Synergistic Effects of Redox Couples and Oxygen Vacancies Improve the Tetracycline Degradation Property of La2NiMnO6

Improving the e– and h+ separation efficiency and promoting the production of more radicals is the key to improving the degradation efficiency of catalytic degradation of antibiotics. On the other hand, intermediate analysis of antibiotics in the dark adsorption and light irradiation process is very important to clarify the entire antibiotic degradation pathway. Here, the La2NiMnO6 (LNMO) catalyst was prepared by the sol–gel method and the calcination method. By changing the calcination temperature (800, 900, and 1000 °C), the LNMO-based catalysts were successfully formed, abbreviated as L-800, L-900, and L-1000. XPS measurements demonstrated the presence of Mn4+, Mn3+, Mn2+, and oxygen vacancies (OVs) in the LNMO-based catalysts. Analysis of PL, PC, EIS, and TR-PL demonstrated that L-900 had the highest separation efficiency and fastest carrier mobility. The LNMO-based catalysts were used to degrade tetracycline (TC). With the optimized catalyst L-900, the decomposition rate of TC reached 99.57% in 120 min. The entire TC degradation pathway was analyzed according to LC–MS measurements. Radical trap experiments and ESR technology revealed that the synergistic effect of Mn4+/Mn3+, Mn4+/Mn2+, and OVs not only effectively separated e– and h+ but also facilitated the formation of superoxide radicals (•O2–) to accelerate TC degradation. Radicals •OH, h+, and •O2– all contributed to TC deterioration in increasing order of importance. In addition, XPS measurements of the L-900 catalyst before and after use indicated that Mn4+/Mn3+, Mn4+/Mn2+, and OVs were not reactants but mediators of e– and h+. Finally, the mechanism of TC degradation with the LNMO-based catalysts was discussed. This work provided new material for TC degradation in the wastewater.