Preparation Of Carbon-based Nanocomposites And Their Adsorption Properties For Uranium Ions

The rapid development of nuclear industry,such as uranium mining,nuclear power generation and spent fuel treatment,has caused radioactive pollution to water bodies and posed a potential threat to the ecological environment and human health.Therefore,safe and effective treatment of uranium contamination is an urgent task.In the past decades,many technologies have been developed to separate,enrich and recover uranium from different uranium-containing water bodies,including chemical precipitation,solvent extraction,ion exchange,membrane separation and adsorption.Among them,adsorption is one of the most promising methods for the separation and enrichment of uranium in aqueous solution due to its wide source of materials,low cost,high selectivity,simple operation,low energy consumption,fast rate and large capacity.In this work,carbon-based nanocomposite with high separation efficiency,excellent selectivity,good chemical and irradiation stability have been successfully constructed,and the adsorption properties of radioactive uranium have been studied in detail.Chapter 1:Single-walled carbon nanohorn?SWCNH?and triethylenetetramine?TETA?were used as starting materials.The hydrophilic carboxylated SWCNH?SWCNH-COOH?was prepared by mixed acid acidification,the nanoporous composite SWCNH-TETA with large surface area and abundant pore structure was prepared by amination.Static adsorption experiments show that:the optimum pH value for uranium is 6.0,the corresponding uranium adsorption capacity is 205.6 mg/g.The adsorption behavior conforms to the quasi-second-order kinetic equation,it can be well described by Langmuir adsorption isotherm,the adsorption of uranium???is controlled by chemical action.Thermodynamic studies show that adsorption is a spontaneous endothermic process.Moreover,the material has good selectivity and recycling performance for uranium adsorption.Chapter 2:Poly?amic acid?was successfully grafted onto Dahlia-like SWCNH?PAA/SWCNH-NH2? via in situ polymerization.Amide groups are active components for enriching metal ions and forming metal ion-amide bonds,static uranium adsorption experiments show that the optimum pH of adsorption uranium is 4.5,the adsorption behavior conforms to the quasi-second-order kinetic equation,it is controlled by chemical action.It can be well described by Langmuir adsorption isotherm,the theoretical adsorption capacity of single layer can reach 200 mg/g.Adsorption thermodynamics studies show that adsorption is a spontaneous endothermic process,and the material has good selectivity and recycling performance for uranium adsorption.Chapter 3:The rod-like ZnO-supported GO composites?ZnO-GO?were prepared by wet chemical method by using graphene oxide?GO?and Zn?NO₃?₂·6H₂O as raw materials in one step.The structure of the composites was characterized by scanning electron microscopy?SEM?,energy dispersive spectroscopy?EDS?and XPS spectroscopy.Static uranium adsorption experiments show that the optimum pH value adsorption of uranium is 4.5 and the maximum adsorption capacity is 179.8 mg/g.The adsorption behavior conforms to the quasi-second-order kinetic equation and is controlled by chemical action.