A novel n-type CdS nanorods/p-type LaFeO3 heterojunction nanocomposite with enhanced visible-light photocatalytic performance

Abstract

In this work, a novel n-type CdS nanorods/p-type LaFeO₃ (CdS NRs/LFO) nanocomposite was prepared, for the first time, via a facile solvothermal method. The as-prepared n-CdS NRs/p-LFO nanocomposite was characterized by using powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray spectroscopy (EDX), UV-visible diffuse reflection spectroscopy (DRS), vibrating sample magnetometry (VSM), photoluminescence (PL) spectroscopy, and Brunauer-Emmett-Teller (BET) surface area analysis. All data revealed the attachment of the LFO nanoparticle on the surface of CdS NRs. This novel nanocomposite was applied as a novel visible light photocatalyst for the degradation of methylene blue (MB), rhodamine B (RhB) and methyl orange (MO) dyes under visible-light irradiation. Under optimized conditions, the degradation efficiency was 97.5% for MB, 80% for RhB and 85% for MO in the presence of H₂O₂ and over CdS NRs/LFO nanocomposite. The photocatalytic activity of CdS NRs/LFO was almost 16 and 8 times as high as those of the pristine CdS NRs and pure LFO, respectively. The photocatalytic activity was enhanced mainly due to the high efficiency in separation of electron-hole pairs induced by the remarkable synergistic effects of CdS and LFO semiconductors. After the photocatalytic reaction, the nanocomposite can be easily separated from the reaction solution and reused several times without loss of its photocatalytic activity. Trapping experiments indicated that ·OH radicals were the main reactive species for dye degradation in the present photocatalytic system. On the basis of the experimental results and estimated energy band positions, the mechanism for the enhanced photocatalytic activity was proposed.

Fig. 1. XRD patterns of (a) LFO, (b) CdS NRs and (c) CdS NRs/LFO.

Fig. 2. FT-IR spectra of (a) LFO, (b) CdS NRs and (c) CdS NRs/LFO.

Fig. 3. SEM images of (a) LFO, (b) CdS, and (c and d) CdS NRs/LFO nanocomposite.

Fig. 4. (a) EDX spectrum and (b) EDX mappings of the CdS NRs/LFO nanocomposite.

Fig. 5. (a and b) TEM images and (c) HR-TEM image of the CdS NRs/LFO nanocomposite.

Fig. 6. (a) UV-Vis diffuse reflectance spectra and (b–d) band gap energies of different photocatalyst samples.

Fig. 7. Room-temperature magnetization (MS) curves of LFO and CdS NRs/LFO.

Fig. 8. N₂ adsorption–desorption isotherms of CdS NRs, LFO and CdS NRs/LFO samples. The inset show the corresponding BJH pore size distribution curves.

Fig. 9. XPS of the CdS NRs/LFO nanocomposite: (a) survey spectrum, (b) S 2p spectrum, (c) Cd 3d spectrum, (d) Fe 2p spectrum and (e) La 3d spectrum.

Fig. 10. (a) Photocatalytic degradation rate of MB under different conditions. Time-dependent UV-Vis spectral changes of (b) MB, (c) RhB and (d) MO solutions over CdS NRs/LFO nanocomposite and under visible irradiation. The inset photos in (b) and (c) show the color change of dyes solutions during irradiation.

Fig. 11. (a) Comparison of the concentration changes (C/C₀) of dyes as a function of irradiation time, and (b) the degradation kinetics of MB dye under different conditions. Conditions: [dye] = 25 mg L⁻¹, 100 mL; [catalyst] = 50 mg; [H₂O₂] = 4 mM at 25 °C ± 2.

Fig. 12. The effects of (a) H₂O₂ amount, (b) photocatalyst dosage, and (c) initial dye concentration on visible-light driven photodegradation efficiency. Conditions: [MB] = 25 mg L⁻¹, 100 mL, [cat] = 50 mg, [H₂O₂] = 4 mM, 25 °C and time = 180 min.

Fig. 13. Schematic diagram of the charge separation and possible photocatalytic degradation mechanism for CdS NRs/LFO heterojunction under visible light irradiation.

Fig. 14. (a) Quenching tests with and without quenching agents, and (b) Photoluminescence (PL) spectra of pure CdS NRs and CdS NRs/LFO nanocomposite.

Fig. 15. (a) Recyclability tests, (b) FT-IR spectrum, (c) XRD pattern and (d) SEM image of the recovered CdS NRs/LFO photocatalyst after five runs.