| In recent years,antibiotics have been widely used in preventing and treating the disease of human and livestocks due to their stable chemical property and high efficacy.Moreover,the negative effects caused by the abuse of antibiotics are drawing much more attention.On the one hand,antibiotic residues in livestocks and poultry are a serious threat to food safety.On the other hand,the residual water soluble antibiotics including Tetracycline(TC)will be enriched in the water environment,and they are not easily degraded by microorganisms,which would lead to drinking water pollution.At present,the methods for removal of antibiotics include chemical oxidation,catalytic degradation,membrane filtration and adsorption.Among these methods,adsorption technology is widely concerned and applied because of its simple operation and low cost.In this work,we developed a one-pot method to fabricate the NiFe2O4-carbon dots nanocomposite as a novel adsorbent for the removal of TC.The structural characterizations and adsorption capacity of the Ni Fe2O4-carbon dots nanocomposites were systematically investigated.In details,the main research work and results of the study are listed as following:1.We reported a solvothermal method to synthesis the multi-functional carbon dots-modified NiFe2O4 nanocomposites and put forward a one-step method to fabricate magnetic ferrite and carbon dots in the meantime.The as-prepared NiFe2O4-carbon dots(NiFeC)were characterized by scanning electron microscopy(SEM)and transmission electron microscopy(TEM),results indicated that the NiFeC has a uniform spherical shape with dimensions ranging from about 130 to 180 nm.X-ray diffraction(XRD)and fourier transform infrared spectrum(FT-IR)analysis showed that NiFeC has all the characteristic peaks of NiFe2O4 and carbon dots,which confirmed the successful synthesis of the novel adsorbent NiFeC.The combination of carbon dots on NiFe2O4 not only could improve the adsorption performance of tetracycline,but also could reduce the easily occurred aggregation between NiFe2O4 and improve the dispersibility of nanocomposites in water.2.To investigate the adsorption properties of the novel adsorbent NiFeC to TC,a series ofbatch adsorption experiments were studied.The adsorption behavior of the as-prepared nanocomposites was systematically studied using kinetic and equilibrium experiments.Results revealed that the experimental data were better fitted to the pseudo-second-order model and Langmuir isotherm,suggesting that the chemisorption may be the controlling step in the TC adsorption process.The maximum adsorption capacity obtained from Langmuir isotherm was591.72 mg g-1.Furthermore,the removal capacity of NiFeC to tetracycline was compared with traditional adsorbents(activated carbon,zeolite,et al.)under the same experimental conditions.The adsorption capacity(530.83 mg g-1)of Ni FeC was higher than those of traditional adsorbents and was even 2 times higher than that of NiFe2O4(262.93 mg g-1),indicating the abundant functional groups and larger specific surface area of carbon dots played a vital role in enhancement of adsorption capacity for TC.What's more,the adsorption mechanisms of NiFeC on tetracycline,analyzed by FT-IR,TGA and XPS before and after TC adsorption,were surface complexation,cation exchange and electrostatic attraction.3.In order to evaluate the applicability of Ni FeC in water,the influence of salt ions on adsorption process and the reusability of NiFeC had been investigated.The results indicated salt ions had little effect on the adsorption capacity of TC.The regeneration study was performed and the results illuminated that the overall removal efficiency could still reach more than 90 % after recycling five times.Therefore,the prepared adsorbent Ni FeC has the advantages of high adsorption performance to tetracycline,easy preparation,separation and recovery,which makes them favorable candidates to remove antibiotics for water purification.It also provides a quick and easy method for the preparation of novel adsorbents. |
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