Adsorption Removal of Antibiotics from Aqueous Solutions by a Triazine-Functionalized Covalent Organic Framework Material

A novel triazine-functionalized crystalline polyimide covalent organic framework material (TF-COF) was designed and prepared by condensation of 2,4,6-tris(4-aminobiphenyl)-1,3,5-triazine (TABT) and pyromellitic dianhydride (PMDA) under solvothermal conditions. The obtained TF-COF material was thoroughly characterized by FT-IR, ¹³C-NMR, PXRD, TGA, SEM, TEM and BET, and then used as a solid adsorbent for water treatment. Because of its characteristics of crystalline structure, high specific surface area and good thermal stability, the TF-COF material exhibited excellent performance in removal of antibiotics from aqueous solutions. In the adsorption experiment, the adsorption selectivity of TF-COF for multiple antibiotics, and the effects of initial concentration, time and pH on adsorption were studied. TF-COF had high adsorption capacity for four common antibiotics including tetracycline hydrochloride (TCH), doxycycline (DOX), ciprofloxacin hydrochloride monohydrate (CIPHM) and moxifloxacin hydrochloride (MXFH). Meanwhile, based on the fitting results of adsorption isotherms, the adsorption process of TCH and DOX on TF-COF accorded with Freundlich model and CIPHM and MXFH on TF-COF conformed to Langmuir model. Fitting through Langmuir model, the maximum adsorption capacity of TF-COF at 25 °C for TCH, DOX, CIPHM and MXFH were 518 , 625, 227, 337 mg/g, respectively. The adsorption kinetic of four antibiotics on TF-COF could be described by pseudo-second-order kinetic model. TF-COF had the best adsorption effect for four antibiotics at pH=7. Furthermore, after five adsorption-desorption cycles, the adsorption effect of the material was almost unchanged, which indicated that TF-COF had good recycling performance.