Relationship between Photocatalytic Activity and Ti3+ Defects in Acid-Leached Titanium Dioxide / Hydroxyapatite Composite

Effect of Ti3+ defect density on the photocatalytic activity was investigated using electron spin resonance (ESR) spectroscopy under UV irradiation at 103K. The Ti3+ signal intensity decreased with increasing heating temperature for the TiO2 powders prepared by hydroxyapatite (HAp) precipitation, heating and acid leaching process. The Ti3+ defect density of the TiO2 powder heat-treated at 700°C was found to be about half that of the starting material, P25, without anatase-to-rutile phase transformation based on the results of X-ray diffraction. The photocatalytic activity of the TiO2 powder determined from the change of methylene blue concentration under UV irradiation became higher with decreasing of the Ti3+ defects without a significant change in the anatase ratio and specific surface area during the heat treatment.