Photocatalytic degradation of organic dyes in the presence of nanostructured titanium dioxide: Influence of the chemical structure of dyes

Synthetic dyes are a major part of our life as they are found in the various products ranging from clothes to leather accessories to furniture. These carcinogenic compounds are the major constituents of the industrial effluents. Various approaches have been developed to remove organic dyes from the natural environment. Over the past few years, there has been an enormous amount of research with advanced oxidation processes (AOPs) as an effective method of wastewater treatment. Among AOPs, heterogeneous photocatalytic process using TiO₂ nanomaterials appears as the most emerging destructive technology due to its cost effectiveness and the catalyst inert nature and photostability. This review deals with the photocatalytic degradation of organic dyes containing different functionalities using TiO₂ nanomaterials in aqueous solution. It first discusses the photocatalytic properties of nanostructured TiO₂. The photocatalytic degradation rate strongly depends on the basic structure of the molecule and the nature of auxiliary groups attached to the aromatic nuclei of the dyes. So, this review then explains the influence of structure of dyes on their photocatalytic degradation rates. The influences of different substitutes such as alkyl side chains, methyl, nitrate, hydroxyl and carboxylic groups as well as the presence of chloro atom have been discussed in detail.