Synthesis of Porous CoFe₂O₄ and Its Application as a Peroxidase Mimetic for Colorimetric Detection of H₂O₂ and Organic Pollutant Degradation

Abstract

Porous CoFe₂O₄ was prepared via a simple and controllable method to develop a low-cost, high-efficiency, and good-stability nanozyme. The morphology and microstructure of the obtained CoFe₂O₄ was investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), specific surface area and pore analysis, and Raman spectroscopy. The results show that the annealing temperature has an important effect on the crystallinity, grain size, and specific surface area of CoFe₂O₄. CoFe₂O₄ obtained at 300 °C (CF300) exhibits the largest surface area (up to 204.1 m² g^−1) and the smallest grain size. The peroxidase-like activity of CoFe₂O₄ was further verified based on the oxidation of peroxidase substrate 3,3’,5,5’-tetramethylbenzidine (TMB) in the presence of H₂O₂. The best peroxidase-like activity for CF300 should be ascribed to its largest surface area and smallest grain size. On this basis, an effective method of colorimetric detection H₂O₂ was established. In addition, the porous CoFe₂O₄ was also used for the catalytic oxidation of methylene blue (MB), indicating potential applications in pollutant removal and water treatment.

Keywords: CoFe2O4; artificial enzyme mimetics; hydrogen peroxide; peroxidase-like activity.

Figure 1

(A) XRD patterns and (B) Raman spectra of CoFe₂O₄ prepared at different temperatures.

Figure 2

(A) SEM image of CF300 and (B) EDX elemental mappings.

Figure 3

Typical images of (A) CF300; (B) CF400; (C) CF500; (D) CF600; and (E); CF700 (F); HRTEM image of CF300, and the inset in (F) is the SAED pattern.

Figure 4

XPS spectra of CF300: (A) survey spectrum, high resolution XPS spectra of (B) Co 2p, (C) Fe 2p, and (D) O 1s.

Figure 5

(A) N₂ adsorption/desorption isotherms and (B) pore size distribution of the porous CoFe₂O₄.

Figure 6

(A) UV-vis absorption spectra and (B) color changes in different reaction systems (a. TMB + CF400; b. H₂O₂ + CF400; c. H₂O₂ + TMB; d. TMB + H₂O₂ + CF400); (C) UV-vis absorption spectra and (D) color changes in the presence of different CoFe₂O₄ samples (a. CF300; b. CF400; c. CF500; d. CF600; e. CF700).

Scheme 1

Schematic illustration of peroxidase-like activity for CF300.

Figure 7

(A) Time-dependence absorbance at 652 nm of the 0.08 mM TMB reaction solution in the absence or presence of different doses of CF300 in 20 mM PBS (pH = 3.0) with 0.8 mM H₂O₂ at room temperature. (B) Time-dependence absorbance at 652 nm of the 0.4 mM TMB reaction solution in the absence or presence of different concentrations of H₂O₂ in 20 mM PBS (pH = 3.0) with 20 μg/mL CF300 at room temperature. Dependence of peroxidase-like activity of CF300 on pH (C) and temperature (D).

Figure 8

Time-dependent absorbance at 652 nm of the 0.4 mM TMB reaction solutions in the absence or presence of scavengers (IPA) in 20 mM PBS (pH = 3) with 20 μg/mL CF300 and 0.8 mM H₂O₂.

Figure 9

Steady-state kinetic assays of CF300, the reaction velocity (v) was measured using 20 μg/mL of CF300 in 20 mM PBS (pH = 3) at room temperature. The TMB concentration was varied and the concentration of H₂O₂ was 4 mM (A); the H₂O₂ concentration was varied and the concentration of TMB was 0.4 mM (B); and the double-reciprocal plots of peroxidase-like activity of CF300 with a fixed concentration of one substrate relative to varying concentration of the other substrate (C,D).

Figure 10

A concentration response curve H₂O₂ detection. Inset: the linear calibration plot.

Figure 11

(A) UV-vis spectra obtained during the MB oxidative degradation over CF300; and (B) the MB degradation rate at various reaction time.