Effects of calcination on the photocatalytic properties of nanosized TiO2 powders prepared by TiCl4 hydrolysis

The ultra fine nanosized TiO2 photocatalysts in the anatase, rutile, and both phases were prepared by the hydrolysis of TiCl4 solution. The resulting materials have been characterized by HREM, XRD, BET and W-VIS absorption spectroscopy. The photoactivity, effective degradation, and the selectivity for complete mineralization of these catalysts were tested in the photocatalytic degradation of phenol. For this reaction, the quantum-sized catalyst particles (4 nm) in the anatase phase shows the highest selectivity, the concentrations of p-benzoquinone and hydroquinol as the photocatalytic products were at very low level. However, the selectivity of the quantum-sized crystallites in the rutile phase was not improved in comparison with that of catalysts which bandgap corresponding bulk rutile. HREM micrographs show the quantum-sized catalysts were crystallized partially or many defects occurred on their crystal planes, they are responsible for their relative low photoactivity. Calcination is an effective treatment to increase the photoactivity of nanosized TiO2 photocatalysts resulting from the improvement of crystallinity. Mixtures of both phases exhibit higher photoactivity as well as effective degradation in comparison with pure anatase or rutile catalysts. To the best of our knowledge, we are first to report that the quantum-sized TiO2 crystallite exhibit high selectivity for complete mineralization in the photocatalytic degradation of phenol solution. (C) 2000 Elsevier Science B.V. All rights reserved.