Impact of pH on the kinetics of photocatalytic oxidation of 2,4-dichlorophenoxy acetic acid in a fluidized bed photocatalytic reactor

Abstract

The impact of pH on the kinetics of photocatalytic oxidation of 2,4-dichlorophenoxy acetic acid (2,4-D) was investigated. Experiments were performed in fluidized bed photocatalytic reactor using TiO2 photocatalyst spheres. The rate of oxidation was affected by the solution pH. In acidic medium, according to the kinetic model, the rate of oxidation was higher because the rate constant was directly related to UV intensity (I); whereas this relationship reduced to a functional square root (i.e., I1/2) at pH 7. In addition, pH resulted in changing the photocatalytic oxidation mechanism. At pH 7, the photocatalytic oxidation took place away from the photocatalyst surface, the oxidation rate followed first order kinetics. Under acidic condition, on the other hand, the oxidation mostly took place on the surface of photocatalyst and the rate of oxidation followed a combination of the Langmuir-Hinshelwood and first order kinetic models.