| Hydrothermal carbon microspheres(HTC) is regarded as an attractive multipurpose matrix material because it possesses distinct novel and attractive characteristics, including simple and mild synthetic conditions, easy access to raw materials, relatively stable physical and chemical properties, and good hydrophilicity. However, few functional groups on the surface and low selectivity to uranium limit its application in radionuclide adsorption in aqueous solution. In this thesis, we add some monomers as functional agents in the synthesis of hydrothermal carbon microspheres to obtain HTC-AO, HTC-AM and HTC-PO4, which greatly improve adsorption capacity and selectivity for uranium(VI). The morphology and functional groups on the surface of the hydrothermal carbon microspheres have been analyzed by SEM, FT-IR and XPS. The factors that affect the adsorption of U(VI) in aqueous solution such as initial p H values, the initial concentrations of U(VI), contact time and temperature have been investigated by batch static adsorption experiments. In addition, the adsorption kinetics, isotherms and thermodynamics have been also discussed. The selectivity, desorption and reuse properties of modified HTC have been also studied.The amidoxime HTC(HTC-AO) was prepared through the hydrothermal method. During the hydrothermal reaction process, starch and water were used as the carbon source and the functional monomers, respectively. HTC-AO retains the perfect spherical appearance of HTC-sta. Adsorption of U(VI) over HTC-AO was fitted well with Langmuir isotherms and pseudo-second-order kinetics, the monolayer saturated capacity was 724.6 mg g-1, and the adsorption process was endothermic and spontaneous. The adsorptive selectivity of HTC-AO was very high in the presence of different metal ions, the uranium-selectivity(Su) could reach 52.2 %. The U(VI) adsorbed on HTC-AO can be eluated by 1.0 mol·L-1 HCl solution, the desorption rate was 93.5%, after 4 cycles, HTC-AO still haves high adsorption capacity to U(VI).The amidated HTC(HTC-AM) has been synthesized via one-step hydrothermal carbonization of glucose and acrylamide. The HTC-AM has a good spherical morphology. Adsorption of U(VI) over HTC-AM was fitted well with Langmuir isotherms and pseudo-second-order kinetics, the monolayer saturated capacity was 262.5 mg g-1. The thermodynamic studies results show that the adsorption process was endothermic and spontaneous. The results of selectivity experiment show that HTC-AM exhibits high selectivity for adsorption of U(VI), the highest uranium-selectivity(Su) was 35.3%. The desorption and reuse studies result show that the U(VI) adsorbed on HTC-AM can be eluated by 1.0 mol·L-1 HNO3 solution, the desorption rate was 96.4%, after several cycles of adsorption-desorption, the adsorption capacity of HTC-AM was not reduced evidently.The phosphorylated HTC(HTC-PO4) has been synthesized via one-step hydrothermal carbonization of glyoxal in the presence of vinylphosphonic acid. In the process of synthesis, the spherical morphology of HTC-PO4 has not been broken. Adsorption of U(VI) over HTC-PO4 was fitted well with Langmuir isotherms and pseudo-second-order kinetics, the monolayer saturated capacity was 319.5 mg g-1, and the adsorption process was endothermic and spontaneous. In the selectivity experiment, the uranium-selectivity(Su) of HTC-PO4 could reach 57.9 %. The results of desorption and reuse studies show that the U(VI) adsorbed on HTC-PO4 can be eluated by 1.0 mol·L-1 HNO3 solution, the desorption rate was 92.9%, after 4 cycles, the adsorption capacity of HTC-AM decreased only by 9.1 %. Keywords: Hydrothermal carbon microspheres, Uranium, Adsorption, Functionalization... |
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