| With the development of modern industry,various pollutants have been produced,the compound pollution has become one of the common pollution situations of water pollution.The high-efficiency and selective removal of heavy metal ions in wastewater and the simultaneous removal of multiple types of pollutants have attracted widespread attention.The adsorption method is widely used in the field of wastewater treatment because of its simple operation,high efficiency,and wide adaptability.In order to cope with the increasingly severe and complex water pollution situation,the development of adsorbents with high adsorption capacity,good regeneration performance,easy solid-liquid separation,high selective removal of heavy metal ions and simultaneous removal of multiple types of pollutants is the focus and hotspot of research.The surface of chitosan contains a large number of amino and hydroxyl groups,it is easy to be chemically modified to introduce functional groups.It also has the advantages of non-toxic,biocompatibility and biodegradability,making it a very ideal water treatment agent,but it also has the disadvantages of difficult solid-liquid separation of traditional adsorbents.Therefore,the magnetic chitosan material prepared by combining chitosan and magnetic nanomaterials have the dual advantages of easy functionalization of the surface and easy magnetic separation,which makes it have broad prospects in the field of wastewater treatment.In order to improve the selective adsorption performance of the magnetic chitosan adsorbent for heavy metal ions and achieve simultaneous removal of multiple types of pollutants in wastewater,it is necessary to functionalize the surface of chitosan to introduce new functional groups to expand the application of magnetic adsorbents.Based on this,the thesis takes the enhancement of the adsorption capacity,solid-liquid separation capacity,regeneration capacity,stability,and functionality of the adsorbent as the starting point,using nano-Fe3O4 as the magnetic core to prepare the magnetic chitosan material,and active functional groups were introduced on the surface of the magnetic chitosan through phosphorylation or amidation reaction.The functionalized magnetic chitosan-based adsorbent was used for the purification of heavy metal wastewater and dye wastewater.The selective removal of metal ions in heavy metal wastewater and the simultaneous removal of heavy metals and dyes in complex wastewater have been realized,and then in-depth study the mechanism of synergistically enhancing the selective removal of heavy metal ions in the presence of dyes.The conclusions of the research are as follows:（1）Firstly,the research used the St（?）ber method to coat the surface of magnetic corewith silica,and then used the inverse emulsion method to prepare the magnetic chitosan adsorbent.A series of characterization methods were used to comprehensively analyze the thermal stability and magnetic properties of the crystal structure of the morphologic group components of the adsorbent.The magnetic chitosan adsorbent exhibits high selective adsorption performance for Ag（Ⅰ）in a mixed solution of multiple metal ions,the selective adsorption capacity of FFO@Chi and FFO@Sil@Chi for Ag（Ⅰ）can reach 85.86 and 86.14 mg/g,respectively.The adsorbents all have good magnetic separation performance,especially in the acid leaching experiment,the adsorbent coated with silica had better stability under acidic conditions.In the single metal pollution system of silver ions,the maximum adsorption capacity of FFO@Sil@Chi for Ag（Ⅰ）was 114.93 mg/g.The adsorption process was a spontaneous,endothermic and ordered monolayer adsorption,and the rate-controlling step was chemical adsorption.The EDS,FTIR and XPS characterization analysis proved that the efficient removal of silver ions by the adsorbent was mainly through the formation of covalent metal complexes with Ag（Ⅰ）through the amino and hydroxyl functional groups on the surface of FFO@Sil@Chi.（2）The adsorbents FC-P and FSC-P were prepared by phosphorylation modification on the surface of magnetic chitosan,and they were used in the study of selective adsorption of Pb（Ⅱ）in aqueous solution.The experimental results showed that the phosphorylated adsorbent showed a high selective adsorption capacity for Pb（Ⅱ）in the multiple metal ions,which indicated that the selective metal type changed from Ag（Ⅰ）to Pb（Ⅱ）before and after phosphorylation.In the Pb（Ⅱ）system,the maximum adsorption capacity of FSC-P and FC-P for Pb（Ⅱ）were reach to 212.8 and 181.8 mg/g,respectively,which was much higher than adsorbents FSC and FC.The calculated results of adsorption isotherms,adsorption thermodynamics and adsorption kinetics showed that the adsorption of Pb（Ⅱ）by the adsorbent was a monomolecular,spontaneous,endothermic and orderly chemical adsorption process.In addition,the adsorbent still had a high adsorption capacity for Pb（Ⅱ）after five adsorption-desorption cycles,indicating that the two adsorbents have regeneration performance and can be used as efficient and rapid separation adsorbents for single pollutant systems removal and pre-enrichment of Pb（Ⅱ）.The characterization analysis by XPS and FTIR analysis showed that the main mechanism of FSC-P adsorbing lead ions was that Pb（Ⅱ）binds to the adsorption sites on the adsorbent surface through complexation,ion exchange and electrostatic interaction.（3）The adsorbents FFO@Chi-DTPA and FFO@Sil@Chi-DTPA were prepared by amidation modification of magnetic chitosan materials,which have high selective adsorption capacity for Pb（Ⅱ）in the mixed solution,and the selectivity coefficients can reach 70.41%and 73.28%,respectively.In the Pb（Ⅱ）system,the Langmuir model could be used to calculate the maximum adsorption capacity of FFO@Sil@Chi-DTPA for Pb（Ⅱ）to 322.58 mg/g.The results of recycling experiments also showed that FFO@Sil@Chi-DTPA had good regeneration performance and could be used as an efficient and rapid separation adsorbent to remove Pb（Ⅱ）in wastewater.The adsorption mechanism of Pb（Ⅱ）was investigated by EDS,FTIR and XPS characterization analysis before and after the adsorption of Pb（Ⅱ）by the adsorbent,showed that the main mechanism of the adsorption of Pb（Ⅱ）by FFO@Sil@Chi-DTPA was the complexation between the carboxyl,hydroxyl and amino functional groups on the adsorbent surface and Pb（Ⅱ）.（4）In order to study the simultaneous removal of different types of pollutants coexisting in wastewater by magnetic adsorbents,firstly,the influence of different conditions on the adsorption of methyl blue by FFO@Sil@Chi-DTPA and FFO@Sil@Chi were systematically studied.The results showed that the adsorption capacity of MB decreased with the increase of p H.Pseudo-second-order kinetics and Langmuir isothermal adsorption model can better describe the adsorption process of MB,and the maximum adsorption capacity is 181.37 and 546.73 mg/g,respectively.The ion strength adsorption experiments showed that salt ions increased the dimerization of MB dye molecules,resulting in the increase of adsorption capacity for MB.After adsorbing MB,the adsorbent can be desorbed by anhydrous ethanol,and have good recycling performance.In the complex wastewater,the coexistence of MB enhanced the selective adsorption of FFO@Sil@Chi for Ag（Ⅰ）and the selective adsorption of FFO@Sil@Chi-DTPA for Pb（Ⅱ）.In the Ag-MB system,FFO@Sil@Chi can simultaneously remove MB and Ag（Ⅰ）,and the presence of MB enhanced the adsorption capacity of FFO@Sil@Chi for Ag（Ⅰ）,while the adsorption effect of MB was almost unaffected by the presence of Ag（Ⅰ）.In the Pb-MB system,FFO@Sil@Chi-DTPA can show a synergistic effect on the adsorption of Pb（Ⅱ）and MB,not only simultaneously remove Pb（Ⅱ）and MB in the wastewater,but also through synergy enhances the adsorption capacity of Pb（Ⅱ）and MB. |
