Zinc oxide nanoparticles biosynthesized using two concentrations of Ocimum gratissimum (Og) plant leaf extracts were annealed at two different temperatures. Their UV-Vis absorbance peaks at 372 nm - 375 nm indicate a blue shift in excitonic absorption and their optical energy band gap values were in the range 3.22 eV – 3.31 eV. SEM images show the nanoparticles to be polydispersed and of a wide range of sizes with smaller nanoparticles clustering around bigger micrometer- sized ones with sharp edges. An annealing temperature of 400 ? resulted in the sintering of the nanoparticles but nanoparticles annealed at 250 ? had porous surfaces suggesting a possible use in gas sensor applications. XRD patterns show that the ZnO nanoparticles have the hexagonal wurtzite structure and are of good crystalline structure. Obtained crystallite sizes increased with annealing temperature and were in the range 14 nm to 29 nm. FTIR spectra show phenols, amines and aldehydes as the available reducing age.....

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