Immobilization of laccase on functionalized multiwalled carbon nanotube membranes and application for dye decolorization

Myceliophthora thermophila laccase was covalently immobilized on functionalized multiwalled carbon nanotubes (MWNT) arranged over a supporting membrane to obtain a permeable bio-barrier that could be applied in multibatch or continuous processes. Initially, several supporting materials, namely cellulose nitrate, agarose and polyvinyl alcohol, were evaluated as supports for the MWNT. The maximum enzyme loading of 0.286 U mg-1of MWNT was obtained for cellulose nitrate support supplemented with 0.21 mg MWNT. Immobilized laccase showed good operational stability (above 95% of its initial activity was maintained after 10 cycles of reaction) and exhibited improved stability towards temperature, pH and acetone: for instance, 21% and 49% for free and immobilized laccase, respectively, when incubated in the presence of 20% of acetone (v/v) for 6 h. The immobilized laccase was applied for Reactive Black 5 (RB5) decolorization. Maximum values of RB5 decolorization were observed in the presence of 1-hydroxybenzotriazole as mediator and at pH 5.0, with 68.09 and 84.26% decolorization after 6 and 24 h, respectively.