Photoelectrochemical study of the spinel CaFe2O4 nanostructure: application to Basic Blue 41 oxidation under solar light

• Published in: Journal of solid state electrochemistry 2021-06, Vol.25 (6), p.1815-1823
• Main Authors: Kenfoud, H., Nasrallah, N., Meziani, D., Trari, M.
• Format: Article
• Language: English
• Subjects: Analytical Chemistry; Catalytic activity; Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; CI Basic Blue 41; Condensed Matter Physics; Corrosion potential; Electrical measurement; Electrochemical impedance spectroscopy; Electrochemistry; Energy gap; Energy Storage; Original Paper; Oxidation; Photocatalysis; Physical Chemistry; Space charge; Spinel; Valence band
• ISSN: 1432-8488; 1433-0768
• DOI: 10.1007/s10008-021-04952-8

Ca[Fe] 2 O 4 prepared by nitrate route is a narrow band gap semiconductor crystallizing in the normal spinel structure. The direct optical band gap E g (1.93 eV), determined from the diffuse reflectance, is due to the lifting of degeneracy of Fe 3+ : 3d orbital, octahedrally coordinated. The semi-logarithm plot of the oxide shows a chemical stability at pH ~ 7 with an exchange current density of 2×10 −7 mA cm −2 and a corrosion potential of −0.664 V SCE . The photoelectrochemical properties of CaFe 2 O 4 are investigated for the first time to assess its photocatalytic activity. A flat band potential ( E fb ) of 0.33 V SCE was obtained from the capacitance measurement in Na 2 SO 4 (0.1 M) solution. The n -type comportment, rare for spinels, is confirmed by the chrono-amperometry and inferred to the metal insertion in the FeO 6 octahedra. The electronic concentration N D (7.1 ×10 15 cm −3 ) agrees with a non-degenerate semi-conductivity and a wide space charge region ( W ~ 850 nm). The electrochemical impedance spectroscopy (EIS) shows depressed semicircles with the existence of a constant phase element (CPE) and a bulk resistance of 10.89 kΩ cm 2 which decreases down to 2.24 kΩ cm 2 under visible irradiation. A Warburg diffusion is observed at low frequencies. The valence band (2.09 V SCE ) deriving from Fe 3+ : e g character is more anodic than the potential of H 2 O/ • OH couple. As an application, the Basic Blue 41 (BB 41), a recalcitrant dye, is successfully oxidized; an abatement of 85% is obtained within 3 h under solar light (980 W m −2 ) and the BB 41 oxidation follows a first-order kinetics with a photocatalytic half-life of 69 min.