Enhanced redox sensing unraveling the electrochemical potential of CdO@g-C3N4 composite on carbon paper for 4-nitrophenol detection

A novel CdO@g-C₃N₄ nanocomposite was synthesized via a simple wet-chemical approach and thoroughly investigated for its structural and electrochemical properties. Morphological analysis using FE-SEM and TEM confirmed the uniform dispersion of CdO nanoparticles on g-C₃N₄ nanosheets, forming a well-integrated heterostructure. Elemental mapping and EDX analysis revealed a homogeneous distribution of Cd, O, C, and N, indicating strong interfacial interaction. XRD and XPS studies confirmed the crystallinity and chemical stability of the composite with no detectable impurities. Electrochemical characterization using CV and EIS revealed significantly enhanced electron transfer kinetics, with a reduced charge transfer resistance (Rct) of ∼40 Ω, much lower than that of pristine CdO (188 Ω) and g-C₃N₄ (127 Ω). The composite exhibited well-defined redox peaks, demonstrating reversible electron transfer and strong electrocatalytic activity toward 4-nitrophenol (4-NP), a persistent environmental pollutant. The sensor showed a wide linear range (0.1–100 µM), high correlation coefficient (R² = 0.9992), and a low detection limit of 2.30 µM. The electrode also demonstrated excellent selectivity, effectively distinguishing 4-NP from its isomers and resisting interference from common ions and organic compounds. Long-term stability tests showed over 96 % signal retention after 60 cycles and consistent performance over six days. Real-sample analysis in tap water, river water, and drinking water yielded recovery rates between 98.8 % and 99.4%, confirming its practical utility. These results highlight the CdO@g-C₃N₄ composite as a promising electrochemical sensor, with enhanced sensitivity, selectivity, and stability, making it a strong candidate for environmental monitoring applications targeting hazardous phenolic pollutants.