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

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 CoFeLDHs was maintained after three reaction cycles, demonstrating the recyclability and stability of this catalyst.