Chitosan-thymolsulfonephthalein-cobalt nanocomposites for colorimetric detection of sulfide anions in aqueous solution

Background: Water pollution by sulfide ions, arising from the exploration and exploitation of sulfide mineral ore, can cause many chronic and acute health challenges. However, owing to the cost of sophisticated equipment and technical expertise required to detect anionic sulfides in water has inspired the preparation of easy-to-use naked-eye colorimetric devices. Methods: In this study, the functionalization of chitosan solution with thymolsulfonephthalein solution (CFTS) at moderate conditions was utilized for the chemical synthesis of cobalt nanocomposites (CFTS-CoNCs) based chemosensors. Results: The prepared material's scanning electron micrograph shows the high Co dispersion on the surface of CFTS with a thorn-shaped morphology in uniform spheres. In contrast, the transmission electron micrograph shows good dispersibility of the tiny rod-like particles distributed on a dendrite-like surface. The interaction of the orange-colored CFTS-CoNCs chemosensor solution with the colorless S2− ions was accompanied by an instant and stable black color change. Furthermore, the selective and sensitive chemosensor could detect ≥ 15 ppm aqueous S2− ions solution at lower pH. The mechanism of detection could be due to a nucleophilic attack of S2− on the cobalt-induced hydroxylmethylpropyl benzoxathiole amine cation giving rise to the strong UV–Vis absorption at 592 nm. Conclusion: The highly selective and sensitive CFTS-CoNCs chemosensor can be applied for real-time and quick on-site analysis. In addition, the colorimetric device will serve as a lifesaver in terms of reducing both time and cost, user-friendly, and hands-on tools for the rapid/accurate detection of sulfide ions in water