Flexible Plastic Electrodes Based on Thiosulfate-Modified gC3N4 Nanosheets for Simultaneous Handheld Monitoring of Hazardous Cationic Dyes in Drinking Water

Abstract

The critical concerns regarding hazardous organic dyes, which cause significant harm to human health and environmental sustainability, require immediate attention. This study demonstrates the development of an innovative disposable electrochemical sensor that employs thiosulfate-modified graphitic carbon nitride (gC₃N₄-S₂O₃) nanosheets as class-selective and cost-efficient flexible plastic electrodes for the remote, handheld monitoring of cationic dyes─a class of perilous water-soluble organic pollutants. This sensor is capable of detecting several cationic dyes, such as methylene blue (MB), rhodamine B (RhB), and thionine (Th), simultaneously in drinking water. Modified gC₃N₄-S₂O₃ nanosheets were produced using a straightforward sonochemical-assisted method, followed by thermal condensation treatment. The produced material is characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV). The DPV measurements span a wide range of dye concentrations, ranging from 1 nM to 1 mM. Under optimized conditions, the electrochemical gC₃N₄-S₂O₃ sensor exhibits excellent performance, with picomolar limits of detection (LOD), i.e., 118 pM for Th, 161 pM for RhB, and 209 pM for MB, respectively. The gC₃N₄-S₂O₃ sensor utilizes electrostatic interactions to distinguish between cationic and anionic dyes and is capable of simultaneously detecting several cationic dyes. The gC₃N₄-S₂O₃ sensor also demonstrates enhanced capability to detect several cationic dyes in solutions, complex mixtures, and drinking water samples, indicating minimal interference from ionic species inherently present in drinking water. This work highlights the potential of gC₃N₄-S₂O₃ sensors for application in monitoring and remediation of the environment.