Oxidation – Reduction Potentials of Hydroxyapatite - Adhered Photocatalysts

Abstract

Hydroxyapatite (HAp) crystals adsorb the many kinds of inorganic and organic compounds and HAp – adhered anatase titanium dioxide, TiO₂, photocatalysts excel in the oxidizing abilities, rather than anatase TiO₂ photocatalysts. The quantitative evaluation about the electrochemical properties of HAp crystals is, however, not discussed. In this study, the oxidation - reduction potentials (ORP) of the suspended solution for HAp - adhered anatase TiO₂ photocatalysts and anatase TiO₂ ones were measured by an ORP meter and the roles of HAp crystals to photocatalytic reactions of anatase TiO₂ photocatalysts were discussed. The maximum ORP differences of suspended solutions for the case of anatase TiO₂ photocatalysts were higher than those for HAp – adhered anatase TiO₂ photocatalysts. The decreasing rates of the ORP differences for the case of HAp – adhered anatase TiO₂ photocatalysts were slower than those for anatase TiO₂ photocatalysts. When UV light is irradiated to HAp – adhered anatase TiO₂ photocatalysts, electrons produced by photocatalytic reactions on anatase TiO₂ photocatalysts transfer to HAp crystals, and then they are stored in HAp crystals. Moreover, their electrons transfer from HAp crystals to anatase TiO₂ photocatalysts and the oxidation reactions occur on anatase TiO₂ photocatalysts in the dark.