Eco-safe degradation of reactive orange 16 via adsorption-enhanced photocatalysis using CoFe₂O₄ nanoparticles

The increasing release of synthetic azo dyes into aquatic systems demands efficient, low-cost, and sustainable remediation strategies. In this study, cobalt ferrite (CoFe₂O₄) nanoparticles were synthesized via the co-precipitation method and applied for the adsorption-assisted photocatalytic removal of Reactive Orange 16 (RO16) dye. The nanoparticles exhibited a mesoporous morphology (average pore diameter 13.32 nm; specific surface area 26.98 m² g^-1) and a narrow optical band gap of 2.91 eV, ensuring strong visible-light activity. Adsorption experiments revealed a maximum dye uptake of 112.3 mg g^-1, with equilibrium data best fitting the Freundlich and Redlich-Peterson models, confirming heterogeneous multilayer adsorption. Kinetic modeling indicated a pseudo-second-order rate mechanism, whereas thermodynamic parameters (ΔH = 51 kJ mol^-1; ΔG < 0) indicated that the process is endothermic and spontaneous. Under visible irradiation, CoFe₂O₄ NPs achieved up to 83.5% photodegradation efficiency at pH 2, following pseudo-first-order kinetics. The integrated adsorption-photocatalysis mechanism involved synergistic electrostatic, π-π, and hydroxyl radical interactions, leading to effective decolorization and mineralization. AI-based Shapley Additive Explanations (SHAP) and Principal Component Analysis (PCA) analyses validated experimental results, identifying contact time and initial concentration as the dominant factors governing removal efficiency. Phytotoxicity and antibacterial studies confirmed the eco-safe nature of CoFe₂O₄ NPs, with over 90% tomato seed germination and no toxic bacterial response. This work presents a dual-functional, environmentally friendly nanomaterial capable of coupling adsorption and photocatalysis for the sustainable removal of complex dye pollutants.