A modified MXene composite sensor with sulphur impurities for electrochemical detection of lead in the aqueous system

The detection of heavy metal ions, particularly Pb²⁺, is critical due to their severe environmental and health impacts. This study introduces a novel sensor based on an alkali-modified Ti-MXene decorated with bismuth and sulphur (S-Bi@TiMX), designed for the ultra-sensitive electrochemical detection of Pb²⁺. Synthesized via hydrothermal deposition, the composite material exhibits a distinctive marigold-like morphology, enhanced active sites, and robust synergistic interactions between its constituents. These features mitigate issues like MXene sheet restacking and promote superior electron transfer kinetics. The composite was drop-cast onto a low-cost, disposable plastic chip electrode (PCE), achieving remarkable sensitivity and an impressive detection limit of 0.0002 μg L^-1 Pb²⁺, well below the WHO safety threshold. The sensor demonstrated good repeatability (RSD < 2.75%), excellent reproducibility (RSD < 2.8%), minimal interference from competing ions, and high recovery rates (99.2%-99.6%) in real water samples. Optimized parameters like pH, preconcentration potential, and time ensured precise, robust performance across a broad linear range (0.01-100 μg L^-1). This work highlights the potential of the S-Bi@TiMX/PCE sensor for environmental monitoring and offers a scalable, cost-effective solution for detecting ultra-trace Pb²⁺ in diverse aqueous systems.