The photocatalytic degradation of phenol in aqueous suspensions of TiO2 under different salt concentrations in an annular reactor has been investigated. In all cases, complete removal of phenol and mineralization degrees above 90% were achieved. The reactor operational parameters were optimized and its hydrodynamics characterized in order to couple mass balance equations with kinetic ones. The photodegradation of the organics followed a Langmuir-Hinshelwood-Hougen-Watson lumped kinetics. From GC/MS analyses, several intermediates formed during oxidation have been identified. The main ones were catechol, hydroquinone, and 3-phenyl-2-propenal, in this order. The formation of negligible concentrations of 4-chlorophenol was observed only in high salinity medium. Acute toxicity was determined by using Artemia sp. as the test organism, which indicated that intermediate products were all less toxic than phenol and a significant abatement of the overall toxicity was accomplished, regardless of the salt concentration.

The photocatalytic activity of bulk and supported TiO2 catalysts were tested using formic acid as a probe molecule. The supported catalysts tested were prepared by impregnation using aluminum oxide (Al2O3) as the support and the bulk catalysts by precipitation, both in sol-gel systems. For purposes of comparison, a photocatalyst supplied by DEGUSSA (P25) was also tested. The photolysis rate was found to be less significant than the photocatalytic rate. The Langmuir-Hinshelwood model was adopted and its constants were estimated and used to compare the various catalysts. The supported catalysts showed no significant activity, in spite of their high specific surface area. The bulk catalysts tested showed the highest photocatalytic rates. The adsorption constants determined experimentally were different from the ones estimated based on the kinetic experiments. The parameter estimation procedures tested were used to clarify this issue.