Photocatalytic Activity of Synthetic Lantern-oxyapatite

Abstract

 Purpose: Oxyapatite (Ca₁₀ (PO₄)₆O: OAP) contains reactive oxygen radicals and acts as an antimicrobial material because it oxidizes and resolves adsorbed materials such as organic matter and bacillus, and also functions as a bone substitute material. It is reported that photocatalytic activity of oxyapatite is observed when a part of the calcium ions in the crystalline lattice are substituted with lantern ions. The purpose of this study was to examine a method of synthesizing lanthanum-doped OAP (Ca₈La₂ (PO₄)₆O₂: La-OAP) and to investigate the photocatalytic activity of the prepared lanthanum-doped OAP.

 Methods: La-OAP was synthesized by the dry method. La-OAP was prepared by heat treating mixtures of La₂O₃ and Ca₂P₂O₇ in a multi-atmosphere furnace at three different temperatures (1,000, 1,200 and 1,400°C) for 4 hours in an oxygen flow or a nitrogen flow. The synthetic La-OAP was characterized by using XRD. The photocatalytic activity of La-OAP was evaluated by degradation of methylene blue (MB) under visible light (irradiation for 10-60 minutes). The antibacterial ability of La-OAP was evaluated by a halo test. The halo test was performed using filter test pieces (5 mmφ) containing the synthetic La-OAP powder. After the filter test piece was placed on the agar medium containing Escherichia coli or Streptococcus mutans, light irradiation was performed by a halogen lamp from the upper and lower sides of the test piece for 30 minutes. The inhibition zone which arose around the test piece was investigated after incubation (37°C, 12 hours).

 Results: XRD analyses confirmed that the heat-treated precipitate was La-OAP. The amount of La-OAP varied according to heating temperature regardless of the type of gas atmosphere. La-OAP samples synthesized by the dry method at 1,000, 1,200 and 1,400°C in oxygen flow completely resolved MB with visible light irradiation for 30-60 minutes. After the irradiation the MB solution became transparent. Inhibition zones were observed around the filter test pieces against both E. coli and S. mutans.

 Conclusion: Lantern-oxyapatite (Ca₈La₂ (PO₄)₆O₂) synthesized by the dry method showed a high photocatalytic activity under visible light and might work as an antimicrobial material.