Photocatalytic activity of synthetic oxyapatite

Objectives: Oxyapatite (Ca₁₀(PO₄)₆O) contains reactive oxygen radicals and acts as an antimicrobial material because it oxidizes and resolves the adsorbed material (organic matter and bacillus, etc.), and functions at the same time as a bone substitute material. It is reported that photocatalytic activity of apatite is observed when a part of calcium ions of apatite are substituted with lantern ions or vanadium ions, and antimicrobial activity rises very much after Ln²⁺-for-Ca²⁺ or V²⁺-for-Ca²⁺ substitution. The purpose of this study is to examine synthesis approach of oxyapatite with photocatalytic activity and to investigate properties of prepared oxyapatite. Methods: Lantern-containing oxyapatite was synthesized by the dry method under oxygen atmosphere or the wet method with H₂O₂. The synthetic oxyapatite was characterized by using XRD, IR, ESR and TG-DTA analysis, and photocatalytic activity of oxyapatite was evaluated by degradation of  methylene blue(MB) under visible light ( the irradiations of 10-60 minutes). Results: It was confirmed by XRD and FT-IR analysis that the synthetic oxyapatite was Ca₈La₂(PO₄)₆O₂. Furthermore, ESR signals due to O^- were observed, indicating that oxyapatite prepared in the present study clearly contains reactive oxygen radicals. Interestingly, the O- signals of oxyapatite samples were quite stable even after heating at high temperature. The oxyapatite synthesized at 1,000°C completely resolved MB with the visible light irradiation for 30 minutes and the MB solution became transparent after the irradiation. Most synthetic oxyapatite showed the photocatalytic degradation of MB under visible light, whereas the efficiency of photocatalytic activity depended on synthesis conditions. Conclusion: The oxyapatite (Ca₈La₂(PO₄)₆O₂)  synthesized under an appropriate condition showed a high photocatalytic activity. Thus, these results suggest that the synthetic oxyapatite (Ca₈La₂(PO₄)₆O₂)  serve as an antimicrobial material under visible light.