An electrochemically enhanced solid-phase microextraction approach based on a multi-walled carbon nanotubes/Nafion composite coating

In this paper, we proposed an approach using a multi-walled carbon nanotubes (MWCNTs)/Nafion composite coating as a working electrode for the electrochemically enhanced solid-phase microextraction (EE-SPME) of charged compounds. Suitable negative and positive potentials were applied to enhance the extraction of cationic (protonated amines) and anionic compounds (deprotonated carboxylic acids) in aqueous solutions, respectively. Compared to the direct SPME mode (DI-SPME) (without applying potential), the EE-SPME presented more effective and selective extraction of charged analytes primarily via electrophoresis and complementary charge interaction. The experimental parameters relating to extraction efficiency of the EE-SPME such as applied potentials, extraction time, ionic strength, sample pH were studied and optimized. The linear dynamic range of developed EE-SPME-GC for the selected amines spanned three orders of magnitude (0.005–1 μg mL⁻¹) with R² larger than 0.9933, and the limits of detection were in the range of 0.048–0.070 ng mL⁻¹. All of these characteristics demonstrate that the proposed MWCNTs/Nafion EE-SPME is an efficient, flexible and versatile sampling and extraction tool which is ideally suited for use with chromatographic methods.     

Iridium-catalyzed asymmetric ring opening of azabicyclic alkenes by amines

The enantioselective ring-opening reactions of azabicyclic alkenes with primary and secondary aromatic amine nucleophiles are reported using an iridium catalyst generated in situ from 1.5 mol % of [Ir(COD)Cl](2) and 3 mol % of (S)-BINAP. The reaction affords the corresponding trans-1,2-diamine derivatives in moderate to good yields with moderate to high enantioselectivities (up to 97% ee). The trans-configuration of the 1,2-diamino product 2g was confirmed by X-ray crystallography.     

Encapsulation of polyaniline in 3-D interconnected mesopores of silica KIT-6

Composite material PANI/KIT-6, with polyaniline (PANI) chains encapsulated in the 3-D interconnected pore channels of mesoporous silica, KIT-6, has been synthesized via a gas-phase method. The composite formation and the presence of PANI inside the pore channels of KIT-6 were evidenced by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), small-angle X-ray scatter (SAXS), transmission electron microscopy (TEM), and N₂ adsorption–desorption isotherms. The PANI/KIT-6 composite showed good electrical conductivity (2.4 × 10^?3 S/cm) due to the formation of 3-D networks of PANI inside the 3-D interconnected channels of KIT-6. The resistance of PANI/KIT-6 composite at different relative humidities (RH) was investigated. An essentially linear relationship between the relative resistance of the composite and the relative humidity of the environment was found from 11.3% to 97.3% RH.     

Experimental evidence that halogen bonding catalyzes the heterogeneous chlorination of alkenes in submicron liquid droplets

A key challenge in predicting the multiphase chemistry of aerosols and droplets is connecting reaction probabilities, observed in an experiment, with the kinetics of individual elementary steps that control the chemistry that occurs across a gas/liquid interface. Here we report evidence that oxygenated molecules accelerate the heterogeneous reaction rate of chlorine gas with an alkene (squalene, Sqe) in submicron droplets. The effective reaction probability for Sqe is sensitive to both the aerosol composition and gas phase environment. In binary aerosol mixtures with 2-decyl-1-tetradecanol, linoleic acid and oleic acid, Sqe reacts 12–23× more rapidly than in a pure aerosol. In contrast, the reactivity of Sqe is diminished by 3× when mixed with an alkane. Additionally, small oxygenated molecules in the gas phase (water, ethanol, acetone, and acetic acid) accelerate (up to 10×) the heterogeneous chlorination rate of Sqe. The overall reaction mechanism is not altered by the presence of these aerosol and gas phase additives, suggesting instead that they act as catalysts. Since the largest rate acceleration occurs in the presence of oxygenated molecules, we conclude that halogen bonding enhances reactivity by slowing the desorption kinetics of Cl₂ at the interface, in a way that is analogous to decreasing temperature. These results highlight the importance of relatively weak interactions in controlling the speed of multiphase reactions important for atmospheric and indoor environments.

The heterogeneous chlorination rate of an alkene is unexpectedly accelerated in the presence of spectator molecules containing oxygenated functional groups, which suggests weak halogen bonds can catalyze reactions at liquid surfaces.     

Spin‐Hamiltonian parameters and local lattice structure for Pd(I) center in γ‐irradiated bis(acetylacetonato)palladium(II)

This paper reports on a theoretical analysis of spin‐Hamiltonian parameters and local lattice structure for Pd(I) center in γ‐irradiated Pd(II)(acac)₂. Through the crystal‐ and ligand‐field theory, the microscopic spin‐Hamiltonian parameters and local molecular structure for Pd(I) center in the γ‐irradiated Pd(II)(acac)₂ system have been studied by using the high‐order perturbation formulas and Newman's superposition model. Based on these calculations, it was found that the distance of the metal‐ligand bonds in the square planar complex for Pd(I) center in the γ‐irradiated Pd(II)(acac)₂ system increases by 0.1Å. To understand the detailed physical and chemical properties of the [Pd(I)(acac)₂]^2– complex, the contributions of the spin‐orbit coupling of ligand to spin‐Hamiltonian parameters for Pd(I) ion are considered. The theoretical results are in reasonable agreement with the experimental values. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

纳米ZnO的制备及其在不同牺牲试剂下的光催化产氢性能

采用沉淀法与异相共沸蒸馏技术相结合制备了ZnO纳米粉体,并利用X射线粉末衍射、扫描电镜、透射电镜和液氮吸-脱附等技术对制备的样品进行了分析与表征．考察了Pt的负载量、煅烧温度以及牺牲试剂的种类和浓度对制备的纳米ZnO的光催化产氢效率的影响．结果表明：与其他温度下煅烧获得的产物相比,400 oC煅烧产物表现出最佳的光催化产氢效率,且以甲醇为牺牲试剂时纳米ZnO悬浮体系的光催化产氢效率远高于以三乙醇胺为牺牲试剂时的产氢效率．其原因在于光催化过程中甲醇氧化也对体系的产氢有贡献．此外,探讨了基于实验结果对含甲醇的     

Diode-pumped Nd:YVO<Subscript>4</Subscript>/Nd:YLF laser at 488 nm

We present a laser architecture to obtain continuous-wave blue radiation at 488 nm. A 808 nm diode-pumped the Nd:YVO₄ crystal emitting at 914 nm. A part of the pump power was then absorbed by the Nd:YVO₄ crystal. The remaining was used to pump the Nd:YLiF₄ (Nd:YLF) crystal emitting at 1047 nm. Intracavity sum-frequency mixing at 914 and 1047 nm was then realized in a BiB₃O₆ (BiBO) crystal to reach the blue radiation. We obtained a continuous-wave output power of 339 mW at 488 nm with a pump laser diode emitting 18.3 W at 808 nm.     

Optimizing fracture design based on a novel RBF neural network

The factors affecting performance of fractured wells are analyzed in this work. The static and dynamic geologic data of fractured well and fracturing treatment parameters obtained from 51 fractured wells in sand reservoirs of Zhongyuan oilfield are analyzed by applying the grey correlation method. Ten parameters are screened, including penetrability, porosity, net thickness, oil saturation, water cut, average daily production, and injection rate, amount cementing front spacer, amount sand-carrying agent and amount sand. With the novel Radial Basis Function neural network model based on immune principles, 13 parameters of 42 wells out of 51 are used as the input samples and the stimulation ratios as the output samples. The nonlinear interrelationship between the input samples and output samples are investigated, and a productivity prediction model of optimizing fracture design is established. The data of the rest 7 wells are used to test the model. The results show that the relative errors are all less than 7%, which proves that the novel Radial Basis Function neural network model based on immune principles has less calculation, high precision and good generalization ability.     

Binaural unmasking with multiple adjacent masking electrodes in bilateral cochlear implant users

Bilateral cochlear implant (BiCI) users gain an advantage in noisy situations from a second implant, but their bilateral performance falls short of normal hearing listeners. Channel interactions due to overlapping electrical fields between electrodes can impair speech perception, but its role in limiting binaural hearing performance has not been well characterized. To address the issue, binaural masking level differences (BMLD) for a 125 Hz tone in narrowband noise were measured using a pair of pitch-matched electrodes while simultaneously presenting the same masking noise to adjacent electrodes, representing a more realistic stimulation condition compared to prior studies that used only a single electrode pair. For five subjects, BMLDs averaged 8.9 ± 1.0 dB (mean ± s.e.) in single electrode pairs but dropped to 2.1 ± 0.4 dB when presenting noise on adjacent masking electrodes, demonstrating a negative impact of the additional maskers. Removing the masking noise from only the pitch-matched electrode pair not only lowered thresholds but also resulted in smaller BMLDs. The degree of channel interaction estimated from auditory nerve evoked potentials in three subjects was significantly and negatively correlated with BMLD. The data suggest that if the amount of channel interactions can be reduced, BiCI users may experience some performance improvements related to binaural hearing.