Synthesis of magnetic graphene-like carbon nitride-cobalt ferrite (g-C3N4/CoFe2O4) nanocomposite for sonocatalytic remediation of toxic organic dyes

Abstract

A novel magnetic g-C₃N₄/CoFe₂O₄ nanocomposite was successfully synthesized by a simple hydrothermal method and applied as a new graphene-like carbon nitride-based sonocatalyst for sonodegradation of pollutant dyes. The as-prepared samples were characterized by using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), X-ray photoelectron spectroscopy (XPS), UV-visible diffuse reflectance spectroscopy (DRS), BET surface area measurements and photoluminescence (PL) spectroscopy. The results indicate that the nanocomposite sample is composed of spherical CoFe₂O₄ nanoparticles adhered to g-C₃N₄ naosheets. The g-C₃N₄/CoFe₂O₄ nanocomposites were used as a new magnetically separable sonocatalyst in H₂O₂-assisted sonodegradation of methylene blue (MB), rhodamine B (RhB) and methyl orange (MO) dyes in aqueous media. The results showed complete degradation (ca. 100%) of dyes within short times (30-35 min). The sonocatalytic activity of graphitic carbon nitride (g-C₃N₄) was greatly enhanced with CoFe₂O₄ modification. Trapping experiments indicated that the g-C₃N₄/CoFe₂O₄ nanocomposites serves as a generator of hydroxyl radical (˙OH) via activation of H₂O₂ for degradation of dyes under ultrasound irradiation. Furthermore, the magnetic sonocatalyst can be separated from solution by an external magnet and reused several times without observable loss of activity. The possible mechanism of sonocatalytic activity was also proposed according to experimental results.

Scheme 1. The preparation process of the g-C₃N₄/CoFe₂O₄ nanocomposite.

Fig. 1. FT-IR spectra of (a) C₃N₄, (b) CoFe₂O₄ and (c) g-C₃N₄/CoFe₂O₄ samples.

Fig. 2. XRD patterns of (a) g-C₃N₄, (b) CoFe₂O₄ and (c) g-C₃N₄/CoFe₂O₄ samples.

Fig. 3. FE-SEM images of (a) CoFe₂O₄, (b) g-C₃N₄, and (c and d) the g-C₃N₄/CoFe₂O₄ hybrid nanocomposite.

Fig. 4. (a) The EDX spectrum and (b) elemental mappings of g-C₃N₄/CoFe₂O₄ nanocomposite.

Fig. 5. The TEM images of the g-C₃N₄/CoFe₂O₄ nanocomposite.

Fig. 6. XPS of the g-C₃N₄/CoFe₂O₄ nanocomposite: (a) survey spectrum, (b) Co 2p spectrum, (c) Fe 2p spectrum, (d) O 1S spectrum, (e) N 1S spectrum and (f) C 1S spectrum.

Fig. 7. UV-vis DRS spectra of (a) g-C₃N₄, (b) CoFe₂O₄ and (c) g-C₃N₄/CoFe₂O₄ nanocomposite.

Fig. 8. Room-temperature magnetization curves of (a) CoFe₂O₄ and (b) g-C₃N₄/CoFe₂O₄ nanocomposite (inset: the magnetic separation of g-C₃N₄/CoFe₂O₄ nanocomposite by a magnet).

Fig. 9. N₂ adsorption–desorption isotherms of (a) C₃N₄ and (b) g-C₃N₄/CoFe₂O₄ nanocomposite. The insets are the pore size distribution curves.

Fig. 10. (a) The UV-vis absorption changes, (b) concentration changes (C_t/C₀), and (c) the pseudo-first-order plots of −ln(C_t/C₀) as a function of irradiation time for MB sonodegradation in the presence of g-C₃N₄/CoFe₂O₄ nanocomposite. Conditions: [MB]₀ = 25 mg L⁻¹,50 mL; [H₂O₂ ] = 0.1 mol L⁻¹, 1 mL; [cat.] = 0.66 g L⁻¹ at room temperature and natural pH = 7.

Fig. 11. Effects of (a) different enhancers, (b) the H₂O₂ amount, (c) the g-C₃N₄/CoFe₂O₄ sonocatalyst dosage, and (d) initial dye concentration on the sonocatalytic degradation of MB in the presence of g-C₃N₄/CoFe₂O₄ nanocomposite. Conditions: [MB]₀ = 25 mg L⁻¹,50 mL; [enhancer] = 0.1 mol L⁻¹, 1 mL; [cat.] = 0.66 g L⁻¹ at room temperature and natural pH = 7.

Fig. 12. The UV-vis absorption spectra changes of (a) rhodamine B (RhB), (b) methyl orange (MO), and (c) comparison of sonodegradation efficiency of dyes as a function of time over the g-C₃N₄/CoFe₂O₄ nanocomposite. Conditions: [dye] = 25 mg L⁻¹, 50 mL; [cat.] = 0.66 g L⁻¹; [H₂O₂] = 0.1 mol L⁻¹, 1 mL; at room temperature and natural pH = 7.

Fig. 13. (a) Effects of different scavengers on the sonocatalytic degradation of MB. Conditions: [MB] = 25 mg L⁻¹, 50 mL; [cat.] = 0.66 g L⁻¹; [H₂O₂] = 0.1 mol L⁻¹, 1 mL; [scavenger] = 0.1 mol L; at room temperature and natural pH = 7. (b) Schematic illustration of the possible sonocatalytic mechanism of the g-C₃N₄/CoFe₂O₄ nanocomposite under ultrasound irradiation.

Fig. 14. PL spectra of (a) pure g-C₃N₄ and (b) g-C₃N₄/CoFe₂O₄ samples.

Fig. 15. (a) Cycling runs of g-C₃N₄/CoFe₂O₄ nanocomposite in the sonodegradation of MB. Each run of photocatalytic reactions lasted for 30 min. (b) FT-IR spectrum, (c) XRD pattern and (d) TEM image (e) SEM image of the recovered nanocomposite after the 5th run.