Synthesis, Characterization and Environmental Application of a Magnetic LDH-Based CoO•CuFe2O4 Nanocatalyst

Herein, we synthesized a multipurpose CoO•CuFe2O4 magnetic mixed metal oxide (MMO) nanocatalyst from its corresponding Layered double hydroxide (CoCuFe LDH) via a simple co-precipitation method. The resultant magnetic CoO•CuFe2O4 MMO was well characterized using SEM, VSM, FTIR, XRD and UV–vis DRS. Thereafter, the potential of the as-synthesized magnetic nanocatalyst, CoO•CuFe2O4 MMO to remove tetracycline (TET) via adsorption and degrade Eriochrome Black T (EBT) via a combination of adsorption and sunlight assisted photocatalysis was then explored. The influence of varying adsorption and photocatalytic operational parameters including; contact time, pH, pollutant initial concentration, dosage, scavengers, temperature, interfering counter ions on the removal and degradation efficiency was also investigated systematically. Finally, the equilibrium adsorption data obtained at 298 K were analyzed using four two-parameter adsorption isotherms. The characteristics results demonstrated that the average pore diameter, surface area and pH point zero charge of the CoO•CuFe2O4 MMO was 5.8 nm, 348.5 m2/g and 5.8 respectively with an optical band gap of 2.1 eV. Also, the saturation magnetization, Ms of the calcined mixed metal oxide (83.2 emu/g) were higher than that of the LDH precursor (61.3 emu/g). The FTIR spectra confirmed the presence of OH-stretching and intercalated anions in the structure of the Co•Fe LDH which disappeared on calcination. Thus, confirming the formation of the CoO•CuFe2O4 MMO. Results obtained from the adsorption studies of both TET and EBT showed that the solution pH had a significant effect on the adsorption potential of the CoO•CuFe2O4 MMO. Equilibrium adsorption data was well simulated by the Langmuir isotherm with maximum adsorption capacity for TET and EBT was 175.4 and 51.8 mg/g at pH 6.0 and 2.0. Thermodynamic parameters, enthalpy ΔH° = 27.35 KJ/mol and Gibbs free energy change, ΔG°= -2.60 ‒ -5.14 KJ/mol confirmed that the adsorptive removal of TET was thermodynamically feasible and endothermic. Catalytic potential of CoO•CuFe2O4 MMO was also evaluated for the removal of EBT. Results obtained shows that the degradation of EBT dye was very rapid and depends on the dye solution pH, catalyst dosage and substrate concentration. Optimum dosage and pH for EBT degradation was 1.0 g/L at pH 2.0. After 60 min of sunlight irradiation, 98%, 93% and 86% degradation was observed for 10, 20 and 40 ppm initial EBT concentration respectively. The proposed mechanism revealed that the photogenerated holes (h+) were the main reactive specie responsible for the degradation of EBT dye. After six consecutive recycling runs, the removal and degradation efficiency of the regenerated CoO•CuFe2O4 MMO was still very high at ~ 93% and 80% for TET and EBT. Overall, the findings in this study confirmed that the CoO•CuFe2O4 MMO can act as a suitable adsorbent for removal of TET and also as adsorbent/photocatalyst in the degradation of EBT from aqueous solution.