γ-Al2O3颗粒溶液浸润过程的原位磁共振成像

在催化剂的制备过程中,常采用浸渍法将金属或活性相负载到多孔固体载体上以获得高性能的负载型催化剂;在浸渍过程中溶剂对载体的浸润能力和效果对负载活性组分的分布和状态至关重要,进而会影响催化剂的催化性能.本文利用磁共振成像(MRI)技术开展了溶剂对γ-Al₂O₃颗粒浸润过程的原位研究.评估了自旋回波(SE)、梯度回波(GRE)和超短时间回波(UTE) 3种不同MRI序列的成像效果,发现UTE序列在观测短横向弛豫时间(T₂)值的¹H MRI信号方面展现出优越的性能,应用小激发角和短恢复时间(TR)可以获得比SE和GRE序列更高时间分辨率(<1 min)的动态图像.利用UTE序列对γ-Al₂O₃在不同极性溶剂中的浸渍过程进行了原位监测,发现极性溶剂水和甲醇均表现出典型的自由扩散过程,即溶剂从颗粒的外缘逐渐扩散到其中心直至饱和;非极性溶剂环己烷展现了不同的浸润行为,γ-Al₂O₃颗粒的整体¹H M...     

一种确定煤基吸附剂内各扩散系数的简易方法

多孔介质内的扩散有分子扩散和表面扩散两种。在吸附温度较高时 ,表面扩散可忽略 ,而在温度较低的吸附过程中 ,两种扩散均须考虑。Ｓｃｈｎｅｉｄｅｒ和Ｓｍｉｔｈ[1 ] 曾用色谱法探讨了一种计算扩散系数的方法。他们认为等温吸附呈线性变化 ,引入了曲折系数 ,计算出分子扩散系数 (下称气相扩散系数 ) ,表面扩散系数 (下称吸附相扩散系数 )则由综合扩散系数减去分子扩散系数得到。文献 [2 ]则认为吸附过程非线性变化 ,服从Ｆｒｕｎｄｌｉｃｈ方程或Ｌａｎｇｍｕｉｒ方程。从质量平衡方程得出相对吸附量方程 ,再求出各扩散系数。前一种方法将…     

痕量氯代甲烷在聚异丁烯中的扩散系数研究

采用填充柱反相气相色谱 ,基于 Hadj- Romdhane和 Danner所提出的扩散分子在色谱柱中扩散模型 ,分别测定了不同温度下痕量的三种氯代甲烷溶剂 :二氯甲烷、三氯甲烷和四氯甲烷在聚异丁烯膜 ( PIB)中的扩散系数。实验结果表明溶剂分子在聚异丁烯中的扩散系数与体系温度和溶剂的分子大小有关。在相同温度下 ,溶剂分子睦菠 ,扩散系数越大 ;温度越高 ,扩散系数越大。同时对所测数据用 Vrentas- Duda自由体积扩散系数方程进行了探讨 ,发现对于 PIB/ CCl4 体系 ,采用预测型 Vrentas- Duda方程计算所得不同温度下的值与实验数据相符 ,而对于PIB/ CHCl3体系计算偏差较大 ,该偏差产生于预测方程中忽略了能量效应。     

(FITC/SiO2-CdTe QDs)-SiO2复合结构编码荧光纳米颗粒的制备

制备了一种(FITC/SiO2-CdTe QDs)-SiO2复合结构编码荧光纳米颗粒。荧光光谱、扫描隧道显微镜和透射电镜对FITC/SiO2和(FITC/SiO2-CdTe QDs)-SiO2等荧光纳米颗粒进行了表征。结果表明,FITC/SiO2NPs和(FITC/SiO2-CdTe QDs)-SiO2均呈球形,粒径分别约为200和300 nm,分布均匀,且具有可分辨的双重荧光信号。并用Cu2+对(FITC/SiO2-CdTe QDs)-SiO2编码荧光纳米颗粒进行了后编码。     

硅胶-氰丙基复合固相萃取柱分离原油中饱和烃及芳烃组分

探讨了硅胶-氰丙基(SiO2/C3-CN,(1 g/0.5 g,6 mL))复合固相萃取柱分离与净化原油中饱和烃和芳烃组分的方法。结果表明:SiO2/C3-CN复合固相萃取柱较单一硅胶(SiO2)小柱的分离效果好,仅使用4.5 mL正己烷和4.5 mL正己烷-二氯甲烷(1∶1)洗脱即可实现饱和烃和芳烃组分的完全分离与满意回收(回收率分别为98%和99%);而单一硅胶小柱存在低环数芳烃化合物(如萘及其甲基系列、苊等)与饱和烃组分的共洗脱现象。通过对原油实物样品的测定,饱和烃和芳烃组分在硅胶-氰丙基复合柱上经正己烷、正己烷-二氯甲烷(体积比1∶1)的洗脱行为与标准混合液完全一致,该方法实用可靠、流程简单、试剂消耗少、精密度良好(RSD为4.2%～8.5%),适用于石油样品中饱和烃和芳烃组分的定量分析。     

CuCl与SiO_2-TiO_2载体相互作用的密度泛函理论研究

以SiO2簇模型为基体,通过Ti原子取代建立Ti中心原子上连接0个或1个OH基团的典型SiO2-TiO2复合氧化物模型来模拟处于体相中和表面上的四配位Ti(IV)中心.采用广义梯度近似的密度泛函理论(DFT-GGA)研究了CuCl与SiO2-TiO2载体的相互作用.计算结果表明,在SiO2基体中嵌入Ti(IV)离子可以大大加强CuCl与氧化物载体之间的相互作用,使CuCl/SiO2-TiO2催化剂的结构更稳定.分子前线轨道表明Cu(I)作为催化剂的活性中心贡献了HOMO轨道,容易失去电子;Ti(IV)中心原子贡献LUMO轨道,容易得到电子,计算结果与实验事实相一致.     

对称性降低的SiO2/Ag核壳结构纳米粒子的制备及表面增强拉曼活性研究

采用湿化学还原法在自组装的单层阵列二氧化硅纳米粒子表面沉积银膜制备了SiO2核/Ag帽复合纳米结构。通过透射电镜(TEM)、扫描电镜(SEM)、X射线衍射(XRD)和紫外-可见分光光度计(UV/Vis)研究和表征了该复合纳米结构的表面形貌、结构及光学性质。所制备的复合纳米粒子表面粗糙,其表面呈现无数纳米级谷粒状结构,SiO2内核粒径为350nm的银纳米帽的表面等离子共振吸收的2个共振峰分别位于382和689nm处。以亚甲基蓝作为探测分子研究了SiO2粒径为350和450nm的SiO2/Ag帽状复合纳米粒子的表面增强拉曼散射(SERS)活性,增强因子分别为3.6×109和3.9×109。结果表明,湿化学还原法制备的SiO2核/Ag帽复合纳米结构是很好的拉曼活性基底。     

ZIF-8材料中CH4/H2吸附与扩散的分子模拟

采用平衡分子动力学和巨正则系综蒙特卡洛模拟方法对多孔沸石咪唑酯骨架材料(ZIF-8)中CH4和H2分子的吸附与扩散特性进行了比较研究.结果表明,采用柔性力场能够很好地复制ZIF-8在不同压力或温度条件下的晶体结构,也能准确地计算不同温度下CH4和H2分子在ZIF-8中的扩散系数,特别是高温下CH4分子因能够摆脱ZIF-8骨架笼口的空间限制而使其扩散系数出现大幅提升.同时,该力场也能粗略地模拟CH4和H2分子在ZIF-8中的等温吸附曲线,通过自编程序得到吸附和扩散平衡时CH4和H2分子在ZIF-8单元晶胞内的几率密度分布数据,并利用VMD软件可视化.结果显示CH4和H2分子在ZIF-8中的优先吸附位置均在大孔中心靠近咪唑环的区域,但CH4分子的优先吸附位置有两个不同层次,而H2分子的优先吸附位置只有一个层次,说明CH4和H2分子在ZIF-8中存在着不同的吸附机理.     

采用分子表面印迹技术构建手性空穴实现对天冬氨酸对映体的识别拆分

在溶液聚合体系中,采用"接出"法("graft from"method)将功能单体4-乙烯基吡啶(4VP)接枝聚合于微米级硅胶表面,制得了功能接枝微粒P4VP/SiO2,采用本课题组建立的新型分子表面印迹技术,以天冬氨酸(Asp)的一种对映体L-Asp为模板分子,二溴己烷为交联剂,对接枝在硅胶表面的大分子P4VP实施了分子印迹,制备了L-Asp分子表面印迹材料MIP-P4VP/SiO2.以天冬氨酸另一种对映体D-Asp为对比物,采用静态与动态两种方法深入研究了MIP-P4VP/SiO2对L-Asp分子的识别性能,重点探索了采用MIP-P4VP/SiO2对天冬氨酸两种对映体进行拆分的可行性.实验结果表明,印迹材料MIP-P4VP/SiO2对模板分子L-Asp具有良好的识别选择性与结合亲和性,相对于D-Asp,识别选择性系数为3.85,对天冬氨酸的外消旋体具有良好的拆分性能.印迹材料MIP-P4VP/SiO2也具有良好的解吸性能,以稀NaOH水溶液作为洗脱液,12个床体积内解吸率即可达到98.52%.     

水和盐分子在反渗透膜内扩散过程的分子模拟

采用分子动力学模拟方法研究了水和盐分子(NaCl, MgCl2, CaSO4, K2SO4)在8种反渗透复合膜中的扩散状态及扩散系数. 并对膜材料的结构单体与水和盐分子在膜内扩散系数相关性进行了分析与讨论. 在所模拟的8种膜内, 随着膜种类的不同, 水分子在其中的扩散系数有明显的变化, 且扩散系数的变化规律与实验所得到的膜的水通量一一对应. NaCl分子中的Na+和Cl-在膜内的扩散速率不一致, 其扩散系数值在同种膜中相差较大, 且当盐分子单独存在时, 制约其在膜内扩散过程的离子只与膜种类有关, 与盐分子本身无关. 在同种膜中, 水分子的扩散过程不受体系中盐分子类型的影响.     

Preparation and characterization of silver/TiO2 composite hollow spheres

Silver-coated poly(methyl acrylic acid) (PSA) core-shell colloid particles were prepared by an in situ chemical reduction method. Crystalline silver/titania composite hollow spheres were obtained by coating the as-prepared PSA/silver particles with an amorphous titania layer and subsequently calcining in Ar atmosphere. SEM and TEM investigation indicated that the size of the as-prepared PSA/silver and PSA/silver/TiO(2) core-shell particles and silver/titania composite hollow particles was fairly uniform and the wall thickness of the hollow spheres was in the range of 40-80 nm. UV-vis absorption spectra were recorded to investigate their optical properties.     

Synthesis of ellipsoidal hematite/silica/polymer hybrid materials and the corresponding hollow polymer ellipsoids

Ellipsoidal trilayer hematite/silica/poly(divinylbenzene) hybrid particles were prepared by distillation precipitation polymerization of divinyl benzene (DVB) in the presence of hematite/3-(methacryloxy)propyl trimethoxysilane (MPS)-modified silica (SiO(2)) core-shell particles as the seeds. The polymerization of DVB was performed in neat acetonitrile with 2,2'-azobisisobtyronitrile (AIBN) as initiator to coat the hematite/MPS-modified SiO(2) seeds through the capture of DVB oligomer radicals with the aid of a vinyl group on the surface of the hematite/MPS-modified silica core-shell particles in the absence of any stabilizer or surfactant. The other hematite/silica/polymer trilayer hybrid particles with different polarity and various functionality, such as hematite/silica/poly(ethylene glycol dimethacrylate) and hematite/silica/poly(divinyl benzene- co-methacrylic acid) could also be prepared by this procedure. Hematite/silica/poly( N, N'-methylenebisacrylamide) composite particles could be prepared with unmodified hematite/silica particles as seeds. Hollow poly(divinyl benzene) (PDVB) and poly( N, N'-methylenebisacrylamide) (PMBAAm) ellipsoids with movable hematite cores were subsequently developed after the selective etching of the silica midlayer in diluted hydrofluoric acid from hematite/silica/PDVB and hematite/silica/PMBAAm trilayer hybrids. Hollow PDVB ellipsoids were obtained by removal of the silica midlayer and hematite core of the trilayer hybrids with concentrated HF solution. The resultant trilayer hybrid particles and hollow polymer ellipsoids were characterized by transmission electron microscopy and vibrating sample magnetometer.     

Facile preparation method of SiO2/PS/TiO2 multilayer core-shell hybrid microspheres

Organic-inorganic hybrid particles have many potential applications, but almost all of this research was focused on the hybrid particles containing one kind of inorganic nanoparticles. This paper presented a facile preparation method for SiO2/PS/TiO2 multilayer core-shell hybrid microspheres. In this approach, positively charged SiO2/PS core-shell hybrid particles were first synthesized by miniemulsion polymerization using cationic initiator and emulsifier. These positively charged SiO2/PS hybrid particles were mixed with tetra-n-butyl titanate for sol-gel reaction to directly form SiO2/PS/TiO2 multilayer core-shell hybrid microspheres. Some influencing parameters such as surfactant concentration, tetra-n-butyl titanate amount, and glacial acetic acid amount were investigated. TEM, TGA, and EDX analyses indicated that titania layers were successfully coated onto the surfaces of hybrid microspheres.     

pH值和前驱体用量对核壳结构PSt/SiO2复合微球结构形态的影响

首先通过无皂乳液聚合法制得表面含羧基、粒径为360 nm的单分散聚苯乙烯(PSt)种子乳液,并在EtOH/H2O混合介质中用γ-氨丙基三乙氧基硅烷(KH-550)对其进行改性,制得表面含有活性硅乙氧基并带有正电荷的改性PSt乳胶粒,然后再加入原硅酸乙酯(TEOS)进行共水解与共缩聚反应,制备出了核壳结构PSt/SiO2...     

种子表面改性法制备核壳结构PSt/SiO_2复合微球

首先采用无皂乳液聚合法合成了表面带负电荷、粒径为360nm的单分散聚苯乙烯(PSt)种子乳液,并以EtOH/H2O混合物为分散介质,利用γ-氨丙基三乙氧基硅烷(KH-550)在25℃下对PSt微球表面进行改性,得到了表面硅烷化并带有正电荷的改性PSt种子乳液,然后在碱性条件下加入原硅酸乙酯(TEOS)使其和微球进行共水解与共缩聚,制备出了核壳结构PSt/SiO2复合微球,并利用电镜对复合微球的结构形态进行了表征.研究表明,PSt种子乳液改性时体系的zeta电位随着KH-550用量的增加而升高,当KH-550用量为PSt种子重量的1/3时,体系的zeta电位从原来的-34.5mV升高到了38mV,达到对PSt微球表面改性的最佳值;在制备PSt/SiO2复合微球时,TEOS水解缩聚形成的SiO2包覆到改性微球上的量随着反应时间的延长而增加,反应24h时达到97.9%的最大值;随介质中水含量的增加,吸附到复合微球表面上的SiO2纳米颗粒逐渐减少,复合微球表面逐渐变得光滑,当EtOH/H2O质量比降低到60/28.5时,得到结构均一、壳层厚度为35nm的核壳结构PSt/SiO2复合微球。     

Silica-dendrimer core-shell microspheres with encapsulated ultrasmall palladium nanoparticles: efficient and easily recyclable heterogeneous nanocatalysts

We report the synthesis, characterization, and catalytic properties of novel monodisperse SiO(2)@Pd-PAMAM core-shell microspheres containing SiO(2) microsphere cores and PAMAM dendrimer-encapsulated Pd nanoparticle (Pd-PAMAM) shells. First, SiO(2) microspheres, which were prepared by the St?ber method, were functionalized with vinyl groups by grafting their surfaces with vinyltriethoxysilane (VTS). The vinyl groups were then converted into epoxides by using m-chloroperoxybenzoic acid. Upon treatment with amine-terminated G4 poly(amidoamine) (PAMAM) dendrimers, the SiO(2)-supported epoxides underwent ring-opening and gave SiO(2)@PAMAM core-shell microspheres. Pd nanoparticles within the cores of the SiO(2)-supported PAMAM dendrimers were synthesized by letting Pd(II) ions complex with the amine groups in the cores of the dendrimers and then reducing them into Pd(0) with NaBH(4). This produced the SiO(2)@Pd-PAMAM core-shell microspheres. The presence of the different functional groups on the materials was monitored by following the changes in FTIR spectra, elemental analyses, and weight losses on thermogravimetric traces. Transmission electron microscopy (TEM) images showed the presence of Pd nanoparticles with average size of 1.56 ± 0.67 nm on the surface of the monodisperse SiO(2)@Pd-PAMAM core-shell microspheres. The SiO(2)@Pd-PAMAM core-shell microspheres were successfully used as an easily recyclable catalyst for hydrogenation of various olefins, alkynes, keto, and nitro groups, giving ~100% conversion and high turnover numbers (TONs) under 10 bar H(2) pressure, at room temperature and in times ranging from 10 min to 3 h. In addition, the SiO(2)@Pd-PAMAM core-shell microspheres were proven to be recyclable catalysts up to five times with barely any leaching of palladium into the reaction mixture.     

碳酸镉@二氧化硅菱形体核壳结构以及二氧化硅菱形体空心结构微粒的制备

利用Stöber种子生长法, 第一次在尺寸为2 μm左右的碳酸镉菱形微粒表面直接包覆二氧化硅层, 得到碳酸镉@二氧化硅核壳结构的胶体粒子. 作为核壳结构的壳层部分, 二氧化硅层的厚度可以通过加入体系中的正硅酸乙酯的量来控制. 作为核层的碳酸镉胶体部分可以被盐酸刻蚀掉, 进而得到具有菱形体空心结构的二氧化硅微粒.     

Synthesis of a Au/silica/polymer trilayer composite and the corresponding hollow polymer microsphere with a movable Au core

Gold/silica/poly(N,N'-methylenebisacrylamide) (Au/SiO2/polyMBAAm) trilayer composite materials were prepared by distillation precipitation polymerization of N,N'-methylenebisacrylamide (MBAAm) in the presence of Au/SiO2 particles as seeds, in which the seeds were prepared by a combination of gold-complexing and silane coupling agent with a further modified St?ber method. The polymerization of MBAAm was performed in neat acetonitrile with 2,2'-azobisisobutyronitrile as an initiator to encapsulate the Au/SiO2 seeds driven by the hydrogen-bonding interaction between the hydroxyl group on the surface of the seeds and the amide unit of polyMBAAm without modification of the Au/SiO2 surface in the absence of any stabilizer or surfactant. Hollow polyMBAAm microspheres with movable Au cores were further developed by the selective removal of the middle silica layer with hydrofluoric acid. The resultant trilayer Au/SiO2/polyMBAAm composite and hollow polyMBAAm microspheres with movable Au cores were characterized by transmission electron microscopy. The diffusion of chemicals across the polyMBAAm shell was investigated by a catalytic reduction of 4-nitrophenol to 4-aminophenol in the presence of sodium borohydride as a reductant.     

The influence of high dielectric constant core on the activity of core-shell structure electrorheological fluid

The core-shell structural dielectric particles are applied widely in the electrorheological (ER) fluids. The properties of the dielectric core are critical factors influencing their ER activity. In this paper, we successfully synthesized two kinds of core-shell hydroxyl titanium oxalate (TOC) particles with SiO(2) and TiO(2) as core, respectively. The obtained core-shell structural SiO(2)-TOC and TiO(2)-TOC particles were well-dispersed spherical nanoparticles with ideal morphology and a narrow size distribution. Under DC electric fields, the TiO(2)-TOC ER fluid showed notable ER activity with a yield stress of about 96 kPa (at 4 kV/mm), which is 3 times of that SiO(2)-TOC ER fluid and outclassed the yield stress of the TOC ER fluid. The dielectric spectra indicated that the higher dielectric constant of TiO(2) core induces the stronger interaction between the neighboring particles, which contribute to the enhancement of ER activity.     

In-situ quantitative analysis of a prostate-specific antigen (PSA) using a nanomechanical PZT cantilever

We report on a novel technique of resonant frequency shift measurement based on a nanomechanical cantilever with a PZT actuating layer for label-free detection of a prostate-specific antigen (PSA) in a liquid environment. The nanomechanical PZT thin film cantilever is composed of SiO(2)/Ta/Pt/PZT/Pt/SiO(2) on a SiN(x) supporting layer for simultaneous self-exciting and sensing; it was fabricated using a standard MEMS (micro electromechanical system) process. The specific binding characteristics of the PSA antigen to its antibody, which is immobilized with Calixcrown self-assembled monolayers (SAMs) on a gold surface deposited on a cantilever, are determined to a high sensitivity. For the bioassay in a liquid environment, a liquid test cell with a 20 microl volume reaction chamber has been fabricated, using a bonding technique between poly(dimethyl siloxane) (PDMS) bilayers. An observed trend of resonant frequency change with respect to time could be explained by the binding kinetics due to the Langmuir isotherm and diffusion and by the effects of a small volume reaction chamber. In the saturated regimes, the resonant frequency of the cantilever increased with increase of the PSA concentration in the reaction chamber, showing that the trend of the resonance frequency change was similar to that of the fluorescence results. The saturated resonance frequency shift of the cantilever was proportional to the PSA antigen concentration of analyte solution.