Electrochemical detection of para-nitrophenol employing a glassy carbon electrode modified with graphene–zinc oxide nanocomposite for enhanced sensitivity

• Development of a GNS/ZnO composite-based sensor for highly sensitive detection of para-nitrophenol. • Enhanced electroactive surface area achieved with GNS/ZnO-modified GCE. • Square-wave adsorptive stripping voltammetry (SW-AdSV) employed for para-nitrophenol determination. • Simultaneous detection of ortho- and para-nitrophenols in the presence of meta-nitrophenol. • Application of SW-AdSV for para-nitrophenol analysis in river and groundwater samples. The graphene-zinc oxide nanocomposite (GN(ZnO)-NC) was investigated as an electrochemical sensing platform for the highly sensitive detection of para-nitrophenol (p-NP). Zinc oxide nanoparticles (ZnO-NPs) were prepared through a modified wet-chemical synthesis, employing zinc nitrate and potassium hydroxide as precursor materials. Starch was incorporated during the synthesis process to function as a capping and stabilizing agent, promoting uniform nanoparticle dispersion and preventing agglomeration. Graphene-oxide was reduced to graphene in the presence of ZnO-NPs using glucose as a reductant in a simple and environmentally friendly method to create GN-ZnO nanocomposite. A comprehensive characterization of the synthesized nanocomposite (NC) was conducted to evaluate its crystal structure, degree of crystallinity, surface morphology, elemental composition, and phase properties. This was achieved using various techniques, including scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and Raman spectroscopy. The electrochemical performance of the GN(ZnO)-NC layer placed on the glassy carbon electrode (GCE) surface was first investigated using the conventional 1 mM K 3 [Fe(CN) 6 ] model complex. The performance of the GN(ZnO)-NC modified glassy carbon electrode (GCE) was evaluated in relation to varying concentrations of p-nitrophenol (p-NP). Employing square wave adsorptive stripping voltammetry, a significantly increased current response was recorded in a 0.1 M phosphate buffer solution at pH 6.8. Under optimized conditions, the method exhibited a linear response toward para-nitrophenol (p-NP) over the concentration range of 0.09 × 10⁻⁶ to 21.80 × 10⁻⁶ M, with a notably low detection limit of 8.8 × 10⁻⁹ M. These results were obtained using a deposition potential of –1.0 V and a deposition time of 300 seconds. With no interference from other potential interfering compounds like ortho-NP, meta-NP, or 2, 4-di-NP, this developed electrochemical sensor exhibited exceptional selectivity toward para-nitrophenol (p-NP). Owing to its high recovery rates, the method proved effective for the sensitive quantification of p-NP in real environmental samples, including ground and river water samples.