Immobilization of horseradish peroxidase on Fe3O4 nanoparticles for enzymatic removal of endocrine disrupting chemicals

The modified Fe3O4 nanoparticles were used as a support for the immobilization of horseradish peroxidase (HRP). The immobilized enzyme (HRP@Fe3O4) was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier-transform infrared spectrometer (FTIR), and vibration sample magnetometer (VSM). According to the results, the optimum concentration of glutaraldehyde (GA) and agitation time were 300 μL and 7 h. HRP was well loaded on the surface of the Fe3O4. There was no change in the crystal structure of HRP@Fe3O4 compared with Fe3O4. The removals of bisphenol A (BPA) and 17α-ethinylestradiol (EE2) using HRP@Fe3O4 had been investigated. The degradation efficiencies of BPA and EE2 catalyzed by HRP@Fe3O4 were higher than that of soluble HRP. In addition, HRP@Fe3O4 can be reused through magnetic separation. After the fifth repeated use, the removal efficiencies of BPA and EE2 were up to 56% and 48%, respectively. Batch studies of catalyzed oxidation and coagulation on the degradation of BPA and EE2 in the presence of humic acid (HA) were also investigated. The order of the removal efficiencies was HRP+PACl (polyaluminum chloride)+SDS (lauryl sodium sulfate)>HRP+PACl>HRP>HRP+PAM (Polyacrylamide)>HRP+PAM+SDS. The coagulation effect of HRP@Fe3O4 and PACl was better than that of HRP@Fe3O4 and PAM. The removals of BPA and EE2 were 90.3% and 64.5% by use HRP@Fe3O4 and PACl as coagulant, while the removals were 78.7% and 57.6% by use HRP@Fe3O4 and PAM as coagulant. SDS had a positive effect on PACl, while a negative effect on PAM. Moreover, the products generated by enzymatic oxidation reaction can be effectively removed after coagulation.