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1.
Direct electrochemical determination of arsenate (AsV) in neutral pH waters is considered impossible due to electro-inactivity of AsV. AsIII on the other hand is readily plated as As0 on a gold electrode and quantified by anodic stripping voltammetry (ASV). We found that the reduction of AsV to AsIII was mediated by elemental Mn on the electrode surface in a novel redox couple in which 2 electrons are exchanged causing the Mn to be oxidised to MnII. Advantage is taken of this redox couple to enable for the first time the electrochemical determination of AsV in natural waters of neutral pH including seawater by ASV using a manganese-coated gold microwire electrode. Thereto Mn is added to excess (∼1 μM Mn) to the water leading to a Mn coating during the deposition of As on the electrode at a deposition potential of −1.3 V. Deposition of As0 from dissolved AsV caused elemental Mn to be re-oxidised to MnII in a 1:1 molar ratio providing evidence for the reaction mechanism. The deposited AsV is subsequently quantified using an ASV scan. AsIII interferes and should be quantified separately at a more positive deposition potential of −0.9 V. Combined inorganic As is quantified after oxidation of AsIII to AsV using hypochlorite. The microwire electrode was vibrated during the deposition step to improve the sensitivity. The detection limit was 0.2 nM AsV using a deposition time of 180 s. 相似文献
2.
E. Makrlík P. Toman P. Vaňura R. Rathore 《Journal of Radioanalytical and Nuclear Chemistry》2013,296(2):775-779
In methods for quantification of 63Ni, in e.g. reactor coolant water, a chemical separation is required due to 63Ni being a pure beta emitter with limited means of quantification. 60Co, a common radionuclide in reactor coolant water, is not completely separated with the commonly used separation procedure, and it is not resolved from 63Ni in the beta spectrum. The separation method discussed in this work consists of TRU resin (Eichrom) and Ni resin (Eichrom). After running the separation procedure, depending on the initial activity of 60Co, there may still remain enough 60Co to interfere in the measurement of 63Ni. The 60Co interference is corrected for via a gamma spectrometric measurement. This correction may, depending on the 63Ni/60Co ratio, introduce a large contribution to the measurement uncertainty. The aim of this work was to evaluate the possibility to reduce the measurement uncertainty of 63Ni measurements by adding a second Ni separation to the method. Double Ni separations were performed on reactor coolant water having a 60Co activity much higher than the 63Ni activity (63Ni/60Co = 0.01), in order to decrease the radioactivity of 60Co in the sample. The measurement uncertainty of the 63Ni measurement result was reduced by a factor of about three. 相似文献
3.
Chellaiah Arunkumar Dr. Yong‐Min Lee Dr. Jung Yoon Lee Shunichi Fukuzumi Prof. Dr. Wonwoo Nam Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(43):11482-11489
High‐valent manganese(IV or V)–oxo porphyrins are considered as reactive intermediates in the oxidation of organic substrates by manganese porphyrin catalysts. We have generated MnV– and MnIV–oxo porphyrins in basic aqueous solution and investigated their reactivities in C? H bond activation of hydrocarbons. We now report that MnV– and MnIV–oxo porphyrins are capable of activating C? H bonds of alkylaromatics, with the reactivity order of MnV–oxo>MnIV–oxo; the reactivity of a MnV–oxo complex is 150 times greater than that of a MnIV–oxo complex in the oxidation of xanthene. The C? H bond activation of alkylaromatics by the MnV– and MnIV–oxo porphyrins is proposed to occur through a hydrogen‐atom abstraction, based on the observations of a good linear correlation between the reaction rates and the C? H bond dissociation energy (BDE) of substrates and high kinetic isotope effect (KIE) values in the oxidation of xanthene and dihydroanthracene (DHA). We have demonstrated that the disproportionation of MnIV–oxo porphyrins to MnV–oxo and MnIII porphyrins is not a feasible pathway in basic aqueous solution and that MnIV–oxo porphyrins are able to abstract hydrogen atoms from alkylaromatics. The C? H bond activation of alkylaromatics by MnV– and MnIV–oxo species proceeds through a one‐electron process, in which a MnIV–‐oxo porphyrin is formed as a product in the C? H bond activation by a MnV–oxo porphyrin, followed by a further reaction of the MnIV–oxo porphyrin with substrates that results in the formation of a MnIII porphyrin complex. This result is in contrast to the oxidation of sulfides by the MnV–oxo porphyrin, in which the oxidation of thioanisole by the MnV–oxo complex produces the starting MnIII porphyrin and thioanisole oxide. This result indicates that the oxidation of sulfides by the MnV–oxo species occurs by means of a two‐electron oxidation process. In contrast, a MnIV–oxo porphyrin complex is not capable of oxidizing sulfides due to a low oxidizing power in basic aqueous solution. 相似文献
4.
Maria Assunta Meli Donatella Desideri Carla Roselli Laura Feduzi 《Microchemical Journal》2011,99(2):273-277
This paper describes the methods of sampling, preconcentration, chemical separation and final count of 210Po and 210Pb present in different marine matrices to determine their background levels in a marine ecosystem. Complex, time consuming and selective radioanalytical methods have been used to prepare final clear sources for alpha spectrometry and beta count; in fact, gamma spectrometry, a method direct and non destructive, cannot be taken into account because the 210Pb activity is very low which does not allow to carry out sufficiently accurate measurements and 210Po is not a gamma emitter but it emits only alpha particle at 5.40 MeV. The results of 210Po and 210Pb activity concentrations obtained in different marine samples collected in the first two campaigns are still very few to discuss about the 210Po and 210Pb behavior in marine environment. 相似文献
5.
A EuII‐Containing Cryptate as a Redox Sensor in Magnetic Resonance Imaging of Living Tissue
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Levi A. Ekanger Prof. Lisa A. Polin Dr. Yimin Shen Prof. E. Mark Haacke Dr. Philip D. Martin Prof. Matthew J. Allen 《Angewandte Chemie (International ed. in English)》2015,54(48):14398-14401
The EuII ion rivals GdIII in its ability to enhance contrast in magnetic resonance imaging. However, all reported EuII‐based complexes have been studied in vitro largely because the tendency of EuII to oxidize to EuIII has been viewed as a major obstacle to in vivo imaging. Herein, we present solid‐ and solution‐phase characterization of a EuII‐containing cryptate and the first in vivo use of EuII to provide contrast enhancement. The results indicate that between one and two water molecules are coordinated to the EuII core upon dissolution. We also demonstrate that EuII‐based contrast enhancement can be observed for hours in a mouse. 相似文献
6.
Polarographic and voltammetric methods were employed to study the influence of N-methylpyrrolidinone(2) (NMP) and N-methylthiopyrrolidinone(2) (NMTP) towards a series of cations. In NMP reversible electrode reactions were observed for Na+, K+, Tl+, Zn2+, Cd2+, Cu2+, Ag+ and irreversible reductions for Ba2+, Mn2+, Co2+ and Ni2+. 0.1 mol l?1 tetraethylammoniumperchlorate solutions served as supporting electrolytes. Li+ was not electroactive in the supporting electrolyte mentioned, but yielded an irreversible cathodic wave in tetra-n-butylammonium perchlorate. In NMTP, Li+, Na+, Tl+, Zn2+, Cd2+, Cu+ and Ag+ gave reversible cathodic waves on the DME, while Mn2+, Co2+ and Ni2+ were reduced in an irreversible electrode process. Bisbiphenylchromium iodide serving as a reference system throughout this study showed reversible behaviour in both solvents. A comparison of E1/2 for given ions in both solvents showed a shift of about 0.5 V to more positive values in the case of a typically hard cation such as Na+ whereas soft cations such as Ag+ and Cu+ shifted by more than 0.8 V to more negative values. The effects of these two solvents on the cations studied is discussed in terms of donor acceptor interactions between the cation and the solvent molecules with special respect to the changes caused by replacing the oxygen atom in NMP by a sulphur atom. 相似文献
7.
Dr. Ioannis Liratzis Dr. Stephan Walleck Dr. Jan Oldengott Anja Stammler Dr. Hartmut Bögge Dr. Eckhard Bill Prof. Dr. Thorsten Glaser 《欧洲无机化学杂志》2023,26(5):e202200650
The ligand H6ioan has been used to synthesize the three dinuclear complexes [(ioan)MnIITiIV], [(ioan)FeIITiIV], and [(ioan)FeIIITiIV]+. The face-sharing bridging mode of the three phenolates provides short M-TiIV distances of ≈3.0 Å. Mössbauer spectra of [(ioan)FeIIITiIV]+ show a magnetically split six-line spectrum at 3 K in zero magnetic field demonstrating a slow magnetic relaxation. Magnetic measurements provide a zero-field splitting of |D|=5 cm−1 in [(ioan)FeIITiIV]. EPR spectroscopy demonstrates sizable zero-field splittings of the S=5/2 spin systems of [(ioan)MnIITiIV] (D=0.246 cm−1) and [(ioan)FeIIITiIV]+ (D<−1 cm−1) that can be related to enforced covalency of the M-Oph bonds. [(ioan)FeIIITiIV]+ exhibits a reversible reduction at −0.26 V vs. Fc+/Fc demonstrating the facile accessibility of FeIII and FeII. In contrast to an irreversible oxidation in [(ioan)NiIITiIV] at 0.78 V vs. Fc+/Fc, the reversible oxidation at 0.25 V vs. Fc+/Fc in [(ioan)MnIITiIV] indicates even the access of MnIII. These results indicate that pentanuclear complexes [(ioan)FeM1M2M1Fe(ioan)]n+ are meaningful targets to access electron delocalization in mixed-valence systems over five ions due to the facile accessibility of both FeII and FeIII in the terminal positions. This study provides important local spin-Hamiltonian and Mössbauer parameters that will be essential for the understanding of the potentially complicated electronic structure in the anticipated pentanuclear complexes. 相似文献
8.
Usha Pandey Yogendra Kumar Ashutosh Dash 《Journal of Radioanalytical and Nuclear Chemistry》2014,300(1):355-360
While the extraction paper chromatography (EPC) technique constitutes a novel paradigm for the determination of few Becquerels of 90Sr in MBq quantities of 90Y obtained from 90Sr/90Y generator, validation of the technique is essential to ensure its usefulness as a real time analytical tool. With a view to explore the relevance and applicability of EPC technique as a real time quality control (QC) technique for the routine estimation of 90Sr content in generator produced 90Y, a systematic validation study was carried out diligently not only to establish its worthiness but also to broaden its horizon. The ability of the EPC technique to separate trace amounts of Sr2+ in the presence of large amounts of Y3+ was verified. The specificity of the technique for Y3+ was demonstrated with 90Y obtained by neutron irradiation. The method was validated under real experimental conditions and compared with a QC method described in US Pharmacopeia for detection of 90Sr levels in 90Y radiopharmaceuticals. 相似文献
9.
Vadithala Ramakrishna Rao Korandla Goverdhan Reddy Utukuri Venkata Seshaiah Vuppalapati Jayathyagaraju 《Transition Metal Chemistry》1993,18(3):258-261
Summary
N-salicylidene anthranilamide (H2SAA) and its CrIII, MnII, FeIII, CoII, NiII and CuII complexes were prepared and characterized by physicochemical and spectroscopic data. H2SAA enolizes to give a dibasic ONO donor set in the divalent metal complexes. It also binds to the trivalent metal ions in a nonenolized form using a monobasic ONN donor set. CoII is oxidized to CoIII during complexation. Octahedral geometries are proposed for CrIII, MnII, FeIII and CoIII complexes, while square planar geometries are suggested for the NiII and CuII complexes. Phenoxide bridging in the CrIII and FeIII complexes and enoxide bridging in the NiII and CuII complexes is proposed. 相似文献
10.
This study describes a highly sensitive and simple method of 169Yb tracing to investigate the uptake of Yb3+ in mouse erythrocyte. The amounts of Yb3+ absorbed by erythrocyte, membrane and cytoplasm at different time were determined after erythrocytes were incubated with
1.0.10-6mol.l-1 169Yb3+ solution at 37°C. The results indicated that Yb3+ absorbed on the membrane was transferred promptly to the cytoplasm during the separation process. The observation of a very
low level of Yb3+ in the cytoplasm could not lead to a verdict that Yb3+ could travel across the erythrocyte membrane
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
Solvent extraction of a mixture of PbII, MnII, FeIII, CoII, NiII and CdII in aqueous perchlorate medium by a phosphorylated hexahomotrioxacalix[3]arene (calix‐3) in dichloromethane shows a significant selectivity towards lead ions. The ligand can also be incorporated into a membrane to provide a new lead ion‐selective electrode (PbII‐ISE). A plasticized PVC membrane containing 30% PVC, 53.5% ortho‐nitrophenyloctylether (NPOE), 4.5% sodium tetraphenylborate (NaTPB) and 12% ionophore was directly coated on a graphite rod. This sensor gave a good Nernstian response of 29.7 ± 0.7 mV decade?1 over a concentration range of 1 × 10?8 – 1 × 10?4 M of lead ions, independent of pH in the range 3‐7, with a detection limit of 0.4 × 10?8 M. The dynamic response time of the electrode to achieve a steady potential was very fast and found to be less than 7 s. The selectivity relative to Ag+, NH4+, Li+, Na+, K+, Ca2+, Sr2+, Ba2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Fe3+, La3+, Sm3+, Dy3+, Er3+, Y3+ and Th4+ was examined. The electrode exhibits adequate stability with good reproducibility (with a slope of 29.6 ± 1.5 mV for 8 weeks). The characteristics of the sensor are compared with those of a tetraphosphorylated calix[4]arene (calix‐4) based PbII‐ISE, reported recently. The electrode was successfully used as an indicator electrode for a potentiometric titration of a lead solution using a standard solution of EDTA. The applicability of the sensor for lead ion measurements in various synthetic samples was also investigated. 相似文献
12.
R. G. Kingston A. G. Brenton M. Guilhaus J. H. Beynon 《Journal of mass spectrometry : JMS》1986,21(10):697-705
Intermediates in the overall charge inversion reaction NO? → O+˙ (la), have been found to be O and NO˙ neutrals, and NO+ ions. The intermediates involved have been characterized by various mass spectrometric techniques; for example, inducing the steps of the reaction in separate field-free regions allows the peaks for the consecutive reactions NO? → NO+ → O+˙ (II) to be recorded free from interference. However, to observe the involvement of a neutral intermediate, techniques such as floating the collision cell and applying a voltage to a deflector plate in front of the collision cell have been employed. Utilizing these methods allows a peak to be obtained due to one or both of the processes, NO? → NO˙ → O+˙ (IIIa) and NO? → O+˙ (IIIb), which cannot be separated. It is shown that the peak for the overall reaction NO? → O+˙ can be modelled and reconstructed by addition of peaks, in a ratio of 1:3, produced by reactions II and III. This provides a reasonable account of the peak shape, in particular, of the tails of the peak which correspond to fragmentations involving large translational energy releases of up to 10 eV. 相似文献
13.
A starter culture ofTrichoderma reesei (Rut-C30) prepared in a liquid fluidized bed reactor (LFBR) gave better growth and greater cellulase production in submerged
fermentation than a conventional shake flask inoculum. The LFBR starter was prepared by first coatingT. reesei spores to 0.25 mm size corncob (1.0x108g-1) in a medium containing 1.0% corncob, 0.5 gL-1 xylose and 0.1 gL-1 lactose in a balanced salt solution, then fluidizing the particles in the LFBR for 36 h to allow germination of the spores,
and covering the particles with an approx 30 μm thick biofilm. This biofilm that developed in constant adherence to the lignocellulosic
carrier, apparently became well adapted to grow rapidly on insoluble cellulose substrates (Solca Floc), and had the enzymes
of the cellulase complex induced for increased cellulase production.
The LFBR starter used in a stirred tank reactor (STR) gave 15 gL-1 biomass production and 6.5 IU mL-1 overall cellulase activity with a volumetric productivity of 64 IU L-1h-1 in a 5 d fermentation, compared with a 7 d shake flask inoculum that gave 11 gL-1 biomass and 3.2 IU mL-1 cellulase activity, with a volumetric productivity of 31IU L-1h-1. The LFBR starter culture retained its viability in dry storage for 6–9 mo. 相似文献
14.
Ni Bangfa Peng Lixin Wang Pingsheng Tian Weizhi 《Journal of Radioanalytical and Nuclear Chemistry》1995,194(1):15-23
A program was initiated at Chalk River Laboratories (CRL) to determine the physical, chemical and radiological properties of wastes intended for disposal in IRUS (Intrusion Resistant Underground Structure), a below ground vault to be constructed at CRL. One of the most restrictive radionuclides for IRUS is129I, which has been assigned a maximum activity concentration in waste of 106 Bq/m3. The limit of detection for radionuclides in waste has been set at 1% of the approximate maximum activity concentration, or 104 Bq/m3 for129I. A radiochemical instrumental neutron activation analysis method has been developed to determine129I in two waste streams, incinerator ash and liquid feed to a bituminizer. Solid samples are spiked with125I tracer, fused at 960°C with Li2B4O7 in a platinum boat in a flowing oxygen stream inside a three zone tube furnace, and the volatilized I2 is trapped on in-line charcoal filters. The charcoal filters are irradiated together with a filter containing a spiked125I/129I standard, in the NRU reactor, and then subjected to post-irradiation chemistry to remove82Br interference. The129I concentration in the sample is determined by comparing the activity of the activated130I in the sample with that of the standard, and the chemical recovery for129I is determined from the activity of125I tracer. Limits of detection for129I in solids are typically 0.005 Bq/g, based on a 4 hour counting period on a 10% efficient HPGe gamma-spectrometer at a source to detector distance of approximately 12 cm. This paper presents a summary of the method and the results from analysis of two waste streams. 相似文献
15.
Health or environmental issue caused by abnormal level of metal ions like Zn2+ or Cd2+ is a worldwide concern. Developing an inexpensive and facile detection method for Zn2+ and Cd2+ is in urgent demand. Due to their super optical properties, fluorescent quantum dots (QDs) have been developed as a promising alternative for organic dyes in fluorescence analysis. In this study, a CdTe QDs-based sensitive and selective probe for Zn2+ and Cd2+ in aqueous media was reported. The proposed probe worked in fluorescence “turn-on” mode. The initial bright fluorescence of CdTe QDs was effectively quenched by sulfur anions (S2−). The presence of Zn2+ (or Cd2+) can “turn-on” the weak fluorescence of QDs quenched by S2− due to the formation of ZnS (or CdS) passivation shell. Under optimal conditions, a good linear relationship between the fluorescence response and concentration of Zn2+ (or Cd2+) could be obtained in the range from 1.6 to 35 μM (1.3–25 μM for Cd2+). The limit of detection (LOD) for Zn2+ and Cd2+ were found to be 1.2 and 0.5 μM, respectively. Furthermore, the present probe exhibited a high selectivity for Zn2+ and Cd2+ over other metal ions and was successfully used in the detection of Zn2+ or Cd2+ in real water samples. 相似文献
16.
A. Yu. Kramchaninov I. V. Chernyshev K. N. Shatagin 《Journal of Analytical Chemistry》2012,67(14):1084-1092
The paper describes a new high-precision method for the simultaneous precise determination of 88Sr/86Sr and 87Sr/86Sr ratios in a single portion of a geological sample by multicollector inductively coupled mass spectrometry (MC-ICP-MS). The isotope analysis is carried out with mass bias effect correction by a combination of internal normalization to the standard Zr-isotope ratio and bracketing standard method (external normalization). Our results for geochemical IAPSO and BCR-1 standard samples are in a good agreement with the published data. The reproducibility of the 88Sr/86Sr ratio varies from ±0.015 to ±0.05?? (depending on the sample features) and, together with the analysis accuracy, is superior to the previously reported methods of MC-ICP-MS analysis. Still ahead is only double spike thermal ionization mass spectrometry with its ±0.02?? reproducibility. However, the new method allows the simultaneous determination of 88Sr/86Sr and 87Sr/86Sr ratios and its productivity is higher by 5 to 6 times. On the other hand, in sample preparation, it is necessary to strive for at least 95% Sr yield from the chromatographic column; otherwise the sorption-desorption process may lead to a 0.6?? 88Sr/86Sr ratio bias relative to the true value. 相似文献
17.
W. L. Robison C. L. Conrado T. F. Hamilton A. C. Stoker 《Journal of Radioanalytical and Nuclear Chemistry》2000,243(2):459-465
The United States conducted a series of nuclear tests from 1946 to 1958 at Bikini, a coral atoll, in the Marshall Islands (MI). The aquatic and terrestrial environments of the atoll are still contaminated with several long-lived radionuclides that were generated during testing. The four major radionuclides found in terrestrial plants and soils are cesium-137, strontium-90, plutonium-239+240 and americium-241. Cesium-137 in the coral soils is more available for uptake by plants than 137Cs associated with continental soils of North America or Europe. Soil-to-plant 137Cs median concentration ratios (CR) (kBq·kg-1 dry weight plant/kBq·kg-1 dry weight soil) for tropical fruits and vegetables range between 0.8 and 36, much larger than the range of 0.005 to 0.5 reported for vegetation in temperate zones. Conversely, 90Sr median CRs range from 0.006 to 1.0 at the atoll versus a range from 0.02 to 3.0 for continental silica-based soils. Thus, the relative uptake of 137Cs and 90Sr by plants in carbonate soils is reversed from that observed in silica-based soils. The CRs for 239+240Pu and 241Am are very similar to those observed in continental soils. Values range from 10-6 to 10-4 for both 239+240Pu and 241Am. No significant difference is observed between the two in coral soil. The uptake of 137Cs by plants is enhanced because of the absence of mineral binding sites and the low concentration of potassium in the coral soil. Cesium-137 is bound to the organic fraction of the soil, whereas 90Sr, 239+240Pu and 241Am are primarily bound to soil particles. Assessment of plant uptake for 137Cs and 90Sr into locally grown food crops was a major contributing factor in: (1) reliably predicting the radiological dose for returning residents and (2) developing a strategy to limit the availability and uptake of 137Cs into locally grown food crops. 相似文献
18.
A Highly K+‐Selective Fluorescent Probe – Tuning the K+‐Complex Stability and the K+/Na+ Selectivity by Varying the Lariat‐Alkoxy Unit of a Phenylaza[18]crown‐6 Ionophore
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Dr. Thomas Schwarze Radu Schneider Janine Riemer Prof. Dr. Hans‐Jürgen Holdt 《化学:亚洲杂志》2016,11(2):241-247
A desirable goal is to synthesize easily accessible and highly K+/Na+‐selective fluoroionophores to monitor physiological K+ levels in vitro and in vivo. Therefore, highly K+/Na+‐selective ionophores have to be developed. Herein, we obtained in a sequence of only four synthetic steps a set of K+‐responsive fluorescent probes 4 , 5 and 6 . In a systematic study, we investigated the influence of the alkoxy substitution in ortho position of the aniline moiety in π‐conjugated aniline‐1,2,3‐triazole‐coumarin‐fluoroionophores 4 , 5 and 6 [R=MeO ( 4 ), EtO ( 5 ) and iPrO ( 6 )] towards the K+‐complex stability and K+/Na+ selectivity. The highest K+‐complex stability showed fluoroionophore 4 with a dissociation constant Kd of 19 mm , but the Kd value increases to 31 mm in combined K+/Na+ solutions, indicating a poor K+/Na+ selectivity. By contrast, 6 showed even in the presence of competitive Na+ ions equal Kd values (KdK+=45 mm and KdK+/Na+=45 mm ) and equal K+‐induced fluorescence enhancement factors (FEFs=2.3). Thus, the fluorescent probe 6 showed an outstanding K+/Na+ selectivity and is a suitable fluorescent tool to measure physiological K+ levels in the range of 10–80 mm in vitro. Further, the isopropoxy‐substituted N‐phenylaza[18]crown‐6 ionophore in 6 is a highly K+‐selective building block with a feasible synthetic route. 相似文献
19.
Ioannis D. Petsalakis Giannoula Theodorakopoulos Anna Grochol Pawel Kowalczyk Wodzimierz Jastrzebski 《Chemical physics》2009,362(3):130-134
Theoretical multireference configuration interaction (MRDCI) calculations on the excited 1Σ+ and 1Π states of NaLi are presented. They improve the results of a previous study by two of the present authors, resolve some differences with other theoretical results and lead to overall good agreement with experimental observations. To extend the experimental data base of electronic states in NaLi, a previously unknown 1Σ+ state is investigated by polarisation labelling spectroscopy. Comparison with accompanying and previous theoretical calculations leads to a conclusion that the observed system consists of two band systems switching smoothly from one adiabatic state to the other and allows assignment of the bands as 51Σ+ ← X1Σ+ in the lower energy part and to 61Σ+ ← X1Σ+ for higher energies. 相似文献
20.
《Microporous Materials》1995,3(4-5):497-510
23Na Magic-angle spinning (MAS), double rotation (DOR) and two-dimensional nutation nuclear magnetic resonance (NMR) and static 139La NMR spectroscopy were applied to study the location and migration of sodium and lanthanum cations in faujasites. Generally, 23Na MAS NMR spectroscopy of as-exchanged and hydrated zeolites LaNaY was used for the quantitative determination of non-localized Na+ in the large cavities at a 23Na NMR shift of −9 ppm and of sodium cations observed at −13 ppm. The latter originate from Na+ ions located on position SII in the large cavities, on position SI in the hexagonal prisms and on positions SII′ and/or SI′ in the sodalite cages. The 23Na MAS NMR signal at about −13 ppm was found to be caused by two coonents. The component that is characterized by a quadrupolar interaction causing a field-dependent shift and a signal at v1 = 2vrf in the two-dimensional quadrupolar nutation spectra is attributed to Na+ enclosed in the sodalite cages. The 23Na MAS NMR spectra of dehydrated lanthanum-exchanged faujasites are characterized by a low-field Gaussian line of Na+ located on SI positions in the hexagonal prisms and a high-field quadrupole pattern of Na+ located on positions SII and SI′. The migration of lanthanum cations from the large cavities to position SI′ in the sodalite cages was monitored by 139La NMR spectroscopy and verified by a theoretical estimation of the electric field gradient. The lanthanum migration was found to be coupled with a strain of SiOT and AlOT angles observed by 29Si and 27Al MAS NMR high-field shifts, respectively. 相似文献