Carbon quantum dots decorated Ag/CuFe2O4 for persulfate-assisted visible light photocatalytic degradation of tetracycline: A comparative study

Tetracycline is a broad-spectrum antibiotic largely found in the environment with many adverse effects on environmental and human health. Recently, the coupling of different advanced oxidation processes has been promised as the effective approach for the degradation of refractory pollutants. In this work, the magnetically separable Ag/CuFe2O4/CQDs photocatalyst was successfully synthesized and characterized by X-ray powder diffraction, Differential reflectance spectroscopy, Transmission Electron Microscopy, Field emission scanning electron microscopy, and Energy-dispersive X-ray spectroscopy analysis. The potential of different systems namely photocatalyst/light, photocatalyst/persulfate and photocatalyst/persulfate/light as well as operation parameters, reusability and involved radicals were evaluated for tetracycline degradation. The highest removal efficiency for the different systems was obtained as photocatalyst/persulfate/light (100%, 30 min) > photocatalyst/persulfate (100%, 55 min) > photocatalyst/light (100%, 75 min). The 47% total organic carbon removal was obtained in optimum condition and intermediate products were proposed based on results of liquid chromatography-mass spectrometry. The results indicated that reaction rate constant (K-obs) decreased from 0.1319 to 0.0270 min(-1 ), 0.0332 min(-1) and 0.0174 min(-1 )with increasing pH, initial tetracycline concentration and humic acid (HA), respectively. The inhibitory effect of inorganic ions was obtained as Cl- < NO3- < HCO3- . The nanocomposite showed high reusability after 5 consecutive cycles (91.5%). The results of the scavenger analysis suggest the superoxide and positive hole are the main species involved in tetracycline degradation.