磁性可见光催化剂BiVO4/Fe3O4的制备及催化活性

采用超声法将磁基体Fe3O4和BiVO4复合,制备了易于固液分离的磁性可见光催化剂BiVO4/Fe3O4。采用X射线衍射(XRD)、傅立叶转换红外光谱(FTIR)、紫外-可见漫反射光谱(DRS)、透射电子显微镜(TEM)和磁学性质测量系统(MPMS)对产物进行了表征,并以亚甲基蓝为目标降解物,考察了BiVO4/Fe3O4的可见光催化活性。当BiVO4与Fe3O4质量比为5:1时,BiVO4/Fe3O4的催化活性最高,反应经过5 h,对亚甲基蓝的降解率达到92.0%,而单独使用BiVO4为催化剂,降解率仅为72.5%。这表明Fe3O4不仅起到磁基体的作用,还起到助催化剂的作用。BiVO4/Fe3O4在外加磁场的作用下很容易被分离,撤消外加磁场后,通过搅拌又可重新分散。BiVO4/Fe3O4 3次回收后的降解率仍高于80%。     

Directly suspended droplet microextraction with in injection-port derivatization coupled to gas chromatography-mass spectrometry for the analysis of polyphenols in herbal infusions, fruits and functional foods

A miniaturized liquid-phase extraction procedure based on directly suspended droplet microextraction is proposed for determining different classes of polyphenols. A derivatization reaction by means of in injection-port reaction with bis(trimethylsilyl)trifluoroacetamide is carried out to convert the polar non-volatile polyphenols into volatile derivatives. The separation and detection is carried out by coupling gas chromatography with mass spectrometry in the selected ion monitoring mode. The procedure uses undecanone, a low density organic solvent, and several factors influencing the extraction, collection efficiency and derivatization reaction are optimized. Excellent linearity was obtained for the range studied (0.05-500ngmL(-1)). The limits of detection are between 0.011 and 0.13ngmL(-1), depending on the compound, and the limits of quantification between 0.037 and 0.43ngmL(-1). The sensitivity and detection limits for polyphenols using the DSDME sample pretreatment method were very low. Enrichment factors are between 413 and 578. The recoveries obtained for spiked samples are satisfactory for all the compounds. The coupled miniaturized method is applied to the sensitive determination of both cis- and trans-resveratrol isomers, piceatannol, catechin, epicatechin, quercetin and fisetin in herbal infusions, fruits, juices and functional foods.     

Determination of chlorophenols in environmental water samples using directly suspended droplet liquid-liquid-liquid phase microextraction prior to high-performance liquid chromatography

A new sample preparation method named directly suspended droplet liquid-liquid-liquid phase microextraction was used in this research for determination of three chlorophenols in environmental water samples. The analytes (2-chlorophenol, 3-chlorophenol and 4-chlorophenol) were extracted from 4.5?mL acidic donor phase, (pH 2, P1) into an organic phase, 350?µL?of benzene/1-octanol (90?:?10 v/v, P2) and then were back-extracted into a 7?µL droplet of an basic (pH 13) aqueous solution (acceptor phase, P3). In this method, contrary to the ordinary single drop liquid-phase microextraction technique, an aqueous large droplet is freely suspended on the surface of the organic solvent, without using a microsyringe as supporting device. This aqueous microdroplet is delivered at the top-centre position of an immiscible organic solvent which is laid over the aqueous donor sample solution while the solution is being agitated. Then, the acceptor phase containing chlorophenols was withdrawn back into a HPLC microsyringe and neutralised by adding of 7?µL HCl 0.1?M. The total amount was eventually injected into the HPLC system with UV detection at 225?nm for further analysis. Parameters such as the organic solvent, phases volumes, extraction and back-extraction times, stirring rate and pH values were optimised. The calibration graphs are linear in the range of 10–2000?µg?L^?1 with r?≥?0.9973. The enrichment factors were ranged from 115 to 170, and the limit of detection (LOD, n?=?7) varied from 5 to 10?µg?L^?1. The relative standard deviations (RSDs, n?=?5) were found 6.8 to 7.4 at S/N?=?3. All experiments were carried out at room temperature, (22?±?0.5°C).     

Design,preparation and characterization of Cu/GA/Fe3O4@SiO2 nanoparticles as a catalyst for the synthesis of benzodiazepines and imidazoles

The synthesis and characterization of an efficient and reusable nanocatalyst, Cu/GA/Fe₃O₄@SiO₂, obtained by ultrasonic‐assisted grafting of guanidineacetic acid on modified Fe₃O₄@SiO₂ core–shell nanocomposite spheres and subsequent immobilization of Cu(II), are described. The catalyst was characterized by means of X‐ray diffraction, scanning and transmission electron microscopies, energy‐dispersive X‐ray spectroscopy, elemental analysis, thermogravimetric analysis, Fourier transform infrared spectroscopy, vibrating sample magnetometry and inductively coupled plasma optical emission spectrometry. The prepared nanocatalyst facilitated an efficient and straightforward friendly procedure for the synthesis of benzodiazepines and imidazoles in ethanol and under solvent‐free conditions, respectively. The nanocatalyst can be easily recovered using a magnet and reused several times without any significant loss of activity. Copyright © 2016 John Wiley & Sons, Ltd.     

Stability analyses on dynamic control for a moving body levitated magnetically over elastic guideways

Based on the Floquet theory on ordinary differential equations with periodically variable coefficients and the bifurcation approach to nonlinear equations, a numerical approach to determining the stability region of control parameters is established for a dynamic control system composed of a moving body levitated magnetically over flexible guideways. The system is nonlinearly coupled among the elastic deformation of guideways, disturbance the levitation position of the body and electromagnetic control forces. The numerical simulation is given for the system in the case in which the control parameters are taken within and out of the stability region respectively. Results show that this approach is reliable. This project is supported by NSFC(No. 19725207), the Pre-research Project of the Committee of Science and Technology for Defence of China and the Science Foundation of Education Ministry of China for Ph. D. Programmes.     

Colorimetric Chemosensor for Chloramphenicol Based on Colloidal Magnetically Assembled Molecularly Imprinted Photonic Crystals

A novel colorimetric chemosensor with good sensitivity, specificity, and self‐reporting capability for chloramphenicol (CAP ) has been successfully constructed based on colloidal, magnetically assembled photonic crystals coupled with molecular imprinting. The colloidal, magnetically assembled, molecularly imprinted photonic crystals (CMA ‐MIPCs ) were prepared by assembling CAP in magnetic, molecularly imprinted nanohydrogels (MMIHs ) in a magnetic field. The magnetic assembly of photonic crystals and the sensing processes could be completed simultaneously when MMIHs were dispersed in CAP solutions and in a magnetic field, and the response time was less than 1 min. The CAP concentration could be visually determined from the color change of the CMA ‐MIPCs sensor. The diffraction color blue‐shifted from luminous yellow of the blank to purple in a 1.0 mg/mL CAP solution, with a determination limit of 1.0 × 10⁻³ mg/mL. It could provide a new strategy for qualitative or semiquantitative detection of CAP .     

小型静电陀螺仪电极面积及电极装配误差研究

介绍了小型静电陀螺仪的电极支承结构和电极面积误差引起的干扰力矩的计算公式,并根据影响电极面积的各种因素推导出了电极面积的误差范围。根据装配误差产生干扰力矩的情况确定了最终的装配精度,为电极的设计提供了重要的参考依据。     

系统压力对含悬浮颗粒油液的影响研究

油液在运行过程中不可避免地会产生颗粒物,影响油液的正常使用,甚至出现设备故障,因而分析含悬浮颗粒油液的动态特征,掌握在不同压力变化条件下油液及颗粒物的变化规律具有重要意义。利用两相流体理论建立了含悬浮颗粒油液的悬浮流动力学模型,通过特征线法进行了数值求解,将数值结果与实验数据比较,具有较好的一致性;根据所建模型,分析了不同系统压力条件下悬浮流中各相的脉动规律。结果表明,流场中各相参数的脉动幅值随着系统压力的增加而增大;管路始端和终端各相参数的脉动时刻分别位于1/4脉动周期(T)的奇数倍和偶数倍处,管路中段各相参数的脉动时刻则位于T/8的奇数倍处;悬浮颗粒速度会受到油液速度拖曳力作用,其变化趋势与油液速度基本一致,颗粒浓度分布与油液压力的变化趋势完全相反。