Tyrosinase immobilized poly(AAm–EH) cryogels for phenolic wastewater treatment

Tyrosinase was immobilized on supermacroporous poly(acrylamide–1,2-epoxy-5-hexene) (poly(AAm–EH)) cryogels via covalent attachment through the enzyme’s epoxy functional groups. The structural, morphological and elemental properties of the fabricated cryogels were characterized in detail using ATR (attenuated total reflection)-FTIR (Fourier transform infra-red spectroscopy), SEM (scanning electron microscopy) and energy-dispersive X-ray (EDX) spectroscopy. Biocatalytic assays revealed that optimal activity of both free and immobilized tyrosinase was exhibited at a pH of 7.0 and a temperature of 35 °C. However, the immobilized enzyme exhibited a marked enhancement in thermal stability at 55 °C in comparison with its free counterpart, owing to the protective microenvironment provided by the cryogel matrix. Kinetic evaluations based on the Lineweaver–Burk plot demonstrated a Km (Michaelis–Menten constant) value of 2.15 mM for the immobilized enzyme. The bioreactor was highly efficient at remediating phenolic contaminants, achieving removal rates of 88.1% for phenol, 76.4% for p-chlorophenol, 69.5% for bisphenol A and 56.2% for p-aminophenol within 90 min. In summary, the poly(AAm–EH) cryogel-based bioreactor is a robust, reusable and efficient platform for treating phenolic wastewater.