Comparison of various titania samples of industrial origin in the solar photocatalytic detoxification of water containing 4-chlorophenol

The degradation of 4-chlorophenol (4-CP) was used as a model reaction to investigate the photocatalytic properties of different industrial TiO(2) catalysts and to compare their efficiencies in the treatment of contaminated waters. Parallel experiments have been performed using either artificial UV-light in a batch photoreactor in laboratory experiments or solar energy in the flow reactor of the pilot plant at Plataforma Solar de Almeria (PSA) in Spain. Depending on the kinetic criteria chosen for comparison ((i) initial rate of pollutant disappearance; (ii) amounts of intermediate products present in solution at a given time; (iii) time necessary to obtain total mineralization), different classifications of photocatalyst activities were observed. Among various physical characteristics such as particle size, structure or active site density, which may intervene on the photocatalytic activity, the influence of the surface area appeared of prime importance. For lower surface area catalysts, there is a decrease in the readsorption rate of intermediate products and consequently in the overall photodegradation rate. By contrast, for higher surface area catalysts, it was observed a lower final rate of total organic carbon (TOC) disappearance because of a very low coverage in pollutant which favors electron-hole recombination. The comparison of the kinetic results for decontaminating water at PSA and in laboratory experiments indicated the same kinetic order (apparent first order) for 4-CP disappearance and the same apparent quantum yield. However, fewer intermediate products and a faster TOC disappearance were observed in the solar pilot reactor at PSA, which, in addition, worked with a smaller optimum concentration of suspended titania. This was ascribed to the design of the photoreactor. (C) 1999 Elsevier Science B.V. All rights reserved.