Solar photodegradation of Rose Bengal in water on the spinel CaFe2O4

Abstract

Solar photo degradation of the Rose Bengal (RB), a recalcitrant dye in water is carried out in the presence of the spinel CaFe2O4 synthetized by sol-gel route. Its structural characterization and FTIR spectroscopy were undertaken. The BET analysis measured is A specific surface area of 29.5 m2 g−1 is determined from the BET analysis. The diffuse reflectance of the normal spinel CaFe2O4 is used to determine a band gap of 1.83 eV. This optical transition directly allowed, is assigned to the crystal field splitting of Fe3+ octahedrally coordinated. The oxide is characterized photo-electrochemically. The absorption of solar light increases the presence of electrons in the conduction band (ECB = −1.45 VSCE). The chrono-amperometry curve indicates that CaFe2O4 exhibits p-type semiconductor. A flat band potential of 0.24 VSCE is determined from the capacitance measurement. The p-type character is corroborated by chrono-photo amperometry. The values of the conductivity increases with raising temperature attesting a semi-conducting character of CaFe2O4 with an activation energy (Ea) of 0.14 eV. As application, CaFe2O4 was successfully used as an efficient photocatalyst for the RB photo-degradation. Due to the good charge separation of photogenerated electron-hole pairs, a quasi-complete degradation of RB occurred within 2 h under sunlight for an initial concentration of 10 mg/L, a CaFe2O4 dose of 1 mg/mL of catalyst and an environmental pH ~ 8. The degradation kinetics are well illustrated by the Langmuir-Hinshelwood (L-H) model, follows pseudo-first order with an apparent constant of 0.016 min−1, corresponding to a half photocatalytic life of 43 min.