Electrochemical Study of CuFe2O4 Synthetized by Sol–Gel and Electro-photo-oxidation of Rhodamine B Under Sunlight

Abstract

The spinel CuFe2O4 elaborated by sol–gel route crystallizes in a tetragonal structure with a crystallite size of 444 ± 2 nm and a zeta potential of − 35 mV. The diffuse reflectance spectroscopy and photo-electrochemistry were undertaken for its characterization. The direct gap (1.55 eV) ideal for the solar energy conversion is assigned to the transition :Feoc3+:t2g→Feoc4+: eg in agreement with the red color, allowing more than half of the solar spectrum to be converted into chemical energy. The narrow valence band deriving from Fe3+: t2g orbital induces a low electron mobility (µ = 8.91 × 10−13 cm2 V−1 s−1). The cyclic voltammetry in Na2SO4 (10−2 M) exhibits low hysteresis that resembles a chemical diode. The electrical conductivity of CuFe2O4 is a characteristic of a non-degenerate semiconductor with activation energy (Ea) of 0.20 eV where the electron transfer occurs by low lattice polaron hopping between mixed valences Fe4+/Fe3+ octahedrally coordinated. The semi-logarithmic plot (logJ–E) indicates a chemical stability of CuFe2O4, while the photo-chronoamperometry corroborates the p-type behavior, a result confirmed by the capacitance measurement where an electron density (NA) of 0.176 × 1023 cm−3 and a flat band potential (Efb) equal to − 0.56 VSCE were extracted. As application and on the basis of the potential diagram, Rhodamine B (Rh B, 20 mg L−1), a cationic dye, is electrostatically attracted by the electrode surface and successfully oxidized by electrocatalysis on CuFe2O4. The kinetics of oxidation of Rh B followed by chemical oxygen demand (COD) analysis, which gave an abatement of 56% under a current of 150 mA, an enhancement up to 70%, was reached by electro-photocatalysis under sunlight smaller than that analyzed by UV–visible spectrophotometry (88%). The color removal follows a pseudo-first-order model with a half-life t1/2 of 57 min; a reaction mechanism by O2•− and •OH radicals is suggested. Graphical Abstract: (Figure presented.)