High-performance CoWO4–CoMn2O4/N-doped graphene nanohybrid carbon paste electrode for trace multi-metal sensing in environmental samples

Abstract

Heavy metal contamination in industrial wastewater is a serious environmental and public health concern due to the toxicity and persistence of metal ions such as Bi3+, Pb2+, and Hg2+. In this study, a nanotechnology-based electrochemical sensor was developed for sensitive and simultaneous detection of these metals in environmental samples. The sensor was made by modifying a carbon paste electrode with a CoWO4–CoMn2O4/nitrogendoped graphene hybrid nanocomposite (CCNG/CPE). The nanocomposite was synthesized using a one-pot hydrothermal method, with urea as the nitrogen source in the presence of graphene oxide. Structural and morphological analyses (FTIR, XRD, EDX, and SEM) conrmed the formation of quasi-spherical nanostructures with sizes of 34 – 48 nm. The combination of metal oxides and graphene improved electron-transfer kinetics, as shown by cyclic voltammetry and electrochemical impedance spectroscopy. Under optimized conditions (pH 1.0, 5 mg modier, differential pulse voltammetry), the sensor achieved ultralow detection limits: 0.0031 μM for Bi3+, 0.0025 μM for Pb2+, and 0.0006 μM for Hg2+. It also showed high selectivity against common interfering ions and delivered satisfactory recoveries (94–110%) in real wastewater samples from metal plating and battery facilities. Thanks to its low-toxicity composition, operational stability, and excellent analytical performance, this nanohybrid sensor provides a practical and reliable tool for monitoring trace heavy metals in environmental waters. 1. Introduction Heavy metals Due to their high density and non-biodegradable nature Heavy metals exhibit long-term environmental persistence and impose signicant risks to human health and ecological systems as a result of bio accumulative and biomagnifying processes. In soils, these metals reduce microbial activity and biomass, ultimately degrading overall soil health. While certain metals such as Fe, Mn, Cu, Zn, and Ni are essential for living organisms in trace amounts, non-essential metals including Cd, Pb, As, and Hg are toxic even at very low concentrations (Yadav, 2025). Heavy metals originate from diverse human activities, including mining, urbanization, chemical industries, unsafe agriculture, and e-waste containing Hg, Cd, and Pb . (Das, 2023) In aquatic environments, persistent, non-degradable compounds enter soil and water, disrupting ecosystems, reducing agricultural productivity, and contaminating the food chain, thereby threatening human health. Some heavy metals are highly toxic even at low concentrations, with mercury among the most concerning. It is primarily released through urban wastewater