An Acylhydrazone Fluorescent Sensor: Bifunctional Detection of Thorium (IV) and Vanadyl Ions over Uranyl and Lanthanide Ions

Thorium is a notable candidate for resolving uranium shortage caused by the global application of nuclear power generation. Uranium extraction from seawater is another attempt to handle its source deficiency, however, vanadium is one of the main competitive elements in that process. Exploration of probes which can discriminatively detect thorium and vanadium from uranium has primary significance for their further separation and for environmental protection. Herein, N'-(2,4-dihydroxybenzylidene)-4-hydroxylphenylhydrazide, <b>AOH</b>, is used as sensor for Th⁴⁺ and vanadyl (VO²⁺) determination. <b>AOH</b> demonstrates a specific "turn-on" fluorescence selectivity towards Th⁴⁺ over f-block and other foreign metal ions, with a detection limit (LOD) of 7.19 nM in acidic solution and a binding constant of 9.97 × 10⁹ M^-2. Meanwhile, it shows a "turn-off" fluorescence response towards VO²⁺ over other metal ions at the coexistence of Th⁴⁺, with a LOD of 0.386 μM in the same media and a binding constant of 4.54 × 10⁴ M^-1. The recognition mechanism, based on HRMS, ¹H NMR, and FT-IR results, demonstrates that VO²⁺ causes the fluorescence quenching by replacing Th⁴⁺ to coordinate with <b>AOH</b>. In real water detection tests, Th⁴⁺ and VO²⁺ exhibited satisfying recoveries. These findings expand the application of sensors in nuclide pollution control.