Design, Synthesis, and Characterization of a Bifunctional Chelator with Ultrahigh Capacity for Uranium Uptake from Seawater Simulant

Informed by density functional theory
calculations, a novel bifunctional
chelator, (Z)-2-[2-(N′-hydroxycarbamimidoyl)­phenoxy]­benzoic
acid, was designed and synthesized for ultrahigh uranium uptake from
seawater. Investigation of the ligand for uranium sorption was conducted
in artificial seawater (pH = 8.2). An exceptional uranium uptake of
553 mg of uranium (g of sorbent)−1 was obtained
with a theoretical saturation capacity of 710 mg g–1 obtained by fitting isotherm data with the Langmuir–Freundlich
model. The resulting yellow precipitate was characterized via X-ray
absorption fine structure (XAFS) at the U LIII-edge, with
the extended XAFS spectra best fitted by a model where uranyl is coordinated
by monodentate amidoxime, one chelating carboxylic acid, and two water
molecules. These results are consistent with the formation of a uranium
coordination polymer. The ultrahigh uranium uptake capacity obtained
by the bifunctional chelating ligand makes it a promising candidate
for deployment as a uranium adsorbent.