Morphological control of zinc oxide and application

In the present study, the ZnO particles of various morphologies, such as mono-dispersed spherical, star-like and rod-like particles were synthesised by the precipitation-crystallisation reaction method in aqueous solutions using zinc nitrate, sodium hydroxide and amine compounds as starting materials to improve the performance for cosmetic applications.  The particle shape could be changed, depending on the concentration of zinc ion, amine compounds and sodium hydroxide. The ZnO products with unique morphologies showed excellent feeling, light diffusing effect, UV shielding effect and visible light transparency, indicating the potential applications in cosmetics.

Many works have been carried out to form various morphologies of ZnO, such as wire, rod, tube, ring, plate, etc., and their unique propertieswere investigated.^3–14 Furthermore, since the bandwidth energy of ZnO is 3.2 eV,¹⁵ it displays a UV light absorbing effect. UV light causes several undesirable influences on human skin, such as sunburn, suntan, cancer, ageing, etc. Therefore, interest in cosmetics which protect human skin from UV light is increasing. The development and research of inorganic UV-shielding materials, which are formulated in cosmetics, have been advanced in terms of the safety of human skin.^1,2,16–18

Also, in recent years, makeup cosmetics have been required to show the natural looking finish and effect of hiding pores and defects on the skin. In order to achieve the above requirements, the control of the shape of the particles may be effective, i.e., it can be expected to control the light diffusion effect and transmit light intensity effect by controlling the morphology of the particles.