Effect of inorganic oxidants in photodecolourization of an azo dye

Abstract

Aqueous solutions of the dye Acid Orange 7 were decolourized in the presence of ultraviolet irradiation (UV) and photocatalyst, TiO 2. Decolourization rate was increased in the presence of UV/TiO 2 compared to UV alone. Addition of hydrogen peroxide, H 2O 2, in concentrations ranging from 8.82 × 10 −3 to 7.1 × 10 −2 M to the solution containing pollutant and TiO 2 (0.5 g l −1) resulted in increased rates of decolourization. The rate of dye decolourization using periodate, NaIO 4, (4.76 × 10 −5 to 1 × 10 −3 M) at TiO 2 concentration of 0.5 g l −1 under UV illumination was higher than that for UV/TiO 2/H 2O 2 and increases with periodate concentration. The rate of decolourization of Acid Orange 7 was found to follow first-order kinetics. Reaction rate orders with respect to the oxidant species were 0.51 and 0.8, respectively for H 2O 2 and NaIO 4. Kinetic parameters of the photodecolourization process such as apparent rate constant ( k app) and initial reaction rate ( R initial) and efficiency parameters such as apparent quantum yield ( Q app) and electrical energy per order (EE/O) were estimated and compared for UV/TiO 2, UV/TiO 2/H 2O 2 and UV/TiO 2/IO 4 − catalytic systems.