Photo-oxidation of gaseous ethanol on photocatalyst prepared by acid leaching of titanium oxide/hydroxyapatite composite

Highly active photocatalysts were synthesized by leaching of heat-treated titanium dioxide (TiO2)/hydroxyapatite (HAp) powder with hydrochloric acid at 0.25, 0.50, 0.75 mol/l, and their photocatalytic activities were evaluated from in situ Fourier transform infrared (FT-IR) study of photo-oxidation of gaseous ethanol. By changing the acid concentration, the TiO2/HAp composite had different atomic ratios of Ca/Ti (0.0–2.8) and P/Ti (0.3–2.1). It was found that phosphate group remained on the surface of TiO2 particle even in the sample treated with concentrated acid (0.75 mol/l). These acid-treated samples showed higher rates for ethanol photo-oxidation than the commercial TiO2 powder, Degussa P25. The highest rate was obtained in the TiO2/HAp composite treated with the dilute (0.25 mol/l) acid in spite of its low content of TiO2 photocatalyst. This enhanced photocatalytic activity was attributed to the result that the deactivation with repeated injections of ethanol gas was suppressed in the TiO2/HAp composites compared with the TiO2 powders.