An intertwined network of Ni-based metal-organic framework nanowires and multiwalled carbon nanotubes as a potent electrocatalyst for real-time detection of environmental toxic heavy metal ions in local tap water

Globally, in the existing situation, providing quality water without contamination to humans is one of the most challenging goals. In this perspective, the present report focuses on the fabrication and real-world application implementation of a flexible, simple and cost-effective electrochemically viable sensor based on a GCE (glassy carbon electrode) fine-tuned with an intertwined network of Ni-based metal-organic framework nanowires (Ni-MOF NWs) and multiwalled carbon nanotubes (MWCNTs) for the real-time detection of environmental toxic heavy metal ions (Cd (II) and Pb (II)) in local tap water. At the outset, for the first time, Ni-MOF NWs were synthesized by the traditional hydrothermal method and their electrocatalytic activity was drastically improved by successfully intertwining with MWCNTs (Ni-MOF NWs/MWCNTs) via a simple ultrasonication process. The structural and morphological characterizations of Ni-MOF NWs/MWCNTs were analyzed by XRD, XPS, TEM and EDS with elemental color mapping. The electrochemical characterizations of the developed electrochemical sensors, like sensing activity and charge transfer capacity, were explored by CV (cyclic voltammetry) and EIS (electrochemical impedance spectroscopy) techniques. The DPV (differential pulse voltammetry) technique was used to investigate the proposed electrode limit of detections (LODs), selectivity and real-time applicability towards the Cd (II) and Pb (II) ions detection. The simultaneous measurements of Cd (II) and Pb (II) were performed and the LODs were found to be as 0.017 and 0.011 µM, respectively, which were well below the drinking water quality guidelines of the WHO (World Health Organization), the Indian government and the U.S. EPA (United States Environmental Protection Agency). Moreover, the proposed sensor exhibited remarkable repeatability, reproducibility and stability results. Our group further tried to apply the Ni-MOF NWs/MWCNTs/GCE towards the practical determination of Cd (II) and Pb (II) in local tap water and acquired agreeable recovery rates between 98.1 and 101.7%. Based on the adequate recovery results, the Ni-MOF NWs/MWCNTs/GCE can become a competent electrocatalyst in the near future to recognize the toxic levels of Cd (II) and Pb (II) at a reliable cost in drinking tap water samples in order to elude the health issues.