A Comparative Study of the Activity of TiO2 Degussa P25 and Millennium PCs in the Photocatalytic Degradation of Bromothymol Blue

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.