Immobilization of horseradish peroxidase on Fe3O4/nanotubes composites for Biocatalysis-degradation of phenol

Magnetic Fe3O4 was successfully combined with carbon nanotubes by hydrothermal reaction to form Fe3O4/nanotubes composites. The properties of composites were evaluated by characterization of TEM, EDS, FT-IR, XRD, XPS and VSM. In order to protect ecological environment, the composite was used as carrier to immobilize horseradish peroxidase so as to remove phenols in wastewater by immobilized enzyme. The results of characterization demonstrated that the magnetic sphere, which was about 340 nm in diameter, was formed on the wall of carbon nanotubes. APTES was simultaneously modified to the surface of magnetic sphere and carbon nanotubes, and the saturation magnetization value of carriers was 45.81 emu/g. Then, the optimal conditions of immobilized enzyme were investigated by the concentration of glutaraldehyde, the cross-linking time of glutaraldehyde, the immobilization time and the optimum temperature of immobilized enzyme. Under the optimum conditions of immobilized enzyme, compared with free enzyme, the activity of immobilized enzyme was more stable within certain range of temperature and pH value. Moreover, the immobilized enzyme activity also had a good effect during long time storage. It also could be separated by external magnet and reached 65% of the initial activity after 6 times, which revealed good reuse capacity.