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

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 (e), 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 (HNMR)-H-1 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 (HNMR)-H-1 titration.

Automated summary

A novel colorimetric Schiff-base receptor was successfully synthesized and used for the selective detection of Cr3+, Fe3+, and Al3+ cations, showing high sensitivity towards Fe3+ ions and rapid detection of HSO4- anions through absorption spectra and color changes. The coordination properties of HSO4- and Al3+ were confirmed by the (HNMR)-H-1 titration method.