Reversible Hydrophobic Deep Eutectic Solvent-Based Uranyl-Sensing Optode Film in Aqueous Streams: Color Transformation and Reusability.

A hydrophobic deep eutectic solvent (HDES)-based optode was designed for the preconcentration and determination of the UO ion in aqueous media using spectroscopic techniques [energy-dispersive X-ray fluorescence (EDXRF) and solid-state absorption]. The optode was developed by incorporation of HDES (tri--octyl phosphine oxide and decanoic acid in an equimolar ratio), tri-(2-ethylhexyl) phosphate, and 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol into a cellulose triacetate matrix. Characterization studies were carried out using different techniques to understand the roles of HDES as a plasticizer, UO extractant, and Br-PADAP immobilizer. Uptake studies revealed that the optimal pH was 3 and sorption followed the type II adsorption isotherm. Uranium in the U-sorbed optode can be directly analyzed over a large concentration range of 0.021 × 10-2.1 × 10 Mol L using EDXRF. The optode film exhibited a linear dynamic range of 0.84 × 10-84 × 10 Mol L for uranium, with a lowest limit of detection of 0.084 × 10 Mol L by colorimetric analysis. This optode-based method was employed for seawater analysis for its UO concentration without any matrix separation, and the concentration was found to be 1.30 ± 0.06 × 10 Mol L. The optode exhibited better selectivity for UO in the presence of various cations including Sr and Cs in an aqueous medium. Compared to other prevailing optical sensors, this optode performed better in terms of key factors like pH, equilibration time, reusability, and detection limit.