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室田 健人*; 青柳 登; Mei, H.; 斉藤 拓巳*
Applied Geochemistry, 152, p.105620_1 - 105620_11, 2023/05
被引用回数：1 パーセンタイル：62.05(Geochemistry & Geophysics)The confinement in small spaces influences the complicated reaction involving water molecules under electrostatic potentials at the solid-liquid interface. It is unclear, in particular, how the hydration state of metal ions adsorbed on the surface changes as a function of the pore size. This study analyzed the adsorption states of europium aqua ions on mesoporous silicas with different pore distributions in comparison with nonporous silica using time-resolved laser-induced fluorescence spectroscopy. The parallel factor analysis was used to differentiate the contribution of different chemical species of Eu(III) to the fluorescence signal and determine the influence of the pore size on each chemical species. The results show that Eu(III) mainly form outer-sphere complexes with silica below pH 6, where Eu(III) adsorption is low. Within nano-sized pores, distortion of the hydration structure and a decrease in the hydration number were suggested in this pH range. As the concentration of the silicate ions derived from the dissolution of silica increases with increasing pH, Eu(III) form the silica/Eu(III) /silicate ternary surface complexes. Within nano-sized pores, the concentration of silicate ions decreases due to the overlap of the electric double layer, which inhibits the formation of the ternary surface complex. Furthermore, at high pH, Eu(III) multinuclear complexes formed only on the mesoporous silica surface. This adsorption behavior specific to nano-sized pores could not be concluded by macroscopic adsorption experiments alone because the amount of Eu
adsorbed per unit surface area did not differ between the mesoporous and nonporous silicas. Consideration of the silicate complexes should be indispensable in future studies on the adsorption of lanthanide ions using mesoporous silica.
BaCo(PO
)Sheng, J.*; Wang, L.*; Candini, A.*; Jiang, W.*; Huang, L.*; Xi, B.*; Zhao, J.*; Ge, H.*; Zhao, N.*; Fu, Y.*; et al.
Proceedings of the National Academy of Sciences of the United States of America, 119(51), p.e2211193119_1 - e2211193119_9, 2022/12
被引用回数：3 パーセンタイル：28(Multidisciplinary Sciences)Although considerable progress has been made in the theoretical understanding of the low-dimensional frustrated quantum magnets, experimental realizations of a well-established scaling analysis are still scarce. This is particularly true for the two-dimensional antiferromagnetic triangular lattices. Owing to the small exchange strength, the newly discovered compound NaBaCo(PO) provides a rare opportunity for clarifying the quantum criticality in an ideal triangular lattice with quantum spin S=1/2. In addition to the establishment of the complete phase diagrams, the spin Hamiltonian with a negligible interplane interaction has been determined through the spin wave dispersion in the polarized state, which is consistent with the observation of a two-dimensional quantum critical point with the Bose-Einstein condensation of diluted free bosons.
Mei, H.; 青柳 登; 斉藤 拓巳*; 香西 直文; 杉浦 佑樹; 舘 幸男
Applied Geochemistry, 136, p.105178_1 - 105178_8, 2022/01
被引用回数：11 パーセンタイル：86.47(Geochemistry & Geophysics)Dissolved inorganic carbonate ions (DIC) present in groundwaters may affect both the aqueous and surface species of U(VI) due to its strong complexation ability with U(VI). However, it is still not clear how DIC affects U(VI) sorption on illite, which is one of the critical components in argillaceous rocks. In this study, the sorption of U(VI) on conditioned illite du Puy in presence of varying DIC concentrations (up to 250 mM DIC) as a function of pH was investigated by combining batch sorption experiments, surface complexation modeling, and the cryogenic time-resolved laser fluorescence spectroscopy (TRLFS). The distribution coefficients of U(VI) were sensitive to the DIC concentration, which decreased with an increase of DIC. There is no sorption of U(VI) under relatively high DIC concentrations (100 mM DIC). The U(VI) sorption behavior on illite was modeled by using the 2 Site Protolysis Non-Electrostatic Surface Complexation and Cation Exchange model. Two ternary surface complexation reactions with carbonate were needed to depict the experimental sorption data in addition to binary and ternary hydroxo surface complexation reactions employed for the description of U sorption to illite without carbonate. The cryogenic TRLFS revealed that U(VI) did sorb to illite in presence of high DIC concentration (up to 10 mM DIC). The spectra were unchanged with DIC at pH 8.5, suggesting the surface speciation of U(VI) remained the same. The decay curves were biexponential, which further indicated that at least two species were responsible for the sorption. Our finding will help to predict the transport and retention behaviors of U(VI) near radioactive waste repositories.
Mei, H.; 青柳 登; 斉藤 拓巳*; 香西 直文; 舘 幸男
no journal, ,
Carbonate ions in groundwater are believed to influence migration behaviors of radionuclides in the geological environment by formation of aqueous carbonate complexes. However, little is known about the possibility of sorption of the radionuclide-carbonate complexes on minerals. We investigate U(VI) sorption on an illite mineral as functions of pH and carbonate concentrations, by combining cryogenic time-resolved laser fluorescence spectroscopy and surface complexation modeling. We will present the macroscopic and microscopic results of the speciation of U(VI) in the presence of carbonate and discuss the modeling of the sorption data, reflecting the speciation data.
室田 健人*; 青柳 登; Mei, H.; 斉藤 拓巳*
no journal, ,
放射性廃棄物から溶出した放射性核種の地下環境中の動態においては、移行の過程での岩石や緩衝材内部の微小な空隙への吸着が重要な機構である。メソスケール(2
50nm)やナノスケール(2nm以下)の微小な空隙内での水の性質がより大きな空隙内でのそれと異なることが報告されているが、イオンの吸着がどのように異なるのかは明らかでない。そこで、微小空隙を有する岩石の模擬物質として、異なる径のメソ空隙を持つメソポーラスシリカに対しEu(III)を吸着させ、その吸着状態をTRLFSで分析した。得られたデータを多変量解析することで、空隙サイズによってEu(III)の吸着状態がどのように変化するのかについて調べた結果を報告する。
Mei, H.; 青柳 登; 斉藤 拓巳*; 香西 直文; 杉浦 佑樹; 舘 幸男
no journal, ,
U(VI) sorption on illite in the presence of varying concentrations of carbonate ions was investigated by using the cryogenic TRLFS technique. The sorption species were differentiated by analyzing the fluorescent spectral shape and lifetime and using Parallel Factor Analysis.
杉浦 佑樹; 石寺 孝充; 青柳 登; Mei, H.; 斉藤 拓巳*; 舘 幸男
no journal, ,
The sorption behavior of trivalent lanthanides (Eu/Sm) onto illite in the presence of dissolved inorganic carbon (DIC) was investigated by batch sorption experiments. The results of the experiments were interpreted using a thermodynamic sorption model (TSM). The TSM predicted that Eu/Sm forms clay mineral-Eu/Sm-carbonate surface ternary complexes. Time-resolved laser fluorescence spectroscopy (TRLFS) measurements were performed to obtain information on the chemical forms of Eu sorbed on illite. Parallel factor (PARAFAC) analysis of the TRLFS data indicated the presence of multiple chemical species. The pH dependence of the relative intensity of the chemical species derived from PARAFAC analysis was consistent with that of the surface species predicted by the TSM. The dominant chemical species in the presence of DIC was inferred to be coordinating carbonate ions based on the fluorescence lifetime. These results confirm the existence of surface ternary complex and the validity of the TSM.
Mei, H.; 青柳 登; 斉藤 拓巳*; 杉浦 佑樹; 石寺 孝充; 田中 万也; 舘 幸男
no journal, ,
The sorption of U(VI) and trivalent lanthanides on illite at different pH and dissolved inorganic carbon (DIC) levels was investigated. The obvious inhibition effect of DIC on U(VI) and trivalent lanthanides sorption was revealed from the macroscopic batch experimental results. The formation of carbonate-containing sorption complexes was needed to be considered in the updated 2-site protolysis non-electrostatic surface complexation and cation exchange model to reproduce the experimental results. Based on the Parallel Factor Analysis analysis on the cryogenic time-resolved laser fluorescence spectroscopy spectra, the formation of ternary carbonate-containing sorption complexes was successfully identified. Identification of the sorption species adds more credibility to the predictive sorption model, which provides more confidence in the safety assessment of deep geological disposal.
