Preparation and characterization of microcellular polystyrene/polystyrene ionomer blends with supercritical carbon dioxide

The preparation of microcellular polystyrene (PS), lightly sulfonated polystyrene (SPS), zinc‐neutralized lightly sulfonated polystyrene (ZnSPS), and blends of PS/SPS and PS/ZnSPS via supercritical CO₂ was carried out with the pressure‐quench process. Both higher foaming temperature and lower pressure result in larger cell sizes, lower cell densities, and lower relative density for microcellular ionomers and blends as for microcellular PS. The difference among various microcellular samples is the change of cell size with the sample composition. The cell size decreases in the sequence from SPS, through PS/SPS blends, PS and PS/ZnSPS blends, to ZnSPS. The diffusivity of CO₂ in samples also decreases in the sequence from SPS, through PS/SPS blends, PS and PS/ZnSPS blends, to ZnSPS. For this series of samples with similar structure and identical solubility of CO₂, the varying diffusivity is responsible for the difference of cell sizes. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 368–377, 2003     

一种控制增益函数未知的自适应模糊控制

针对一类控制增益函数未知的、含有不确定项的非线性系统,为实现其跟踪控制目标,提出了一种鲁棒直接自适应模糊控制方法.该方法仅要求控制增益函数为有界函数,用广义模糊双曲正切模型逼近一个与控制增益函数无关的新颖的等价控制器,并为消除系统中的不确定项和逼近误差设计了一个双曲形式的鲁棒补偿控制项,从而保证了系统跟踪误差收敛到原点的一个小的邻域内,且所有的变量一致有界,控制输入平滑没有抖振.利用Lyapunov函数证明了该算法的有效性,并用倒立摆仿真实例进行了验证.     

硫化氢供体型去氢枞酸衍生物的合成及其细胞毒性

以去氢枞酸为原料,通过不同的长度碳链与硫化氢供体4-羟基硫代苯甲酰胺偶联,合成了5个新型硫化氢供体型去氢枞酸衍生物,所得化合物结构经¹H NMR、 ¹³C NMR和HR-MS表征。以阿霉素为阳性对照药,采用MTT法测定目标化合物对HepG2、 MGC803、 T24、 A549和LO2的细胞抑制作用。结果表明：大部分化合物对4种肿瘤细胞株的抑制活性优于母体化合物去氢枞酸,其中化合物4c对HepG2、 T24和A549细胞株的IC50值分别为4.63±0.18、 6.06±0.49和5.79±0.14 μmol·L^-1,优于或接近阳性对照药阿霉素（5.44±0.87、 3.69±0.78和3.75±0.11μmol·L^-1）。     

Synthesis,Structure and Catalytic Properties of a Cu(II) Coordination Polymer Constructed from Paddle-Wheel Building Blocks

A novel dinuclear Cu(II) coordination polymer, [Cu(BCPPO)H₂O]_n (1) [H₂BCPPO = bis -4-carboxyphenyl phenyl phosphine oxide], has been synthesized and structurally characterized by single crystal X-ray diffraction, powder X-ray diffraction, thermogravimetric analysis, elemental analysis and infrared spectroscopy. As revealed by the single crystal X-ray diffraction, in complex 1, two paddle-wheel-type Cu₂ units were connected by two BCPPO ligands to form one-dimensional infinite chain. The A³ coupling reaction of phenylacetylene, aldehyde and amine (piperidine) in the presence of the dinuclear Cu(II) coordination polymer as an efficient heterogeneous catalyst has also been studied. Complex 1 displayed high activity and afforded the corresponding propargylamines with moderate yields.     

Tetrahydrofuran hydrate decomposition characteristics in porous media

Many tetrahydrofuran (THF) hydrate properties are similar to those of gas hydrates. In the present work THF hydrate dissociation in four types of porous media is studied. THF solution was cooled to 275.15 K with formation of the hydrate under ambient pressure, and then it dissociated under ambient conditions. THF hydrate dissociation experiments in each porous medium were conducted three times. Magnetic resonance imaging (MRI) was used to obtain images. Decomposition time, THF hydrate saturation and MRI mean intensity (MI) were measured and analyzed. The experimental results showed that the hydrate decomposition time in BZ-4 and BZ-3 was similar and longer than that in BZ-02. In each dissociation process, the hydrate decomposition time of the second and third cycles was shorter than that of the first cycle in BZ-4, BZ-3, and BZ-02. The relationship between THF hydrate saturation and time is almost linear.     

Effect of Xanthan Gum on the Performance of Aqueous Film-Forming Foam

Solution properties of aqueous film-forming foam (AFFF) formulations containing different xanthan gum contents were investigated first by varying the mass fraction of xanthan gum in the range of 0.1–0.5%. Foam properties and fire-extinguishing performance of the AFFF formulations were then evaluated. Results indicated that xanthan gum content slightly affected surface tension of foam solutions. However, xanthan gum significantly affected viscosity of AFFF concentrates. Foaming of the AFFF formulations was hardly affected by xanthan gum, but foam stability of the compounds was obviously enhanced with the addition of xanthan gum. Optimal xanthan gum content was determined as 0.3%, which resulted in the shortest 90% control time and fire extinguishment time. Burnback time of foams increased with the addition of xanthan gum because of the enhanced foam stability.     

溶剂热法合成UiO-66金属有机框架限域的钴取代磷钼酸及其催化烯烃环氧化性能

金属有机框架材料是一类新型晶体孔性材料,在气体储存、物质分离、非线性光学及催化等领域中具有潜在应用价值.其中,基于锆氧簇和有机配体构筑的锆基金属有机框架材料(ZrMOFs)因其具有更高的结构稳定性而备受关注.研究表明,将多金属氧酸盐(POM)负载在ZrMOFs载体上能够获得一类新型复合材料催化剂.这类材料具有可调控的酸性和氧化还原性,已在一些固体酸催化及选择氧化(包括烯烃环氧化)等反应中表现出优异的催化性能.多金属氧酸盐通常可以通过简单的浸渍法引入到ZrMOFs载体上,但这种方法制备的催化剂普遍存在活性组分分散不均匀且易于在液相催化反应过程中发生活性组分流失的问题.因此,当前的研究重点主要集中在如何通过简单有效的制备方法获得结构更加稳定、性能更加优异的复合材料催化剂.近期,国内外多个研究小组分别报道了采用溶剂热法能够一步合成出POM@ZrMOFs复合材料,这类材料的主要特点是POM团簇能够均匀的分散在ZrMOFs孔道中,从而使其在氧化脱硫及烯烃选择氧化等反应中表现出更高的稳定性.考虑到POMs及ZrMOFs种类和结构的多样性,可以预期这类复合材料的合成及催化性能研究仍有很大的发展空间.本文采用溶剂热法将磷钼酸(PMo12)及钴取代磷钼酸(PMo11Co)限域在一类ZrMOFs材料(UiO-66)的孔道中,得到了两种复合材料催化剂,分别记为PMo12@UiO-66和PMo11Co@UiO-66.通过以叔丁基过氧化氢(t-BuOOH)为氧化剂烯烃环氧化反应考察了其催化性能.相较于PMo12@UiO-66,含有钴取代磷钼酸的PMo11Co@UiO-66杂化材料表现出了更高的催化活性和稳定性.催化剂经简单的过滤和洗涤后即可循环使用多次,且催化性能基本保持不变.值得一提的是,PMo11Co@UiO-66对多种类型烯烃的环氧化反应均表现出较高的催化活性和环氧选择性.例如,在加入自由基抑制剂对二苯酚后,柠檬烯选择性氧化为柠檬烯-1,2-环氧化物的选择性可以达到91%,性能明显优于文献中报道的其它类型催化剂.此外,溶剂种类对PMo11Co@UiO-66的催化活性有着显著的影响,在极性相对较强的乙醇、乙腈等溶剂中,催化剂的活性较低;在极性较弱的甲苯、氯仿,四氯化碳等溶剂中,催化剂的活性则相对较高.溶剂极性的差异会影响反应物分子与催化剂活性中心的接触情况,继而对催化剂的活性产生较大影响.采用X射线衍射、氮吸附-脱附、X射线光电子能谱、傅立叶变换红外光谱(FT-IR)等手段对催化反应前后的PMo11Co@UiO-66催化剂进行了表征.结果表明,在溶剂热法合成的杂化材料催化剂中,引入的POM团簇能够均匀的分散在UiO-66框架材料的孔道和笼中;催化剂反应前后的组成与结构没有发生明显的变化.结合相关文献报道的结果,可以认为杂原子Co的引入能够产生类似于Co–O–Mo的新的活性中心,从而使PMo11Co@UiO-66表现出更高的催化活性.催化剂的高稳定性应主要归因于UiO-66框架对PMo11Co团簇的空间限域作用.这种空间限域作用能够使PMo11Co团簇被封装在UiO-66的八面体笼中,且二者之间还存在着较强的金属-载体间相互作用.在后续的工作中,我们还将继续深入研究PMo11Co@UiO-66催化剂的活性中心性质及其对分子氧的活化能力,加深对催化作用机制等问题的理解,进一步扩大这类复合材料催化剂的应用范围.     

Reversible doping polarity and ultrahigh carrier density in two-dimensional van der Waals ferroelectric heterostructures

Van der Waals semiconductor heterostructures (VSHs) composed of two or more two-dimensional (2D) materials with different band gaps exhibit huge potential for exploiting high-performance multifunctional devices. The application of 2D VSHs in atomically thin devices highly depends on the control of their carrier type and density. Herein, on the basis of comprehensive first-principles calculations, we report a new strategy to manipulate the doping polarity and carrier density in a class of 2D VSHs consisting of atomically thin transition metal dichalcogenides (TMDs) and α-In₂X₃ (X = S, Se) ferroelectrics via switchable polarization field. Our calculated results indicate that the band bending of In₂X₃ layer driven by the FE polarization can be utilized for engineering the band alignment and doping polarity of TMD/In₂X₃ VSHs, which enables us to control their carrier density and type of the VSHs by the orientation and magnitude of local FE polarization field. Inspired by these findings, we demonstrate that doping-free p−n junctions achieved in MoTe₂/In₂Se₃ VSHs exhibit high carrier density (10¹³−10¹⁴ cm⁻²), and the inversion of the VHSs from n−p junctions to p−i−n junctions has been realized by the polarization switching from upward to downward states. This work provides a nonvolatile and nondestructive doping strategy for obtaining programmable p−n van der Waals (vdW) junctions and opens the possibilities for self-powered and multifunctional device applications.     

快速时变信道下的基扩展模型信道估计性能分析

针对快速时变信道,提出了一种基于复指数基扩展模型(CE-BEM)的线性最小均方误差(LMMSE)信道估计方法,对信道估计的结果使用离散长椭球序列(DPSS)进行平滑处理,并相应提出了基于迭代的载波间干扰(ICI)消除信道均衡方法.仿真结果表明:在高多普勒信道场景下,该方法系统误码性能较传统信道估计方法有一定程度的提升.     

不同硅铝比ZSM-5分子筛作为助催化剂在渣油裂化中的应用

采用不同方法表征了硅铝比(SiO2/Al2O3)为33、266和487的质子型ZSM-5分子筛,并研究了ZSM-5分子筛作为助催化剂在渣油裂解中的应用。与USY分子筛基催化剂混合后,在固定流化床上,评价了ZSM-5分子筛助催化剂的催化裂化性能。研究发现,提高ZSM-5分子筛硅铝比,可以有效抑制混合催化剂对汽油烯烃的裂解,从而避免了汽油烷烃的大量损失。加入ZSM-5助催化剂后,伴随着液化气(LPG)产率的增加,异丁烷和异戊烷产率增加,这可能是由USY基催化剂和ZSM-5助催化剂的综合效应引起的。汽油烷烃和芳烃含量的变化,引起了汽油辛烷值的增加。高硅铝比ZSM-5分子筛(硅铝比为266和487)不仅可以显著改善汽油的辛烷值,而且有效避免了汽油的大量损失。催化汽油辛烷值的改善主要是由于高硅铝比ZSM-5分子筛具有适宜的芳构化和异构化活性,这些变化主要源于高硅铝比ZSM-5分子筛小的孔道直径和适宜的酸性。