Photocatalytic degradation of Azo dyes in aqueous solution using mesoporous-assembled TiO2 nancorystal photocatalyst

Abstract

Azo compounds are an important class of synthetic dyes and are characterized by the presence of one or more azo groups (-N=N-) linked between aromatic rings. The release of this coloring agent causes wastewater problems. Photocatalysis is an efficient technique for removing dye pollutants because of several advantages it has. In this work, several operational parameters affecting the photocatalytic degradation of mixtures of two azo dyes—Acid Yellow 23 (AY) with 1 azo group and Acid Black 1 (AB) with 2 azo groups—including types of dye, initial dye concentration, photocatalyst dosage, dissolved oxygen level, initial solution pH, and water hardness concentration, were investigated by using a mesoporous-assembled TiO₂ nanocrystal photocatalyst. The experimental results showed that for the mixture of AY and AB, the λ[subscript max] values of both dyes from UV-Visible spectroscopy did not change upon their mixing at different irradiation times during the course of photocatalytic degradation. At AY and AB concentrations of 2.5 and 5 mg/1, the optimum conditions were a photocatalyst dosage of 10 g/1, a dissolved oxygen level of 37.7 mg/1, and an initial solution pH of 4.5, providing the highest degradation efficiency of azo dyes. Moreover, even though water hardness negatively affected the degradation efficiency, the pH adjustment could be used to enhance the degradation of dyes present in hard solution.