| In the past two decades,the nuclear industry in China arose from nowhere to the rapid development currently.However,with the rapid growth of the number of nuclear power plants,tremendous amount of radioactive wastes are generated from the nuclear fuel cycle processes.As a result,the long-term safe handling of strong radioactive spent nuclear fuel has become a worldwide public concern,and it's one of the key factors affecting the sustainable development of the nuclear industry.Owing to their strong radioactivity and long half-lives,actinide elements are the main contributor to the radioactivity of the spent nuclear fuel,especially in long terms.Therefore,efficient recovery and immobilization of the actinides has been extensively studied,but questions remain regarding the basic understanding the interaction between actinide elements with multiple sequestration ligands under those reprocess conditions.Consequently,the study of the crystalline actinide phosphite/phosphate compounds would provide the accurate description of the coordination modes of actinides(especially uranium and thorium)with inorganic phosphite/phosphate ligands under different conditions,which offers an opportunity to further understand the process of spent nuclear waste recycling.In this study,a series of complex phosphite/phosphate uranyl/thorium compounds have been synthesized by adjusting the reaction conditions and the types of ionic liquids via ionothermal method.The obtained crystalline products were characterized by X-ray single crystal diffraction technique to obtain the precise structural description.The solid-state UV-Vis-NIR absorption and fluorescence spectra,as well as Raman spectrum for those compounds were obtained.Based on the structural elucidation and spectral characterization,potential application of these structures were explored.1)The crystalline compound containing mixed phosphite/phosphate nanoporous thorium element with special structure was prepared under ionothermal condition(denoted as ThP-1).The compound was characterized by X-ray single crystal diffraction technique,revealing that the structure of ThP-1 presented the largest three-dimensional channels(pore size of 11.32 ? x 11.32 ?)among all actinide-based inorganic compounds.More specially,ThP-1 adopted the same structural topology of MOF-5.Further hydrolytic stability test showed that the acid-base stability of ThP-1 was excellent.We further explored its ion exchange ability and demonstrated that ThP-1 exhibited sufficient ion exchange capability of uranium and was recyclable,based on the analysis of fluorescence spectroscopy,UV-Vis absorption spectroscopy and EDX data of ThP-1 before and after the ion-exchange experiments.2)By adjusting the reaction starting material and reaction time,two kinds of layered uranyl phosphite and uranyl phosphate compounds were successfully synthesized via ionothermal method(UP-1 and UP-2).The structures of the two compounds were characterized by X-ray single crystal diffraction technique.The structure analysis and comparison of the two compounds showed that the lamellar structures are consisted of the negatively charged uranyl layers with different cations to compensate the charge.Those cations in the free space between the layers also played a role as the structure directing agent,which resulted in the deviation of their crystal symmetries as indicated by different space groups,and their physical and chemical properties,consequently.The fluorescence spectra and UV-Vis absorption spectra of UP-1 and UP-2 were collected,showing typical absorption and emission features of the uranyl units.Moreover,compound of UP-2 is crystallized in a non-centrosymmetric space group and therefore exhibited strong SHG signal.The proton conductivity measurement showed that compound UP-1 was not able to conduct protons at the measured conditions,whereas UP-2 exhibited excellent proton conductivity ability in low temperature and high humidity environment. |
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