Gd3+ doped CoFe2O4 coupled with bismuth oxybromide for visible-light-driven removal of organic contaminants: Reactive Red 120 and Acid Violet 7 and its mechanism insights

In the current study novel magnetic BiOBr-Gd³⁺ doped CoFe₂O₄ heterojunction nanocomposites fabricated by chemical precipitation method for Acid Violet 7 (AV 7) and Reactive Red 120 (RR 120) dye degradation under sunlight are presented. The samples were well characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), UV–visible near infrared (NIR), photoluminescence (PL), TRF, EIS, Mott–Schottky, and BET analysis. X-ray diffractograms of BiOBr-Gd³⁺ doped CoFe₂O₄ nanocomposites authenticate the formation of the composite composed of diffraction peaks of both BiOBr and Gd³⁺ doped CoFe₂O₄ samples. Photoluminescence (PL), Time Resolved Fluorescence Spectrocopy (TRF) and Electrochemical Impedance Spectroscopy (EIS) investigations were explored to examine the transfer efficiency of photoinduced charge carriers. Among the synthesized materials, the BiOBr-Gd³⁺ doped CoFe₂O₄-2 nanocomposite presents superior degradation capability for RR 120 of 87.34% and AV 7 dyes of 98.41%. The apparent rate constant (k) value of 0.1317 min⁻¹ for AV 7 is sixteen times higher and RR 120 (0.0135 min⁻¹) is 2 times higher than pristine BiOBr. The radical trapping experiments also proved the role of photogenerated h⁺, O₂^·−, and ^·OH radicals in the degradation mechanism. The superior performance of BiOBr-Gd³⁺ doped CoFe₂O₄-2 is ascribed to the formation of the heterostructure, the in-built electric field, and energy-band alignment, which thermodynamically and kinetically favors the photoactivity and stability of the heterojunction.