Abstract:

Objective The discharge of dyeing effluents presents a serious environmental challenge. The release of dye wastewater generated by the textile industry is considered to be the major sources of water pollution. Dyes pose significant obstacles for conventional treatment methods due to their remarkable photolytic stability and resistance to microbial degradation. Moreover, the majority of dyes, along with their degradation byproducts, exhibit toxic, carcinogenic, mutagenic, and allergenic properties that pose significant risks to human health. Consequently, there exists an urgent demand for effective strategies aiming at the removal of dyes from wastewater.

Method Amine-functionalized Fe₃O₄ nanoparticles were synthesized for the immobilization of laccase, aiming at enhancing the efficient degradation of dyes. The morphology, structure, magnetic properties, and surface characteristics of the Fe₃O₄ nanoparticles were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), magnetic measurements, and Fourier transform infrared spectroscopy (FT-IR). The activity assays of laccase, including optimal temperature and pH conditions, thermostability, pH stability, tolerance to metal ions and organic solvents, resistance to inhibitors, and recyclability of the immobilized laccase, were systematically investigated. Additionally, the degradation kinetics and reusability concerning dyes were also evaluated.

Results TEM images revealed that the synthesized Fe₃O₄ nanoparticles exhibited a spherical morphology, with a size range of 110-130 nm. XRD analysis confirmed that the resultant product displayed a cubic crystalline structure characteristic of Fe₃O₄. FT-IR spectra illustrated the presence of abundant amide groups on the surface of these nanoparticles. Magnetic measurements demonstrated that the prepared material possessed ferromagnetic properties, exhibiting a saturation magnetization of 42.3 emu/g. The Bradford protein assay indicated that approximately 3.1 mg of laccase was loaded per gram onto the amino-functionalized Fe₃O₄ nanoparticles. The optimal temperature for both immobilized laccase and free laccase was 50 ℃, the former however exhibited a broader temperature distribution range compared to its free counterpart. The optimal pH for immobilized laccase was 3.0, representing a shift of 1.5 towards acidity when contrasted with the free laccase. After undergoing treatment at 60 ℃ for 10 h, the immobilized laccase retained 71.3% of its initial activity, demonstrating an enhancement of 14.4% over that of the free laccase. Moreover, the pH stability of immobilized laccase showed increased resistance to organic solvents, metal ions, and inhibitors in comparison to its free enzyme counterpart. The immobilized laccase maintained remarkable reusability, preserving 59.3% of its initial activity even after 10 cycles of reuse. Furthermore, the immobilized laccase showcased exceptional efficacy in treating dye wastewater, achieving degradation rates between 81.6% and 98.8% for triphenylmethane, azo, and anthraquinone dyes. The degradation of dyes by the immobilized laccase was a relatively swift process. The initial 30 min interval performed 79.1% to 97.9% of the total degradation achieved. Subsequently, within the span of 60 min, the maximum degradation rate was gradually attained. Additionally, after undergoing 10 consecutive degradation cycles, the efficiency level was kept in the range from 62.2% to 90.5%, underscoring its potential as an effective strategy for biodegrading dye effluents.

Conclusion An innovative method for the synthesis of amino-functionalized Fe₃O₄ nanoparticles has been developed, positioning them as magnetic carriers for laccase immobilization. These magnetic nanoparticles have been thoroughly characterized, demonstrating their promising applicability in studies focused on laccase immobilization. The amino-functionalized Fe₃O₄, can be easily separated using an external magnet and exhibits a straightforward immobilization process along with remarkable loading capacity and catalytic activity for the immobilized laccase. The immobilized laccase demonstrated to possess excellent reusability and enhanced thermal and pH stability, and remarkable organic compounds, inhibitors and metal ions tolerance. Additionally, the immobilized laccase showcases effective and sustainable degradation capabilities for high concentrations of dyes. This highlights the exceptional potential of immobilized laccase in addressing textile wastewater treatment within practical applications.

Key words: immobilized laccase, reusability, stability, anti-polluting, dye, biodegradation, degradation rate, wastewater treatment