Decolorization of dyes with different molecular properties using free and immobilized laccases from Trametes versicolor

Abstract

Laccases from Trametes versicolor have been used for the decolorization of acid and reactive dye solutions. The dyes considered were the acid orange 7 (AO7), acid blue 74 (AB74), reactive red 2 (RR2) and reactive black 5 (RB5). The decolorization of dye solutions was performed in batch systems under constant agitation at 30°C, using both free laccases and laccases immobilized on a mesoporous carbon obtained from pecan shells. Results obtained pointed out that the biocatalysts tested are more effective in the decolorization of acid dyes (AO7 and AB74), with more than 90% of decolorization percentages attained, than reactive dyes. Furthermore, the laccase used in this study, either freely dissolved or supported on the carbon materials, was inactive towards RB5, which was the larger dye molecule (992gmol−1). Immobilization of the laccase on the mesoporous carbons brought about a considerable decrease of their activity. However, an enzyme stabilization effect was also observed as the activity of the supported laccase was maintained over a wide pH span. Finally, the combination of spectrophotometric and chromatographic (HPLC) techniques allowed us to get a more precise picture of the influence of adsorption/oxidation mechanisms during the degradation of dyes by the supported enzymes.