The titania/hydroxyapatite (TiO2/HAp) product was prepared by precipitating hydroxyapatite in the presence of TiO(OH)2 gel in the hydrothermal system. The characteristics of the material were determined by using the measurements such as X-ray photoemission spectroscopy (XPS), X-ray diffraction (XRD), diffuse reflectance spectra (DRS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX). The XPS analysis showed that the binding energy values of Ca (2p1/2, 2p3/2), P (2p1/2, 2p3/2), and O 1s levels related to hydroxyapatite phase whereas those of Ti (2p3/2, 2p1/2) levels corresponded with the characterization of titanium (IV) in TiO2. The XRD result revealed that TiO2/HAp sample had hydroxyapatite phase, but anatase or rutile phases were not found out. TEM image of TiO2/HAp product showed that the surface of the plate-shaped HAp particles had a lot of smaller particles which were considered as the compound of Ti. The experimental band gap of TiO2/HAp material calculated by the DRS measurement was 3.6？eV, while that of HAp pure was 5.3？eV and that of TiO2 pure was around 3.2？eV. The shift of the band gap energy of TiO2 in the range of 3.2–3.6？eV may be related to the shifts of Ti signals of XPS spectrum. 1. Introduction TiO2 photocatalysis has gained much attention because of its low cost, nontoxicity, high stability, and easy preparation. However, the slow rates of the photocatalytic chemical transformations, compared with other methods, the low quantum yields, the lack of visible-light utilization, and the low adsorption capacity of TiO2 have hindered it from the practical application. To solve these problems, much effort has been made to enhance the photocatalytic efficiency and visible-light utilization of TiO2 by the additional components doping [1], improving its sensitization and metallization [2], or combining TiO2 and absorbable inorganic materials [3]. Recently, the preparation of titania/hydroxyapatite (TiO2/HAp) materials was attracting considerable attention thanks to the photocatalytic property of TiO2 and great adsorption ability of HAp. Among various features of the TiO2/HAp material which have been studied, the band gap evaluation was an important one because it decided the energy separation between the valence and conduction bands, the quantum effect, and the effect of visible-light utilization of that material [4]. The band gap of HAp was reported in [5] to be 3.95？eV by photoluminescence measurement, meanwhile, in some papers, that of HAp was calculated to be around 4.51–5.4？eV
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