Hexagonal Fe-based MIL-88B nanocrystals with NH2 functional groups accelerating oxytetracycline capture via hydrogen bonding

Abstract

Here, the importance of hydrogen bonding from amino (NH2) functional group on NH2−MIL-88B in oxytetracycline (OTC) adsorption mechanism has been reported. To clarify this finding, two materials including MIL-88B and NH2−MIL-88B derived from two different ligands of 1,4-benzene-dicarboxylic acid (H2BDC) and 2-aminobenzene-1,4-dicarboxylic acid (NH2-BDC) were synthesized and characterized. The X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FT–IR) were adopted, and proving the existence of NH2 functional group in the material structure. Comparing the adsorption efficiency among adsorbents with/without NH2 groups was evaluated through several fundamental investigations including the effect of solution pH (3.2–10.8), Na+ ionic strength (25–800 mmol/L), contact time (0–120 min) and initial concentration (20–100 mg/L). The investigations indicated that the best adsorption condition was found at pH 5.7. The OTC sorption process reached out the equilibrium nature rapidly, at 60 min. It was also demonstrated the negligible effect of Na+ ions on OTC adsorption over both MIL-88B and NH2-MIL-88B Some statistical error functions (R2, MRE, χ2, HYBRID, and MPSD) were also selected for better evaluating several nonlinearised kinetic and isothermal models. The principal outcomes revealed that the maximum adsorption capacity (94.9 mg/g) obtained from Langmuir equation by NH2−MIL-88B was above 4-fold higher than that by MIL-88B. Based on these vital evidences, the role of hydrogen bonding and plausible mechanisms in accelerating OTC adsorption has been suggested.