Preparation Of Magnetic Nanocomposites For Adsorption Of Heavy Metal Ions

With the development of the society and the improvement of industrialization,the pollution that the heavy metal ions in water destroy ecology and harm human health is more and more obvious.Magnetic nanocomposites have been considered to be one of the most attractive functional materials around the world,due to their unique superparamagnetism,good biocompatibility,stable chemical property,strong adsorption capacity and easy to recycle,etc.Based on the research progress of such materials,there are still many issues to further discussion,such as,the monodispersity and stability of magnetic nanocomposites,selective adsorption ability,regeneration and recycle,adsorption mechanism,and so on.In this dissertation,Fe3O4,CaFe2O4 and CoFe2O4 magnetic nanoparticles as magnetic part in composites have been synthesized and characterized.Considering the chemical stability of materials,simple preparation technique and suitable magnetic property,CoFe2O4 nanoparticles and SiO2 are selected as magnetic and nonmagnetic components in composites,respectively.Core-shell structure with different morphologies,and porous structure have been designed.The as-prepared magnetic nanocomposites can be used in removal of heavy metal ions from aqueous solutions.The adsorption kinetics,adsorption thermodynamics,adsorption equilibrium,regeneration and recycle,etc.have been studied,which lays the foundation for practical application of the composite material.The main research contents are as follows:(1)The catenulate core-shell magnetic nanocomposite(CoFe2O4@SiO2-NH2)has been prepared and its successful application in adsorption of heavy metal ions(Cu(?),Cd(?)and Mn(?))from aqueous solution.The functionalized magnetic composite is composed of amorphous silica shell and CoFe2O4 magnetic core.CoFe2O4@SiO2-NH2 with a high saturated magnetization(28.09 emu/g)can be easily separated under a moderate external magnetic field.The equlibrium adsorption capacity of the adsorbent for Cu(?),Cd(?)and Mn(?)is 170.83?144.95 and 110.80 mg/g,respectively.In addition,the adsorption process of the composites is fitted by pseudo-second-order kinetics and a Langmuir isotherm model,showing the chemical adsorption mechanism.The adsorbent can be regenerated by HCl and reused for at least four times with a high adsorption efficiency of 85.41%.Based on results,the magnetic adsorbent could find potential applications in heavy metal wastewatertreatment.(2)Synthesis of core-shell superparamagnetic monodisperse nanospheres based on amino-functionalized CoFe2O4@SiO2 and study on their adsorption properties for heavy metal ions in water.The nanosphere is composed of a magnetic CoFe2O4 core(?10 nm),a non-porous silica layer(?35 nm)and an amino-functionalized layer.The monodisperse nanosphere with large specific surface area can graft many amino groups,which can improve its adsorption performance for heavy metal ions(Cu(?),Cd(?)and Pb(?)).The adsorption process on the nanospheres was well described by Langmuir model,and the maximum adsorption capacity for Cu(?)is achieved with a result of 410.72 mg/g.The adsorption kinetics can be best fitted by the pseudo-second-order model,indicating the chemical adsorption process.Analysis of a thermodynamic study shows that the adsorption process is spontaneous and endothermic in nature.After acid treatment,the as-synthesized adsorbent could be regenerated and reused for up to five cycles with high chemical and magnetic stability.Therefore,the monodisperse nanospheres can be employed as an adsorbent with excellent performance in the field of removal of heavy metal ions.(3)Preparation of novel magnetic porous composites modified with amino groups for heavy metals removal.The composite with high yield is prepared by a simple and low-cost method,which makes it conductive to industrialization application.The BET surface area of the porous CoFe2O4/SiO2 is 167.51 m2/g.Since that a variety of heavy metal ions exist together in actual heavy metal waste water,the adsorptions of Cu(?),Mn(?),Cd(?)and Pb(?)ions in single ion and mixed ions solutions are studied.The results show that the adsorbent affinity for heavy metal ions is not affected by other competing ion,showing large adsorption capacity and high removal efficiency(>90%).Adsorption mechanism was analyzed by the Langmuir adsorption isotherm model,quasi secondary adsorption dynamic model and adsorption thermodynamic.The results show that the novel magnetic composite with excellent adsorption properties is attributed to the strong surface complexation and its special chemical structure.