PERFORMANCE OF HETEROGENEOUS PHOTOCATALYTIC SYSTEMS - INFLUENCE OF OPERATIONAL VARIABLES ON PHOTOACTIVITY OF AQUEOUS SUSPENSION OF TIO2

The influence of incident light intensity and of some physical and che mical parameters on the absorbed and backward reflected photon how and on the reactivity of a heterogeneous photocatalytic system was invest igated. The oxidation of phenol in aqueous solution in the presence of polycrystalline TiO2 powder was used as a test reaction. Home-prepare d TiO2 (anatase) specimens, subjected to various thermal treatments, w ere used for the experimental runs performed in a batch photoreactor d irectly irradiated. The physical parameters investigated were the surf ace area and the size of particles, while the chemical parameters stud ied were the initial pH of the suspension and the presence in the reac ting medium of additives affecting the photoreactivity such as Cl- and H2O2. It was found that the ratio between backward reflected and inci dent photon flow does not depend on the used operative variables, whil e the apparent Napierian extinctance coefficient, which is a parameter related to the photon absorption rate, depends only on the particle s ize and decreases as the particle size increases. The photoreaction qu antum yield, defined as the ratio between the phenol reaction rate and the photon absorption rate, was determined for the various experiment al conditions used in this work. The results showed that at equivalent conditions the quantum yield is an intrinsic feature of the semicondu ctor material; the quantum yield varies only by varying the reaction r ate which, in our case, was affected only by the initial pH of the sus pension and by the presence of Cl- and H2O2. (C) 1995 Academic Press, Inc.