| In the past decade, in view of the unique structure and excellent performance, the micro-/nanostructured magnetic silica/carbon composites have been some fascinating developments. One of the major challenges in the synthesis of micro-/nanostructured magnetic composites is how to design and prepare the desired structure with specific functions for water pollution. In this paper, in view of micro-/nanostructured magnetic composites applied research in removal of Hg2+ from wasterwater, we synthesized magnetic chitosan microspheres and magnetic silica microspheres with high specific surface area, good biological compatibility magnetic recycling and the renewable ability.This thesis mainly includes the following content:Firstly, nanostructured magnetic chitosan microspheres (Fe3O4@CS) were successfully synthesized by a facile solvothermal method. The microspheres were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), fourier transform infrared spectroscopy (FTIR), and vibrating sample magnetometer (VSM). Analysis results revealed that the Fe3O4@CS microspheres were 220-250 nm in diameter with high magnetic saturation (> 38.5 emu/g). The microsphere was the accumulation body of small ferroferric oxide crystal particles coated with chitosan, and the size of ferroferric oxide crystal grain was about 10 nm. The magnetic saturation and monodispersity would be reduced with the increase of chitosan content in the as-prepared samples. The adsorption behavior of the Fe3O4@CS microspheres for Hg2+ was further investigated. The results revealed that the maximum adsorption for Hg2+ was 0.83 mmol g-1. The affinity towards Hg2+ was attributed to the amount of exposure amino and hydroxyl groups, and the monodispersity of the samples:when the chitosan content increased, the number of amino and hydroxyl groups would be increased, which helped to adsorb Hg2+; but at the same time the monodispersity of samples would be reduced, which reduced the number of exposure surface functional groups. The adsorption process of the sample for Hg2+ could reach equilibrium within 10 min, which showed that the adsorbent required a short time to achieve high adsorption efficiency. Moreover, the microspheres as adsorbents could be easily separated by an external magnetic field, and the adsorbed Hg2+ on the adsorbents could be removed by using disodium ethylenediaminetetraacetic acid (EDTA-2Na) solution, thus the adsorbents are readily reusable.Secondly, novel magnetic cores within hollow mesoporous silica microspheres were successfully synthesized by using the hybrid magnetic carbon (Fe3O4/C) spheres as templates. The microspheres were further functionalized with (3-mercaptopropyl) trimethoxysilane (MPTS) to produce the thiol functional groups, and their ability to adsorb trace of toxic Hg2+ was evaluated. The characterization results revealed that the hollow microspheres were 250-300 nm in diameter. The synthesized microspheres have a core-shell structure with an outer silica shell in thickness of 50 nm and a inner core of Fe3O4 particles with the size of about 10 nm. It was also found that the saturation magnetization of the sample was 62.5 emu g-1 and their BET surface area was 421 m2 g-1. These magnetic hybrid silica microspheres with thiol functional groups were found to have a high affinity to Hg2+, and were able to reduce even low concentration Hg2+ (<1 ppb) down to about 0.53 ppb, which was less than the Hg2+ content in the drinking water standard. The super strong affinity towards Hg2+ was attributed to the synergistic effect of the thiol groups and the unique structure of the microspheres. Moreover, the microspheres as adsorbents could be easily separated by an external magnetic field, and the adsorbed Hg2+ on the adsorbents could be removed by using hydrochloric acid, thus the adsorbents are readily reusable. |
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