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Influence of Phosphoric Acid Treatment on the Photocatalytic Activity of Zinc Oxide
H. Onoda, Y. Sato
Abstract
Zinc oxide is often used as a white pigment for cosmetics; however, it exhibits photocatalytic activity that causes the decomposition of sebum on the skin when exposed to the ultraviolet radiation in sunlight. In this work, zinc oxide was reacted with various concentrations of phosphoric acid for several hours to synthesize a novel white pigment for cosmetics. The chemical composition, powder properties, photocatalytic activities, colors, and smoothness of these pigments were studied. The obtained materials exhibited x-ray diffraction peaks relating to zinc oxide and phosphate after phosphoric acid treatment. The ratio of zinc phosphate to zinc oxide was estimated from inductively coupled plasma results. The sample treated for 6 hours had a high P/Zn ratio, therefore this sample contained a larger amount of zinc phosphate. The concentration of phosphoric acid had less influence on the P/Zn ratio than the processing time. The particle size of the samples became larger with phosphoric acid treatment. The photocatalytic activity of the zinc oxide was inhibited by the phosphoric acid treatment. The obtained samples had enough high reflectance in the visible light region.
Keywords
Zinc oxide, phosphoric acid treatment, photocatalytic activity, particle size
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