A quinolinol-based colorimetric chemosensor for highly sensitive and selective detection of Cu2+: Experimental and DFT studies and its application in real samples

Abstract

A novel molecular chemosensor (E)-5-(2-(4-nitrophenyl) azo)-2-methylquinolin-8-ol (NPAMQ) was synthesized and characterized by FT-IR, UV–Vis, 1H NMR, 13C NMR, and TGA. The sensing ability of NPAMQ towards several cations and anions was evaluated by UV–Vis absorption spectroscopy and naked-eye detection. The chemosensor NPAMQ displayed a distinct color change (from yellow to red) towards Cu2+ ions in less than a hundredth of a second, which is easily recognized by the naked eye. UV–Vis spectroscopic studies also proved a bathochromic shift (lower energy) in absorption spectra of NPAMQ in the presence of Cu2+ ions due to the formation of the stable complex NPAMQ-Cu2+. The NPAMQ showed a linear response toward Cu2+ ions (0–50 μM) with detection limits (LOD) of 81.7 nM (0.0197 mg/L). Job's plot showed formation of a complex between Cu2+ ions and chemosensor NPAMQ (NPAMQ-Cu2+ complex) which reveals presence of a stoichiometric ratio of 1:1. Moreover, the binding constant of the NPAMQ-Cu2+ complex was measured to be 3.07 × 104 M−1. NPAMQ can be easily recycled using EDTA and reused for over 5 times preserving a high level of detection efficiency. For better understanding the optical characteristics of the sensor, density functional theory (DFT) calculations were performed for NPAMQ and NPAMQ-Cu2+. Furthermore, the chemosensor NPAMQ was applied for the quantitative and qualitative analysis of Cu2+ ions in foodstuff and water samples. The paper test strips containing NPAMQ chemosensor were also fabricated and applied for detection of Cu2+ ions in aqueous solutions. This designed sensor with great features like cost-effective, short response times, excellent selectivity and sensitively can be used at different pH for detection of copper ions in industrial and biological samples.