Voltammetric and impedimetric behaviour of phytosynthesized nickel nanoparticles

The biosynthesis of nickel nanoparticles from nickel chloride using Moringa oleifera leaf extract as reducing agent was successfully carried out; the formation of nickel nanoparticles was confirmed by the use of UV–visible spectroscopy, FTIR spectroscopy, atomic force microscopy, cyclic voltammetry and electrochemical impedance spectroscopy techniques. Optical property showed a colour change from faint light blue of the nickel chloride to dark reddish brown of the nickel nanoparticle after addition of the plant extract, while FTIR confirmed the possible biomolecule responsible for the reduction as anthraquinones; the UV–visible spectroscopy showed the wavelength of nickel nanoparticles at 297 nm, and atomic force microscopy gave images of the nickel nanoparticles as aggregate nanoclusters. Voltammetric and impedimetric behaviour of the nickel nanoparticles towards a one-electron-transfer redox probe was interrogated using cyclic voltammetry and impedance spectroscopy. The equivalent electrical circuit used to fit the measured impedance data indicates that the nanoparticles exhibited patterns characteristic of superimposed porous layer. Electron transfer rate constant K s and the apparent heterogeneous electron transfer constant K app were calculated as 6.18 × 1018 and 1.60 × 10−3 cm s−1, respectively. Such high value is an indication of how fast the nickel nanoparticle can transfer electron from the nanoparticle to the underlying platinum electrode, implying that the nanoparticle can be a potential candidate in the fabrication of biosensors and in catalysis.