Radiolytic Treatment of the Next-Generation Caustic-Side Solvent Extraction (NGS) Solvent and its Effect on the NGS Process

<div><p>It is shown in this work that the solvent used in the Next Generation Caustic-Side Solvent Extraction (NGS) process can withstand a radiation dose well in excess of the dose it would receive in multiple years of treating legacy salt waste at the US Department of Energy Savannah River Site. The solvent was subjected to a maximum of 50 kGy of gamma radiation while in dynamic contact with each of the aqueous phases of the current NGS process, namely SRS−15 (a highly caustic waste simulant), sodium hydroxide scrub solution (0.025 M), and boric acid strip solution (0.01 M). Bench-top testing of irradiated solvent confirmed that irradiation has inconsequential impact on the extraction, scrubbing, and stripping performance of the solvent up to 13 times the estimated 0.73 kGy/y annual absorbed dose. Stripping performance is the most sensitive step to radiation, deteriorating more due to buildup of p-sec-butylphenol (SBP) and possibly other proton-ionizable products than to degradation of the guanidine suppressor, as shown by chemical analyses. </p></div

Urea-Functionalized M₄L₆ Cage Receptors: Anion-Templated Self-Assembly and Selective Guest Exchange in Aqueous Solutions

We present an extensive study of a novel class of <i>de novo</i> designed tetrahedral M₄L₆ (M = Ni, Zn) cage receptors, wherein internal decoration of the cage cavities with urea anion-binding groups, via functionalization of the organic components L, led to selective encapsulation of tetrahedral oxoanions EO₄^<i>n</i>– (E = S, Se, Cr, Mo, W, <i>n</i> = 2; E = P, <i>n</i> = 3) from aqueous solutions, based on shape, size, and charge recognition. External functionalization with <i>t</i>Bu groups led to enhanced solubility of the cages in aqueous methanol solutions, thereby allowing for their thorough characterization by multinuclear (¹H, ¹³C, ⁷⁷Se) and diffusion NMR spectroscopies. Additional experimental characterization by electrospray ionization mass spectrometry, UV–vis spectroscopy, and single-crystal X-ray diffraction, as well as theoretical calculations, led to a detailed understanding of the cage structures, self-assembly, and anion encapsulation. We found that the cage self-assembly is templated by EO₄^<i>n</i>– oxoanions (<i>n</i> ≥ 2), and upon removal of the templating anion the tetrahedral M₄L₆ cages rearrange into different coordination assemblies. The exchange selectivity among EO₄^<i>n</i>– oxoanions has been investigated with ⁷⁷Se NMR spectroscopy using ⁷⁷SeO₄^2– as an anionic probe, which found the following selectivity trend: PO₄^3– ≫ CrO₄^2– > SO₄^2– > SeO₄^2– > MoO₄^2– > WO₄^2–. In addition to the complementarity and flexibility of the cage receptor, a combination of factors have been found to contribute to the observed anion selectivity, including the anions’ charge, size, hydration, basicity, and hydrogen-bond acceptor abilities

Urea-Functionalized M₄L₆ Cage Receptors: Anion-Templated Self-Assembly and Selective Guest Exchange in Aqueous Solutions

We present an extensive study of a novel class of <i>de novo</i> designed tetrahedral M₄L₆ (M = Ni, Zn) cage receptors, wherein internal decoration of the cage cavities with urea anion-binding groups, via functionalization of the organic components L, led to selective encapsulation of tetrahedral oxoanions EO₄^<i>n</i>– (E = S, Se, Cr, Mo, W, <i>n</i> = 2; E = P, <i>n</i> = 3) from aqueous solutions, based on shape, size, and charge recognition. External functionalization with <i>t</i>Bu groups led to enhanced solubility of the cages in aqueous methanol solutions, thereby allowing for their thorough characterization by multinuclear (¹H, ¹³C, ⁷⁷Se) and diffusion NMR spectroscopies. Additional experimental characterization by electrospray ionization mass spectrometry, UV–vis spectroscopy, and single-crystal X-ray diffraction, as well as theoretical calculations, led to a detailed understanding of the cage structures, self-assembly, and anion encapsulation. We found that the cage self-assembly is templated by EO₄^<i>n</i>– oxoanions (<i>n</i> ≥ 2), and upon removal of the templating anion the tetrahedral M₄L₆ cages rearrange into different coordination assemblies. The exchange selectivity among EO₄^<i>n</i>– oxoanions has been investigated with ⁷⁷Se NMR spectroscopy using ⁷⁷SeO₄^2– as an anionic probe, which found the following selectivity trend: PO₄^3– ≫ CrO₄^2– > SO₄^2– > SeO₄^2– > MoO₄^2– > WO₄^2–. In addition to the complementarity and flexibility of the cage receptor, a combination of factors have been found to contribute to the observed anion selectivity, including the anions’ charge, size, hydration, basicity, and hydrogen-bond acceptor abilities