A highly selective Schiff base chemosensor for rapid colorimetric detection of Fe2+ and fluorometric detection of Al3+ ions: Synthesis, characterization, real water sample analysis and DFT studies

Abstract

This study reports a new Schiff base ligand, ( Z )-1-(4-methoxyphenyl)- N -(2-nitrophenyl)methanimine) (MNP) and its characterization using ESI-MS, 1 H NMR, 13 C NMR, FT-IR, UV-Visible spectroscopic and fluorometric techniques. Further, MNP showed a significant colour shift from yellow to colourless in the presence of Fe 2+ ion and it also exhibited a fluorometric "turn off" response when Al 3+ ion was present in DMSO solution (HEPES 0.01 M, pH = 7.4) at room temperature. It was found that the binding propensity of MNP to Al 3+ and Fe 2+ ions were identified to be in 2:1 ratio (ligand:metal) by employing Job's plot. It is worth to mention that the MNP probe showed an excellent selectivity and sensitivity in detecting Al 3+ and Fe 2+ metal ions, in contrast with the other metal ions (Cu 2+ , Co 2+ , Mn 2+ , Zn 2+ , Ni 2+ , Fe 3+ , Pb 2+ , V 5+ , Na + , K + , Hg 2+ , Cr 2+ and Ce 3+ ). From the results obtained the detection limits (LOD) for Fe 2+ and Al 3+ were found to be 0.1 μM and 0.2 μM, respectively. Additionally, MNP was successfully employed in smart phone application, which was used to calculate the LOD for both Al 3+ and Fe 2+ ions and found the similar detection limits as obtained through spectrophotometric measurements. This will help to determine solution of unknown concentration by calculating the RGB values. Furthermore, MNP was effectively utilised for construction of logic gates and quantitative detection of Al 3+ and Fe 2+ in real water samples. In addition, we conducted a detailed computational modelling analysis of MNP and its Al 3+ complex, utilizing a combination of density functional tight binding (DFTB) and density functional theory (DFT) calculations. The findings provide valuable insights into their local reactivity properties

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