Photocatalytic Oxidation Using a New CatalystTiO2 Microspherefor Water and Wastewater Treatment

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Abstract
Since the suspended TiO 2 powder enjoys free contact with UV irradiation in a photoreactor system, it can generally achieve better efficiency than the immobilized TiO 2 catalysts. However, the separation and reuse of this catalyst powder from treated water often limit its application in practice. In this study, a new type of TiO 2 catalyst called TiO 2 microsphere was prepared by a sol-spraying-calcination method, which can easily settle in its aqueous suspensions under gravity. The SEM image of the TiO 2 microsphere samples demonstrated that they had an almost spherical shape with a particle size of 30-160 μm, while the XRD analysis indicated that these TiO 2 microspheres still had a crystal size of 8.1 nm. Since these TiO 2 microspheres had a porous structure with higher specific surface area and pore volume than normal TiO 2 powders, they appeared to have strong adsorption ability in its aqueous suspensions. The photocatalytic activity of the TiO 2 microspheres was evaluated in the photodegradations of salicylic acid (SA) and sulfosalicylic acid (SSA). The experimental results showed that the reaction rate using the TiO 2 microspheres was similar to that using the TiO 2 powders in the SA suspensions and even higher than that in the SSA suspensions. Chemical and physical properties of the TiO 2 microspheres and powders that are attributed to photoactivity were discussed based on the Langmuir-Hinshelwood kinetic model. The prepared TiO 2 microsphere samples were reused in the photooxidation reaction more than 50 times. It was found that there was no significant weakening in their photoactivity and no change in their particle shape. This TiO 2 microsphere catalyst can be simply used to conduct an effective photooxidation in its suspension for water and wastewater treatment with ease of recovery from treated water.Department of Civil and Environmental Engineerin