Synthesis and performance of a photocatalytic titania-hydroxyapatite composite

The photocatalytic degradation of methylene blue (NIB) over a porous titania-hydroxyapatite (HAp) composite under ultraviolet radiation was studied. The catalyst was prepared by coating porous HAp with a titanium butoxide [Ti(OBu)(4)] sol at titania loadings of 17-49 wt%. Quantitative powder x-ray diffraction showed higher proportions of anatase as the calcination temperature increased from 500 to 800 degrees C due to crystallization of an amorphous precursor. The transformation of anatase to rutile was delayed until 900 degrees C, demonstrating the high thermal stability of the composite. Decomposition of HAp to alpha- and beta- tricalcium phosphates takes place at 900 degrees C and is accompanied by the formation of perovskite at 1000 degrees C. A systematic study of the influence of calcination temperature and titania:HAp ratios demonstrated that for the optimal material, a surface area of 100 m(2) g(-1) was obtained at a titania loading of 49 wt% and calcination temperature of 600 degrees C. A highly dispersed suspension of finely ground titania-HAp enhanced the photodegradation of MB, allowed a high percentage recovery of catalyst, and was shown to be recyclable.