Abstract
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.
Highlights
The economy and development of the present world are essentially dependent on the industries
The spinel ferrite was confirmed due to the clear bands that appeared in the region of 400.0 to 600.0 cm−1 [32], which confirms the X-ray diffraction (XRD) results
Stretching vibrations of N–H and Si–O–Fe that appeared as new bands in the spectra of nanoparticle-immobilized laccase were observed at 3481 and 1201 cm−1, respectively [33], and appeared due to the immobilization that followed the silanization
Summary
The economy and development of the present world are essentially dependent on the industries. Dyes that are released into the environment through different printing and textile activities are an example of these dangerous pollutants [4,5] These dyes were removed from contaminated industrial wastewater via several biological and chemical methods. Besides the non-reusability and low stability of soluble laccase, it is very sensitive towards denaturing agents that retard its function and hinder its use in real sample applications These problems can be resolved by the laccase hold method on different types of supports, to enhance enzyme stability. Many studies reported the successful immobilization of laccase on the surface of nanomaterials, to improve its stability and catalytic properties, for the removal of the dye from aqueous media. The kinetics and reusability of the nanobiocatalysts for the removal of the dye were determined
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