Influence of processing time in phosphoric acid treatment of titanium dioxide

Abstract

Photocatalytically active titanium dioxide is used as a white pigment in cosmetics. However, it may promote a certain degree of sebum decomposition on the skin exposed to ultraviolet radiation in sunlight. In this work, titanium dioxide was shaken with phosphoric acid to synthesize a novel white pigment for cosmetic applications. Titanium dioxide particles were added to 0.5 mol/L of phosphoric acid at a P/Ti molar ratio of 1:2 with and without urea, and then shaken in hot water for 1, 3, 6 or 12 h. The chemical composition, powder properties, photocatalytic activity, colour phase and smoothness of the produced powders were studied. The obtained materials exhibited the X-ray diffraction peaks of titanium dioxide, although the peak intensities were weakened by the formation of a surface layer of titanium phosphate. These samples consisted of particles with sub-micrometre sizes, and the photocatalytic activity of the powders was reduced sufficiently to prevent the degradation of sebum on the skin. In addition, the shaking time affected the smoothness of the obtained materials. The treatment of titanium dioxide particles with phosphoric acid for 1 h is an effective method for inhibiting photocatalytic activity and allows the application of this material as a novel white pigment.

Keywords:

• Titanium dioxide
• Phosphoric acid treatment
• Photocatalytic activity
• Particle size

Acknowledgements

The authors are grateful to Dr Takeshi Toyama, Nihon University, Japan for the smoothness measurements. The authors also thank Dr Nobuyuki Takeuchi, Kyoto Institute of Technology, Japan for the measurements of the X-ray photoelectron spectra.