A colorimetric sensor based on thiourea–polyvinyl alcohol microspheres for the selective recognition of Hg2+ and Cu2+

Abstract

In this study, an optical analytical naked-eye sensor based on thiourea–polyvinyl alcohol (PVA) microspheres was designed for the selective recognition of heavy metals in aqueous solutions. The colorimetric sensor was characterized by scanning electron microscopy and Fourier transform infrared spectroscopy to confirm the linkage of the chromophore with the surface of PVA microspheres. In the sensing system, notable changes in absorbance intensity of the colorimetric sensor for Hg²⁺ and Cu²⁺ were observed at pH 3 and 4, respectively. The sensor could selectively recognize heavy metals, as shown by the change in color from faint yellow to orange for Hg²⁺ and from faint yellow to dark green for Cu²⁺. The sensor provided consistent data reliability, with a detection limit of 0.209 and 0.320 μM by UV-vis spectrometry for Hg²⁺ and Cu²⁺, respectively. The prepared colorimetric sensor can be used to monitor Hg²⁺ and Cu²⁺ with satisfactory results because of its selectivity, reversibility, sensitivity, and signal stability.