Low Temperature Phosphoric Acid Treatment of Zinc Oxide for Nobel White Pigments

Abstract

Zinc oxide that has the photocatalytic activity is used as white pigment for cosmetics. A certain degree of sebum on the skin is decomposed by the ultraviolet radiation in sunlight. In this work, zinc oxide was shaken with phosphoric acid to synthesize a white pigment for cosmetics. Zinc oxide was set with 0.

Preparation of novel cosmetic white pigment by pyrophosphate treatment of zinc oxide

“…The resulting samples were suitable as white pigments, as all samples showed more than 90. In a previous study [20], some samples prepared with uncondensed phosphoric acid had an L* value of less than 90. It was found that the condensed phosphate solution was superior in maintaining high whiteness.…”

“…5 shows UV-vis reflectance spectra of samples treated in various P/Zn ratios for 6 h. All samples indicated high reflectance at the visible light region. Zinc phosphate had high reflectance at the ultraviolet range, therefore samples were expected to have some reflectance at that range [19,20]. However, the reflectance of all the samples prepared in this study was low in the ultraviolet region due to the low reaction rate.…”

“…Especially, samples prepared in P/Zn=1/1 (1 and 6 h) indicated high smoothness. In previous studies with uncondensed phosphoric acid, the lowest static friction resistance was 0.242 [20]. It was found that using a condensed phosphate solution is useful for producing a novel white pigment for cosmetics.…”

Synthesis of Novel Cosmetic White Pigment by Condensed Phosphoric Acid Treatment of Zinc Oxide

“…Zinc phosphate particles without photocatalytic activity were too large, while zinc oxide particles with a smaller particle size had photocatalytic activity. In a previous study, zinc oxide was shaken in phosphoric acid at 30, 40, and 50 °C to obtain zinc oxide particles coated with zinc phosphate [13]. The target particles have a core-shell structure with a core of zinc oxide and a shell of zinc phosphate without photocatalytic activity.…”

“…Zinc oxide was added to 50 mL of the above condensed phosphate solution or condensed phosphoric acid at a P/Zn molar ratio of 1/2 in a glass tube. These mixtures were shaken in hot water (50 ºC) at a shaking rate of 100 times/min for 1 h [13,14]. The powder samples were decanted, washed with water, and dried at 50 ºC over 3 days.…”