Mg doped CuO–Fe₂O₃ composites activated by persulfate as highly active heterogeneous catalysts for the degradation of organic pollutants

Mg doped CuO–Fe₂O₃ composites were hydrothermally synthesized and characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy. Mg doping improved the catalytic performance of CuO–Fe₂O₃ for phenol degradation as the removal efficiency of phenol (33 mg/L) reached up to 84.36% within 45 min using 3.2% Mg doped CuO–Fe₂O₃ when coupled with persulfate (PS) system. The results revealed that Mg doping generated more defects (oxygen vacancies), which result in the generation of more active species during the degradation process. The influence of catalysts and PS dosages were investigated to obtain the optimum conditions. The effects of pH and dissolved oxygen were also evaluated. Increase of solution pH was found to be beneficial for the removal of phenol because of reduced copper leaching at higher pH. However, decrease in dissolved oxygen concentration retarded the degradation of phenol because of the reduced production of O₂•^-. Based on the quenching experiments and ESR experiments, ¹O₂, O₂•^-, ·OH and ·SO₄⁻ were confirmed as the active species in the phenol degradation process and a phenol degradation pathway was proposed. Other contaminants such as nitrobenzene (NB), P-nitrophenol (PNP) and P-Chlorophenol (4-CP) could also be removed to some extent using the present catalyst system.