PREPARATION AND CHARACTERIZATION OF AL2O3 SUPPORTED TIO2 CATALYSTS EMPLOYED FOR 4-NITROPHENOL PHOTODEGRADATION IN AQUEOUS-MEDIUM

In this paper the preparation and some bulk and surface characterizati ons of a set of Al2O3 supported TiO2 photocatalysts are reported. The powders were home prepared by a wet impregnation method using titanium (IV) isopropylate. The impregnation was followed by thermal treatment s and this procedure was repeated several times in order to obtain sam ples with different amounts of TiO2. The solids were characterized by X-ray diffraction. specific surface area determination, scanning elect ron microscopy coupled with an electron microprobe used in an energy-d ispersive mode and diffuse reflectance spectroscopy. Moreover, all of them were tested as photocatalysts by using different kinds of batch p hotoreactors for 4-nitrophenol photodegradation in aqueous medium chos en as a 'probe' reaction. The characterization results indicate that a layer of anatase TiO2 formed on the surface of Al2O3 particles. its e xtent depending on the number of impregnations. The photoactivity of t he powders increased by increasing the number of impregnations up to s even times. For samples obtained by impregnating seven times, the phot oreactivity was higher, but not much different from that observed by u sing samples impregnated five times. The photoactivities of the sample s obtained with five and seven impregnations were found to be not much lower than that of a pure home prepared TiO2 sample, but quite lower than that of a Degussa P25 TiO2 sample. Finally, it is worth noting th at the alumina supported TiO2 catalysts are easily separated from wate r by decantation and no significant deactivation due to disaggregation of the particles and/or erosion of their surface was shown to occur i n some of the used experimental conditions, i.e. when photoreactors co upled with an electric impeller were used. (C) 1998 Elsevier Science S .A. All rights reserved.