Fabrication and photocatalytic property of magnetic SrTiO3/NiFe2O4 heterojunction nanocomposites

Abstract

Novel multifunctional SrTiO₃/NiFe₂O₄ nanocomposites were successfully fabricated via a two-step route. The as-prepared samples were characterized by using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), field-emission transmission electron microscopy (TEM), UV-visible diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectroscopy and vibrating sample magnetometry (VSM). The results indicate that the SrTiO₃/NiFe₂O₄ heterostructures are composed of SrTiO₃ spheroidal nanoparticles adhered to NiFe₂O₄ polyhedra. The heterojunction established in the composite material accelerates the process of electron-hole pair separation and boosts the photo-Fenton reaction. Among the samples, 15 wt% SrTiO₃/NiFe₂O₄ nanocomposites exhibit a powerful light response and excellent room temperature ferromagnetism. Subsequently, the photocatalytic degradation of RhB over the as-prepared samples was investigated and optimized, revealing that the 15 wt% SrTiO₃/NiFe₂O₄ nanocomposites exhibit the best photocatalytic activity and stability under simulated solar light irradiation. Furthermore, according to experimental results, the possible mechanism of improved photocatalytic activity was also proposed.

Fig. 1. XRD patterns of pure SrTiO₃, pure NiFe₂O₄ and 15 wt% SrTiO₃/NiFe₂O₄ nanocomposites.

Fig. 2. XPS spectra of the 15 wt% SrTiO₃/NiFe₂O₄ nanocomposites: the XPS survey spectrum (a), Ni 2p (b), Fe 2p (c), Sr 3d (d), Ti 2p (e) and O 1s (f).

Fig. 3. SEM image of pure NiFe₂O₄ (a), pure SrTiO₃ (b), 15 wt% SrTiO₃/NiFe₂O₄ nanocomposites (c) and EDS spectrum of 15 wt% SrTiO₃/NiFe₂O₄ nanocomposites (d).

Fig. 4. TEM (a), HRTEM image (b–d) and the SAED pattern (e) for the SrTiO₃/NiFe₂O₄ nanocomposites.

Fig. 5. The corresponding elemental mapping images (a–f) and spot EDS pattern (g) for the SrTiO₃/NiFe₂O₄ nanocomposites.

Fig. 6. UV-vis DRS (a) and band gap energy (E_g) (b) of the pure NiFe₂O₄, pureSrTiO₃ and 15 wt% SrTiO₃/NiFe₂O₄ nanocomposite.

Fig. 7. The hysteresis loops of pure NiFe₂O₄ and 15 wt% SrTiO₃/NiFe₂O₄ nanocomposite (inset: the magnetic separation of 15-NFO/BOI nanocomposites by a magnet).

Fig. 8. Photocatalytic degradation of RhB for all samples under simulated solar light illumination (a), absorption spectra of RhB over 15 wt% SrTiO₃/NiFe₂O₄ nanocomposites (b), −ln(C_t/C₀) vs. time for photodegradation of RhB by different catalysts (c), cycling degradation rate (d) for RhB of 15 wt% SrTiO₃/NiFe₂O₄ nanocomposites under simulated solar light illumination.

Fig. 9. Reactive species trapping experiments over 15 wt% SrTiO₃/NiFe₂O₄ nanocomposites.

Fig. 10. PL spectra (excited at 325 nm) of pure NiFe₂O₄ and 15 wt% SrTiO₃/NiFe₂O₄ nanocomposites.

Fig. 11. Schematic illustration of excitation and separation of photoinduced electron–hole pairs for SrTiO₃/NiFe₂O₄ heterojunction nanocomposites under simulated solar light irradiation.