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

Abstract

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 Pb²⁺ 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 cm²s⁻¹. The sensor gave a relatively low limit of detection 2.56 ppb for Pb²⁺ ions. This was lower than most commercially available heavy metal detectors with a detection limit of 3.5 ppb.