Study on the effect of Ocimum gratissimum and Vernonia amygdalina plant leaf extracts and ph in the synthesis of zinc oxide nanoparticles

Abstract

Zinc oxide nanoparticles were synthesized at three different pH levels in the presence of Ocimum gratissimum (Og) and Vernonia amygdalina (Va) plant leaf extracts. The nanoparticles were characterized using optical spectroscopy and electron microscopy and their optical response, sizes and optical energy band gap values were found to be pH and leaf extract dependent. While the Og nanoparticles had mean sizes in the range 38 nm – 63 nm, the Va nanoparticles were slightly larger with mean sizes ranging from 44 nm – 62 nm. The peak absorbance for the Og and Va zinc oxide nanoparticles occurred at 360 nm and 355 nm respectively. The SEM images of the nanoparticles showed them to be spherical and in clusters, with sizes which were pH dependent and decreased in the order pH 12 > pH 10 > pH 8. The FTIR scans showed that phenols and flavonoids among others were the phytochemicals that took part in the synthesis of the derived ZnO nanostructures. The Photoluminescence spectra of the ZnO nanoparticles showed two emission peaks namely a UV emission peak at 2.2 -2.3 eV and a green emission peak at 3.2 eV and the nanoparticles showed band edge photoluminescence, with spectral intensities which were also leaf extract and synthesis pH dependent. While the optical energy band gap(??) values of the Og zinc oxide nanoparticles increased with synthesis pH with obtained values in the range 3.22 – 3.24 eV that of the Va zinc oxide nanoparticles decreased with increase in pH of synthesis and was in the range 3.29 – 3.20 eV

Keywords: plant leaf extracts, optical energy bandgap, optical spectroscopy, electron microscopy, photoluminescence