Preparation, characterization, and enzymatic properties of laccase immobilized on MnO₂ nanoparticles via adsorption method.

Laccase is an environmentally friendly biocatalyst widely used in wastewater treatment, the food industry, and biosensors. However, free laccase is susceptible to environmental factors such as pH and temperature. Immobilizing it on nanomaterials can significantly mitigate these issues. This approach also enhances the reusability of laccase, demonstrating broad application prospects. Four different morphologies of MnO₂ were compared, with δ-MnO₂ (sheet) demonstrating the most effective immobilization effect as a carrier. Under conditions of pH=5, 30 °C, and laccase concentration of 1 mg/L, the reaction achieves optimal immobilization after 4 h of adsorption. Characterization of δ-MnO₂ and immobilized laccase was performed using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The enzymatic properties of immobilized laccase were also investigated. The results indicate that the optimal temperature for immobilized laccase is 75 °C, with an optimal pH of 3. Compared to free laccase, stability has been significantly enhanced. Furthermore, even after 30 days of storage at -4 °C the relative enzyme activity of the immobilized laccase remained as high as 74.51%. The kinetic constants demonstrate that immobilized laccase not only enhances the maximum reaction rate but also significantly improves substrate affinity. Compared to free laccase, the relative enzyme activity of MnO₂-immobilized laccase (MnO₂@Lac) is significantly enhanced. This may be attributed to the synergistic effect between MnO₂ nanoparticles and laccase during substrate conversion. This study creates favorable conditions for the further application of immobilized laccase in the treatment of organic pollutants.