Photocatalytic decolorization of methylene blue using TiO2/UV system enhanced by air sparging

Abstract

In this work, the photocatalytic degradation of wastewater containing an organic dye (Methylene Blue) was investigated in a slurry-type reactor enhanced by air sparging. Commercial TiO2 was used as the photocatalyst which was activated using ultraviolet irradiation. The effects of initial dye concentration, photocatalyst loading, solution pH and air’s superficial velocity on the degradation efficiency were evaluated. The degradation efficiency of the dye increased with increasing the pH of the solution and decreasing the initial dye concentration. Moreover, increasing the catalyst loading up to 1 g/l showed an improvement in the degradation efficiency. However, the efficiency deteriorated with a further increase in the catalyst loading. Introducing air into the reaction medium in the form of micro-bubbles significantly improved the degradation efficiency by providing oxygen molecules required for the oxidation reaction. Furthermore, these air bubbles created turbulence in the reaction medium, which resulted in the enhancement of the mass transfer rate of dye molecules from the solution bulk to the catalyst surface with a subsequent increase in the degradation efficiency. A complete decolorization of 10 ppm dye solution was achieved in the neutral solution (pH = 7) with a catalyst loading of 1 g/l and an air superficial velocity around 2 cm/s. The effect of the air superficial velocity on the degradation reaction kinetics was investigated and the reaction was found to follow the pseudo second order rate law. Keywords: Photocatalysis, TiO2, Air sparging, Methylene blue, Ultraviolet