Laccase immobilized on magnetic nanoparticles by dopamine polymerization for 4-chlorophenol removal

In this work, a new immobilization method based on dopamine (DA) self-polymerization was developed for laccase immobilization on magnetic nanoparticles (Fe₃O₄ NPs). To optimize the immobilization condition including reaction pH, DA concentration and enzyme concentration, a central composite response surface method was applied. The optimal condition was determined as pH value of 5.92, laccase concentration of 0.25 mg mL ⁻¹ and DA concentration of 12.74 mg mL⁻¹, under which a high enzyme activity recovery of 88.17% was obtained. By comparing with free laccase, the stabilities of immobilized laccase towards pH, thermostability, storage were enhanced significantly. Approximately 60% of relative activity for immobilized laccase was remained after being incubated for 6 h at 50 °C, but the free laccase only remained 25%. After 40 days of storage at 4 °C, the laccase immobilized by DA kept about 89% of its original activity, but the free laccase only retained 48%. After recycled 10 times, the relative activity of immobilized laccase still retained 70%. The immobilized laccase was then applied to catalyze the degradation of 4-chlorophenol (4-CP), 86% percentage of 4-CP was removed within 2 h. After degraded 10 times, the relative activity of immobilized laccase still remained 64% of its initial activity, which exhibits an excellent reusability and operational stability.