Micro-electrolytic degradation of rhodamine B by Cu-Fe-Co trimetallic catalysts: Synergistic mechanisms and reaction pathways

The persistent dye rhodamine B (RhB) in textile wastewater poses severe ecological threats, demanding efficient and sustainable treatment technologies. This study synthesized a novel trimetallic Cu-Fe-Co catalyst via a nitrogen-atmosphere co-reduction method. The catalyst’s unique advantage lies in the synergistic effects of Cu, Fe, and Co, which significantly enhance catalytic performance. The redox-active phases of Cu, combined with the Fenton-like reactivity of Fe, are further optimized by Co doping to improve reactive oxygen species (ROS) generation and electron transfer efficiency. Characterization revealed a dendritic structure dominated by Cu, Cu₂O, and FeO phases, with Co-induced lattice expansion (Δ d / d = +0.25 %) enhancing surface reactivity. Under optimized conditions (pH 3, 1.5 g/L catalyst, 20 mg/L RhB), the ternary Cu-Fe-Co catalyst achieved 99.8 % RhB degradation within 40 min, with high mineralization efficiency (46.5 % TOC removal, 82.1 % COD removal). Mechanistic studies demonstrated that Co incorporation promotes the conversion of superoxide radicals (·O₂⁻) into long-lived singlet oxygen (¹O₂), synergistically enhancing oxidative effects from ·OH and ¹O₂, while in situ H₂O₂ generation drives radical chain reactions. Compared to binary catalysts, the ternary system exhibits superior degradation kinetics for RhB and maintains 95.8 % degradation efficiency even after five cycles. This study provides new insights into trimetallic catalyst design, highlighting its practical potential for wastewater treatment.