Synthesis,conformational preferences in gas and solution,and molecular gear rotation in 1-(dimethylamino)-1-phenyl-1-silacyclohexane by gas phase electron diffraction (GED), LT NMR and theoretical calculations

1-(Dimethylamino)-1-phenyl-1-silacyclohexane 1, was synthesized, and its molecular structure and conformational properties studied by gas-phase electron diffraction (GED), low temperature ¹³C NMR spectroscopy and quantum-chemical calculations. The predominance of the 1-Ph_ax conformer (1-Ph_eq:1-Ph_ax ratio of 20:80%, ΔG°(317?K)?=??0.87?kcal/mol) in the gas phase is close to the theoretically estimated conformational equilibrium. In solution, low temperature NMR spectroscopy showed analyzable decoalescence of C_ipso and C(1,5) carbon signals in ¹³C NMR spectra at 103?K. Opposite to the gas state in the freon solution employed (CD₂Cl₂/CHFCl₂/CHFCl₂?=?1:1:3), which is still liquid at 100?K, the 1-Ph_eq conformer was found to be the preferred one [(1-Ph_eq: 1-Ph_ax?=?77%: 23%, K?=?77/23?=?2.8; ?ΔG°?=??RT ln K (at 103?K)?=?0.44?±?0.1?kcal/mol]. When comparing 1 with 1-phenyl-1-(X)silacylohexanes (X?=?H, Me, OMe, F, Cl), studied so far, the trend of predominance of the Ph_ax conformer in the gas phase and of the Ph_eq conformer in solution is confirmed.     

以ZrO2-TiO2为载体的整体式锰基催化剂应用于低温NH3-SCR反应

以MnO2为活性组分, Fe2O3为助剂, 制备了以TiO2及ZrO2-TiO2为载体的整体式催化剂. 考察了它们在不同温度焙烧后应用于富氧条件下, NH3选择性催化还原(NH3-SCR)氮氧化物的低温反应性能和高温稳定性. 用X射线衍射(XRD)实验、比表面积测定(BET)、储氧性能测定(OSC)及程序升温还原(H2-TPR)等方法对催化剂进行了表征. 结果表明, 以ZrO2-TiO2为载体的催化剂具有很好的高温热稳定性, 并具有较高的比表面积和储氧能力, 同时具有较强的氧化能力. 催化剂的活性测试结果表明, 以ZrO2-TiO2为载体的整体式锰基催化剂明显地提高了NH3-SCR反应的低温活性, 具有良好的应用前景.     

Multi-component electrocatalyst for low-temperature fuel cells synthesized via sonochemical reactions

This review presents recent advances in multi-component electrocatalysts for low-temperature fuel cells (FCs) synthesized via sonochemical reactions. As a feasible approach to develop novel electrocatalysts that can overcome the many problems of the prevailing Pt electrocatalysts, Pt- or Pd-based alloy and core–shell M@Pt nanoparticles (NPs) have been pursued. Synthesizing NPs with desirable properties often turn out to be challenging. Sonochemistry generates extreme conditions via acoustic cavitation, which have been utilized in the syntheses of various Pt and Pd NPs and Pt- and Pd-based alloy NPs. Especially, it has been reported that several M@Pt core–shell NPs can be synthesized by sonochemistry, which is hard to achieve by other methods. The principles of sonochemistry are presented with examples. Also alloy NPs and core–shell NPs synthesized by sonochemistry and those by other methods are compared.     

Thermoluminescence and low-temperature luminescence of beryllium oxide

Beryllium oxide in the forms of either single crystals (pristine, additively-colored) or hot-pressed ceramic samples was studied in the energy range of 1.2–6.2 eV using both the thermoluminescence (TL) and steady-state X-ray induced luminescence (XRL) techniques. The XRL emission spectra were recorded at 6 and 293 K, whereas TL glow curves were studied after X-ray exposure at T₀ = 6 K upon linear heating in the temperature range from 6 to 293 K. A search for TL manifestations of shallow trapping centers was carried out using a sensitive channel for TL registration in the range of more than six decades of change in intensity. The participation of shallow trapping centers in the process of recombination luminescence excitation at 6–293 K; branching electronic excitations between different recombination channels; the dominance of the self-trapped exciton and F-center emissions in spectra of the low-temperature recombination luminescence in BeO at 6–293 K were discussed.     

Dynamic scanning force microscopy at low temperatures on a van der Waals surface: graphite (0001)

The (0001) surface of highly oriented pyrolytic graphite is studied by scanning force microscopy in both contact and dynamic mode. Low temperatures were necessary for the dynamic mode measurements in order to achieve the required signal to noise ratio. At 22 K, atomic scale structures with 2.46 Å periodicity and trigonal symmetry of the individual maxima were obtained in both modes. Since graphite exhibits a van der Waals surface in good approximation, this result shows that comparatively weak forces of van der Waals type are sufficient for successful imaging in the dynamic mode on the atomic scale. However, since the positions of the observed maxima correspond to the ones found by scanning tunneling microscopy and contact scanning force microscopy, but not to the positions of the carbon atoms, it also opens new questions on the imaging mechanism in the dynamic mode.     

Fluorescent carbon nanoparticles: A low-temperature trypsin-assisted preparation and Fe sensing

In recent years, extensive researches are focused on the fluorescent carbon nanoparticles (CNPs) due to their excellent photochemical, biocompatible and water-soluble properties. However, these synthesis methods are generally suffered from tedious processes. In this paper, fluorescent carbon nanoparticles are synthesized by a facile, one-pot, low-temperature method with trypsin and dopamine as precursors. The synthesis process avoids any heating operation and organic solvent, which provides a “green” and effective preparation route. The obtained CNPs exhibit excellent water-solubility, salt-tolerance and photostability. Based on the synergistic action of the inner filter effect and static quenching mechanism, the CNPs are exploited as a “turn-off” fluorescence sensor for sensitive and selective detection of Fe³⁺ ions. The probe shows a wide linear range from 0.1 to 500 μM, with a limit of detection of 30 nM. Furthermore, the as-fabricated fluorescent sensing system is successfully applied to the analysis of Fe³⁺ in biological samples such as human urine and serum samples with satisfactory recoveries (92.8–113.3%).     

Low-temperature Heat Capacity and Standard Thermodynamic Functions of D-Galactose and Galactitol

The heat capacities of D-galactose and galactitol were measured on a quantum design physical property measurement system(PPMS) over a temperature range of 1.9―300 K, and the experimental data were fitted to a function of T using a series of theoretical and empirical models in appropriate temperature ranges. The fit results were used to calculate thermodynamic function values,C_p,m^θ,Δ₀^TS_m^θ, and Δ₀^TH_m^θfrom 0 K to 300 K. The standard molar heat capacity, entropy and enthalpy values of D-galactose and galactitol at 298.15 K and 0.1 MPa were determined to be C_p,m^θ =(227.96±2.28) and (239.50±2.40) J·K^-1·mol^-1,S_m^θ= (211.22±2.11) and (230.82±2.30) J·K^-1·mol^-1 and = H_m^θ (33.95±0.34) and (36.57± 0.37) kJ/mol, respectively.     

Enhanced energy storage and pyroelectric properties of highly (100)-oriented (Pb1−x−yLaxCay)Ti1−x/4O3 thin films derived at low temperature

Highly (100)-oriented (Pb_1?x?yLa_xCa_y)Ti_1?x/4O₃ ($x=0.15$, $y=0.05$; $x=0.1$, $y=0.1$; $x=0.05$, $y=0.15$) thin films were deposited on Pt/Ti/SiO₂/Si substrates at a low temperature of 450?°C via a sol–gel route. It was found that all the (Pb_1?x?yLa_xCa_y)Ti_1?x/4O₃ thin films could be completely crystallized and the content of La/Ca showed a significant effect on the electrical properties of films. Among the three films, the (Pb_1?x?yLa_xCa_y)Ti_1?x/4O₃ ($x=0.1$, $y=0.1$) thin film exhibited the enhanced overall electrical properties, such as a low dielectric loss ($\tan ?\delta <0.08$) and leakage current ($J～4.6\times {10}^{?5}$ A/cm²), a high recoverable energy density (W_re ～ 15 J/cm³), as well as a large pyroelectric coefficient (p ～ 190 μC/m²K) and figure of merit ($F_{\mathrm{d}}^{\prime }～77\mathrm{\mu }\text{C}/{\text{m}}^2$K). The findings suggest that the fabricated thin films with a good (100) orientation can be an attractive candidate for applications in Si-based energy storage and pyroelectric devices.     

Magnetic irreversibility of the Fe antidot arrays film by depositing on the porous alumina templates

An Fe layer was sputter-deposited onto porous alumina templates and Kapton respectively. Fe layer on the porous alumina templates formed an antidot arrays nanostructure, while Fe layer on the Kapton substrate formed a continuous film. Scanning electron microscopy and grazing incidence X-ray diffraction were employed to characterize the morphology and crystal structure of the Fe antidot arrays and continuous film, respectively. The temperature dependence of magnetic properties was shown in the temperature range 2-300 K. The irreversibility of the magnetization of Fe antidot arrays film, as measured in zero-field cooling (ZFC) and field cooling (FC) states, was attributed to the pinning effect of the holes.     

低温恒能量同步荧光法同时快速检测食品中多种多环芳烃

恒能量同步荧光法应用于多环芳烃的检测可以提高选择性,低温可使谱带呈指纹特征,提供常温光谱无法获得的光谱细节信息,有助于实现对复杂基体中多环芳烃的检测。文章结合恒能量同步荧光扫描技术与斯波斯基低温技术,建立了食品中多种多环芳烃的低温恒能量同步荧光同时快速分析方法。对低油脂样品直接用正辛烷浸泡,高油脂样品也只需要增加皂化萃取,即可进行光谱扫描来检测食品样中的多种多环芳烃。对两种类型的实际样进行加标回收实验,回收率为80.2%～98.9%,定量工作曲线线性较好(r≥0.993 8)。该方法选择性好、操作简便快捷、费用低廉。