Composite hydroxyapatite/TiO2 materials for photocatalytic oxidation of NOx

Hydroxyapatite/TiO2 composite photocatalysts were obtained from sol-gel prepared TiO2 and commercial hydroxyapatite (HA) powders. Composites with different HA/TiO2 ratio were studied to assess the influence of HA on the morphology and the photocatalytic behavior of the materials. Morphological SEM analysis revealed that the presence of HA diminishes the aggregation of TiO2 particles and leads to their higher dispersion in the composites that was confirmed by the N-2 adsorption-desorption isotherms and Barret-Joyner-Halenda analysis. The photocatalytic activity of the prepared catalysts was examined by monitoring photocatalytic oxidation of NOx model gases over catalysts under UV illumination. The NOx oxidation over the composite catalysts was improved in comparison with pure TiO2 powder. Moreover, the decrease of the TiO2 content, which is the photocatalytically active component in the composites, resulted in enhanced NOx removal. Maximum activity was recorded for composites with HA/TiO2 ratios 1 and 2 that was related to improved TiO2 dispersion and NO2 trapping by the composite materials. (C) 2012 Elsevier B.V. All rights reserved.