Catalytic potential of laccase immobilized on transition metal oxides nanomaterials: Degradation of alizarin red S dye

Recently, nanoparticle-based immobilization of biocatalytic systems is getting interested in bioremediation efficiency. Therefore, green synthesized ZnO (< 50 nm) and MnO2 (< 10 nm) nanoparticles were chelated with Cu2+ to immobilize laccase (Lac) through metal affinity adsorption. Nanospheres (similar to 300 nm) of lac-ZnO and nanoclusters of lac-MnO2(< 50 nm) were confirmed by SEM. Lac was strongly immobilized on ZnO followed by MnO2 and their activities were doubled than free lac prepared by solid state fermentation. Further, catalytic potential of lac-ZnO and lac-MnO2 was examined for in vitro degradation of alizarin red S dye in simulated-water. Degradation of dye was highest with lac-ZnO (95%) followed by lac-MnO2 (85%) and free lac (49%) at initial pH (similar to 7.0), dye (20 mg/L) and catalyst (50 mg). Control experiment indicated that lac-ZnO was the better catalyst than ZnO and free lac. MnO2 seemed to enhance stability and activity of lac-MnO2 over free lac. Moreover, a combination of nanomaterial and enzyme is required for achieving biocompatibility and inert condition without denaturing of the enzyme. Overall, ZnO and MnO2 are potential for large-scale lac immobilization with improved properties and reuse. Lac-ZnO and lac-MnO2 may be used as important adsorbents in waste water treatment with a bright future.