In situ preparation of MOF-199 into the carrageenan-grafted-polyacrylamide@Fe3O4 matrix for enhanced adsorption of levofloxacin and cefixime antibiotics from water

Abstract

In this research study, a novel method, an in-situ growth approach, to incorporate metal-organic framework (MOF) into carrageenan-grafted- polyacrylamide-Fe₃O₄ substrate was introduced. Carrageenan-grafted-polyacrylamide-Fe₃O₄/MOF nanocomposite (kC-g-PAAm@Fe₃O₄-MOF-199) was fabricated utilizing three stages. In this way, the polyacrylamide (PAAm) was grafted onto the carrageenan (kC) backbone via free radical polymerization in the presence of methylene bisacrylamide (MBA) as cross-linker and Fe₃O₄ magnetic nanoparticles. Next, the kC-g-PAAm@Fe₃O₄ was modified by MOF-199 via an in-situ solvothermal approach. Several analyses such as Fourier transform infrared spectroscopy (FT-IR), X-Ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-Dispersive X-ray Spectroscopy (EDX), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM), Brunauer-Emmett-Teller (BET) demonstrated the successful synthesis of kC-g-PAAm@Fe₃O₄-MOF-199 magnetic hydrogel nanocomposite. The XRD pattern of magnetic hydrogel nanocomposite illustrated characteristic peaks of Fe₃O_4, neat kC, and MOF-199 with enhanced crystallinity in comparison with kC-g-PAAm@Fe₃O₄. TGA showed it has a char yield of 24 wt% at 800 °C. VSM confirmed its superparamagnetic behavior (with Ms of 8.04 emu g^-1), and the BET surface area of kC-g-PAAm@Fe₃O₄-MOF-199 was measured at 64.864 m² g^-1, which was higher than that of kC-g-PAAm@Fe₃O₄ due to the highly porous MOF-199 incorporation with a BET surface area of 905.12 m² g^-1). The adsorption effectiveness of kC-g-PAAm@Fe₃O₄-MOF-199 for eliminating cephalosporin and quinolones antibiotics, i.e., Cefixime (CFX) and Levofloxacin (LEV) from the aquatic area was considered. Several experimental setups were used to evaluate the efficacy of adsorption, such as solution pH, amount of adsorbent, contact duration, and initial concentration. The maximum adsorption capacity (Q_max) of the prepared magnetic hydrogel nanocomposite was found to be 2000 and 1666.667 mg^-1 for LEV and CFX using employing 0.0025 g of adsorbent. The Freundlich isotherm model well described the experimental adsorption data with R²_CFX = 0.9986, and R²_LEV = 0.9939. And the adsorption kinetic data were successfully represented by the pseudo-second-order model with R²_LEV = 0.9949 and R²_CFX = 0.9906. Hydrogen bonding, π-π interaction, diffusion, and entrapment in the hydrogel network all contributed to the successful adsorption of both antibiotics onto the kC-g-PAAm@Fe₃O₄-MOF-199 adsorbent. Other notable physicochemical properties include the three-dimensional structure and availability of the reactive adsorption sites. Moreover, the adsorption/desorption efficacy of magnetic hydrogel nanocomposites was not significantly diminished after four cycles of recovery.

Keywords: Carrageenan; Cefixime; Hydrogel magnetic nanocomposite; Levofloxacin; MOF-199; Pharmaceutical wastewater treatment.