Selective separation of uranyl ions from some lanthanide elements using a promising β-enaminoester ligand by cloud point extraction

Abstract

For uranyl extraction, a distinctive chelating ligand, namely ethyl 2-amino-6-hydroxy-5-(4-methoxyphenyldiazenyl)-4-phenyl-4H-benzo[f]chromene-3-carboxylate, has been synthesized and characterized using FT-IR, NMR, and ESI-MS. Subsequently, a cloud point extraction (CPE) protocol has been developed for the selective separation of the trace amounts of uranyl ions from some lanthanide ions after being captured by the ligand in the presence of non-ionic surfactant (Triton X-114). The extraction procedure has been optimized based on the concentration of the complexing agent and the non-ionic surfactant, phase separation temperatures, pH, and ionic strength. The developed CPE procedure exhibited a relatively low detection limit of 0.5 ng mL⁻¹ in the linear range from 3 ng mL⁻¹ to 250 ng mL⁻¹. Furthermore, interference studies have been carried out to study the selectivity of our protocol. These studies revealed that the recoveries of uranyl ions were in the range from 96.1% to 99.9% in the presence of some lanthanide ions such as Th⁴⁺, Gd³⁺, and Sm³⁺. It is worth mentioning that the geometry optimization, reactivity, and molecular electrostatic potential maps of the ligand and the proposed UO₂²⁺ complex were acquired via DFT calculations to study their stabilities based on the geometry and binding affinity. The theoretical data confirmed the octahedral geometry of the UO₂²⁺ complex with the lowest energy and excellent stability. The robustness of the proposed methodology was evaluated by the detection of uranyl ions in different environmental samples and synthetic mixtures.