首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
A family of cesium aryloxides [Cs(OAr)](n) were synthesized and structurally characterized from the reaction of 1:1 or 1:excess stoichiometry of Cs(0) and the appropriate alkyl-substituted phenol: 2-alkylphenol [alkyl = methyl (H-oMP), isopropyl (H-oPP), and tert-butyl (H-oBP)] and 2,6-dialkylphenol [alkyl = methyl (H-DMP), isopropyl (H-DIP), tert-butyl (H-DBP), and phenyl (H-DPhP)]. The products were structurally identified as [Cs(oMP)(H-oMP)(2)](n) (1), [Cs(5)(oPP)(5)](n) (2), [Cs(4)(oBP)(4)(H-oBP)(6)](n) (3x, shown), [Cs(3)(DMP)(3)](n) (4), [Cs(2)(DIP)(2)](n) (5), [Cs(DIP)(H-DIP)](n) (5x), and [Cs(DPhP)](n) (7). Compounds 1-7 were found to adopt complex polymeric structures employing π interactions from the neighboring pendant phenoxide ligands. The solution behavior of these compounds was studied using solution (133)Cs NMR spectroscopy, and for each compound, a single (133)Cs NMR resonance was observed, with chemical shift values found to be strongly solvent-dependent. This implies that monomeric cesium salt species involving solvent interactions exist in solution.  相似文献   

2.
本文报道1^H、7^Li、23^Na、133^Cs NMR测定N, N'-二羧甲基大环醚双内酯(1-4)和大环胺双内酰胺(5), N-对甲苯磺酰基大环醚双内酯(6, 7), 4'-丹磺酰氨基苯并-18-冠-6(8)与Li^+、Na^+、K^+、Cs^+、Cd^2+和Pb^2+金属离子的配位作用, 并以非线性最小二乘法拟合计算了配合物的形成常数; 同时, 发展了一种用133^Cs NMR测量冠醚和碘离子竞争配合Cs^+的配合物形成常数的新技术。  相似文献   

3.
H-MFI type zeolitic materials of different Si/Al ratios have been completely or partially cesium-exchanged (cesium content ranging from 0.7 to 7.7 Cs/unit-cell (uc)). Examined with synchrotron X-ray powder diffractometry, an anhydrous sample with the Cs6.6H0.3Al6.9Si89.1O192 chemical composition revealed at ambient temperature the presence of five discrete Cs locations: Cs1 located in the channel intersection near a 10-ring window of the zigzag channel; Cs2 and Cs2', both located in the straight channel but 1.23 A apart; Cs3 and Cs3', both located in the zigzag channel and rather close to each other (2.51 A). The populations of the Cs species amounted to 2.61/0.81/1.85/0.86/0.47/uc for Cs1/2/2'/3/3', respectively. The continuous but multimodal nature of the C2 split site is well-described by a joint-probability density function. The 10-ring of the straight channel in the framework is highly elliptical (epsilon = 1.218). The populations for the same sites were also determined at higher temperatures: 131, 237, 344, and 450 degrees C. At 450 degrees C, Cs2' has migrated toward the center of the channel intersection, and the site separation between Cs2 and Cs2' has lengthened to 2.23 A. Using a temperature-controlled laboratory X-ray diffractometer, similar studies were carried out on partially or almost totally Cs-exchanged samples from various sources with differing Cs contents. They show that over the 0.7 to 4 Cs/uc range all the individual Cs populations vary linearly as a function of total Cs/uc present. At higher total Cs/uc content (4 to approximately 7 Cs/uc) solely Cs1 continues to do so. For Cs2+Cs2' and Cs3+Cs3', the variation is almost linear over the whole concentration range. Computer simulations using a 6-exp-1 Buckingham-type atom-atom van der Waals interaction model yield six possible Cs sites in the actual Cs6.6MFI framework structure. Four of them lie very close to those determined from difference Fourier maps using the room temperature data. A fifth one is close to the Cs2' species after thermal migration at 450 degrees C, and the sixth one is close to the center of the channel intersection. However, this latter site is observed experimentally only in the case of hydrated CsMFI phases. In the anhydrous Cs6.6MFI phase at room temperature, the shortest Cs-framework oxygen distance is Cs3'-O25 = 3.08 A, and the next shortest distances are Cs1-O26 = 3.37, Cs2-O11 = 3.34, Cs2'-O22 = 3.47, and Cs3-O20 = 3.34 A. The framework T(Si,Al) sites most involved in these contacts are the T9, T11, T12, T10, and T3 sites. This implies that these sites are prime candidates for Si/Al substitution.  相似文献   

4.
For the disposal of the high efficiency particulate air (HEPA) glass filter to environment, the glass fiber should be leached to lower its radioactive concentration. To derive the optimum method for removal of Co and Cs from HEPA glass fiber, four methods were applied in this study. Results of electrochemical leaching of glass fiber by 4.0 M HNO3–0.1 M Ce(IV) solution showed that the removal efficiency of 134Cs, 137Cs, and 60Cs from glass fiber after 5 h was 96.4, 93.6, and 93.8%, respectively. Results by 5 wt% NaOH solution showed that the removal efficiency of 134Cs, 137Cs, and 60Cs after 30 h was 81.7, 82.1, and 10.0%, respectively. Results by repeat 2.0 M HNO3 solution showed that the removal efficiencies of 134Cs, 137Cs, and 60Cs after 2 h of three repetitions were 96.2, 99.4, and 99.1%, respectively. Finally, results by repeat 4.0 M HNO3 solution showed that the removal efficiencies of 134Cs, 137Cs, and 60Cs after 4 h of three repetitions were 100, 99.9, and 99.9%, respectively, and their radioactivities were below 0.1 Bq/g. Therefore, the chemical leaching method by 4.0 M HNO3 solution was considered as an optimum one for removal of cesium and cobalt from HEPA glass fiber for self disposal. Also the removal efficiencies of 60Co, 134Cs, and 137Cs from the waste-solution after its precipitation-filtration treatment for reuse of 4.0 M HNO3 waste-solution were 88.0, 95.0, and 99.8%.  相似文献   

5.
The fluorescence properties of 2-aryl-3-hydroxyquinolin-4(1H)-one-carboxamides (3HQCs) with carboxylic alkylamide groups at positions 6, 7 or 8 (3HQ6Cs, 3HQ7Cs, and 3HQ8Cs) have been studied to evaluate their potential as molecular probes.  相似文献   

6.
A new Cs(I) magnetic ion-imprinted polymer (Cs(I)-MIIP) aimed at the selective adsorption and separation of Cs(I) from salt lake brine was prepared. The Fe3O4@SiO2 was used as supporter, Cs(I) as template ion, and carboxymethyl chitosan as functional monomer. The product was characterized by Fourier transform infrared spectra, XRD, energy-dispersive spectrometry, scanning electron microcopy, thermogravimetric analysis, and vibrating sample magnetometer. The adsorption of the Cs(I)-MIIP in solution was investigated, which indicated the maximum adsorption capacity was 36.15?mg·g?1 under the optimum conditions. The pseudo-first-order kinetic model and the Freundlich isotherm model were applied to predict the adsorption process of Cs(I) onto Cs(I)-MIIP. Selectivity experiments showed that the relative selectivity coefficient (k′) were 24.995, 1.73, 1.43, 4.83, and 1.63 to Cs(I)/Li(I), Cs(I)/Na(I), Cs(I)/K(I), Cs(I)/Rb(I), and Cs(I)/Sr(II) binary solutions, higher than those of NIP, respectively. Furthermore, the Cs(I)-MIIP was successfully applied to the enrichment and separation of Cs(I) from the salt lake brine of Qinghai, with satisfactory Cs(I) recovery rates.  相似文献   

7.
A variety of wild mushrooms were collected in a forest on the Noto Peninsula, Japan, to determine the concentration of 137Cs and 40K. The wild mushroom species belong to the orders Agaricales and Aphyllophorales. The concentration of 137Cs varied widely (1.4–4,100 Bq/kg dry weight) in mushrooms growing in soil. On the contrary, 137Cs concentration levels were relatively low (1.9–20 Bq/kg-dry weight) in mushrooms growing on wood. The concentration of 40K varied widely (12–2,400 Bq/kg-dry weight) in contrast with several previous reports that suggest relatively constant 40K levels in mushrooms. Unusually low concentrations of 40K were observed in a few mushroom species that had very hard fruiting bodies with peculiar shapes. The mean and median of 137Cs concentration in the present study were similar to those previously reported for Japanese mushrooms. Among the Agaricales mushrooms, Entolomataceae and Tricholomataceae families growing in soil had the highest concentration of 137Cs. Among the Aphyllophorales mushrooms, Gomphaceae and Ramariaceae families growing in soil also had the highest 137Cs concentrations. The concentrations of 137Cs and stable Cs in mushroom samples were positively correlated. The concentration ratio of 137Cs/Cs differed between Agaricales and Aphyllophorales mushrooms. The average 137Cs/Cs ratio in mushrooms growing in soil was similar to that calculated for the top soil (<5 cm deep) alone because the mycelia of the mushrooms were mainly distributed near the surface of the soil.  相似文献   

8.
In relation to the interaction between (137)Cs and soil organic matter, electrospray mass spectrometry experiments and density functional theory (DFT) calculations were carried out on the dissociation of positively charged adducts formed by cesium nitrate and cesium organic salts attached to a cesium cation [Cs(CsNO(3))(CsA)](+) (A = benzoate, salicylate, hydrogen phthalate, hydrogen maleate, hydrogen fumarate, hydrogen oxalate, and hydrogen malonate ion). These mixed clusters were generated by electrospray from methanol solutions containing cesium nitrate and an organic acid. Collision-induced dissociation of [Cs(CsNO(3))(CsA)](+) in a quadrupole ion trap gave [Cs(CsNO(3))](+) and [Cs(CsA)](+) as major product ions. Loss of HNO(3) was observed, and also CO(2) loss in the case of A = hydrogen malonate. Branching ratios for the dissociation into [Cs(CsNO(3))](+) and [Cs(CsA)](+) were treated by the Cooks' kinetic method to obtain a quantitative order of bonding energetics (enthalpies and Gibbs free energies) between Cs(+) and the molecular salt (ion pair) CsA, and were correlated with the corresponding values calculated using DFT. The kinetic method leads to relative scales of Cs(+) affinities and basicities that are consistent with the DFT-calculated values. This study brings new data on the strong interaction between the cesium cation and molecular salts CsA.  相似文献   

9.
Due to the mismanagement of nuclear waste as well as heat exchanger degradation for the primary coolant of the one megawatt nuclear research reactor, the fission product137Cs has been leaking to the environment ever since 1969. In the past thirty years, the long-lived137Cs was accumulated and eventually trapped in the mud of the discharge pond right in front of the waste storage and the reactor facility. The distribution of137Cs in mud was measured and contour-mapped to reveal the migration of trace levels of137Cs in a period of three decades.  相似文献   

10.
131Cs has been a useful radionuclide for myocardial scanning and localisation of certain tumors in man. It has a half-life of 9.7 days and the decay product of131Ba (T=11.6 d). The authors have developed a131Ba−131Cs generator based on ion exchange chromatography over hydrous zirconium oxide yielding131Cs quantitatively and in a pure form. This method can also be employed in any isotope laboratory for the large scale production of131Cs.  相似文献   

11.
Infrared spectra of the 1/1 complex between water and carbon dioxide isolated in a nitrogen matrix are reported. Isotopic substitution of water (HOD, D2O) suggests the existence of two very weak complexes with a nearly T-shaped structure where the C atom is bonded to the water oxygen: one of C2v symmetry and another one of Cs symmetry, in which a slight distortion results in a very weak interaction between one hydrogen atom of water and one oxygen atom of carbon dioxide. This result is supported by force constant calculations, consistent with a double, symmetrical, and unsymmetrical force field, and ab initio calculations. At the MP2/aug-cc-PVTZ level corrected from basis set superposition error the C2v structure is a saddle point with an imaginary frequency for H2O rocking, in contrast to a Cs structure, which would have nonequivalent hydrogen atoms. Nevertheless, the energies of both structures, with a stabilization energy of 1.97 kcal mol-1, differ by less than 0.01 kcal mol-1 from each other. A comparison of calculated and observed frequency shifts allows us to suggest the presence in the matrix of both C2v and Cs complexes.  相似文献   

12.
The removal of cesium from concentrated aqueous solutions into Ca/Mg-bentonite for a wide range of bentonite-to-water (m/V) ratios was studied experimentally and theoretically. Using the batch technique, the equilibrium of Cs uptake was measured. The nonlinear character of cesium sorption substantially influenced by the m/V ratio was observed. The experimental data were evaluated using the multicomponent Langmuir isotherm and an ion-exchange model based on the ion-exchange reaction between Cs+ and M2+ (Ca2+/Mg2+) initially sorbed on bentonite. Constants k1,Cs = 0.521 mmol.g-1, k2,Cs = 968 L.mol-1, and k2,M = 592 L.mol-1 were obtained for Cs uptake described by multicomponent Langmuir isotherm. For the ion-exchange model, the thermodynamic equilibrium constant K = 75.5 mL.g-1 with a standard deviation of sK = 17.4 mL.g-1 was determined. Using the t test, the calculated data of multicomponent Langmuir and ion-exchange isotherms were fit to experimental data, and the best agreement was obtained for the ion-exchange model. The results show that Cs uptake by bentonite could be substantially decreased in systems with a high bentonite-to-water (m/V) ratio as a consequence of the presence of desorbed divalent cations in the liquid phase.  相似文献   

13.
In this present work, the kinetic reaction constants including the forward (kf, Cs adsorption onto granite) and backward (kb, Cs desorption from granite) rate constants of Cs on granite were determined by fitting the experimental data from both adsorption and desorption experiments with a pseudo first-order reaction model. In the case of Cs adsorption, both forward and backward rate constants are consistent with one another as Cs loading less than 0.1 mM. In contrast, both forward and backward reaction constants from desorption experiment dramatically increase as the Cs loading increases. Rearrangement of these desorption data by linearization technique, a notable instantaneous desorption process appears, which profoundly influences the determination of the rate constants. Based on our fitting results, the rate constants including both forward and backward reactions determined from Cs adsorption onto granite are much suitable to represent the adsorption behavior, in which the recommended values are of 0.42 and 0.03 h−1, respectively.  相似文献   

14.
Natural 210Pb and artificial 137Cs were applied for estimation of sedimentation rates for 14 cores collected in the White Sea, Franz Victoria and Novaya Zemlya troughs. Vertical profiles of 137Cs with high resolution (0.5–1 cm) are presented for 18 cores. The agreement between sedimentation rates obtained from 210Pb age-dating and 137Cs vertical profiles was found. Two maxima of 137Cs specific activity were observed in the cores near the North Dvina and Onega mouths, which may be correspond to the Chernobyl accident and global fallouts in early 1960-s.  相似文献   

15.
Extending our previous investigation of dehydrated, Cs-exchanged MFI zeolites (J. Phys. Chem. B 2006, 110, 97-106) to hydrated analogues, we have determined the crystal structures of members of the Cs(6.6)H(0.3)MFI.xH(2)O series, for 0 < x < 28, from synchrotron-radiation powder diffraction data. In the fully hydrated phase, three independent Cs(+) cations and six water molecules are identified in difference Fourier maps. The populations of the cations amount to 2.79/3.40/0.41 Cs/unit cell (uc) for the Cs1/Cs2/Cs3 sites, respectively, and those of the water molecules to 4/4/4/4/8/4 H(2)O/uc for the Ow1/Ow2/Ow3/Ow4/Ow5/Ow6 sites, respectively. Close to water saturation, the Cs3 and Ow6 sites are near each other (approximately 1.44 A) and are not occupied simultaneously. At saturation, Cs cations and water molecules form three interconnected Cs(H(2)O)(n) clusters and one (H(2)O)(4) cluster in the MFI channel system: Cs2(H(2)O)(5) centered at x/y/z approximately -0.018/0.146/0.546 (midway between the intersection and the straight channels), Cs1(H(2)O)(4) centered at approximately 0.056/0.240/0.889 (the zigzag channel openings), Cs3(H(2)O)(2) centered at approximately 0.228/0.25/0.899 (in the zigzag channel), and the (H(2)O)(4) cluster (in the zigzag channel) bonded to Cs1 and Ow1. (H(2)O)(4) and Cs3(H(2)O)(2) exclude each other. The Cs2(H(2)O)(5) clusters are connected through weak Ow5...Ow5' hydrogen bonds (2.88 A) and form polymeric chains in the straight channel direction (010). During progressive hydration this Cs2 cation enlarges its hydration shell, stepwise, from Cs2(H(2)O)(2) to Cs2(H(2)O)(3), to Cs2(H(2)O)(4), and finally to a Cs2(H(2)O)(5) cluster. During the dehydration process, these extraframework species migrate, and it is shown that for varying total H(2)O/uc loadings the individual populations of the Cs(+) cations and H(2)O molecules strongly depend on experimental and measurement (in situ vs ex situ) conditions. The shapes of the channels change also; except for T > 150 degrees C, in all the Cs(6.6)H(0.3)MFI.xH(2)O phases, the straight channel D10R (double 10-ring) pore openings (1.16 < epsilon < 1.23) become strongly elliptical. The framework structure of all the investigated phases conforms to orthorhombic Pnma space group symmetry. Hydration and dehydration in Cs(6.6)MFI are fully reversible processes. From a knowledge of the Cs(+) locations, we are able to estimate, by computer simulations, the positions of H(2)O molecules in Cs(6.6)H(0.3)MFI.28H(2)O. The maximum theoretically possible water loading in an hypothetical and idealized cationless [Cs(6.6)H(0.3)]MFI structure amounts to 48 H(2)O/uc (nine independent water species), which is in fair agreement with existing high-pressure data (47 H(2)O/uc). This value is to be compared with the water saturation capacity obtained in a structural refinement of sealed-tube diffraction data of a proton-exchanged H(6.9)MFI.38H(2)O (seven independent water molecules). In the crystal structure of this H-ZSM-5 phase, the straight channel openings are almost circular (epsilon = 1.08). From this we conclude that the main factor responsible for the flexibility of the MFI framework is the presence of the Cs(H(2)O)(n)() clusters residing in, or close to, the straight channel double 10-rings.  相似文献   

16.
The cesium isotope 135Cs has an extremely long half-life (τ1/2 = 2.3 · 106 y) and its high water solubility leads to the anxiety of exudation to ground water during geological disposal. Such a LLFP 135Cs would be converted into 136Cs (Its half-life is 13.16 d and it becomes stable 136Ba) by neutron capture reaction. However intermingling 133Cs of which the natural abundance is 100% disturbs this nuclear converting reaction because 133Cs also absorbs neutrons and produces 135Cs again. For separating 135Cs from other cesium isotopes, laser-chemical isotope separation (LCIS) is believed to be suitable mainly due to the light absorption and emission stability. Isotope separation of alkali metal 85Rb/87Rb was successfully achieved, showed 23.9 of head separation factor by LCIS. The measured isotope shift of Cs D2 line is within the reach of available semiconductor lasers having emission line width of less than 1 MHz, which shows that the selective excitation of 135Cs may turn to be possible. It is known that cesium excited to the 62P3/2 state may forms cesium hydride while ground-state cesium does not. Therefore if the lifetime of 62P3/2 state is sufficiently longer than the inverse rate of the chemical reaction, 135Cs can be extracted as cesium hydride. Applicability of the Doppler-free two-photon absorption method for selective excitation and further evaluation on Rydberg states and ionization should be investigated.  相似文献   

17.
The alkaline 1-phenyl-1H-1, 2, 3, 4-tetrazole-5-thiolate salts, M[C6H5N4CS] (M = Li ( 1 ), Na ( 2 ), K ( 3 ), Rb ( 4 ) and Cs ( 5 )) were obtained and characterized by means of mass spectrometry (FAB+) and NMR (1H; 13C) spectroscopy. The structures of Na ( 2 ), K ( 3 ), Rb ( 4 ) and Cs ( 5 ) compounds were determined by X-ray diffraction methods. The ligand shows a rich variety of coordination patterns with the alkaline cations. The formation of a four-membered ring MSCN in the compounds with heavier alkali cations (K, Rb and Cs) is shown. In all the cations the coordination number around it increases with the ionic radius. Compounds with Cs+ and Rb+ exhibited the formation of Cs-C and Rb-C interactions with the phenyl group.  相似文献   

18.
The radioactive contamination following the Chernobyl accident resulted in high concentrations of 137Cs in several mushrooms species. Mushroom samples were collected in a forest environment between 1986 and 2007 and the transfer of 137Cs to two edible species, Suillus variegatus and Cantharellus spp., was investigated. The 137Cs uptake by the collected samples did not decrease over time and in Cantharellus spp. a significant increase was observed. Most of the 137Cs in soil still appears to be available for uptake and radioactive decay of the radionuclide is likely the main factor for the reduction of 137Cs in a forest ecosystem.  相似文献   

19.
Measurements performed in 1986–1988 demonstrate that most of the radiocesium isotopes (137Cs and134Cs) deposited after the Chernobyl accident are still located in the upper soil layers (0–2 cm). The vertical migration appears to be slow, and only a small fraction of the radiocesium has been transferred into the biological cycle. Sequential extraction techniques have been utilized in order to investigate the degree of binding or association between deposited radionuclides (137Cs,134Cs and90Sr) and components in soil. The results indicate that a major fraction of the radiocesium is associated strongly with organic and mineral materials in the litter or upper soil layers: less than 10% is easily leachable. The distribution of137Cs throughout the fractions was similar to that determined for naturally occurring stable cesium (133Cs), implying that isotopic exchange had been extensive. For90Sr, the results show a relatively high leachable fraction. Therefore, present results indicate that radiocesium should be less mobile, and less available for root uptake, than90Sr in soil.  相似文献   

20.
The equilibrium geometric structures, stabilities, and electronic properties of bimetallic Au(n)Cs (n = 1-10) and pure gold Au(n) (n ≤ 11) clusters have been systematically investigated by using density functional theory with meta-generalized gradient approximation. The optimized geometries show that one Au atom capped on Au(n-1)Cs structures and Cs atom capped Au(n) structures for different sized Au(n)Cs (n = 1-10) clusters are two dominant growth patterns. Theoretical calculated results indicate that the most stable isomers have three-dimensional structures at n = 4 and 6-10. Averaged atomic binding energies, fragmentation energies, and second-order difference of energies exhibit a pronounced even-odd alternations phenomenon. The same even-odd alternations are found in the highest occupied-lowest unoccupied molecular orbital gaps, vertical ionization potential, vertical electron affinity, and hardnesses. In addition, it is found that the charge in corresponding Au(n)Cs clusters transfers from the Cs atom to the Au(n) host in the range of 0.851-1.036 electrons.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号