Synthesis Of Uranyl Ion Imprinted Polymers And Their Adsorption Performance

Uranium contaminated wastewater resulted from nuclear reactors and nuclear industries such as uranium mining and metallurgy may cause serious environmental pollution. Since uranium is a chemically toxic and radioactive heavy metal element, the inhalation of uranium or its compounds may lead to progressive or irreversible renal injury and in acute case may lead to kidney failure and death. Accordingly, the determination of uranium in environmental samples is an important task. However, uranium concentrations in environment samples are usually very low and high concentration of interfering ions are present, which makes it difficult for direct determination. Thus, the separation and preconcentration techniques are prerequisite for the accurate determination of uranium in environmental samples. Compared with those methods such as chemical precipitation, liquid–liquid extraction and ion exchange, adsorption appears to be a particularly effective method for the separation and preconcentration of uranium and an adsorbent with high selectivity and good affinity towards UO22+ is required. The ion- imprinted polymer is a promising adsorbent in selective separation and preconcentration of UO22+ due to its high selectivity and good affinity for the target ion. In this dissertation, three uranyl ion imprinted polymers were successfully prepared by using surface ion imprinting technique and their adsorption performances were investigated by batch adsorption experiments. The main results are described as following:Firstly, a uranyl ion imprinted polymer based on silica particles was prepared by co-polymerization of methacrylic acid-UO22+ complex with ethylene glycol dimethacrylate as the cross- linker at the surface of vinyl functionalized silica particles. The vinyl groups introduced onto the surface can direct the selective occurrence of imprinting polymerization at the surface. Then, the product was characterized by FT-IR, SEM and elemental analysis. The adsorption experiments suggested that this imprinted polymer exhibited high adsorption efficiency towards UO22+ and the adsorption was endothermic and spontaneous in nature. Furthermore, the adsorption kinetics followed the pseudo second-order kinetic model and the chemical adsorption might be the rate-controlling step. Also, the Langmuir adsorption isotherm was fitted better with the experimental data and the maximum adsorption capacity of imprinted and non- imprinted polymers was 35.92 and 22.58 mg g-1, respectively. Moreover, this imprinted polymer exhibited IV high adsorption selectivity towards UO22+, which indicated that this imprinted polymer could be used as an adsorbent for the separation and preconcentration of uranium from environmental samples.Secondly, the uranyl ion- imprinted polymer with higher selectivity and adsorption capacity was prepared by pre- irradiated surface- initiated graft polymerization in the presence of the UO22+–methacrylic acid complex. A high grafting density and rigid polymer structure could be obtained by surface-initiated graft polymerization. Meanwhile, pre- irradiation in air is a green, convenient, effective and low-cost approach for immobilization of peroxides as initiators onto the surface and the introduced peroxides are stable at room temperature. Moreover, UO22+ can promote the decomposition of peroxides to the oxy radicals to induce graft polymerization. The n, the adsorption behavior of the synthesized imprinted polymer towards uranium was investigated by batch experiments. The results revealed that the adsorption kinetics followed the pseudo second-order kinetic model and was endothermic and spontaneous in nature. Also, the Langmuir adsorption isotherm model was fitted better with the experimental data and the maximum adsorption capacity calculated was 46.42 mg g-1. Moreover, the imprinted polymer exhibited excellent adsorption selectivity and affinity towards UO22+. Meanwhile, the imprinted polymer has good reusability and stability.Finally, another surface ion-imprinted polymer based on Si O2-coated graphene oxide with fast adsorption kinetics has been synthesized by surface imprinting technique. The product was characterized by FT-IR, SEM, TGA and Raman spectroscopy and the adsorption behaviors of the imprinted polymer were investigated by batch experiments. The adsorption kinetics followed pseudo-second order kinetic model and a fast adsorption kinetics was clearly observed, which might be attributed to the high specific surface area of GO. Furthermore, the adsorption was endothermic and spontaneous in nature. The calculated maximum adsorption capacity of imprinted and non- imprinted polymers was 17.89 and 10.32 mg g-1, respectively and the adsorption followed Langmuir adsorption isotherm. Moreover, the selectivity study revealed that the imprinted polymer exhibited high selectivity and good affinity to UO22+. Meanwhile, the prepared imprinted polymer showed good reusability and stability.In conclusion,the ion imprinting technique is a powerful method for synthesizing highly selective sorbent for UO22+ and an imprinted polymer with higher selectivity and adsorption capacity could be prepared by pre-irradiated surface- initiated graft polymerization. Meanwhile, a rapid adsorption to UO22+ could be obtained by using Si O2-coated graphene oxide as the supporting material.