溶胶－凝胶法制备超细SiO_2──制备参数对气凝胶织构性质的影响

ＳｉＯ_２气凝胶超细粉由ＴＥＯＳ（正硅酸乙酯）在乙醇溶液中水解聚合后经超临界流体干燥（ＳＣＦＤ）制得。本文考察了ＴＥＯＳ的浓度、水和ＴＥＯＳ的摩尔比以及焙烧温度对超细粉织构性能的影响。结果表明，超细ＳｉＯ_２的比表面积、总孔容、孔分布、最可几孔径及表现堆密度均随制备参数而改变。而以ＳｉＯ_２气凝胶超细粉体为基本载体材料的Ｃｏ／ＺｒＯ_２－ＳｉＯ_２催化剂显示出高的ＣＯ＋Ｈ_２合成重质烃的活性和选择性。     

溶胶-凝胶法原位生成SiO_2改性硅基耐烧蚀材料

建立了在硅基耐烧蚀材料中用溶胶-凝胶法原位生成SiO2的方法.首先将硅橡胶、气相白炭黑、纤维等原料混炼硫化制备出硫化胶.然后将硫化胶依次浸入四氢呋喃、原硅酸乙酯和正丁基胺水溶液中进行预溶胀处理、物理扩散和化学反应,得到原位生成SiO2.SEM照片显示,在硅基耐烧蚀材料中原位生成的SiO2颗粒呈球形,粒径在40~60 nm,但分布不均匀,在硫化胶表层存在富集现象.实验结果表明,原位生成SiO2平均含量增加,硅基耐烧蚀材料的抗拉强度增加,线烧蚀率下降;含13.7%原位生成SiO2硅基耐烧蚀材料抗拉强度为5.82 MPa,线烧蚀率为0.071 mm/s.     

SiO2-PEG凝胶体系织构特性的研究

采用溶胶-凝胶法,以正硅酸乙酯(TEOS)为前驱体,以不同分子量的聚乙二醇(PEG)为改性剂,制备结构可控的多孔SiO₂干凝胶.结果表明:PEG限制了TEOS的水解反应,进而对溶胶粒子的表面进行修饰,形成“粒子团-PEG”聚集体及短程有序的环状网络结构,由此对SiO₂干凝胶的结构性质进行调控.经真空热处理后,PEG等有机残留物被脱除的同时,SiO₂-PEG干凝胶柔性骨架得到加强,孔分布更趋集中,干凝胶结构的热稳定性得到进一步提高.     

含氟高分子/SiO_2杂化疏水材料的制备及涂层表面性质

采用自由基溶液聚合与溶胶-凝胶法相结合的方法制备了含氟高分子/SiO2杂化疏水材料.通过甲基丙烯酸十二氟庚酯(FA)与乙烯基三乙氧基硅烷(VTES)共聚合成了含氟硅共聚物(PFAS),进一步通过原硅酸乙酯(TEOS)与PFAS共聚物溶液共水解缩聚制备了具有含氟侧基的碳碳主链高分子和硅氧网络的含氟高分子/SiO2杂化疏水材料.研究结果表明,SiO2组分含量提高可以显著增加杂化材料薄膜的涂敷厚度,改善其耐久性能,而对杂化材料疏水性能的影响不大.     

Preparation of nanosize silica in reverse micelles: ethanol produced during TEOS hydrolysis affects the microemulsion structure

Microemulsions have been widely used as microreactors for the synthesis of nanoparticles and mesoporous materials. The correlation between the microstructure of a microemulsion and the features of the obtained materials is the most intriguing problem. On this point, many investigations have their ground on the structure of the precursor microemulsion, i.e., the system before the reaction takes place. Nevertheless, any reactions usually involve the formation of byproducts (aside from the nanoparticles). Several of these byproducts (e.g., ions, amphiphilic molecules) could modify the microemulsion structure during the course of the reaction. Here we examine the hydrolysis of tetraethoxysilane (TEOS) in the water-in-oil microemulsion hexadecyl-trimethylammonium bromide (CTAB)/pentanol/hexane/water. Conductivity and NMR measurements performed during the course of the reaction, in combination with dynamic light scattering and pulsed field gradient spin-echo NMR investigation performed on the microemulsion upon the addition of ethanol, indicate that a byproduct (ethanol) modifies the microreactor structure. The ethanol produced by the TEOS hydrolysis drives the microemulsion structure from small disconnected reverse micelles toward large connected aggregates until (for high enough ethanol loading) the system phase separates into two coexisting liquid phases (a dense interconnected network and a dilute reverse micellar phase).     

Hybrid organic-inorganic phenyl monolithic column for capillary electrochromatography

A novel hybrid organic-inorganic silica-based monolithic column possessing phenyl ligands for reversed-phase (RP) capillary electrochromatography (CEC) is described. The monolithic stationary phase was prepared by in situ co-condensation of tetraethoxysilane (TEOS) with phenyltriethoxysilane (PTES) via a two-step catalytic sol-gel procedure to introduce phenyl groups distributed throughout the silica matrix for chromatographic interaction. The hydrolysis and condensation reactions of precursors were chemically controlled through pH variation by adding hydrochloric acid and dodecylamine, respectively. The structural property of the monolithic column can be easily tailored through adjusting the composition of starting sol solution. The effect of PTES/TEOS ratios on the morphology of the created stationary phases was investigated. A variety of neutral and basic analytes were used to evaluate the column performance. The CEC columns exhibited typical RP chromatographic retention mechanism for neutral compounds and had improved peak shape for basic solutes.     

Unveiling the elusive role of tetraethyl orthosilicate hydrolysis in ionic-liquid-templated zeolite synthesis

Despite previous reports showing that crystallization kinetics affects zeolite phase selectivity because zeolites are metastable species in their synthesis solution rather than thermodynamic end points, the critical kinetics-controlling parameter is yet to be determined. This work elucidated the effect of tetraethyl orthosilicate (TEOS) hydrolysis before hydrothermal treatment on the final zeolite phase selectivity in the ionic liquid-templated synthesis of 10-membered ring zeolites (MFI- or TON-type zeolites). The results showed that the dissolved silica concentration in the synthesis solution, which is controlled by varying the TEOS hydrolysis temperature and addition rate, induced heterogeneous nuclear growth. Specifically, in 1-butyl-3-methylimidazolium ([BMIM]Br)-directed syntheses, the high and low concentrations of dissolved silica species led to MFI and TON zeolite formation, respectively. The experimental results are supported by silica polymerization modeling using the Reaction Ensemble Monte Carlo method and theoretical calculations on composite building unit formation. The results are valuable for understanding the nucleation mechanism in zeolite crystallization.     

甲基丙烯酸(3-三甲氧基硅)丙酯-马来酸二丁基锡共聚物/二氧化硅杂化材料的制备

甲基丙烯酸（３ 三甲氧基硅）丙酯 马来酸二丁基锡共聚物／二氧化硅杂化材料的制备周文董建华丘坤元（北京大学化学与分子工程学院高分子科学与工程系，１００８７１北京）ＷｅｉＹｅｎ（危岩）（ＤｅｐａｒｔｍｅｎｔｏｆＣｈｅｍｉｓｔｒｙ，Ｄｒｅｘｅｌ...     

Hydrolysis and polycondensation of ethyl silicates. 1. Effect of pH and catalyst on the hydrolysis and polycondensation of tetraethoxysilane (TEOS)

The effect of pH and of catalysts on the course of the hydrolysis and condensation of tetraethoxysilane (TEOS) in water—ethanol solution was studied with the aid of chromatography, potentiometry and gelation tests. Strong acids (HCl, HClO₄, HNO₃, H₂SO₄, p-toluenesulphonic acid), weak acids (Cl₃CCOOH, (COOH)₂, ClCH₂COOH, CH₃COOH, HCOOH) and LiOH were used as catalysts. The rate of hydrolysis depended on the pH of the solution and not on the chemical structure of the catalyst. The hydrolysis was both acid and base catalysed and its rate was at a minimum at pH 7.0.

The rate of condensation of the reaction products of the hydrolysis of TEOS (water—ethanol solutions of ethoxyhydroxysiloxanes) was at a minimum at a pH of about 2.0. The condensation was both acid and base catalysed and was markedly accelerated by both HF and H₃PO₄.     

Effects of the Water Quantity on the Solventless TEOS Hydrolysis Under Ultrasound Stimulation

The acid hydrolysis under ultrasound stimulation of solventless tetraethoxysilane(TEOS)-water mixtures was studied at 40°C, by means of a heat flux calorimetric method, as a function of the initial water/TEOS molar ratio (r) ranging from 2 to 10. The method is based on the time record of the exothermic heat peak of hydrolysis, arising after an induction time under ultrasound stimulation, which is a measure of the reaction rate. The hydrolysed quantity was found to be approximately independent of the water/TEOS molar ratio, even for r < 4. Polycondensation reaction takes place mainly for low water/TEOS molar ratio in order to supply water to allow almost complete hydrolysis. The overall process of dissolution and hydrolysis has reasonably been described by a previous modelling. The dissolution process of water in TEOS, under ultrasound stimulation and acid conditions, was found to be rather dependent of the alcohol produced in the hydrolysis reaction instead of the initial water quantity present in the mixture.     

微波辅助Ni-B/SiO2非晶态催化剂的制备及其在硝基苯加氢中催化性能的研究

采用微波辐射干燥浸渍法获得的Ni2 /SiO2,再由液相KBH4还原制备Ni-B/SiO2非晶态催化剂,在液相硝基苯加氢反应中,该催化剂对苯胺的选择性为100%,催化活性显著高于由传统加热法制备的Ni-B/SiO2.根据XRD、XPS、SEM和氢吸附等表征,两种催化剂具有相似的活性中心本质,催化性能的不同主要归因于分散度的区别.与传统加热法相比,微波加热具有受热均匀以及增强Ni2 与载体SiO2相互结合力的特点,导致Ni-B/SiO2(MW)分散度增加,并能减少催化反应过程中活性相的脱落流失,延长催化剂使用寿命.     

Theoretical study on the alkaline hydrolysis of methyl thioacetate in aqueous solution

A base-catalyzed hydrolysis reaction of thiolester has been studied in both gas and solution phases using two ab initio quantum mechanics calculations such as Gaussian09 and CPMD. The free-energy surface along the reaction path is also constructed using a configuration sampling technique, namely, the metadynamics method. While there are two different reaction paths obtained for the potential profile of the base-catalyzed hydrolysis reaction for thiolester in the gas phase, a triple-well reaction path is computed for the reaction in the solution phase by two quantum mechanics calculations. Unlike the S(N)2 mechanism (a concerted mechanism) found for the gas-phase reaction, a nucleophilic attack from the hydroxide ion on the carbonyl carbon to yield a tetrahedral intermediate (a stepwise mechanism) is observed for the solution-phase reaction. Moreover, the energy profiles computed by these two theoretical calculations are found to be very comparable with those determined experimentally.     

Heat of Reaction of the Hydrolysis-Polymerization Process of Tetraethyl Orthosilicate in Acidic Condition

Heat of reaction of the hydrolysis-polymerization process of tetraethyl orthosilicate with water in acidic condition was investigated to clarify the thermodynamic driving force of sol-gel reactions. Heat of reaction was measured using an isoperibol calorimeter by mixing a dilute tetraethyl orthosilicate (TEOS) ethanolic solution with another solution of water, ethanol, and hydrochloric acid. The temperature change of the reaction cell had been measured more than 24 hours after mixing under the quasi-isothermal condition. Large exothermic reaction (12.9 kJ·mol^–1 for 1 mole of TEOS) due to the hydrolysis of TEOS was observed. A slow exothermic reaction followed it, and after that, the sol-gel reaction was changed to a small endothermic one.     

Novel Nafion®/ORMOSIL hybrids via in situ sol-gel reactions: 2. Probe of ORMOSIL phase nanostructure by 29Si solid state NMR spectroscopy

Perfluorosulfonic Acid (PFSA)]/[Organically-Modified Silicon Oxide (ORMOSIL)] hybrids were formulated via sol-gel reactions of mixtures of tetraethoxysilane (TEOS) and diethoxydimethylsilane (DEDMS) in the nanophase-separated morphology of a PFSA membrane (Nafion^®). The molecular structures of the ORMOSIL phases were investigated by ²⁹Si solid state NMR spectroscopy and the spectra compared with those of corresponding bulk ORMOSILs. PFSA-in situ ORMOSIL composition can be tailored by manipulating TEOS/DEDMS source solution composition and quantified by ²⁹Si solid state NMR spectroscopy. Copolymerization of TEOS and DEDMS monomers, rather than block formation, occurs within the PFSA as well as in the bulk. As DEDMS feed concentration increases, ORMOSIL nanostructures are more hydrophobic and more flexible. Dimethylsiloxane rings are dominant in PFSAs in which hydrolysis + condensation of pure DEDMS occurs.     

纳米Fe@SiO_2一步合成及其对Cr(Ⅵ)的去除

利用液相还原与改进的Stbr法相结合,在不使用表面改性剂和氨水的条件下,通过向原硅酸乙酯(TEOS)和氯化铁混合溶液直接添加硼氢化钾,一步合成了二氧化硅包覆的纳米铁复合材料(Fe@SiO_2).通过X射线粉末衍射(XRD)仪、能量色散X射线仪(EDAX)、透射电子显微镜(TEM)、紫外-可见(UV-Vis)吸收分光光度计、傅里叶红外(FTIR)光谱仪、X射线光电子能谱仪(XPS)等对所得样品的形貌、结构和组成进行表征.将制备的Fe@SiO_2用于水体中Cr(Ⅵ)还原去除并考察了TEOS添加量对其去除能力的影响.结果表明Fe@SiO_2具有清晰的核壳结构,多孔的SiO_2包裹1-2个球形纳米铁粒子.纳米铁粒径主要分布在20-30 nm之间,随着TEOS投加量的增加,SiO_2层变厚,纳米铁核具有更好的分散性.与未包覆型纳米铁相比,Fe@SiO_2对Cr(Ⅵ)的去除能力显著提高.TEOS投加量为0.1 mL所制备的Fe@SiO_3对Cr(Ⅵ)去除能力(以Fe的质量计算)达到量大,为466.67 mg·g~(-1),而未包覆型纳米铁仅为76.35 mg·g~(-1).     

TEOS-MTES基SiO2溶胶微结构的SAXS研究

正硅酸乙酯(TEOS)为前驱体,在碱性条件下制备含有无定形SiO2颗粒的溶胶,以甲基三乙氧基硅烷(MTES)在酸性条件下获得聚甲基硅氧链,二者混合后应用同步辐射X射线进行混合溶胶的SAXS散射强度测定,计算了溶胶的平均回转半径、平均粒径、两相界面层厚度、散射体体积分数、两相间比表面积等参数,辅以光子相关光谱法(PCS)和透射电子显微镜(TEM)观测溶胶粒度,证实SiO2颗粒被MTES混合物连接成族团.实验发现所测混合溶胶样品均表现出对Porod定理的负偏离,说明溶胶中颗粒与溶剂之间存在很明显的两相间界面层.     

色谱质谱联用技术研究30%二甲基二乙氧基硅烷/70%正硅酸乙酯复合醇盐的水解聚合行为

采用色谱质谱联用技术研究了1种复合醇盐：30％二甲基二乙氧基硅烷／70％正硅酸乙酯（DDS／TEOS）的水解聚合过程，并由此分析了这两种有机-无机酸盐的相互作用机制和聚合方式，实验结果指出，DDS的添加抑制了TEOS的自聚合，使得体系中形成了大量的DDS的自聚合环状分子（（（CH3）2Si—O—）n）以及TEOS和DDS的共聚合高分子，由于后者对水解聚合的加速作用，使得30％DDS／70％TEOS系统具有最短的凝胶时间。     

One pot synthesis of Ru(bpy)_3~(2+) doped graphene oxide-silica composite film for constructing high performance solid-state electrochemiluminescent sensor

The Ru(bpy)_3~(2+) doped graphene oxide-silica composite film(Ru/GO-SiCF) was synthesized by one pot hydrolysis and condensation of tetraethylorthosilicate(TEOS) in the water-alcohol solution of graphene oxide and Ru(bpy)_3~(2+) at room temperature.The prepared Ru/GO-SiCF modified glassy carbon electrode(GCE) showed excellent electrochemiluminescence(ECL) behavior for the determination of tripropylamine(TPA) with high sensitivity and good stability.We expected this simple and novel material will find further application in construction of other targets sensors.     

TS-1分子筛的合成Ⅰ.29Si和1H NMR研究正硅酸乙酯的水解

利用29Si和1H NMR方法研究了TS-1分子筛合成过程中正硅酸乙酯(TEOS)的水解行为.1H NMR结果表明,TEOS在四丙基氢氧化铵(TPAOH)溶液中的水解速度快于在四乙基氢氧化铵(TEAOH)中的水解速度.TEOS水解后的29Si NMR谱显示,TEOS在TPAOH中水解产生的聚合硅酸根物种的分布与在TEAOH中的类似,都存在着单体、二聚、三聚及环聚等硅酸根物种的平衡,但TEOS-TEAOH体系中低聚硅酸根物种的浓度明显大于TEOS-TPAOH中的浓度.向水解后的样品中添加水,可促使多聚硅酸根物种转化为低聚物种.大量异丙醇的加入将导致单聚和二聚硅酸根物种的高聚.钛酸四丁酯加入到TEOS-TPAOH水解体系中得到的29Si NMR结果明显不同于TEOS-TEAOH水解体系.     

Preparation of nearly monodisperse multiply coated submicrospheres with a high refractive index

Nearly monodisperse SiO2/TiO2/SiO2 multiply coated submicrospheres with nearly monodisperse silica submicrospheres as cores, thick titania layers, and thin silica skin were prepared to increase the refractive index of complex submicrospheres while keeping their near monodispersity and perfect surface properties. Nearly monodisperse colloidal silica submicrospheres as cores with a diameter of 200 nm were synthesized by a seeding technique on the basis of the hydrolysis of tetraethyl orthosilicate (TEOS) in an aqueous ethanol solution with ammonia as catalyst. On the basis of the hydrolysis of tetrabutyl orthotitanate, a procedure combining continuous feeding with multistep coating was determined to prepare titania coatings about 40 nm thick and increase the refractive index of the complex submicrospheres. The hydrolysis of TEOS was still used to get the outmost silica coating about 10 nm thick on titania coated silica submicrospheres to eliminate random aggregation caused by the TiO2 surface properties of the TiO2/SiO2 complex submicrospheres during the final fabrication of photonic crystals.