Redox mediator system: Expanding the potential of laccase-like nanozymes towards pollutant remediation

• Redox mediator system boosts pollutant remediation with laccase-like nanozymes. • MnFe₂O₄, Mn₃O₄, and CuO synergy boosts nanocomposite's laccase-like activity. • Natural redox mediators enhance degradation efficiency of methyl orange. • Nanozyme plus acetosyringone achieved near-complete degradation of methyl orange. • Multimetallic nanozymes have higher catalytic power than natural laccase. This study investigates the use of a redox mediator system to enhance the pollutant remediation capabilities of laccase-like nanozymes. A three-phase magnetic nanocomposite, composed of MnFe₂O₄, Mn₃O₄, and CuO in various precursor ratios, was synthesized. The 1:2:2 nanocomposite demonstrated the highest specific laccase-like activity, with values of 8.9 U mg⁻¹ at pH 4 and 9.2 U mg⁻¹ at pH 5. In contrast, single-phase nanozymes exhibited much lower activities. Cyclic voltammetry (CV) revealed that the 1:2:2 composite had a MnFe₂O₄ core and a Mn₃O₄|CuO alloy shell. The study also evaluated natural and synthetic redox mediators—acetosyringone, syringaldehyde, vanillin, and 1-hydroxybenzotriazole (HBT)—for their effect on methyl orange degradation. Acetosyringone was the most effective, achieving near-complete degradation at 50 µM and above, resulting in a 6.3-fold increase in degradation rate compared to treatments without mediators. Syringaldehyde and vanillin also enhanced degradation, with syringaldehyde reaching near-complete degradation at 75 µM and 100 µM, while vanillin required higher concentrations for 80 % degradation. CV was used to analyze the electrochemical properties of reactions involving the 1:2:2 nanocomposite and redox mediators. These findings highlight the potential of combining nanozymes with natural redox mediators for improved degradation of harmful compounds in environmental remediation. While laccase-like nanozymes have typically been used for sensor applications, this study opens new possibilities for their use in environmental challenges and catalytic systems.