Studies on Coordination and Fluorescence Behaviors of a Novel Uranyl Ion-Selective Chemosensor Bearing Diaza 18-Crown-6 Ether and Naphthalimide Moieties

To avoid environmental and biological impacts linked to uranium-contaminating solutions, the development of sensitive and selective uranium detection techniques for solutions has become a critical issue. Although various kinds of detection methodologies have been developed, they are still not totally satisfactory in terms of simplicity, efficiency, and versatility. In this work, a novel chemosensor bearing a diaza-18-crown-6 ether and two naphthalimides (PN-DCE) was synthesized for simple, selective, rapid, and cost-effective detection of uranyl ions (UO22+) and characterized by H-1-, C-13-NMR, FT-IR, ESI-TOF-MS, and elemental analysis. Effects of various metal ions (Na+, K+, Cs+, Mg2+, Ca2+, Sr2+, La3+, and UO22+) on the H-1-NMR chemical shifts of PN-DCE were examined, and selective complexation of UO22+ with PN-DCE was verified. Moreover, the stoichiometry of the UO22+/PN-DCE complex was elucidated from the correlation between UO22+ concentration and the peak area ratios of the H-1-NMR spectra of PN-DCE, indicating the formation of 1:1 and 2:1 complexes depending on the concentration ratios of UO22+ and PN-DCE ([UO22+]/[PN-DCE]). Furthermore, visual and fluorescence spectroscopic methods showed that drastic fluorescence quenching of PN-DCE is induced by adding UO22+ and not other metal ions. From a combination of quenching percentages estimated from fluorometric titration experiments and Stern-Volmer analysis, the detection limit of PN-DCE for UO22+ was successfully determined to be 4.13 mu M, which is almost comparable to the maximum permissible concentration of uranium in wastewater discharged from facilities related to the utilization of nuclear energy. Based on these results, we conclude that the developed PN-DCE would act as a sensing material for UO22+ in waste solutions.