PAR immobilized colorimetric fiber for heavy metal ion detection and adsorption

Abstract

A new wearable colorimetric fiber for heavy metal ion detection and adsorption has been synthesized by first aminating a commercially available polyacrylonitrile fiber with ethylenediamine and then covalently immobilizing 4-(2-pyridylazo)-1,3-benzenediol (PAR) on the modified fiber through a Mannich reaction. The fiber was characterized by X-ray powder diffraction spectra (XRD), scanning electron microscope (SEM), FTIR and UV–vis spectroscopy, and its acid exchange capacity, colorimetric properties, response speed, selectivity, reusability, photostability and adsorption capacity were investigated. In neutral aqueous solutions, the PAR immobilized fiber responds selectively to heavy metal ions, such as Hg 2+, Pb 2+, Cd 2+, Zn 2+, Ni 2+ and Cu 2+ with a color change from red-orange to dark-brown. Its visual detection limit for Pb 2+ is 1 × 10 −6 mol/L. Moreover, the selectivity increases with a decrease in pH, i.e. at pH 3.0, it shows a color change only for Hg 2+ and Cu 2+. This fiber also shows excellent reusability (>50 times), high photostability (>30 days under direct exposure to sunlight) and high adsorption capacity for Hg 2+ (0.74 mmol/g).