Green synthesis of thiadiazole Schiff bases and specific recognition of Cr2O72−, SiO32− and S2−

Abstract

Sulfide (S2−), silicate (SiO32−) and dichromate (Cr2O72−) ions are prevalent contaminants in industrial effluents, and their rapid and accurate detection is of critical importance for environmental monitoring. In this study, we utilized an environmentally friendly, highly efficient, and biodegradable deep eutectic solvent (DES) to catalyze the synthesis of 2-(((5-phenyl-1,3,4-thiadiazol-2-yl)imino)methyl)phenol (Probe M). Probe M exhibits excellent selectivity for S2−, SiO32− and Cr2O72−, and the corresponding color changes can be readily detected by the naked eye. Upon addition of S2− and SiO32− to the probe solution, the solution turns a distinct orange-red, while the addition of Cr2O72− results in a pronounced darkening of the solution. The detection of S2− and SiO32− by probe M under alkaline condition is stable, and the detection of Cr2O72− under acidic condition is stable. Fluorescence titration experiments revealed that probe M forms a 1:2 stoichiometric complex with S2−, SiO32− and Cr2O72−, with binding constants of 3.84 × 104 M−1, 1.86 × 104 M−1 and 3.19 × 104 M−1, respectively. The detection limits were determined to be 1.76 × 10−4 M for S2−, 9.15 × 10−5 M for SiO32−, and 2.13 × 10−4 M for Cr2O72−. The dipstick experiment demonstrates the probe M can be used as a solid-state sensor to identify S2−, SiO32− and Cr2O72−.