Factors influencing the photocatalytic decolorization of Bromophenol blue in aqueous solution with different types of TiO2 as photocatalysts

The photocatalytic decolorization of Bromophenol blue (BPB) in aqueous solution with different types of TiO2 as photocatalysts in slurry form has been carried out using UV-A light at 365 nm under a variety of conditions. The efficiency of P25-Degussa and PC500-Millennium photocatalysts were compared. The effects of various parameters such as catalyst loading, light intensity, temperature, pH and initial concentration of the dye on decolorization have been investigated. The adsorption of BPB on TiO2-P25 and PC500 was found favorable by the Langmuir approach. Under the operating conditions of this study, the photocatalytic degradation of BPB followed pseudo first-order decay kinetics. The kapp values indicated an inverse dependence on the initial dye concentration and were fitted to the Langmuir–Hinshelwood model. The degradation efficiency was found to increase with the pH at neutral to acidic ranges, however the reaction was gradually retarded at the alkaline medium due to the effect of charge repulsion. The degradation rate constants increase slightly with an increase in temperature from 10 to 50 °C. The kinetics was strongly enhanced in the presence of electron acceptors such as H2O2 at low dosage.

Research highlights
► TiO2 P25 is more efficient than other photocatalysts used for decolorization of BPB.
► Correlation between dark adsorption and photocatalytic degradation of BPB was found.
► Decolorization of BPB followed pseudo first-order decay kinetics.
► Photocatalytic efficiency reached a maximum near the TiO2 PZC (pH= 6.8).
► Low H2O2 dosages enhance the decolorization of BPB but over-dosages retard it.