Hydrothermal synthesis of CuCoFe layered double hydroxide and its performance in the degradation of antibiotics: Influencing factors, degradation pathways, and reaction mechanism

In this study, the CuCoFe-LDH catalyst was synthesized by hydrothermal method and applied to degrade levofloxacin (LFX) by peroxymonosulfate (PMS) activation. The physicochemical properties of the synthesized samples were analyzed by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The influence of various factors such as catalyst system, pH, catalyst content, PMS, pH, and coexisting ions on the degradation of LFX was systematically investigated. The results showed that after 10 min, 94.57 % of LFX was decomposed under the conditions of 200 mg/L of catalyst, 500 mg/L of PMS, 10 mg/L of LFX, and pH 7.0. Besides, the CuCoFe-LDH/PMS system can effectively remove LFX over a wide pH range from 3.5 to 9.0. Both radical superoxide (O2•-) and non-radical singlet oxygen (1O2) were major reactive oxygen species in the CuCoFe-LDH/PMS system. Mass spectrometry identified 16 major degradation products of LFX, and 38.43 % of LFX was mineralized after 30 min of reaction. Besides, the CuCoFe-LDH/PMS system had the ability to effectively degrade different groups of antibiotics (e.g., fluoroquinolone, tetracycline, and sulfonamide). The mechanism of PMS activation by CuCoFe-LDH and the LFX degradation pathway were proposed. Finally, testing the reusability of CuCoFe-LDH in LFX degradation showed that a decrease of nearly 7 % occurred after five consecutive cycles, suggesting its stability for practical applications.