Soybean peroxidase‐catalyzed degradation of a sulfonated dye and its azo‐cleavage product
Amanpreet Kaur, Keith E. Taylor, Nihar Biswas
Abstract
Abstract BACKGROUND The presence of azo dyes in wastewater from the textile industry is a major environmental concern. The dyes not only make water aesthetically unacceptable, but also have severe toxicological concerns. Research into treatment processes for removal of dyes has focused primarily on decolourization and little attention has been focused on analysis of the degradation products, that could plausibly be more toxic than the parent compound. This study focusses on soybean peroxidase (SBP)‐catalyzed treatment of two azo dyes, Methyl Orange (MO) and CI Direct Yellow 12 (DY12) in water, chosen because they lack phenolic and primary anilino functional groups, which are usually expected to form free radicals under peroxidase catalysis. RESULTS DY12 was found not to be a substrate of SBP, but optimized reaction conditions for 0.50 mmol L –1 MO and 1.0 mmol L –1 p ‐anisidine (structurally analogous to 4‐ethoxyaniline, a possible azo‐cleavage product of DY12) achieved ≥95% conversion at exceptionally low minimum effective SBP activities (0.0070 and 0.0018 U mL –1 ) at pH optima of 4.0 and 5.5 and [hydrogen peroxide]/[substrate] of 2 and 1, respectively. CONCLUSIONS Mass spectrometric (MS) analysis for the substrates revealed formation of dimers and trimers for p‐ anisidine. For MO, high‐performance liquid chromatography, UV‐visible spectrophotometry and MS provided evidence of azo‐bond cleavage, hetero‐coupling of the dye with the cleavage product and also self‐coupling of the dye through tertiary amine activation. © 2020 Society of Chemical Industry (SCI)