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 R-2 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 m(2) 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 C=O double bonds on the surface of ZIF-8 indicating the presence of antibiotics. The adsorption mechanism most likely involved pi-pi interactions between the conjugated groups in TC/OTC and the imidazole rings of ZIF-8.