Evaluation of functionalized graphene oxide as a nanostructured sensor for lead ion detection in aqueous solutions...

Since heavy metals are not subject to biodegradation and can accumulate in living organisms, rising levels of lead ion (Pb²⁺) and other heavy metal pollutants in water sources pose a significant threat to environmental health and public safety. Although conventional detection techniques are accurate, they are often expensive, time-consuming, and unsuitable for field use. Accordingly, it is highly required but remains exceedingly challenging to improve a facile detection approach for heavy metal pollutants in water. Here, we present the creation of a novel, cost-effective, and highly sensitive quartz crystal microbalance (QCM) sensor designed for the detection of Pb²⁺, utilizing 3-mercaptopropyltrimethoxysilane-functionalized graphene oxide (3-MPTMS-GO). A modified Hummer's method was employed to synthesize GO, which was then functionalized with 3-MPTMS through a cross-linking method. Various characterization techniques, including Transmission electron microscopy (TEM), Atomic force microscopy (AFM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray Photoelectron Spectroscopy (XPS), Raman spectroscopy, UV-Vis spectroscopy, contact angle measurements, and Zeta potential analysis, were performed to confirm effective functionalization and enhanced surface properties. The QCM sensor coated with 3-MPTMS-GO demonstrated excellent sensitivity to Pb²⁺ across various pH levels at different concentrations: 0.05 mg L^- 1, 1 mg L^- 1, and 2 mg L^- 1. Through the calibration curve, the sensor revealed a linear detection range of Pb²⁺ concentration from 0.05 mg L^- 1 to 1.5 mg L^- 1 (R² = 0.999) with a limit of detection (LOD) of 0.01 mg L^- 1, which aligns with WHO standards. Furthermore, the sensor verified outstanding regeneration capability over 10 reuse cycles using EDTA treatment and excellent stability towards selective lead ions. This preliminary investigation illustrates the significant potential of the 3-MPTMS-GO-based QCM sensor as a proof-of-concept platform for Pb²⁺ detection under controlled laboratory conditions, necessitating extensive validation prior to implementation in practical environmental monitoring applications.