Preparation of Rare Earth Metal Doped with Co₃O₄ Composite Catalyst and Its Properties and Thermodynamics Studies on Tetracycline Degradation

Abstract

Herein, we successfully synthesized a series of M-CoCoPBA, where M is the rare earth metal, by a chemical precipitation method and prepared M-Co 3 O 4 by air pyrolysis with M-CoCoPBA as the precursor. The catalytic performance of M-Co 3 O 4 as heterogeneous catalysts was studied for activating PMS to degrade tetracycline (TC), and it is noteworthy that Er-Co 3 O 4 has the strongest catalytic activity. The degradation efficiency of TC in the Er-Co 3 O 4 /PMS system could reach 82% as a reaction time of 4 min at 25 °C, and the catalyst also has good cyclic stability after 5 cycles. The morphology and composition of the Co 3 O 4 and Er-Co 3 O 4 were systematically characterized by various techniques, and it is found that ErCoO x significantly enhanced the catalytic activity of PMS activation and TC degradation, owing to bigger surface area, more lattice defects, oxidation state of Co, and vacancy oxygen of the catalysts with Er doping, compared with CoO x . Free radical quenching and EPR experiments showed that singlet oxygen ( 1 O 2 ), SO 4 −• , and • OH were generated in the ErCoO x / PMS system. The intermediate products and degradation pathway of TC by Er-Co 3 O 4 /PMS system were proposed according to the results of liquid chromatography−mass spectrometry. In addition, the kinetics of activating PMS to produce active substances by Co 3 O 4 and Er-Co 3 O 4 catalysts was systematically explored by using isothermal titration calorimetry (ITC) technology in the temperature range of 298.19−323.19 K, and the results indicate that E a , ΔH ⧧ , ΔS ⧧ , and ΔG ⧧ of Er-Co 3 O 4 are all smaller than those of Co 3 O 4 and demonstrate the inner mechanism of bigger rate constant and much higher catalytic property of Er-Co 3 O 4 .