Kinetic Modelling of the Photocatalytic Degradation of Diisobutyl Phthalate and Coupling with Acoustic Cavitation

Phthalates are widely used plasticizers, but have endocrine-disrupting effects, which cause harm to both humans and the wider environment. Photocatalytic technologies have been shown to be promising methods for removal of a range of environmental pollutants in water. In this paper the photocatalytic oxidation of Diisobutyl phthalate (DiBP) using two common commercial catalysts, TiO2 and ZnO is assessed. Both photocatalysts proved to be effective in removing > 90% of the compound in less than 25 minutes of treatment. Pseudo-first kinetics were initially used to describe the kinetics of the process, but were found to poorly describe the kinetics, which was believed to be a result of not accounting for the influence of intermediates. A new kinetic model is proposed to account for intermediate formation, which described the experimental data better. In addition, the incorporation of acoustic cavitation (AC) with photocatalysis (PC) was tested for DiBP degradation. The hybrid process enhanced the DiBP degradation rate and a synergistic index of 1.5 and 2.2 observed for TiO2 and ZnO respectively. The effect of pH on DiBP degradation was investigated and it showed that on both photocatalysts, reaction rates were higher when pH was greater than the point of zero charge for the photocatalyst. These results demonstrated the feasibility of photocatalysis for DiBP removal and the potential of AC to enhance the PC process for removal of phthalates from water. This new kinetic model proposed will be useful for the design of AOP based water treatment as it predicts the kinetics of the process more accurately than the commonly used pseudo first order kinetic model.