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The fungal metabolite 3-hydroxyanthranilic acid (3-HAA) was used as a redox mediator with the aim of increasing dye degradation by Fenton oxidative processes (Fe2+/H2O2, Fe3+/H2O2). Its Fe3+-reducing activity can enhance the generation of reactive oxygen species as HO● radicals. Initially, the influence of 3-HAA on decolorization kinetics of five dyes (methylene blue, chromotrope 2R, methyl orange, phenol red, and safranin T) was investigated using decolorization data from a previous work conducted by the present research group. Fe3+-containing reaction data were well fitted with first-order and mainly second-order kinetic models, whereas the BMG (Behnajady, Modirshahla and Ghanbary) model obtained optimal fit to Fe2+. Improvements in kinetic parameters (i.e., apparent rate constants and maximum oxidation capacity) were observed with the addition of 3-HAA. In another set of experiments, a decrease in apparent activation energy was observed due to introducing 3-HAA into reactions containing either Fe2+ or Fe3+ in order to decolorize phenol red at different temperatures. This indicates that the redox mediator decreases the energy barrier so as to allow reactions to occur. Thus, based on recent experiments and the reaction kinetics models evaluated herein, pro-oxidant properties have been observed for 3-HAA in Fenton processes.

Recebido em 31/07/2018; aceito em 18/10/2018; publicado na web em 06/12/2018 A KINETIC STUDY ABOUT THE INFLUENCE OF PHENOLIC MEDIATORS IN THE DECOLORIZATION OF DIFFERENT DYES BY FENTON SYSTEMS.The present work evaluated the influence of phenolic mediators (five dihydroxybenzenes and gallic acid) on the decolorization kinetics of phenol red, chromotrope 2R, and methylene blue by Fenton systems. The reactions were performed with H 2 O 2 , iron salts as catalysts, and the absence or presence of phenolic mediators. Based on the decolorization data from previous study of our group, the 1 st and 2 nd order kinetic models were analyzed, as well as the alternative BMG model. It was found that the mediators accelerated the reactions, based in 1 st and 2 nd order kinetic models. Reactions containing Fe 2+ fitted better to the BMG model, while reactions containing Fe 3+ fitted better to the 2 nd order kinetic model, independent of mediators. Based on the three evaluated kinetic models, pro-oxidant properties were observed for the mediators in Fenton systems.

RESUMO-O presente trabalho avaliou a influência de diferentes mediadores fenólicos individualmente (di-hidroxibenzenos e ácido gálico) na cinética de descoloração do corante alaranjado de metila por reagentes Fenton (Fe/H 2 O 2). As reações foram realizadas com sais de Fe 2+ ou Fe 3+ , H 2 O 2 , na ausência e presença de seis mediadores fenólicos. Com base nos dados de descoloração, foram analisados os modelos cinéticos de 1 a e 2 a ordens, além do modelo alternativo BMG. Constatou-se que os compostos fenólicos aumentaram a velocidade das reações promovendo maiores porcentagens de descoloração do corante. As reações na presença de mediadores fenólicos se adequaram bem aos três modelos propostos, com exceção do sistema Fe 3+ /H 2 O 2 /mediadores fenólicos para o modelo BMG, enquanto para as reações sem mediadores somente esse último modelo foi apropriado.

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