Dynamic properties of water in silicalite-1 powder

Self-diffusion of D₂O in partially filled silicalite-1 crystals was studied at 25°C by ²H nuclear magnetic resonance (NMR) with bipolar field gradient pulses and longitudinal Eddy-current-delay. For the first time, reliable experimental diffusion data for this system were obtained. Analysis of NMR diffusion decays revealed the presence of a continuous distribution of apparent self-diffusion coefficients (SDCs) of water, ranging from 10⁻⁷ to ∼10⁻¹⁰ m²/s, which include values much higher and lower than that of bulk water (∼10⁻⁹ m²/s) in liquid phase. The observed distribution of SDC changes with variation of the diffusion time in the range of 10–200 ms. A two-site Kärger exchange model was successfully fitted to the data. Finally, the water distribution and exchange in silicalite-1 pores were described by taking into account (a) a gas-like phase in the zeolite pores, a gas-like phase in mesopores and an intercrystalline gas-like phase and (b) intercrystalline liquid droplets with intermediate exchange rate with the other phases. The other phases experience fast exchange on the NMR diffusion time scale. Diffusion coefficients and mean residence times of water in some of these states were estimated.     

Adsorption and diffusion of cyclopentane in silicalite-1: a thermodynamic and kinetic study

The adsorption isotherm, differential thermal gravimetry (DTG), thermal gravimetry (TG), diffusion and thermodynamic parameters of cyclopentane at various adsorption coverages have been investigated using microgravimetric technique over a range of temperature. The differences in equilibrium adsorption capacity and in diffusion coefficient at different temperature are discussed in terms of the characteristics of silicalite-1 and the features of cyclopentane molecule. The heat of sorption Q_st varies significantly with sorption coverage indicating that the adsorption and diffusion mechanism is complex. The dependences of thermodynamic properties like free energy change (ΔG) and entropy change (ΔS) on sorption coverage show a sharp decrease and increase suggesting that the adsorption sites of the silicalite-1 are not energetically uniform to cyclopentane. Two desorption peaks in the DTG and TG curves suggest that two heterogenous binding sites surely exist in silicalite-1 to cyclopentane.     

NMR Study of Laser-polarized 129Xe in Low Pressure Natural Xenon Gas

The NMR signal from the laser-polarized t29 Xe in low-pressure natural xenon gas has been observed with a Bruker WP-80SY NMR spectrometer. The laser-polarized 129 Xe was produced by the method of laser pumping and spin exchange in a magnetic field of 1.87 Tesla. It is obtained experimentally that the nuclear spin relaxation rate 1/T1 of laser-polarized 129Xe are (4.03±1.97)×10-3/see～(2.21±0.78)×10-3/see in the range of the 3.33×103 Pa～8.29×104 Pa Xe gas pressures, the apparent wall relaxation rate 1/Tw* =(1.98±0.18)×10-3/see, and the relaxation rate coefficient C of 133Cs-129Xe spin exchange is (2.81±0.74)×10-16 em3/sec.     

NMR Study of Laser polarized ~(129) Xe in Low Pressure Natural Xenon Gas

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Tracer diffusion measurements in solid lithium: a test case for the comparison between NMR in static and pulsed magnetic field gradients after upgrading a standard solid state NMR spectrometer

This paper reports on the upgrading of a standard solid state NMR spectrometer, which has been used in combination with a field variable 7 T cryomagnet, to a low-cost combined SFG and PFG NMR spectrometer. Both methods are applied to solid lithium as a simple test case. The results show that under the given conditions SFG NMR and PFG NMR can provide tracer diffusion coefficients for 7 Li diffusion down to about 10(-14) and 10(-13) m2/s, respectively. SFG and PFG NMR are complementary methods. The paper demonstrates advantages and disadvantages of each method with a concrete example and why it is desirable to be able to apply both methods to the same sample.     

Evidence of red cell alignment in the magnetic field of an NMR spectrometer based on the diffusion tensor of water

The alignment of human erythrocytes in aqueous suspensions in the magnetic field B(0) (called the z-direction) of an NMR spectrometer was shown by calculating the diffusion tensor for water in the sample. The diffusion was measured using a pulsed-field-gradient spin-echo NMR method. The extent of diffusion anisotropy for water was exemplified by the values of the apparent diffusion coefficients with erythrocytes of normal shape and volume: for a typical experiment the values for the x-, y-, and z-directions were (6.88 +/- 0.17) x 10(-10), (7.07 +/- 0.17) x 10(-10), and (10.20 +/- 0.17) x 10(-10) m(2) s(-1), respectively. Cells in hypo- and hyperosmotic media were also studied and they too showed the anisotropy of the apparent diffusion coefficients but the extents were different. A new method of data analysis was developed using the Standard Add-On Packages in a Mathematica program. The experimental findings support evidence of erythrocyte alignment that was previously obtained with a high-field-gradient q-space method.     

路易氏剂红外吸收截面积的测定与光谱模拟

采用长程傅里叶红外光谱仪在600～1 600 cm-1波段内对不同浓度路易氏剂-1的气相红外透射光谱进行了测量,其特征频率为814,930,1 563 cm-1;并运用比尔-朗伯定律计算了对应特征频率的红外吸收截面积σ值,依次为3.89±0.01, 1.43±0.06, 4.47±0.05(×10-20 cm2·molecule-1)。路易氏剂-1测量光谱在1 158和1 288 cm-1处也有微弱的吸收峰。利用Gaussian09软件包中的密度泛函理论对系列路易氏剂的红外光谱进行理论模拟,其稳定构型和振动频率在b3lyp/6-311+g(d,p)水平上计算。并利用可视化软件Gaussview5.08对各频率的振动模式进行归属。理论计算的红外光谱和实测光谱在600～1 600 cm-1波段内非常吻合,特征频率的相关系数为0.999 1。计算光谱还发现了0～600 cm-1波段内与砷原子有关的振动频率,为293,360和374 cm-1。用最小二乘法处理试验和计算结果中的特征频率,得到了适合路易氏剂-1的红外光谱频率矫正因子为0.977。利用该矫正因子对路易氏剂-1,路易氏剂-2,路易氏剂-3的红外光谱计算频率进行矫正。结果表明获得的路易氏剂理论红外吸收光谱可为该系列化合物的结构性质预测和远程红外光谱监测等提供参考。     

基于红外热辐射光源的光声气体分析仪

研制了一种基于红外热辐射光源的光声气体分析仪,给出了该光声气体分析仪的设计理论、硬件结构、软件系统和实验测试结果。根据红外热辐射光源的光谱特性,通过比较吸收气体在不同吸收带中多线的综合吸收系数,确定了光声池的最优设计参数、滤光片的中心波长和带宽。实验结果表明,该光声气体分析仪对CO,NO和H₂S的极限检测灵敏度分别达到1.6×10-6,4.5×10-6和4.0×10-4(被测气体与背景气体的分压比),并且对0～987×10-6 的CO测量显示了其良好的测量重复精度和线性度。此外,通过增加特定中心波长的滤光片还能够对其他多种小分子气体实现高灵敏度、实时、连续、自动地测量。     

Microcombustion of ng Amounts of Carbon in Non-Volatile Materials for isotope Ratio Evaluation

Abstract A novel microcombustion technique for carbon isotopic analysis of nanogram amounts of carbon in non-volatile materials based on isotope ratio monitoring (irm) mass spectrometry is described. Liquid or solid samples placed in a quartz sleeve are combusted at 1000°C in a continuous stream of helium and oxygen. CO(2) removed from the carrier gas stream by cryogenic trapping is transferred onto a GC column. Following GC separation, the CO(2) is transferred via an open split to the ion source of a gas isotope ratio mass spectrometer. Reproducibility for samples >25 nmol carbon is <1‰. Problems associated with blanks from various sources and with reproducible deposition of small sample amounts led to variable accuracy, which was dependent on the compound class being analysed. Minimum sample size was in the range from 5 to 10 nmol carbon. Measurements of dissolved organic carbon (DOC) of groundwater from Germany yielded consistent values of δ(13)C = -28.8‰.     

Methodology for the measurement and analysis of relaxation times in proton imaging

Measurements of proton T1 and T2 were performed on GdCl3 solutions (20 less than T2 less than 500 msec, 90 less than T1 less than 1000 msec) on large-bore NMR imaging systems operating at 1.0T and 1.5T. CPMG multi-echo (ME), multiple saturation recovery (MSR) and modified fast inversion recovery (MFIR) pulse sequences as well as a sequence that combines and interleaves T1 and T2 weighted data acquisition (which we call "multiple saturation-recovery multiple-echo" (MSRME) were used. The relaxation data are compared to those obtained on a small bore NMR spectrometer operated at 1.5T. T1 and T2 values for the solutions were found to be the same within 10% for the two fields. Reproducibility of measurements of T1, T2 and the unnormalized spin density of the solutions was better than 5%. Systematic errors, amenable to correction through calibration, are noted in the imager T1 and T2 values. T1 and T2 values for some typical neural tissues at 1.5T and body tissue at 1.0T for human volunteers were obtained and are tabulated.     

A Superconducting Quantum Interference Device Measurement System for Ultra Low-Field Nuclear Magnetic Resonance

We describe a superconducting quantum interference device (SQUID)-based nuclear magnetic resonance (NMR) spectrometer operating at ultralow magnetic fields far below the Earth’s field. The spectrometer consists of a helium-cooled magnetic sensor system and two Helmholtz coils, one for pre-polarizing the sample by fields of up to 5 mT, and one for the detection in fields of the nanotesla and microtesla range. The spectrometer represents the current state of the art in ultralow-field NMR and enables the observation of phenomena that are difficult or impossible to achieve by a conventional NMR setting. In particular, one can obtain broad band spectra covering different nuclei, such as ¹H and ³¹P, with a frequency resolution in the millihertz range, observe the variation of their heteronuclear coupling with the detection field strength, and investigate relaxation processes that reflect molecular dynamics in the millisecond range.     

Slow turning reveals enormous quadrupolar interactions (STREAQI)

We introduce a new solid-state NMR method, which uses very slow sample rotation to visualize NMR spectra whose width exceeds feasible spectrometer bandwidths. It is based on the idea that if we reorient a tensor by a known angle about a known axis, the shifts in the NMR frequencies observed across the spectral width allow us to reconstruct the entire tensor. Called STREAQI (Slow Turning Reveals Enormous Anisotropic Quadrupolar Interactions), this method allows us to probe NMR nuclei that are intractable to current methods. To prove the concept and demonstrate its promise we have implemented the method for several 79Br containing samples with quadrupolar coupling constants in the range of 10-50 MHz.     

格尔木地区整层大气臭氧浓度激光外差测量与反演研究

搭建了便于外场观测的3.3μm激光外差光谱仪,实测其光谱分辨率为0.004 cm^-1。利用该设备测量了青海格尔木地区整层大气臭氧的吸收光谱,并结合最优估算法反演了该地区的臭氧浓度。测量期间,格尔木地区臭氧柱浓度均值约241.7 DU,且浓度随观测时间呈上升趋势,上升速度约4 DU/h。结果表明,该激光外差光谱仪结合最优估算法能够实现高海拔地区整层大气臭氧浓度的测量,在环境、气象及激光大气传输等研究领域具有重要的应用前景。     

Novel two-layered zeolite NaA-silicalite-1 membranes

A two-layered zeolite NaA-silicalite-1 membrane has been successfully prepared on a porous α-alumina tube by using seeded hydrothermal synthesis. The procedure involves pre-seeding with nanosized seed and subsequent regrowth by hydrothermal treatment. Single-layered NaA and silicalite-1 membranes were also synthesized for comparison. The membrane was composed of a silicalite-1 layer on top and a NaA layer on the porous support. SEM results of the membrane indicate that both the silicalite-1 layer and the NaA layer are uniform and well-intergrown. The silicalite-1 and NaA layers in the ‘sandwich’ mode have similar thickness of 3-4 μm, whereas the thickness of their respective seed layer is different. The NaA seed layer is much thicker than the silicalite-1seed layer. This may be attributed to the different capillary action on the support and NaA layer during using a slip-casting seeding method. XRD analysis has also proved both zeolite NaA and zeolite silicalite-1 layers coexist in the dual-layered membrane. This method is also suitable for preparing other multi-layer zeolite membranes.     

插层化合物Li1+xV3O8的合成及其物理性能的初步研究

本文成功地合成了插层化合物Li_1+xV₃O₈,并用X射线粉末衍射和等离子体发射光谱元素定量分析进行了鉴定。同时进行了NMR研究。在298—400K之间观察到了锂离子的运动致窄效应,并以此求得它的离子运动激活能为0.18eV。还测得该材料的室温电导率为10^-3Ω^-1·cm^-1数量级。 关键词：     

Highly Selective and Sensitive Chemosensor for Hg2+ Based on the Naphthalimide Fluorophore

A new OFF-ON fluorescent chemosensor (H1) composed of a naphthalimide fluorophore and a 6-[(quinolin-8-yloxy)methyl]pyridin-2-ylmethanamine receptor has been synthesized and characterized by infra-red, (1)H NMR, (13)C NMR and mass spectrometry. The developed chemosensor H1 exhibited good turn-on and reversible responses toward Hg(2+), with excellent selectivity and sensitivity, in a neutral buffered aqueous solution. Other common metal ions did not interfere with the fluorescence-enhancement response to Hg(2+). Furthermore, the chemosensor H1, at a concentration of 10?μM, showed a rapid and linear response toward Hg(2+) in the concentration range 0-10?μM. On addition of 10?μM Hg(2+), the fluorescence intensity of H1 was enhanced about 4-fold. The detection limit was calculated to be 63?nM. The association constant was 1.11?×?10(5)?M(-1). The fluorescence quantum yield and lifetime of H1/Hg(2+) were 0.42 and 3.83?ns, respectively.     

Thermal conductivity of nitrogen in the temperature range 350–2500 K

The thermal conductivity of nitrogen is determined in a conductivity column instrument in the temperature range of 338 to 2518 K with an estimated uncertainty of about ± 1·5 per cent. The experimental data points are correlated by a cubic polynomial in temperature, viz. k(T)/(mW m^-1 K^-1) = 12·18 + 0·05224(T/K) - 0·6482 × 10^-6(T/K)² - 0·2765 × 10^-9(T/K)³. These conductivity values determined from heat transfer data taken in the continuum regime are found to be in fair agreement with the values obtained from similar data referring to low pressure range.

The present results are compared with the conductivity determinations of other workers and with the predictions of various theories developed for polyatomic gases. It is pointed out that a reliable calculation of thermal conductivity over an extended temperature range is impossible at the present time due to the absence of a large variety of experimental molecular data needed for such an effort. Average values of the vibrational energy diffusion coefficient, D _vib, are computed from the present k(T) data.     

FNR-Ⅰ核磁共振波谱仪

基于自旋回波的原理研制成功了一台专用于分析磁性材料的核磁共振波谱仪。其工作频率为25-80MHz;输出功率10W,可用它在77-300°k范围测量铁磁材料的共振谱线,增强因数和自旋-自旋弛豫时间T₂;它也可用于测量非磁性固体的宽核磁共振谱线。     

Quadrupole parameters of 11B in crystalline CaO.B2O3.

The quadrupole coupling constant (Qcc) and asymmetry parameter (eta) of 11B in crystalline CaO.B2O3 have been measured employing three different NQR and NMR methods: (1) 11B and 10B NQR; (2) 11B NQR and NMR; and (3) the 11B Zeeman NQR powder pattern. It is found that Qcc = 2594.3 +/- 0.5 kHz and eta = 0.515 +/- 0.001 at 77 K, and Qcc = 2573.5 +/- 0.5 kHz and eta = 0.511 +/- 0.002 at 300 K. These values are in agreement with, but far more accurate than, values obtained from a fourth procedure: measurement of the second-order quadrupolar effects evident in the m = + 1/2<-->m = - 1/2 transition of the 11B NMR spectrum.     

From ultraslow to fast lithium diffusion in the 2D ion conductor Li0.7TiS2 probed directly by stimulated-echo NMR and nuclear magnetic relaxation

7Li stimulated-echo NMR and classical relaxation NMR techniques are jointly used for the first time for a comprehensive investigation of Li diffusion in layer-structured Li0.7TiS2. One single 2D Li diffusion process was probed over a dynamic range of almost 10 orders of magnitude. So far, this is the largest dynamic range being measured by 7Li NMR spectroscopy directly, i.e., without the help of a specific theoretical model. The jump rates obey a strict Arrhenius law, determined by an activation energy of 0.41(1) eV and a preexponential factor of 6.3(1)x10(12) s-1, and range between 1x10(-1) s-1 and 7.8x10(8) s-1 (148-510 K). Ultraslow Li jumps in the kHz to sub-Hz range were measured directly by recording 7Li spin-alignment correlation functions. The temperature and, in particular, the frequency dependence of the relaxation rates fully agree with results expected for 2D diffusion.