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The photocatalytic activities of TiO2 Degussa P25 and Millennium PCs (PC50, PC100, PC105 and PC500) were evaluated by the photocatalytic degradation of Bromothymol Blue (BTB). The relationship between the photocatalytic reaction and the adsorption of BTB on the TiO2 catalysts at acidic, natural and basic mediums of pH was investigated. The crystalline phase, average crystalline size and surface area of the catalyst were found to have a significant influence on the adsorption and photocatalytic activity of the TiO2 samples. The mixed phase of anatase/rutile (Degussa P25) was found to be the most efficient photocatalytical material than pure phase anatase (Millennium PCs) and faster degradation is observed for PC500 compared to other Millennium PCs, this was attributed to the high surface area of PC500. Within the PC50, PC100 and PC105 series, the photocatalytic efficiency increased with the decrease of the surface area. The COD and TOC removals increased slowly, however, the decolorization ratio of BTB increased rapidly at the same time. Thereafter, the efficiency of P25 and PC500 were compared in presence of H2O2, Cl− and HCO3− at different mediums of pH. H2O2 was found to enhance strongly the BTB degradation in presence of P25 with an optimum at natural pH. In contrast, the reaction was inhibited in the presence of PC500, due to the inhibition of dye adsorption. At different pH, the BTB degradation has been significantly inhibited in the presence of the mixtures of HCO3−/H2O2. In contrast, the mixtures of Cl−/H2O2 accelerate the BTB degradation at acidic pH.

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Zinc oxide ZnO nanoparticles synthesized by sol-gel method and commercial titanium dioxide TiO2 were studied in the present work. The structural properties of the ZnO and TiO2 nanoparticles were determined by Fourier transform infrared (FTIR), X-ray diffraction (XRD) and Raman spectra techniques (RS). The average crystallite sizes were calculated by using the powder X-ray and were found to be 48 nm and 20 nm and the specific surface areas were about 1047 m 2 g −1 and 381 m 2 g −1 for ZnO and TiO2, respectively. The FTIR and Raman spectroscopy results have shown high purity of the ZnO and TiO2 samples and they are consistent with the one obtained from XRD. The ZnO and TiO2 nanoparticles were used as catalysts for the elimination of an azo dye, Mordant Violet 5 (MV5), in aqueous solution, by an advanced oxidation process which is heterogeneous photocatalysis. Synthesized ZnO was more efficient than commercial TiO2 to degrade MV5 under UV irradiation. The adsorption of MV5 on TiO2 and ZnO was found favorable by the Langmuir approach. The MV5 adsorption constant on TiO2 was higher than that obtained in the case of ZnO. The photocatalytic reaction of MV5 in presence of each catalyst was investigated at different concentration of the dye and at different conditions of pH. The solar radiation of MV5 in the presence of each catalyst was also tested.