| Since industrial revolution,with the rapid development of social economy and the continuous improvement of industrialization,a large number of pollutants have been discharged into the environment,causing increasingly serious environmental pollution and ecological destruction,among which the problem of water pollution is the most serious.There are many kinds of pollutants in the water,including organic dyes,heavy metals and tetracycline etc.Because these pollutants are highly toxic,difficult to degrade,and easy to enrich,they pose a great threat to human health and ecological environment security.Therefore,how to efficiently remove pollutants in the water has become a key research area in the environmental field.In recent years,with the innovation and development of nanotechnology,magnetic nanocomposites have become one of the most researched hotspots due to their advantages of good biocompatibility,high porosity,high adsorption capacity,and easy recycling.In this dissertation,Fe3O4 was used as the magnetic core component,and SiO2 was a non-magnetic shell component of the composite materials.Three types of magnetic nano-derived composites were prepared by cross-linking and grafting.In view of the above three common pollutants（organic dyes,heavy metals and tetracycline）,the removal performance and mechanism of these magnetic nanocomposites on contaminants in water were systematically studied.The specific research work and results of this article can be summarized in the following five aspects:（1）A magnetic nanocomposite（Fe3O4@SiO2/PEI）was prepared by coating the polymer PEI on the surface of the magnetic nanoparticles with Fe3O4@SiO2 magnetic core-shell nanoparticle as a carrier and used for the selective adsorption of anionic dyes in water.A variety of techniques such as transmission electron microscopy（TEM）,thermogravimetry（TG-DTA）,X-ray diffraction（XRD）,vibrating sample magnetometer（VSM）,infrared spectrometer（FT-IR）and X-ray photoelectron spectroscopy（XPS）have been used to characterize the material.The experimental results showed that the effect of Fe3O4@SiO2/PEI on the removal of methyl orange（MO）and Congo red（CR）from the water was greatly affected by the pH value,and the adsorption of MO reached a maximum of 233.5 mg/g at pH 4.0.Adsorption of CR reached a maximum of 134.6 mg/g at pH 6.0.Adsorption data were fitted by Langmuir isotherm model and Freundlich isotherm model,and the results showed that the adsorption of MO and CR by Fe3O4@SiO2/PEI were more consistent with the Freundlich model.With the increase of temperature,the amount of adsorption also increases.Thermodynamic studies showed that the adsorption reaction was an endothermic and spontaneous process.Kinetic studies showed that the adsorption of MO and CR by Fe3O4@SiO2/PEI conforms to the second-order-kinetic model,indicating that the rate-limiting step of the adsorption process is a chemical adsorption process.The study of selective adsorption in binary systems showed that Fe3O4@SiO2/PEI was excellent in the selective adsorption of anionic dyes and has the potential to selectively adsorb anionic dyes in wastewater from actual dyes.In addition,Fe3O4@SiO2/PEI has a good regeneration capability.（chapter 2）（2）Based on the Fe3O4@SiO2/PEI material,Fe3O4@SiO2/PEI was grafted onto GO surface through a simple chemical synthesis method to form the Fe3O4@SiO2/PEI modified graphene oxide composite（MSPG）,and it was used for the treatment of waste water containing anions and cationic dyes.It can be observed by scanning electron microscopy（SEM）that the addition of GO causes the MSPG to form a layered,uneven surface structure with numerous wrinkles,which increased the possibility of contact and adsorption of MSPG with organic dyes.The change of pH value had a great influence on the effect of MSPG on the adsorption of MO,CR and MB.Among them,the maximum adsorption capacity of MO was 233.5 mg/g at pH 4.0,the maximum adsorption capacity was 213.5 mg/g for CR at pH 6.0,and the maximum adsorption capacity was 99.89mg/g for MB at pH 10.0.The adsorption process of CR and MB by MSPG was more in accordance with the Freundlich adsorption model.While the adsorption of MO by MSPG was more consistent with the Langmuir adsorption model.At the same time,MSPG had positive values for theΔH°values of MO,CR,and MB.The Gibbs free energyΔG°was negative,showing that the adsorption process was an endothermic and spontaneous process.Compared with Fe3O4@SiO2/PEI,the MSPG not only had higher adsorption of anionic dyes MO and CR,but also had certain adsorption to MB,indicating that the addition of GO made the ability of MSPG to remove CR and MB significantly enhanced,and has more extensive practicality.（Chapter 3）（3）Fe3O4@SiO2/PEI modified graphene oxide（MSPG）was used as an adsorbent to remove Cu（Ⅱ）ions in water.Three variables of the initial concentration of Cu（Ⅱ）ions、pH and reaction temperature were optimized by Box-Behnken response surface method,and the predicted maximum adsorption was compared with the actual maximum adsorption.Fitting by Box-Behnken method,the optimal adsorption conditions of MSPG for Cu（Ⅱ）ion adsorption were as follows:initial concentration 80mg/L,initial pH 5,reaction temperature 40oC,and the maximum theoretical adsorption amount was 61.48 mg/g.Under the optimal conditions,the experimental value was 61.55 mg/g,which was similar to the theoretical value.Adsorption kinetics studies and isotherm studies showed that the adsorption process reached equilibrium at6 h,which was consistent with the pseudo-second-order kinetic model and Freundlich isothermal model.And the intra-particle diffusion was not the only rate control step in the entire process.Thermodynamic studies have shown that the adsorption of Cu（Ⅱ）by MSPG was an endothermic spontaneous process.（Chapter 4）（4）Using Fe3O4@SiO2 magnetic core-shell nanoparticles as carrier,the magnetic nano-composite（MSCG）was formed by glutaraldehyde cross-linked chitosan and modified graphene oxide to increase the mechanical properties and functional groups of adsorbents for the removal of Cr（VI）in aqueous solution.The results of characterization by scanning electron microscopy（SEM）,high resolution transmission electron microscopy（TEM）,Fourier transform infrared（FTIR）,vibrating sample magnetometer（VSM）andX-raydiffraction（XRD）indicatedthat Fe3O4@SiO2/Chitosan particles were successfully assembled on the surface of the GO layer.The adsorption kinetics follow the pseudo second-order model,and the MSCG adsorbent showed better Cr（VI）removal efficiency in solution at low pH.Thermodynamic parameters showed that the adsorption reaction was an endothermic and spontaneous process.In addition,the adsorption capacity was about 90%of the initial saturated adsorption after four uses.By using permanent magnets,the recycling process of MSCG adsorbent and adsorbed Cr（VI）was economically more sustainable.These results indicated that MSCG is a potential and suitable candidate for the enrichment and separation of Cr（VI）in wastewater and the deep purification of wastewater.（Chapter 5）（5）By using Fe3O4@SiO2/Chitosan modified graphene oxide composite（MSCG）as an adsorbent,the adsorption properties of TC in the presence or absence of Cu（Ⅱ）were studied.The adsorption results showed that the four background cations(Na+,K+,Ca2+and Mg2+)with a concentration of 0.01 M had almost no effect on the adsorption of TC in the studied pH range,while the divalent heavy metal cation Cu（Ⅱ）could significantly enhanced the adsorption of TC,and the highest adsorption capacity of TC on MSCG with and without Cu（Ⅱ）were 183.47 mmol/kg and 67.57 mmol/kg,respectively.The adsorption kinetics data can be better fitted to the pseudo-second-order model,indicating that the dominant rate-limiting step of the adsorption mechanism may be due to the chemisorption.With the addition of Cu（Ⅱ）,the adsorption time of TC on MSCG was significantly shortened from 480 min to 240min.Compared with the Langmuir model,the Freundlich model fits the adsorption isotherms better,indicating that the adsorption followed a multilayer adsorption process.Based on the study of the effect of pH and XPS analysis on the mechanism of TC adsorption,it was found that Cu（Ⅱ）can act as a bridge between TC and MSCG,which significantly improving the adsorption of TC.This study provides valuable guidance and effective methods for removing TC from the aquatic environment.（Chapter 6）... |
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