Development of a Co3O4:SnO2 nanocomposite-modified GCE for sensitive and stable electrochemical detection of organophosphate pesticides

Abstract

Parathion methyl (PM) pesticide, widely used in agricultural practices, poses significant risks to human health and the environment due to its high toxicity and persistence in water and soil. Its detection at trace levels is critical for safeguarding public health and ensuring compliance with environmental regulations. This study presents the development of an electrochemical sensor for the detection of PM pesticide, utilizing a glassy carbon electrode (GCE) modified with Co₃O₄:SnO₂ nanocomposites in different ratios of 1:9, 2:8, and 3:7. The nanocomposites were extensively characterized using a range of techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS), which confirmed both the successful synthesis and the uniform distribution of the nanocomposites. To evaluate the electrochemical properties, cyclic voltammetry (CV) was employed, revealing that the Co₃O₄:SnO₂ (3:7) nanocomposite exhibited the highest oxidation peak current (Ipa) at pH 7, indicating superior catalytic activity for the sensing of PM. The electrochemical reaction was identified as an irreversible two-electron transfer process. Subsequent optimization of experimental conditions, such as pH, scan rate, and PM concentration, was conducted to maximize sensitivity, with pH 7 identified as the optimal condition. In addition, electrochemical impedance spectroscopy (EIS) was utilized to investigate the electron transfer dynamics at the electrode surface. The Nyquist plots showed a notable decrease in charge transfer resistance (Rct) for the Co₃O₄:SnO₂ (3:7) modified GCE, signifying improved electron transfer kinetics and faster response times compared to the bare GCE. This reduction in Rct contributed significantly to the enhanced electrochemical performance observed. Moreover, CV demonstrated excellent sensitivity (0.74 × 10⁻² mA mM⁻¹ cm⁻²). Additionally, differential pulse voltammetry (DPV) was used to calculate a low detection limit (LOD) of 0.015 mM and a limit of quantification (LOQ) of 0.045 mM for PM. To further assess the electrochemical behavior and sensitivity of the sensor, chronoamperometry showed excellent linearity over a wide concentration range. The recyclability and real sample studies were conducted using both CV and DPV techniques. Lastly, the coated Co₃O₄:SnO₂ (3:7) CGE are highly effective for the electrochemical detection of PM, offering superior sensitivity, stability, and reproducibility, making them promise for environmental monitoring and pesticide detection in agricultural water sources.