Cobalt-enhanced CoxFe3−xO4 photoanode for ultrafast photoelectrodegradation of organic dyes with integrated RSM optimization

Abstract

In this work, two compositions of cobalt ferrite (Co_xFe_3−xO₄: x = 1 and 1.5) were investigated as photoanodes for the photoelectrocatalytic (PEC) degradation of rhodamine B. The structural and textural investigations confirmed the cubic spinel structure with a monocrystalline grain size around 8 nm and high surface area (>100 m² g⁻¹). The bandgap values of the samples, 2.32 eV (for x = 1) and 2.18 eV (for x = 1.5), enable visible light absorption and activation under sunlight. The catalytic results showed that complete degradation with a complete mineralization of rhodamine B was obtained. The RSM optimization studies allowed us to identify the optimum degradation (100%) conditions in terms of Na₂SO₄ concentration, current density, initial RhB concentration and reaction time. The chemical trapping tests and redox potential study have confirmed that OH˙ and h⁺ are the primary species driving the degradation process. Advanced characterization techniques were carried out to investigate the electrocatalytic and photoelectrochemical properties. A high cobalt content improves lifetime and charge carrier transfer, as well as increasing the number of photogenerated electron–hole, confirming an enhancement in photocatalytic potential. Photons with wavelengths corresponding to an energy higher than that of the bandgap allowed an efficient degradation (100% in 6 minutes). Furthermore, a comparative investigation of photocatalytic, electrocatalytic, and photo-electrocatalytic processes revealed a pronounced synergistic effect in the combined PEC system using the Co_xFe_3−xO₄ spinel as a photoanode.