Carbon-based magnetic nanostructures in several instances have resulted in improved physicochemical and catalytic properties when compared to multi-wall carbon nanotubes (MWCNTs) and magnetic nanoparticles. In this study, magnetic MWCNTs with a structure of NixZnxFe2O4/MWCNT as peroxidase mimics were fabricated by the one-pot hydrothermal method. The structure, composition and morphology of the nanocomposites were characterized with X-ray diffraction (XRD), Fourier transform infrared spectroscopy and transmission electron microscopy. The magnetic properties were investigated with a vibrating sample magnetometer. The peroxidase-like catalytic activity of the nanocomposites was investigated by colorimetric and electrochemical tests with 3,3´,5,5´-tetramethylbenzidine (TMB) and H2O2 as the substrates. The results show that the synthesis of the nanocomposites was successfully performed. XRD analysis confirmed the crystalline structures of the NixZnxFe2O4/ MWCNT nanohybrids and MWCNTs. The main peaks of the NixZnxFe2O4/MWCNTs crystals were presented. The Ni0.25Zn0.25Fe2O4/MWCNT and Ni0.5Zn0.5Fe2O4/MWCNT nanocatalysts showed nearly similar physicochemical properties, but the Ni0.5Zn0.5Fe2O4/MWCNT nanocatalyst was more appropriate than the Ni0.25Zn0.25Fe2O4/MWCNT nanocatalyst in terms of the magnetic properties and catalytic activity. The optimum peroxidase-like activity of the nanocatalysts was obtained at pH 3.0. The Ni0.5Zn0.5Fe2O4/MWCNT nanocatalyst exhibited a good peroxidase-like activity. These magnetic nanocatalysts can be suitable candidates for future enzyme-based applications such as the detection of glucose and H2O2.

Abstract
 1. Introduction
 2. Experimental
  2.1. Materials and methods
  2.2. Synthesis of the NixZnxFe2O4/MWCNTnanocomposites
  2.3. Characterization of the nanocomposites
  2.4. Colorimetric assay of the peroxidase-likeactivity of the nanocomposites
  2.5. Electrochemical analysis
 3. Results and Discussion
  3.1. Characterization of the NixZnxFe2O4/MWCNTnanocomposites
  3.2. Colorimetric assay of the peroxidase-likeactivity of the NixZnxFe2O4/MWCNT nanocomposites
  3.3. The effect of pH on the nanocatalyst activity
  3.4. Effect of the H2O2 amount
  3.5. Electrochemical analysis of the electrocatalysisactivity of the NixZnxFe2O4/MWCNTnanocomposites
 4. Conclusions
 Conflict of Interest
 Acknowledgements
 References

• Navvabeh Salarizadeh(Department of Biochemistry and Biophysics, Education and Research Center of Science and Biotechnology, Malek Ashtar Universityof Technology)
• Minoo Sadri(Department of Biochemistry and Biophysics, Education and Research Center of Science and Biotechnology, Malek Ashtar Universityof Technology) Corresponding Author
• Hassan Hosseini(Department of Chemistry, Faculty of Sciences, Imam Hossein University)
• Reza. H. Sajedi(Department of Biochemistry, Faculty of Biological Sciences, Tarbiat Modares University)