Light Induced Oxidative Degradation Studies of Organic Dyes and Their Intermediates

Abstract

ABSTRACT Problem Formulation Reactive dyes are the largest single group of dyes used in the textile industry and have been selected for our study because they are difficult to eliminate by biodegradation and sludge adsorption techniques in the wastewater treatment plants. The work on photocatalytic oxidative degradation studies of reactive dyes in literature is limited as compared to other dyes. Reactive dyes are known to form a covalent bond with the fibre in the dyeing process. This leads to favorable properties such as wash-fastness. However, unfixed dye reacts with water to form hydrolyzed or an oxo-dye intermediate that has lost its bonding capacity and thus cannot be reused. Therefore dye recovery is not an option with reactive dyes and the treatment process must lead to final destruction or disposal of these contaminants. One method to remove reactive dyes from the wastewater is sorption into sorbents in fixed bed filters but no successful regeneration has been reported. Moreover, adsorption transfers the toxic dyes from one medium to the other without converting it to harmless non-toxic substances. The application of novel treatment methods encompasses investigations of advanced oxidation processes (AOP s), which are characterized by production of the hydroxyl radical (OH) as a primary oxidant. Examples of AOP s include the use of (H2O2/UV), semiconductor photocatalysis, ozonolysis and ultrasonic irradiation (sonolysis), (ultrasound/O3) as important segmental or parallel processes and are found to enhance OH radical production leading to higher oxidation rates and organic matter mineralization. In this work, we investigated the photocatalytic oxidative degradation and discoloration of various reactive dyes and dye intermediates using light (UV/visible)/semiconductor catalyst by optimizing the operational parameters to ensure the rapid and complete transformation of the toxic organic compounds to benign chemicals.