The Biocatalytic Degradation of Organic Dyes Using Laccase Immobilized Magnetic Nanoparticles

Free laccase has limitations for its use in industrial applications that require laccase immobilization on proper support, to improve its catalytic activity. Herein, the nanoparticles of magnetic iron oxide (Fe3O4) and copper ferrite (CuFe2O4) were successfully used as support for the immobilization of free laccase, using glutaraldehyde as a cross-linker. The immobilization conditions of laccase on the surface of nanoparticles were optimized to reach the maximum activity of the immobilized enzyme. The synthesized free nanoparticles and the nanoparticle-immobilized laccase were characterized using different techniques, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), vibrating sample magnetometer (VSM), and thermogravimetric analysis (TGA). CuFe2O4 nanoparticles, as support, enhanced laccase activity compared to free laccase and Fe3O4 nanoparticle-immobilized laccase that appeared during the study of pH, temperature, and storage stability on free and immobilized laccase. The CuFe2O4 and Fe3O4 nanoparticle-immobilized laccase showed superior activity in a wide pH range, temperature range, and storage period, up to 20 days at 4.0 °C, when compared to free laccase. Additionally, the synthesized nanobiocatalysts were examined and optimized for the biodegradation of the anionic dye Direct Red 23 (DR23). HPLC analysis was used to confirm the dye degradation. The reusability of immobilized laccases for the biodegradation of DR23 dye was investigated for up to six successive cycles, with a decolorization efficiency over 70.0%, which indicated good reusability and excellent stability.