Ultrasound-assisted heterogeneous activation of peroxydisulfate by cobalt‑iron layered double hydroxide for efficient pharmaceutics degradation

Abstract

In this study, CoFe layered double hydroxide (LDH) was synthesized using the co-precipitation method, and the successful synthesis of it was confirmed by the X-ray diffraction pattern. The surface functional group of LDH was assessed by Fourier-transform infrared spectroscopy, and its elemental composition was analyzed using energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. Scanning and transmission electron microscopy analyses verified the layered structure of the LDH. The catalytic activity of CoFe LDH, with a band gap of 2.42 eV, was investigated for the activation of peroxydisulfate (PDS) under ultrasonic irradiation (US) for the degradation of levofloxacin. The effect of operational parameters, including pH, pollutant concentration, catalyst dosage, and PDS concentration, was investigated. The highest degradation efficiency of 97.1 % was obtained for levofloxacin with an initial concentration of 15 mg/L under optimized conditions of 0.4 mmol/L of PDS, 0.5 g/L of CoFe LDH, and pH 6 within 120 min of reaction. The prominent roles of reactive radical and non-radical species, including sulfate radicals, hydroxyl, singlet oxygen, and generated holes, were revealed by employing various scavengers, indicating that the singlet oxygen played the most significant role in this system. The degradation intermediates were identified using gas chromatography–mass spectrometry, and a probable mechanism was proposed for the levofloxacin degradation. Finally, the developed ternary CoFe LDH/PDS/US system was successfully used to treat three other diverse pharmaceuticals, including tilmicosin, oxytetracycline, and cefixime, achieving 100 % degradation efficiency and highlighting the potential of this process in water treatment applications.