Polyaniline/Graphitized Carboxylated Multi-Walled Carbon Nanotube Composite Electrode for Highly Sensitive Electrochemical Detection of Pb2+ in Seawater

In this study, an electrochemical sensor based on a graphitized carboxylated multi-walled carbon nanotube/polyaniline (G-COOH-MWCNTs/PANI) composite was developed for the highly sensitive detection of Pb2+ in seawater. A G-COOH-MWCNTs/PANI composite dispersion was prepared via a solution blending method and subsequently drop-cast onto a glassy carbon electrode (GCE) to fabricate the modified electrode. Differential pulse anodic stripping voltammetry (DPASV) was employed for the quantitative determination of Pb2+. The morphology of the composite was characterized by scanning electron microscopy (SEM), while the electrochemical behavior of the modified electrode was investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Critical experimental parameters, including the type and pH of the supporting electrolyte, deposition potential, deposition time, and loading amount of the composite film, were systematically optimized. In addition, the optimal concentration ratio of G-COOH-MWCNTs to PANI was determined using an orthogonal experimental design. Under the optimized experimental conditions, the proposed sensor exhibited a linear response toward Pb2+ over the concentration range of 25–220 μg/L, with the regression equation Ip = 2.757C + 4.316 (R2 = 0.997). The limit of detection (LOD), calculated at a signal-to-noise ratio (S/N) of 3, was 0.0337 μg/L. The sensor also demonstrated excellent reproducibility (relative standard deviation, RSD = 1.7%), satisfactory anti-interference capability, and good long-term stability, retaining 94.1% of its initial response after 35 days of storage. Spike recovery experiments using real seawater samples yielded recoveries ranging from 96.73% to 99.73%, with RSD values below 3%, indicating excellent accuracy and precision in complex seawater matrices. These results demonstrate that the proposed sensor enables accurate determination of Pb2+ in seawater without complicated sample pretreatment and exhibits considerable potential for applications in marine environmental monitoring of heavy metal contamination.