Effect of Dye Structure on the Photodegradation Kinetic Using TiO<sub>2</sub> Nanoparticles

Abstract

In this study the effect of pH, adsorption behavior and the chemical struc-tures of two dyes (Methyl Orange and Bromothymol Blue) on the photo-degradation rate constant, was investigated. Adsorption isotherm shows that the adsorption amount of dyes on TiO2 surface is highly related to the pH of the solution and to the pKa of each dye. In acidic medium the adsorption percentage of Methyl Orange on TiO2 surface was 76% facing 5% for Bromothymol Blue. The kinetic study shows compatibility between the degradation rate constant and the adsorption percentage on the surface. In basic medium the adsorption percentage of Methyl orange and Bromothymol Blue is similar while the degradation rate of Methyl orange is two times faster than that of Bromothymol Blue which reveals the role of chemical structure in the photodegradation rate.