A magnetically separable plate-like cadmium titanate-copper ferrite nanocomposite with enhanced visible-light photocatalytic degradation performance for organic contaminants

Abstract

A novel magnetic cadmium titanate-copper ferrite (CdTiO₃/CuFe₂O₄) nanocomposite, in which spherical CuFe₂O₄ nanoparticles were loaded onto the surface of CdTiO₃ nanoplates, was successfully synthesized via a sol-gel hydrothermal route at 180 °C. The structure, morphology, magnetic and optical properties of the as-prepared nanocomposite were respectively characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) surface area analysis, UV-visible diffuse reflectance spectroscopy (DRS), vibrating sample magnetometry (VSM) and photoluminescence (PL) spectroscopy. The photocatalytic activity of this novel CdTiO₃-based magnetic nanocomposite was investigated for the degradation of organic dye pollutants such as methylene blue (MB), rhodamine B (RhB), and methyl orange (MO) in the presence of H₂O₂ under visible light irradiation. The results showed that the photocatalyst completely degraded three dyes within 90-100 min. Compared with pure CdTiO₃ and CuFe₂O₄, the heterogeneous CdTiO₃/CuFe₂O₄ nanocomposite exhibited significantly enhanced photocatalytic efficiency. On the basis of the results of the OH trapping and photoluminescence (PL) experiments, the enhanced photocatalytic performance was mainly ascribed to the efficient separation of photo-induced electron-hole pairs and the formation of highly active hydroxyl radicals (OH) species in the CdTiO₃/CuFe₂O₄ photocatalytic oxidation system. The PL measurements of the CdTiO₃/CuFe₂O₄ nanocomposite also indicated an enhanced separation of photo-induced electron-hole pairs. Moreover, the nanocomposite could be easily separated and recycled from contaminant solution using a magnet without a decrease in their photocatalytic activity due to their good magnetic separation performance and excellent chemical stability. Based on these findings, CdTiO₃/CuFe₂O₄ nanocomposite could be a promising visible-light-driven magnetic photocatalyst for converting solar energy to chemical energy for environmental remediation.

Fig. 1. FT-IR spectra of (a) CuFe₂O₄, (b) CdTiO₃ and (c) CdTiO₃/CuFe₂O₄.

Fig. 2. XRD patterns of (a) CuFe₂O₄, (b) CdTiO₃ and (c) CdTiO₃/CuFe₂O₄.

Fig. 3. SEM images (a) CuFe₂O₄, (b and c) CdTiO₃, and (d–f) CdTiO₃/CuFe₂O₄.

Fig. 4. (a) EDX spectrum and (b) elemental mappings of the CdTiO₃/CuFe₂O₄ nanocomposite.

Fig. 5. TEM images of the CdTiO₃/CuFe₂O₄ nanocomposite.

Fig. 6. Nitrogen adsorption–desorption isotherms of (a) pure CuFe₂O₄ and (b) pristine CdTiO₃ and CdTiO₃/CuFe₂O₄ nanocomposite samples. The insets show pore size distribution curves.

Fig. 7. (a) UV-vis DRS and (b) band gap energies of: (i) CdTiO₃, (ii) CuFe₂O₄ and (iii) CdTiO₃/CuFe₂O₄ nanocomposite.

Fig. 8. Room-temperature magnetic hysteresis loops of (a) pure CuFe₂O₄ and (b) CdTiO₃/CuFe₂O₄ nanocomposite. The photo inset shows magnetic separation of the photocatalyst from aqueous dye solution before and after dye degradation using a magnet.

Fig. 9. (a) Photocatalytic degradation of MB under different conditions. (b) Concentration changes of MB at 664 nm as a function of irradiation time. (c) Plot of ln(C₀/C) against the irradiation time. Conditions: MB (25 mg L⁻¹, 30 mL), H₂O₂ (0.15 M), catalyst (1 g L⁻¹) and reaction time of 90 min.

Fig. 10. Effects of (a) H₂O₂ amount, (b) CdTiO₃/CuFe₂O₄ dosage and (c) initial dye concentration on the photocatalytic degradation. Conditions: MB (25 mg L⁻¹, 30 mL), H₂O₂ (0.15 M), catalyst (30 mg) and time = 90 min.

Fig. 11. Photocatalytic degradation of (a) RhB and (b) MO. (c) Comparison of the photocatalytic degradation of MB, RhB and MO dyes. Conditions: [dye] = 25 mg L⁻¹; [catalyst] = 0.1 g L⁻¹; [H₂O₂] = 0.15 mol L⁻¹ and reaction times of 90–100 min.

Fig. 12. Schematic illustration of excitation and separation of photoinduced electron–hole pairs for CdTiO₃/CuFe₂O₄ heterojunction under visible-light irradiation.

Fig. 13. (a) PL spectra excited at 325 nm of (i) pure CdTiO₃ and (ii) CdTiO₃/CuFe₂O₄ samples and (b) the photocatalytic degradation of MB over the CdTiO₃/CuFe₂O₄ in the presence of different scavengers under visible-light irradiation.

Fig. 14. (a) Cycling runs of CdTiO₃/CuFe₂O₄ in the photodegradation of MB. Each run of photocatalytic reactions lasted for 90 min. (b) XRD and (c) FT-IR of the recovered nanocomposite after the 3rd run.