Immobilization and photocatalytic efficiency of titania nanoparticles on silica carrier spheres
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Immobilization of titania nanoparticles on submicron-sized silica carrier spheres was achieved, and the relevant photocatalytic efficiency was studied. In contrast to the commonly adopted practice of either free suspending nano-sized catalyst particles or immobilized catalyst particles on large supports for photocatalytic applications, the present approach offers a third option, avoiding the disadvantages of the above-mentioned two practices. In the model system of photo-degradation of methylene blue, the photocatalytic efficiency of the present catalyst form was found comparable to that of free-suspending P25 nanoparticles, a popular commercial titania photocatalyst, of the same total catalyst surface area. The present photocatalytic process was found to be diffusion dominant, and its impressive catalytic performance was attributed to the well-separated, smaller than usual titania particles immobilized on the surfaces of submicron-sized silica spheres.
I. INTRODUCTION
Titania nanoparticles are probably currently the most widely used photocatalyst, particularly in treatment of air and water pollution, and thus have received extensive and intensive research attention. When in use, titana nanoparticles are either dispersed in the treated stream or immobilized on fixed or fluidized supports of large size such as glass tubes,1,2 pumice stone pellets on cement or polycarbonate surfaces, 3 quartz sands, 4 Cuddapah stones,5 glass fibers,6 etc. It has been a well known fact that free-suspending systems are much more efficient than the immobilized ones,4–7 and over one order of magnitude difference in photocatalytic efficiency has been observed.4 However, the free-suspending systems suffer severe drawbacks of catalyst loss and difficulty in catalyst recovery because of the nano-size of the catalyst particles, making it inefficient in separation of the catalyst from the treated stream. On the other hand, although immobilization of nano-sized catalyst particles on the surfaces of fixed or fluidized supports of large size can eliminate the need for catalyst-stream separation, the restricted access of the catalyst surfaces for reacting species, arising from the immobilization, can also significantly hamper the full utilization of the catalysts. In this work, we propose a compromise option between the two extremes: immobilizing the nano-sized
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0275 2290 J. Mater. Res., Vol. 21, No. 9, Sep 2006 http://journals.cambridge.org Downloaded: 30 Dec 2014
catalyst particles on the surfaces of submicron-sized carrier colloids (silica spheres here). There are many advantages associated with this design. First, the size of the carrier spheres is large enough to enable easy separation from the treated stream through low-speed centrifuge but small enough for easy dispersion in and mixing with the stream via low-power agitation. The well-dispersed and well-mixed state of the carrier colloids in the stream is critical to the performance of the ca
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