Quick removal of metronidazole from aqueous solutions using metal–organic frameworks

Abstract

The growing release of antibiotics into the environment has motivated extensive studies on the elimination of these harmful substances and the development of advanced adsorbents. Metronidazole is a major example of antibiotic pollutants due to its extensive usage, high solubility in water and considerable resistance to degradation. The present research focuses on assessing the removal efficiency of metronidazole (MNZ) using two model metal–organic frameworks (MOFs), namely [Fe₃(μ₃-O)(μ₄-atpa)₃Cl]_n (NH₂-MIL-101-Fe; H₂atpa = 2-aminoterephthalic acid) and [Cu₃(μ₆-tma)₂]_n (HKUST-1; H₃tma = trimesic acid), which feature high specific surface areas of 3874 and 569 m² g⁻¹, respectively, and minute-scale adsorption rates. The effects of the solution pH, contact time, adsorbent loading and recycling, and initial concentration of MNZ were investigated in detail. In particular, NH₂-MIL-101-Fe exhibited an excellent MNZ adsorption and removal efficiency (above 90%) which can be attributed to its unsaturated metal sites, superior specific surface area, hydrogen bonding, and robust host–guest π–π interactions. The Langmuir and pseudo-second-order models allowed the adsorption isotherms and kinetics to be described, respectively, reflecting a homogenous adsorption surface and the dominance of chemisorption. The adsorption of MNZ by these MOFs can be considered as environmentally benign and the results of this research are expected to further motivate the application of metal–organic frameworks as promising adsorbents for removal of antibiotics from wastewater.