Biocatalytic enhancement of laccase immobilized on ZnFe2O4 nanoparticles and its application for degradation of textile dyes

Efficient and convenient treatment of industrial dyeing wastewater is of a great significance to guarantee human and animal health. This work presented the enhanced catalytic activity at pH 3.0 of laccase immobilized on amino-functionalized ZnFe2O4 nanoparticles (ZnFe2O4-laccase) and its application for degradation of textile dyes. Due to the existence of a large number of oxygen vacancies on the surface of the ZnFe2O4 nanoparticles, negative ions accumulated on the magnetic carriers, which resulted in a harsh optimal pH value of the ZnFe2O4-laccase. Laccase activity assays revealed that the ZnFe2O4-laccase possessed superior pH and thermal stabilities, excellent reusability, and noticeable organic solvent tolerance. Meanwhile, the ZnFe2O4-laccase presented efficient and sustainable degradation of high concentrations of textile dyes. The initial decoloration efficiencies of malachite green (MG), brilliant green (BG), azophloxine, crystal violet (CV), reactive blue 19 (RB19) and procion red MX-5B were approximately 99.1%, 95.0%, 93.3%, 87.4%, 86.1% and 85.3%, respectively. After 10 consecutive reuses, the degradation rates of the textile dyes still maintained about 98.2%, 92.5%, 83.2%, 81.5%, 79.8% and 65.9%, respectively. The excellent dye degradation properties indicate that the ZnFe2O4-laccase has a technical application in high concentrations of dyestuffs treatment.