Rational Design of Mn-APTES/1-Methylimidazole Nanozymes: Enhanced Laccase-like Activity at Near-Neutral pH for Environmental Remediation

Natural laccases are a widely reported option for pollutant degradation; however, their widespread application is severely restricted by high production costs, limited storage stability, and rapid inactivation at the neutral pH typical of wastewater treatment plants. To overcome these limitations, we rationally designed manganese-based nanozymes (Mn-APTES/1MeIm) that mimic natural metal-histidine coordination within a protective siloxane network. Optimization via Response Surface Methodology produced two variants, Mn-APTES/1MeIm-6 and Mn-APTES/1MeIm-7, revealing distinct synthesis mechanisms: catalytic activity at pH 6 is driven by synthesis temperature, whereas activity at pH 7 is controlled by the APTES:1MeIm molar ratio. TEM and XRD analysis confirmed a delaminated aminoclay architecture composed of electron-transparent nanosheets, while FTIR verified Mn-N coordination through characteristic blue shifts. The optimized nanozymes retained robust activity, exhibiting maximum reaction velocities of 4.331 µM min^-1 (Mn-APTES/1MeIm-6) and 1.71 µM min^-1 (Mn-APTES/1MeIm-7), whereas <i>Trametes versicolor</i> laccase was practically inactive. Practically, Mn-APTES/1MeIm-6 achieved 75% degradation of oxytetracycline in 120 min without detectable manganese leaching, significantly outperforming the natural enzyme (<13%). These findings present a robust, pH-stable alternative for sustainable environmental remediation.