Enhanced catalytic performance of Cu-doped MnFe2O4 magnetic ferrites: Tetracycline hydrochloride attacked by superoxide radicals efficiently in a strong alkaline environment

It is important to develop a catalyst that can maintain good activity in alkaline environment for Fenton or Fenton-like reactions. In order to achieve stable Fenton catalytic degradation in a wide pH range, this study reports Cu-doped MnFe2O4 heterogeneous catalysts still has excellent effect when the pH is extended to 11 for removing organic pollutants, such as tetracycline hydrochloride (TC-HCl). The synergistic effect among Fe, Mn and Cu ions has been proved to enhanced the catalytic activity in this work. When the molar ratio of Cu/Mn = 4:1, the porous Cu0·8Mn0·2Fe2O4 materials had the highest photo-Fenton catalytic activity compared with pure MnFe2O4, CuFe2O4 and other CuxMn1-xFe2O4. The XPS showed that Cu0·8Mn0·2Fe2O4 formed oxygen vacancies, which exposed more active sites to attract more H2O2 for TC-HCl degradation. Results indicated 94.3% of TC-HCl was efficiently degraded by 0.1 g/L Cu0·8Mn0·2Fe2O4 with 50 mM H2O2 at pH = 11 under 30 min visible light irradiation, and the corresponding apparent rate constant was 0.08286 min-1. With free radicals quenching experiment, O2- was responsible for the high catalytic degradation and OH was participated in the photo-Fenton reaction. To sum up, Cu0·8Mn0·2Fe2O4 exhibited high activity, great stability and easily recyclable, which eliminated the pH limitation of the Fenton reaction and provided practical application performance for water purification.