Influence of phosphate source on preparation of zinc phosphate white pigments

Abstract

Photocatalytically active zinc oxide is used as a white pigment for cosmetics, leading to decomposition of a certain degree of sebum on the skin upon exposure to the ultraviolet radiation in sunlight. Herein, as novel white pigments for use in cosmetics, zinc phosphates were prepared from zinc nitrate and various phosphate compounds, viz., phosphoric acid, sodium di-hydrogen phosphate, di-sodium hydrogen phosphate, sodium pyrophosphate, or sodium triphosphate. The chemical composition, powder properties, photocatalytic activity, color phase, moisture retention, and smoothness of the zinc phosphates were evaluated. The obtained materials had Zn/P ratios corresponding to those of zinc orthophosphate Zn3(PO4)2, zinc pyrophosphate Zn2P2O7, and zinc triphosphate Zn5(P3O10)2. The photocatalytic activity of these zinc phosphate particles was low; thus, these pigments should not induce decomposition of sebum on the skin. All samples prepared in this study exhibited high reflectance within the range of visible light.