Synthesis and performance of a photocatalytic titania-hydroxyapatite composite
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The photocatalytic degradation of methylene blue (MB) 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 °C due to crystallization of an amorphous precursor. The transformation of anatase to rutile was delayed until 900 °C, demonstrating the high thermal stability of the composite. Decomposition of HAp to ␣- and - tricalcium phosphates takes place at 900 °C and is accompanied by the formation of perovskite at 1000 °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 m2 g−1 was obtained at a titania loading of 49 wt% and calcination temperature of 600 °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.
I. INTRODUCTION
The growing world population and decreasing natural resources makes the development of efficient treatments for industrial wastewaters and contaminated drinking water a pressing need. Photocatalytic oxidation is one strategy that has attracted attention as an environmentally benign method for purifying waters tainted by organic pollutants, including textile dyes and colorants. While established methods such as flocculation, activated carbon adsorption, and biological treatment can capture and concentrate toxic substances, these are usually not degraded and remain potentially hazardous.1 In contrast, photocatalysis ruptures organic molecules through reaction with free radicals (O2•− and •OH) in a process called mineralization.2 Titanium dioxides (conventionally, though incorrectly, described as TiO2)3,4 have been extensively studied as ultraviolet (UV) photocatalysts because of their chemical stability and high activity.5 While nano-sized titania powders are commonly used and have high catalytic activity, reuse can be difficult, as they are not easily separated from solution. To address this limitation various strategies have been considered, including the deposition of thin titania films on UV transparent substrates or the
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0290 2398
http://journals.cambridge.org
J. Mater. Res., Vol. 23, No. 9, Sep 2008 Downloaded: 11 Mar 2015
decoration of inert scaffolds with titania. In practice, optimization is complicated by the need to introduce cocatalysts, such as gold, to slow electron-hole recombination. Therefore, novel approaches to enhance the effectiveness and practicality of titania as a catalyst continue to be investigated. Hydroxyapatite (HAp), a biologically benign material, has been considered as both a carrier for titania photocatalysts and an intrinsic photocatalyst.6 For HAp th
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