Colorimetric Detection of Pollutant Trivalent Cations and HSO₄⁻ in Aqueous Media Using a New Schiff-base Probe: An Experimental and DFT Studies

Abstract

In the present study, a novel colorimetric Schiff-base receptor 4-((2-nitrophenyl) diazenyl)-2-((3-methylpyridin-2-ylimino)methyl)phenol was successfully synthesized via the condensation reaction of an azo-coupled precursor to 2-amino-3-methylpyridine in absolute ethanol and a good yield. The probe provided the selective detection of trivalent Cr³⁺, Fe³⁺, and Al³⁺ cations with different color changes. The binding constants of complexation (k_a), the molar absorption coefficient (ɛ), and the limit of detection parameters of trivalent ions were measured for Cr³⁺, Fe³⁺, and Al³⁺. The results revealed a high sensitivity for the selective detection of Fe³⁺ ions. Moreover, the devised receptor rapidly detected the HSO₄⁻ anion through absorption spectra and color changes. The HSO₄⁻ and Al³⁺ coordination properties were checked by the ¹HNMR titration method. The sensing behavior of the L receptor was further emphasized in computational studies. Accordingly, quantum-chemical studies via Density Functional Theory (DFT) were carried out using the 6–31 + G (d) basis set of the Gaussian 03 program package in order to more supplement the detecting behavior of the L receptor in case of HSO₄⁻ anions. The HSO₄⁻ and Al³⁺ coordination properties were investigated by the ¹HNMR titration.

Keywords:

• Sensor
• colorimetric
• aqueous media
• DFT study

Acknowledgments

We would like to thank the Research Council of Arak University for financial support of this research.