Non-covalent interactions-advanced selective trapping of flexible nitrilotriacetamide towards radioactive pertechnetate

Abstract

Pertechnetate is one of the most prevalent forms of radioactive 99Tc element. Most of traditional extractants have failed in its extraction and separation due to the almost no complexing nature. Recent studies have found that nitrilotriacetamide (NTAamide) derivatives worked well in selectively extracting TcO4−. Herein, the involved extraction process has been visualized by molecular dynamics (MD) simulations, and the mechanism comprehensively examined by further combining density functional theory (DFT) calculations. Study has been extended to other anions MO4− (M = Mn, Re and Pm) of the same group. The competing extraction of TcO4− against SO42−, H2PO4− and F− co-existed in spent nuclear fuels was also delineated. Thermally and structurally stable ternary [HNTAamide+·MO4−·H2O] was recognized for the extracted complex, which well reproduced TcO4−/ReO4− ones from X-ray crystal diffraction and other experimental characterizations. The extraction to MO4− (M = Mn, Tc and Re) is thermodynamically favored, but it is not to PmO4−. Similar overall structures and close interfacial interactions were attained in extracting TcO4− and ReO4−, but the former had more negative reaction energy and narrower HOMO-LUMO gap. This validates the widely-used simulation handling, where ReO4− is used to replace radioactive, toxic and scarce TcO4−. Non-covalent interactions, including hydrogen bonds and weak van der Waals interaction, have been revealed, enabling selective and effective extraction of TcO4− by NTAamide.