Adsorption Of U(Ⅵ) By Functionalized Mesoporous Silicas

With the fast consumption of traditional fossile energy, nuclear power as an abundant, low-carbon source based-load power is attracting renewed interest. Safe treatment of nuclear wastes which are released at various nuclear fuel cycle stages has been an essential environmental issue, and is also significant for the sustainable development of nuclear energy. Uranium, as a predominant fuel ingredient for most nuclear reactors, is the key element in nuclear fuel cycle. Efficient removal or recovery of mobile hexavalent uranium(U(VI)) from radioactive waste water and nuclear industry involved environment is of great importance for human health and environmental safety. In this thesis, a dihydroimidazole functionalized magnetic mesoporous silica(Fe3O4@n Si O2@m Si O2-DIM) with core-shell structure and KIT-6-DAPhen which grafted phenanthrolineamide groups onto a large pore three-dimensional(3-D) cubic silica support(KIT-6) were fabricated by post-grafting method, aiming to convenient remove U(VI) from aqueous solution. The sorption of U(VI) ions by the two materials were investigated under different conditions of p H, contact time, initial U(VI) concentration, ionic strength and solid-liquid ratio. The selectivity experiments were also conducted. The main results and conclusions are summarized as follows:(1) A dihydroimidazole functionalized magnetic mesoporous silica(Fe3O4@n Si O2@m Si O2-DIM) with core-shell structure was successfully fabricated by post-grafting method. The synthesized material were found to possess highly ordered mesoporous structure with large surface area, uniform pore size, excellent thermal stability, and quick magnetic response, characterized by SEM, FTIR, XRD, N2 sorption/desorption measurements and TGA.(2) A novel U(VI)-selective sorbent KIT-6-DAPhen was prepared by grafting phenanthrolineamide groups on its large pore three-dimensional(3-D) cubic silica support(KIT-6). Compared to mesoporous SBA-15 and MCM-41 support, KIT-6 support holds interconnected large pore 3-D cubic mesoporous nature, which is beneficial for reducing the risk of pore blocking during functionalization with large ligands. In addition, the three dimensional mesopore is highly accessible for the solution and metal ions during sorption process. The as-synthesized sorbent were found to possess highly ordered mesoporous structure with large surface area, and the phenanthrolineamide groups were successfully anchored onto the mesoporous KIT-6 support, characterized by SEM, HRTEM, N2 adsorption/desorption, XRD, FT-IR, 13 C CP/MAS NMR, and TGA techniques.(3) The sorption tests under various condition demonstrated that Fe3O4@n Si O2@m Si O2-DIM is indeed an effective U(VI) sorbent with fast sorption kinetics of less than 2 h, large sorption capacity of more than 100 mg/g at p H 5.5±0.1, and desirable selectivity for U(VI) ions over a range of competing metal ions. The sorbent can be readily separated from solution by simply adding an external magnetic field. FTIR analysis were employed for an in-depth probe into the sorption mode of U(VI) onto the Fe3O4@n Si O2@m Si O2-DIM; The interconnected 3-D pore network of KIT-6-DAPhen material exhibit fast sorption kinetics of less than 30 min, large sorption capacity of more than 328 mg/g at p H 5.0±0.1. The preorganized tetradentate phenanthrolineamide(DAPhen) ligand with hard-soft donors combined in the same molecule has been found to possess high selectivity towards U(VI). Above results clearly reveal the potential utility of the two materials prepared in this work as an effective sorbents for removal of U(VI) from wastewater.