Synthesis of reduced graphene oxide/magnetite composites and investigation of their adsorption performance of fluoroquinolone antibiotics
Graphical abstract
Highlights
► Reduced graphene oxide/magnetite composites were synthesized by an in situ reaction. ► CIP or NOR with a maximum adsorption capacity of 18.22 or 22.20 mg g−1. ► CIP and NOR adsorption could be well described by the pseudo-second order kinetics model. ► Adsorption process was a spontaneous and exothermic process.
Introduction
Pharmaceutical antibiotics are used extensively worldwide in human therapy and the farming industry. Fluoroquinolones are among the five class of antibiotics (fluoroquinolones,β-lactam, macrolides, sulfonamides, and tetracyclines) frequently detected at relatively high concentrations in the environment [1]. Residues of them discharged from agricultural runoff and municipal wastewater treatment plants are frequently detected in surface water, groundwater, and drinking water [2], [3]. The widespread of fluoroquinolones has become a serious problem as it has a variety of potential adverse effects, including acute and chronic toxicity [4]. Because fluoroquinolones antibiotics have been shown to disrupt microbial respiration and be poorly metabolized, the removal of fluoroquinolones antibiotics by conventional water and wastewater treatment technologies is generally incomplete [5], [6]. The adsorption and removal of fluoroquinolones antibiotics by several materials, including kaolite [7], montmorillonite [8], clay [9], zeolite [10], goethite [11], aluminum alumina [12], activated carbon [13], single-walled carbon nanotubes and multiwall carbon nanotubes [14], [15] was studied in previous studies.
Recently, graphene oxide (GO), a kind of novel two-dimensional carbon nanomaterial, was developed for the removal of pollutants in the aquatic environment [16]. GO with large quantities of oxygen atoms on the surface are present in the forms of epoxy, hydroxyl, and carboxyl groups. These functional groups make GO hydrophilic and suitable to be an adsorbent [17]. The reduced graphene oxide (RGO) was also applied for the removal of toxic elements and compounds from contaminated water [18]. At the same time, some typical metal oxide nanomaterials were prepared and applied in water treatment [19], [20]. However, centrifugation or filtration of GO and RGO was normally needed during the treatment, which was troublesome and tedious. Especially, some iron oxide nanomaterials composited with GO and RGO as magnetic adsorbents were a better solution [21]. The reduced graphene oxide/magnetite composites (RGO-M) responded to a magnet, which could realize the retrieval and separation of RGO rapidly and effectively [22], [23], [24]. Zhang et al. reported the synthesis of RGO-M via multi-step process and preliminary study on removal of tetracycline antibiotics [25]. So far, the equilibrium, isotherm, kinetics and thermodynamics analysis of fluoroquinolone antibiotics adsorption on RGO-M has not been reported yet.
Herein, the reduced graphene oxide/magnetite composites (RGO-M) were synthesized by an in situ reaction, and the adsorption characteristics and mechanisms of two representative fluoroquinolone antibiotics, ciprofloxacin (CIP) and norfloxacin (NOR) were investigated by batch adsorption tests. The adsorption kinetics, isotherm, thermodynamics, and the impacts of contact time, pH and temperature on adsorption were also studied.
Section snippets
Materials
Ciprofloxacin hydrochloride (CIP, >98%) and Norfloxacin (NOR, >98%) were purchased from TCI Development Co., Ltd (Shanghai, China). Stock solutions of 50 mg L−1 were prepared in Millipore reverse osmosis water and diluted as required. Acetonitrile for high performance liquid chromatograph (HPLC) was obtained from Sigma–Aldrich (Shanghai, China). Graphene oxide was purchased from XF nano company (Nanjing, China). Ferric chloride (FeCl3·6H2O) was purchased from Shanghai Chemical Reagents Company.
Materials characterization
Fig. 1 shows TEM images of RGO-M composites. The monodispersed Fe3O4 microspheres were decorated to the whole reduced graphene oxide surface homogeneously. There were seldom aggregation of the Fe3O4 microspheres, which implied the nucleation and growth of the Fe3O4 crystals mediated by the oxygen-groups on the graphene oxide surface. The average diameter of the Fe3O4 microspheres obtained via a solvothermal method is about 130 nm. The loading density of Fe3O4 microspheres on the RGO surface was
Conclusions
In this study, the reduced graphene oxide/magnetite composites were synthesized by an in situ reaction. Ciprofloxacin and norfloxacin adsorption on RGO-M were investigated with the maximum adsorption capacity of 18.22 or 22.20 mg g−1. The equilibrium adsorption of CIP and NOR on RGO-M at 298 K could be well fitted by both Langmuir and Temkin models. The kinetics process of CIP and NOR on RGO-M was well described by the pseudo second-order model. The adsorption performances were strongly affected
Acknowledgements
This work was supported by National Natural Science Foundation of China (21007048), Key Projects in the National Science & Technology Pillar Program during the Twelfth Five-year Plan Period (2012BAJ25B06), Shanghai Nano-program (No. 11nm0506100), State Key Laboratory of Pollution Control and Resource Reuse Foundation (PCRRY11011) and the Fundamental Research Funds for the Central Universities.
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