Simultaneous Electrochemical Sensing of Ultra-Trace Multiple Heavy Metals Using Metal–Organic Frameworks-Graphene Oxide Nanocomposite-Modified Electrodes

The relentless pace of industrialization has significantly exacerbated environmental pollution, with heavy-metal ions (HMIs) emerging as some of the most persistent and toxic pollutants in natural ecosystems. Growing concerns over environmental pollution have created a need for advanced sensing technologies that offer superior sensing sensitivity, selectivity, and reliability. This work reports the development of an electrochemical sensor based on a UiO-66-NH₂(Zr) metal-organic framework (MOF)/graphene oxide (GO) nanocomposite for the simultaneous detection of HMIs in aqueous environments. Using one-pot hydrothermal synthesis, MOFs and conductive GO materials were integrated into a single nanostructure via <i>in situ</i> growth of the UiO-66-NH₂(Zr) MOF on the GO matrix, resulting in the formation of a stable MOF/GO nanocomposite with enhanced conductivity and increased number of effective reaction sites. The amino groups (-NH₂) on UiO-66-NH₂(Zr) porous materials serve as adsorption sites to capture HMIs. The morphological, structural, and electrochemical properties of the UiO-66-NH₂(Zr)-GO nanocomposite were examined by using scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS), powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR) spectroscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Differential pulse anodic stripping voltammetry (DPASV) was subsequently employed for the detection of heavy-metal ions over nanomolar to micromolar concentration ranges using a UiO-66-NH₂(Zr)-GO-modified glassy carbon (GC) electrode. The electrochemical sensor developed in this study was successfully utilized for the selective and concurrent detection of multiple HMIs, namely, copper ion (Cu²⁺), cadmium ion (Cd²⁺), and lead ion (Pb²⁺) in electrolyte solution. The sensor demonstrated achieving high selectivity and sensitivity (1.30 μA μM^-1 for Cu²⁺, 0.50 μA μM^-1 for Cd²⁺, and 12.38 μA μM^-1 for Pb²⁺) with low limit of detection (LOD) (0.59 ng/mL for Cu²⁺, 0.84 ng/mL for Cd²⁺, and 2.9 ng/mL for Pb²⁺), and observed ≥85% reproducibility. The sensor demonstrated excellent long-term stability and operated effectively within a temperature range of 283-313 K, enabling the simultaneous detection of multiple heavy-metal ions from small sample volumes. The developed electrochemical method can equally be employed to detect HMIs at trace (parts-per-billion (ppb)) levels in diverse environmental matrices such as lake, river, tap water, river sediments, and wastewater.