Synthesis and characterization of MFe₂O₄ (M = Ca, Co) nano-spinels: application for photochemical hydrogen generation under visible LED light irradiation
摘要
This study focuses on the synthesis of iron-based spinel ferrites MFe₂O₄ (M = Ca, Co) by the nitrate method and examines their efficacy as visible-light-driven photocatalysts for hydrogen production. Structural and optical characterizations were performed using ATG (Thermogravimetric Analysis), XRD (X-ray diffraction), FTIR (Fourier transform infrared spectroscopy), DRS (Diffuse reflectance), SEM–EDX (scanning electron microscopy with energy-dispersive X-ray spectroscopy), and XPS (X-ray photoelectron spectroscopy). XRD patterns confirmed the formation of pure spinel phases at 850 °C, with crystallite sizes of 31 nm for CaFe₂O₄ and 27 nm for CoFe₂O₄. SEM images revealed relatively uniform grains with moderate porosity, while EDX confirmed high purity of materials without detectable contaminants. The optical band gaps derived from diffuse reflectance spectra were estimated at 1.85 eV and 1.27 eV for CaFe₂O₄ and CoFe₂O₄. XPS analysis identified Fe(III), O, Ca(II), and Co(II) species on the photocatalyst surfaces. Photocatalytic evaluation demonstrated efficient hydrogen evolution, reaching 396.56 µmol g⁻1 h⁻1 with CaFe₂O₄ at pH ~ 7 and 50 °C, and 195.33 µmol g⁻1 h⁻1 with CoFe₂O₄ at pH ~ 12 after 30 min of irradiation. The influence of pH, hole scavengers, and photocatalyst recyclability was also examined. The inclusion of hole scavengers results in a significant enhancement in hydrogen evolution, 660 µmol g⁻1 h⁻1 (78.59%) for CaFe₂O₄ and 588 µmol g⁻1 h⁻1 (124%) for CoFe₂O₄. The photocatalysts exhibited good stability over three successive cycles. These results highlight the potential of CaFe₂O₄ and CoFe₂O₄ as efficient photocatalysts for sustainable hydrogen production under visible light.
Graphical abstract