231, PO Box 808, Livermore, California 94550, USA.
³ Department of Chemistry, University of California, Berkeley, Berkeley, California 94720, USA. [email protected] and Glenn T. Seaborg Institute, Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, L-231, PO Box 808, Livermore, California 94550, USA.

PMID: 27265020
DOI: 10.1039/c6dt01200k

Abstract

The fundamental interaction of U(vi) with diethylphosphatoethyl triethoxysilane functionalized SBA-15 mesoporous silica is studied by macroscopic batch experiments and solid-state NMR spectroscopy. DPTS-functionalized silica has been shown to extract U(vi) from nitric acid solutions at or above pH 3. Extraction is dependent on pH and ionic strength. Single-pulse (31)P NMR on U(vi) contacted samples revealed that U(vi) only interacts with a fraction of the ligands present on the surface. At pH 4 the U(vi) extraction capacity of the material is limited to 27-37% of the theoretical capacity, based on ligand loading. We combined single pulse (31)P NMR on U(vi)-contacted samples with batch studies to measure a ligand-to-metal ratio of approximately 2 : 1 at pH 3 and 4. Batch studies and cross-polarization NMR measurements reveal that U(vi) binds to deprotonated phosphonate and/or silanol sites. We use (31)P-(31)P DQ-DRENAR NMR studies to compare the average dipolar coupling between phosphorus spins for both U(vi)-complexed and non-complexed ligand environments. These measurements reveal that U(vi) extraction is not limited by inadequate surface distribution of ligands, but rather by low stability of the surface phosphonate complex.