Immobilization of horseradish peroxidase on polyglycerol-functionalized magnetic Fe3O4/nanodiamond nanocomposites and its application in phenol biodegradation

In this study, Fe3O4/nanodiamond nanocomposites (MND) were synthesized by polyglycerol-mediated covalent bonding. The horseradish peroxidase (HRP) was successfully immobilized on PG layer of MND by interaction between functional groups of MND and HRP, where the HRP molecules became tridimensionally connected outside the MND. The physicochemical properties of MND were analyzed by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy measurements, vibrating sample magnetometer, Fourier transform infrared spectroscopy and zeta potential. The optimal conditions for the immobilization of HRP by MND are 7 mg/L, 35 degrees C and 3 h, respectively. Then, the effects of temperature, pH and storage time on the activity of immobilized enzyme and free enzyme were studied. The results showed that the relative activities of immobilized enzymes were higher than free enzymes at different temperatures, pH and storage time. In addition, the reusability experiments of immobilized enzymes showed that after six cycles, the immobilized HRP retained a relative activity of 75%. Applied to the removal of phenol, the effects of phenol concentration, H2O2/phenol molar concentration, immobilized HRP concentration and temperature on phenol removal were investigated. The results displayed that the removal efficiency of phenol reached a maximum when the phenol concentration was 75 mg/L, the ratio of H2O2 to phenol was 1, the immobilized HRP concentration was 0.25 mg/L and the temperature was 30 degrees C. The above results indicate that the immobilized HRP exhibits high removal efficiency and has great potential for removing phenol.