Oxidative degradation of Acid Red 1 in aqueous medium

• Oxidative degradation of Acid Red 1 in aqueous medium is investigated.
• Complete decolorization and a high level of mineralization is achieved.
• Pulse radiolysis technique is used to probe kinetics and spectroscopic details of transient intermediates.
• Stable intermediate products were identified by LC-Q-TOF-MS.

The oxidative degradation of an azo dye, Acid Red1 (AR1), in aqueous solution using Advanced Oxidation Processes (AOPs), has been investigated. The fast reaction kinetics and the details on the short-lived intermediate radicals from the reaction of hydroxyl radicals (OH) with AR1 were investigated by pulse radiolysis technique. Three selected AOPs such as Fenton and photo Fenton reactions, ferric perchlorate (FPC) photolysis and H2O2 photolysis, are found to be successful in the complete decolorization within a short time of treatment. The decolorization is understood as a result of destruction of the most reactive conjugated electronic position having CNNC bridge. A considerable amount of TOC reduction is also observed using these methodologies. A second order rate constant of 3.9 × 109 dm3 mol−1 s−1 is determined for the reaction of OH with AR1 by pulse radiolysis. The transient absorption spectra obtained from the reaction of OH is different from the reaction of the specific one electron oxidants such as N3, SO4- and O-O-. OH reacts with the dye by addition to form OH-adducts with aromatic ring as well as with the azo bond. Other oxidizing radicals undergo electron transfer to form the corresponding naphthoxyl type radical. Some of the stable intermediate products were identified by LC-Q-TOF-MS. These products are the result of hydroxylation of azo bond and ring cleavage. A plausible reaction mechanism for the degradation is elucidated from these results. The significant decolorization and mineralization demonstrate the potential application of these methodologies for the treatment of azo dyes containing effluents.