Ligands for Complexation, Extraction, and Sensing of Mercury(II) for Application to High-Level Waste (HLW) at the Savannah River Site (SRS)
Doctor of Philosophy (PhD)
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mercury, complexation, extraction, chemosensor, mercury remediation, alkaline high-level waste, Savannah River Site
Date of Defense
Mercury (Hg) separation and sensing is of high significance due to Hg(II) environmental mobility and toxicity. Furthermore, the use of Hg in nuclear applications has resulted in its accumulation in several DOE sites, such as in Oak Ridge and Savannah River reservations. Organic mercury species have been found in low activity waste (LAW) streams resulting from high-level waste (HLW) processing at the Savannah River Site (SRS), therefore posing a threat to humans and the environment. Mercury, being a soft Lewis acid, has a strong affinity for softer Lewis bases, such as S- or N-donor ligands. Therefore, we focus on synthesizing and studying soft-donor organic ligands, such as thioamides and sulfonamides, as effective complexants, extractants or chemosensors for inorganic mercury.
We studied the interaction of Hg(II) with bis-arylsulfonamide ligand derivatives derived from substituted o-phenylenediamine and several sulfonyl chlorides. Successful extraction of Hg(II) from alkaline aqueous phases into dichloroethane was observed, with extraction efficiency and recovery as high as 97.4 % and 81.5 %, respectively, at pH 12.0 by the disulfonamide ligand L4. The influence of pH, ligand concentration, and the presence of the organic base (triethylamine) was studied in detail. The crystal structure of the isolated Hg(II) complex with the disulfonamide analog L2 shows a 1:2 Hg(II):L2 stoichiometry with two triethylammonium countercations (Et3NH+) coordinating in the outer sphere. The bis-dansylsulfonamide (LD) derivative was shown to be an effective Hg(II) sensor, as fluorescence quenching was observed upon gradual addition of HgCl2 solution with complete quenching occurring at Hg(II):LD molar ratio of 1:1.
Thioamide ligands derived from 2,6-diaminopyridine were also studied. The pyridine N atom and the thiocarbonyl moiety on these ligands result in strong Hg(II) binding (log K = 7.43). The lipophilic derivative of this thioamide ligand (PDT) is a potential extractant for industrial solvent extraction processes. PDT extracts Hg(II) with an extraction efficiency of 99.7% and discriminates the presence of mercury over various competing metal ions, which are present in higher concentrations at HLW. We also carried out a spectroscopic and structural study on a Hg(II)-mediated cyclization reaction of a dithioamide ligand derived from o-phenylenediamine to a benzimidazole derivative, which has led to a potentially new paradigm for Hg(II) sensing.
Overall, with high observed recovery for extracted Hg(II), strong binding, and high selectivity for several of our studied ligands, this research has demonstrated new pathways for application of Hg(II) sensing, complexation, and recovery from alkaline high-level tank waste.
Previously Published In
Adenike O. Fasiku, Matthew T. Fortunato, Indranil Chakraborty, and Konstantinos Kavallieratos. ”Mercury (II) Sensing via Cyclization of a Dithioamide into a Benzimidazole Derivative: A Structural and Spectroscopic Study." Inorganica Chim. Acta. 2020, 510, 119680
Fasiku, Adenike O., "Ligands for Complexation, Extraction, and Sensing of Mercury(II) for Application to High-Level Waste (HLW) at the Savannah River Site (SRS)" (2021). FIU Electronic Theses and Dissertations. 4865.
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