Yerba mate tea mediated synthesis of nanoscale zero valent iron particles and their application in detection of Pb ions in water

Yerba-mate tea extracts were used to successfully synthesise nanoscale zero-valent iron (NZVI) particles. The tea extracts acted as both the reducing and capping agents. The morphological, optical and structural properties were characterized using Transmission Electron Microscope (TEM), X-ray Diffraction (XRD), UV–vis absorption spectroscopy and Fourier Transform Infrared (FTIR) spectroscopy, respectively. The XRD and FTIR confirmed a complete reduction of Fe ions forming nanoparticles with an average size of 3 to 3.5 nm synthesized at 25 °C as shown by TEM images, indicating enhanced electrocatalytic sites. The as-synthesized NZVI particles were immobilized on AuSPE and evaluated on the electrocatalytic behaviour using ferri/ferrocyanide as a redox probe. Thus, they were modified on the screen-printed carbon electrodes to fabricate an electrochemical sensor for Pb 2+ detection. The sensor was optimised to detect traces of Pb ions from 5 to 9 parts per billion concentrations. The surface concentration of the adsorbed electro-active film on the reduction half of AuSPE/NZVI modified electrodes was determined and estimated to be 1.32 × 10 −10 mol cm −2 . Moreover, the charge transfer coefficient of AuSPE/NZVI particles was estimated to be 5.43 × 10 −17 cm 2 s −1 . The sensor gave a relatively low limit of detection 2.56 ppb for Pb 2+ ions. This was lower than most commercially available heavy metal detectors with a detection limit of 3.5 ppb. • The nano Zero Valent Iron (NZVI) particles were successfully using yeba mate tea extract as reducing agents. • The NZVI modified AuSPE exhibited enhanced rapid electron and charge transfer kinetics towards ferri/ferro cyanide redox probe. • The NZVI based sensor demonstrated excellent limits of detection for Pb 2+ ions in water • High selectivity in the presence of competing ions.