Executive Summary : | Continuous urbanization, industrialization, and poor agricultural and domestic waste management led to the release of heavy metal ions, such as Pb2+, Cd2+, Hg2+, and As3+ in the environment, posing a serious threat to the ecosystem and human health. The conventional methods for sensing heavy metal ions include atomic absorption spectroscopy, atomic emission spectroscopy, X-ray fluorescence spectrometry, and inductively coupled plasma technique, which are time-consuming, costly, demand sophisticated instrumentation, high precision, and trained technicians. Hence, a simple, cheap, reliable, and accurate alternative method is required for sensing heavy metal ions. An electrochemical process is a promising approach for detecting heavy metal ions both in online and in-situ modes due to its high sensitivity, selectivity, quick response, cost-effectiveness, and easy miniaturization. However, the working electrode faces issues like low catalytic activity, slow charge transfer kinetics, and fouling of the surface, which lower the performance of the sensor. Therefore, electrode modified materials with excellent performance are essential in electrochemical sensing. However, low porosity and lack of structural tunability limit most electrode modified materials. Thus, porous materials with tuneable chemical structures have attracted great attention for the fabrication of high-performance electrochemical sensors. To this end, composites based on Zr-MOF (UiO-66-NH2) are potential candidates for obtaining high conductivity, selectivity, and excellent electrocatalytic performance. Here, the composite is formed by combining Zr-MOFs with functional materials such as carbon nanomaterials, metal/metal oxides, and conducting polymers to improve their electrical conductivity. In this study, polydopamine-coated gold nanoparticles (Au@PDA) will be integrated with UiO-66-NH2 to prepare the composite MOFs (Au@PDA@UiO-66-NH2) via bottle around ship method. This composite electrode material is expected to show excellent electrochemical activity with a low detection limit, high sensitivity, and reproducibility due to improved electrical conductivity via redox hopping mechanism of AuNPs; efficient adsorption and diffusion of heavy metal ions owing to a several surface-active sites (-C=O, -NH2) and interconnected pores of Zr-MOF; better binding ability, metal chelation, and enhanced redox activity coming from the catechol/o-quinone moieties of PDA. Next, practical utility of the MOF-based composite material will be demonstrated by embedding the electrode material onto a paper-based scaffold via the screen-printing method to create flexible paper-test strips. This paper-test strip would consist of a screen-printed Au@PDA@UiO-66-NH2 modified working electrode, counter electrode, and Ag/AgCl based reference electrode. This paper-test strip would be analogous to the three-electrode system incorporated in a beaker containing the sample solution of heavy metal ion. |