Simultaneous removal of tetracycline and oxytetracycline antibiotics from wastewater using a ZIF-8 metal organic-framework

In this paper, a Zeolite Imidazole Framework-8 (ZIF-8), was investigated for the removal of a mixture of two common antibiotics, tetracycline (TC) and oxytetracycline hydrochloride (OTC). Batch experiments showed that 90.7% of TC and 82.5% of OTC were simultaneously removed using ZIF-8. The maximum adsorption capacities for TC and OTC were 303.0 and 312.5 mg g-1, respectively. For both antibiotics' adsorption followed pseudo-second-order kinetics and best fit the Langmuir adsorption model with R2 of 0.963 and 0.981, for TC and OTC at 303 K, respectively. The relatively large specific surface area of ZIF-8 (1158.2 m2 g-1) combined with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated that both antibiotics were adsorbed on to the surface of ZIF-8. X-ray powder diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy both indicated the presence of benzene ring structures, associated with both pollutants, on ZIF-8 after reaction; which confirmed adsorption was occurring. XPS also showed the presence of CO double bonds on the surface of ZIF-8 indicating the presence of antibiotics. The adsorption mechanism most likely involved π-π interactions between the conjugated groups in TC/OTC and the imidazole rings of ZIF-8.