Co–Fe hydrotalcites for efficient removal of dye pollutants via synergistic adsorption and degradation

Abstract

Layered double hydroxides (LDHs) with hydrotalcite-like structures containing Co(II) and Fe(III) were prepared and used for the removal of direct red 23 (DR23) from water solution. These CoFe–LDHs were characterized before and after reaction by XRD, FTIR, BET, and XPS. The factors affecting the adsorption and catalytic performance of the CoFe–LDHs were systematically investigated. The adsorption process followed pseudo-first-order kinetics, while equilibrium adsorption isotherm data were well fitted by the Freundlich model. Moreover, CoFe–LDHs exhibited high catalytic activity in the degradation of direct red 23 in the pH range 4–10. Under a catalyst dosage of 0.5 g L⁻¹ and H₂O₂ concentration of 6.5 mmol L⁻¹, the degradation ratio of direct red 23 was 95.6% after 30 min. The adsorption–degradation relationship in the presence of CoFe–LDHs was investigated. Intermediates were detected by GC/MS and a possible pathway for DR23 degradation was proposed. The reaction mechanism showed that cobalt ions play a critical role in the catalytic performance of CoFe–LDHs. Furthermore, the catalytic activity of CoFe–LDHs was maintained after three reaction cycles, demonstrating the recyclability and stability of this catalyst.