Selective and sensitive anodic stripping voltammetric determination of Hg2⁺, Cu2⁺, and Pb2⁺ in food and water samples using a sulfur-doped graphitic carbon nitride–carbon dots nanocomposite modified screen-printed carbon electrode

A novel sulfur-doped graphitic carbon nitride with sulfur-doped carbon quantum dots (S-g-C₃N₄@S-CDs) nanocomposite was synthesized using 5-amino-1,3,4-thiadiazole-2-thiol as a precursor. The nanocomposite was synthesized using thermal condensation and hydrothermal techniques, which exhibited excellent physicochemical properties, as confirmed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Field emission scanning-electron microscopy (FE-SEM) analyses. The prepared S-g-C₃N₄@S-CDs nantocomposite was employed to modify the surface of a screen-printed carbon electrode (SPCE) and was used as a novel electrochemical sensor for the sensitive detection of heavy metals in water and food samples. The electrochemical performance of S-g-C₃N₄@S-CDs was evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Differential pulse anodic stripping voltammetry (DPASV) was employed for the simultaneous determination of Hg²⁺, Cu²⁺, and Pb²⁺ ions in 0.1 M HCl (pH, 1) as supporting electrolyte solution. The developed sensor exhibited excellent sensitivity due to the enhanced conductivity and electrocatalytic activity imparted by sulfur doping in the composite material. The linear ranges were 1.5 – 300.0 µgL⁻¹ for Hg²⁺, 16.0 – 600.0 µgL⁻¹ for Cu²⁺ and 26.0 – 1100.0 µgL⁻¹ for Pb²⁺ with the limits of detection (LOD) of 0.56 µgL⁻¹ (2.8 nM), 6.0 µgL⁻¹ (94.0 nm), and 10.0 µgL⁻¹ (48.3 nM) and sensitivity values of 5.5, 1.3 and 0.8 µA µgL⁻¹ cm⁻², respectively. The applications of the S-g- C₃N₄@S-CDs-based sensor for heavy metal ions were validated in food and water samples, which gave good recoveries in the range from 95.3% to 106.4%, with RSD values below 4.2%, demonstrating the good accuracy and precision of the developed sensor.

Graphical Abstract