Electrochemical properties of CoFe2O4 prepared by sol–gel route. Sono-photocatalysis degradation of Rhodamine B by solar light

Abstract

The present work deals with removing Rhodamine B (Rh B) from aqueous solution by Photo Sono-assisted catalytic process on CoFe2O4 elaborated by sol–gel method. The spinel identified by X-ray diffraction presents a face-centered cubic lattice with a grain size of 360 (± 2 nm) and a zeta potential of − 33 mV. The oxide is characterized by diffuse reflectance and photo-electrochemistry. The direct gap (1.42 eV) is assigned to the internal transition: Feoc3+:t2g→Feoc4+:eg in agreement with the red color. The narrow valence band deriving from Fe3+: 3d parentage induces a low hole mobility (µh = 8.91 × 10−6 cm2 V−1 s−1). The electrical conductivity of CoFe2O4 is characteristic of semiconducting comportment with activation energy (Ea) of 0.57 eV, where the electron jump occurs by small lattice polaron between mixed valences Fe3+/Fe4+. The intensity potential J(E) profile in Na2SO4 (10–2 M) exhibits a small hysteresis loop. The chrono-amperometry shows p-type conductivity due to metal insertion, a result confirmed by the capacitance measurement where a hole density (NA) of 0.176 × 1023 cm−3 and a flat band potential (Efb) equal to − 0.8 V are determined. As an application, Rh B (20 mg L−1) is successfully oxidized by photocatalysis on CoFe2O4 with a reduction of 53% under solar light. An enhancement up to 88% has been reached by sono-photocatalysis at an ultrasonic wave (USW) frequency (60 kHz, 550 W) within 105 min.; the Rh B elimination follows a pseudo-first-order kinetic with a rate constant of 1.23 × 10–2 mn−1 (t1/2 = 56 min), and a reaction mechanism is suggested, was entirely discolored in the USW/solar light/CoFe2O4 system. The Sono-photocatalytic degradation of Rh B depends on the initial Rh B concentration, acoustic power, and catalyst dose. At low ultrasound frequency, the results indicated a total chemical oxygen demand (COD) when applying the system USW/solar light/CoFe2O4, signifying its great potentiality for the treatment of water.