Removal of tetracycline from aqueous solution by MOF/graphite oxide pellets: Preparation, characteristic, adsorption performance and mechanism.

Tetracycline (TC) as a typical antibiotic has been used extensively and detected in soil, surface water, ground water and drinking water, which results in toxic effect and bacterial resistance. In this study, aluminum-based metal organic framework/graphite oxide (MIL-68(Al)/GO) pellets were prepared through the addition of sodium alginate (SA), a natural crosslinking agent, and applied as a novel adsorbent for aqueous TC removal. The adsorption materials were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2 adsorption-desorption analysis and X-ray photoelectron spectroscopy (XPS). Results demonstrated that the pellets maintained similar chemical structure with parent MIL-68(Al)/GO powder. It is noted that the surface area and total volume of the pellets decreased obviously due to the disappearance of micropores. Besides, the efficiency of MIL-68(Al)/GO pellets for TC removal was evaluated by adsorption properties compared with parent powder, including key influential parameters, and adsorption isotherms, kinetics and mechanisms. It is found that the adsorption process was conformed to pseudo-first-order kinetics model and more suitably described through Langmuir isotherm model, with 228 mg g-1 of the maximum adsorption capacity. Moreover, these pellets which were separated easily and quickly presented high adsorption capacity and good stability in a wide pH range. The adsorption mechanism of the pellets may be ascribed to the complex interactions of hydrogen bonding, π-π stacking as well as Al-N covalent bonding. Overall, the MIL-68(Al)/GO pellets might be a promising adsorbent and show great potential for the removal of aqueous TC.