Selective colorimetric sensing of Co²⁺ and Cu²⁺ using 1-(2-pyridylazo)-2-naphthol derivative immobilized polyvinyl alcohol microspheres

Abstract

An optical analytical naked-eye sensor was proposed based on the complexation reactions of 1-(2-pyridylazo)-2-naphthol derivative with heavy metals in aqueous solutions. The prepared colorimetric sensor was characterized by scanning electron microscopy, energy-dispersive X-ray fluorescence spectrometry, and Fourier 10 transform infrared spectroscopy, which indicated a spherical sensor and its molecular composition. In the sensing experiment, notable changes in color and absorbance intensity of the colorimetric sensor for Co 2+ and Cu 2+ were observed at pH 5 and 4, respectively. The proposed method provided consistent data reliability, with a detection limit of 1 and 5 µM by naked eye and 0.23 and 0.95 µM by UV-vis 15 spectrometry for Co 2+ and Cu 2+ , respectively. The prepared chemosensor can be used as a colorimetric sensor to monitor Co 2+ and Cu 2+ with satisfactory results, which validate its value in practical applications in environmental systems. 3 nanocomposites, which could simultaneously detect Hg 2+ and Pb 2+ . In the present work, 1-(2-pyridylazo)-2-naphthol (PAN) was selected as a chromophore because it is a heterocyclic azo compound and has been extensively used as a highly sensitive photometric reagent for the determination of metal ions 26, 27 . PAN can coordinate through the azo group and the nitrogen atom of pyridyl with metal ions to form a 5 chelate, which results in a significant change in the absorbance intensity and color of the solution. Metal nanoparticles and organic polymers are selected as matrix materials of colorimetric sensors. Gold and silver nanoparticles are often used as matrix materials of colorimetric sensors because of their excellent optical properties 28-30 . These 10 sensors have advantageous selectivity and low detection limit (L D ), but expensive metal nanoparticles are unstable and have poor repeatability 31, 32 . In comparison, organic materials are stable and possess an adequate number of groups by nature, which have the advantage of modification of other functional groups 33-35 . Polyvinyl alcohol (PVA), which is common, inexpensive, nontoxic, and biodegradable and has 15 high mechanical strength, physical and chemical properties of stability, and large specific surface area, can provide sufficient sites for immobilization of functional groups. PVA also contains a large number of hydroxyl groups that can be easily modified with various functional groups 36-38 .In this study, we proposed a method for developing colorimetric sensors for the 20 determination of low concentrations of heavy metals based on PAN derivative immobilized PVA microspheres. The synthesis route of the sensor was simple, and the 5 recorded with a Nicolet iS10 FTIR spectrometer (Nicolet Co., Madison, WI, USA). 1 H NMR measurement was performed using JNM-ECS 400 spectrometer (JEOL Ltd., Japan) with TMS as an internal standard and CD 3 SOCD 3 as solvent. Mass spectra were recorded on Bruker-MicrOTOF Ⅱ (USA). The absorption spectra of the colorimetric sensor were recorded using a DR 5000 spectroph...

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Colorimetric Co2+ sensor based on an anionic pyridylazo dye and a cationic polyelectrolyte in aqueous solution

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