Catalytic phenol removal using entrapped cross-linked laccase aggregates

Laccase was immobilized using a combinatorial strategy of cross-linking and entrapping in mesoporous silica to prepare entrapped enzyme species including simply adsorbed, entrapped cross-linked enzyme (E-CLE) and entrapped cross-linked enzyme aggregate (E-CLEA) to explore their potential in phenol removal. Parameters including pH, temperature, time and cross-linker concentration were optimized to achieve an immobilized product with highest laccase specific activity. Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the immobilization products. The storage and operational stability analysis were also carried out. Accordingly, E-CLEAs showed improved thermal and pH stabilities and activity retention in hydrophobic and hydrophilic solvents. Moreover, based on the resulted half-lives (t1/2) for free and insoluble laccases, the improved storage stability is reported for E-CLEAs at 1.71 and 20.88 days for them, respectively. In addition, the immobilized biocatalyst exhibited good operational stability and reusability through maintaining up to 79% of its initial activity after 20 cycles of successive operations. In conclusion, E-CLEAs have catalytic potential in efficient phenol removal and advantages of the insolubilized form of laccase as E-CLEAs make it an appealing system in applications such as possible treatment of phenol-contaminated wastewater.