Monodispersed ZnS nano-spheres were synthesized by a simple precipitation. By adjusting the concentration of Zn and S sources, the particle size and morphology were easily controlled. Careful examination of the obtained particles suggested porous structures composed of building blocks of small crystallites, ca. 4–13.4 nm in diameter. A higher [S]/[Zn]-precursor ratio resulted in a bigger crystallite size but a smaller particle size, and vice versa, for the lower precursor ratio. However, an extreme [S]/[Zn] ratio of 20 provided no spherical aggregation, but a formation of amorphous aggregates. We consider the rate to nucleation and the diffusion-controlled aggregation of crystallites to be important parameters in determining particle sizes and size distributions. Size homogeneity of the obtained ZnS nano-spheres, especially with a [S]/[Zn]-precursor ratio of 5, afforded a photonic crystal array that can potentially benefit the photocatalytic activity. When the photocatalytic activities of the ZnS nano-spheres obtained via different conditions were compared, it was found that spherical aggregation and high surface areas have a positive effect on catalytic activity. Although using a [S]/[Zn] ratio of 20 provided the highest surface area, the amorphous aggregation and overly excessive use of S caused a detrimental influence on the catalytic activity.
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