crystallite size of ZnO particles was determined by Sherrer's equation
(where D = 0.89λ/β cosθ where D is the crystallite size (nm),
λ is the wavelength of incident X-ray (nm), β is the full width at
half maximum, and θ is the diffraction angle). The obtained particle
size was 13 nm for pure ZnO. There was a small shift to lower angle
width and change in the line width revealing that silica coating was
successfully conducted (Fig. 3b–h). This leads in slight change of
the particle size of the coated zinc oxide. The zinc oxide free silica
(Fig. 3a & i) showed no XRD peaks, this may confirm that complete
removal of zinc oxide nanoparticles form silica coated zinc oxide microspheres,
when treated with hydrochloric acid.