Designing a colorimetric sensor containing nitrogen and oxygen atoms for uranyl ions identification: Chromatic mechanism, binding feature and on-site application

It is still a challenge for scientists to eliminate interference and improve chromatic aberration in designing colorimetric uranyl ions sensors, and it is also not clear how the species of uranium and sensor synergistically affect the coloration mechanism and coordination mode of ligands containing nitrogen or oxygen atoms at different pH. Herein, we design and synthesize 2-(5′-(p-(diphenylamino)phenyl)-2′-pyridylazo)-5-(diethylamino)phenol (abbr. S-LH) for the colorimetric detection of uranyl ions in mixed solvents. The rational introduced triphenylamine group by density functional theory (DFT) calculation enhances the chromaticity difference of the S-LH toward uranyl ions, making the detection limits of the uranyl ions approximately one order of magnitude lower than that of the present UV–vis and visual method. The species of S-LH and uranium at different pH are clarified and it well explains the reason of different color changes after adding uranyl ions. Stability constant experiments show that S-LH has excellent anti-interference to other metal ions during detecting uranium. The coordination structure of S-LH towards UO22+ is further confirmed by HRMS, 1H NMR titration, and DFT calculation. Finally, colorimetric test strips with S-LH are prepared to detect uranium in Xiang River, providing an on-site and real-time method to detect uranyl ions in the environment.