Eco-Friendly Photodegradation of Direct Red 80 Dye Mediated by Biochar Decorated with Cobalt Ferrite

In this work, a new biochar (BC) derived from woody forest residues and decorated with cobalt ferrite (BC/CoFe₂O₄) was synthesized via co-precipitation. This innovative approach entails a straightforward and cost-effective process. BC was produced via slow pyrolysis (1.66 °C min⁻¹ up to 450 °C, residence time: 72 h). The material was applied for the first time to remove direct red 80 dye (DR80). BC and BC/CoFe₂O₄ had moisture contents of 5.8% and 8.4%, ash of 24.1% and 30.0%, and volatile of 75.5% and 69.5%, respectively. These parameters are crucial for assessing BC quality. The H/C ratio was ~ 0.5, and the O/C ratio was ~ 0.2 for both materials. The materials exhibited thermal stability, with oxygenated groups. The pH_PZC of BC and BC/CoFe₂O₄ were 7.01 and 6.78, respectively. The ratios of D and G bands (I_D/I_G ratio) were 1.07 and 0.74 for BC and BC/CoFe₂O₄, respectively. BC presented peaks related to quartz, dolomite, and calcite, whereas BC/CoFe₂O₄ displayed peaks of CoFe₂O₄. BC presented a morphology of plate-shaped surface, while BC/CoFe₂O₄ presented irregular spheres of 6.6 ± 0.9 nm. The selected area diffraction pattern of BC/CoFe₂O₄ showed crystalline planes of CoFe₂O₄. The oxygen (74.97%), cobalt (8.86%), and iron (16.17%) were detected in BC/CoFe₂O₄ through Energy Dispersive Spectroscopy analysis, confirmed by Inductively Coupled Plasma Optical Emission Spectrometry. The BC/CoFe₂O₄ promoted practically 100% degradation of DR80 in 180 min. The species responsible for the degradation were identified as the photogenerated hole (h⁺) and O₂^•−. The material can be reused without a significant loss of efficiency.