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The heterogeneous photocatalytic oxidation of phenol in aqueous diluted solutions over TiO2 particles under UV‐illumination has been investigated. It has been observed that the yield of the phenol photooxidation depends strongly on the pH of the solution. Maximum yields are obtained at pH 8 and also in very alkaline media. These results are explained considering the processes that take place at the surface of the semiconductor, in which OH radicals have an important role. With respect to the initial charge transfer steps a kinetic analysis has been performed. From this analysis it was deduced that the constant rate of formation of OH radicals is about 4.0 × 104 times greater than the constant rate of the direct reaction between phenol and photogenerated holes in the TiO2 particles. Finally, from HPLC analysis, hydroquinone, paraquinone and 1,2.4‐benzenetriol have been detected as intermediate products prior to the total phenol mineralization.

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Procedure for illustrating heterogeneous photochemistry through the photochemical reduction of methyl orange by TiO2 powder; includes sample data.

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The photocatalytic elimination of Cr(VI) from aqueous solutions using CdS supported on glass pearls as catalyst is investigated. The study has been carried out by measuring the amount of Cr(VI) eliminated at different pH, initial Cr(VI) concentrations and temperatures. It has been observed that after flushing dilute Cr(VI) solutions at a wide range of pH (from 5 to 10) through the CdS-coated glass pearls, 100% of Cr(VI) elimination is achieved.