介孔SiO2气凝胶的常压干燥制备研究

以廉价的水玻璃为硅源，用乙醇(EtOH) / 三甲基氯硅烷(TMCS) / 庚烷(Heptane)溶液对湿凝胶进行改性，采用一种新的常压干燥工艺合成了SiO₂气凝胶。通过TMCS与乙醇、湿凝胶孔隙水及Si-OH基团之间的反应，使湿凝胶的溶剂交换和表面改性得以在一步完成。所合成的SiO₂气凝胶为轻质透明的块状固体，密度为0.128～0.136 g·cm^-3，孔隙率93.8%～94.2%。利用FTIR、SEM、TEM和BET吸附对气凝胶的微观结构、形貌和性质进行了研究。结果表明，气凝胶为海绵状结构，粒子直径和孔径分布均匀，比表面积559～618 m²·g^-1，表面带有较多的Si-CH₃基团，呈现出明显的疏水性。     

常压干燥制备二氧化硅气凝胶*

二氧化硅气凝胶是典型的纳米多孔轻质材料,由于具有独特的性能并在许多领域存在潜在的应用价值而受到广泛关注。二氧化硅气凝胶的制备传统上采用超临界干燥工艺,但此工艺成本高、工艺复杂而且具有一定的危险性。为了实现二氧化硅气凝胶的大批量生产和商品化应用,研究低成本常压干燥制备技术非常必要。目前常压干燥制备工艺已取得了较大进展,本文主要介绍了二氧化硅气凝胶的常压干燥制备方法及其特点,并概述了二氧化硅气凝胶复合材料制备的最新研究进展。以纤维和聚和物为增强体的二氧化硅气凝胶复合材料改善了气凝胶的力学性能,进一步扩宽了其应用范围。     

Drying of Large Monolithic Aerogels between Atmospheric and Supercritical Pressures

The objectives of this investigation are to show the feasibility of producing large monoliths with minimal shrinkage at subcritical conditions, and to understand the drying behavior. Crack-free SiO2 monoliths (5.6 cm in diameter and 25 cm in length) were repeatedly dried with little shrinkage (<2%). Some gels showed increasing shrinkage with decreasing pressure. However, this shrinkage was reduced to negligible levels at conditions considerably less than supercritical pressure by increasing both the pore size and the gel strength. This moderate pressure drying (MPD) process may make aerogel fabrication economically more feasible due to reduced pressure chamber costs.     

Hydrophobic Silica Aerogels Strengthened with Nonwoven Fibers

Hydrophobic silica aerogels were prepared via a sol‐gel process by surface modification at ambient pressure. Nonwoven fibers were distributed inside the silica aerogels as a composite to act as a supporting skeleton which increased the mechanical property of the silica aerogels. The morphology and pore structure of the composites were characterized by scanning electron microscopy (SEM) and N₂ adsorption analyzer. The contact angle and the adsorption capacities of the composites were also determined. The results show that silica aerogels dispersed uniformly and maintained high porosity in the aerogel‐fiber composites. They have excellent hydrophobic properties and are excellent adsorptive materials.     

Effects of Ti Addition on Alumina/Titania Composite Aerogels Synthesized by Sol–Gel Process and Supercritical Ethanol Drying

Alumina/titania composite aerogels with different titania contents were synthesized by the sol–gel process and supercritical ethanol drying. The structures and morphologies of synthesized aerogels were analyzed by X‐ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetry, and N₂ adsorption–desorption tests. Supercritical ethanol drying induced the crystallization of titania, which prompted the transformation of the structure from pseudoboehmite to γ‐Al₂O₃ . Reversely, alumina retarded the anatase‐to‐rutile transformation of titania. The content of titania significantly affected the structure and morphology of alumina/titania composite aerogels. A high content of titania (≥40%) resulted in the phase separation of titania particles, which grew to form the anatase phase octahedral particles with well‐developed facets. When the titania content was low, titania particles could be homogeneously dispersed in alumina particles to form spherical clusters with the poor crystallinity. Titania particles were in the anatase phase, and no rutile phase was formed until the temperature rose to 1000°C. In addition, titania addition resulted in a decrease in the specific surface area (SSA) of alumina aerogels because the SSA of titania was lower than that of alumina aerogels.     

超临界流体干燥过程的分析

以ZrOCl2•8H2O为原料，采用超临界流体干燥（SCFD）法，在短时间内制备出大孔体积高比表面ZrO2气凝胶超细粉．该法具有良好的稳定性和可靠性．建立了醇凝胶中液相含水量的分析方法，为产品质量控制及确认体系是否处于超临界状态提供了依据．对抽提后的溶剂分析表明，SCFD过程是一物理过程．对水的抽提干燥过程亦进行了初步的理论探讨．     

常压干燥法制备气凝胶的研究进展

气凝胶是一类轻质、低密度的三维纳米多孔固态材料,因其独特的高孔隙率、高比表面积和低导热系数等特性,使其在吸附、催化、保温隔热和隔音等诸多领域具有广泛的用途,目前其相关研究在材料科学领域受到了广泛的关注。气凝胶的制备主要包括溶胶-凝胶过程和湿凝胶干燥两个步骤,湿凝胶的干燥是制备气凝胶过程中至关重要而又较为困难的一步。传统的气凝胶通过超临界干燥制备,工艺复杂、成本高,而且由于干燥过程在高温高压条件下进行,有一定的危险性并且不适宜大规模生产,因此如何通过常压干燥获得高比表面积、高孔隙率、低密度的性能优异的气凝胶是其研究的重要方向之一。本文简要介绍了湿凝胶的制备以及凝胶干燥理论,详细介绍了近年来常压干燥方法气凝胶制备的研究进展,并对其未来发展前景做出了展望。     

Physical Properties of Silica Aerogels Prepared with Polyethoxydisiloxanes

Silica aerogels were made by sol-gel techniques using industrial silicon derivatives (polyethoxydisiloxanes, E-40), followed by supercritical drying with ethanol. The morphology and microstructure of the silica aerogels were investigated by using specific surface area, S_BET, SEM, TEM and the pore size distribution techniques. The thermal conductivity was also measured as a function of air pressure. The results show that the diameter of the silica particles is about 13 nm and the pore size of the silica aerogels is 20–80 nm. The specific surface area of the silica aerogel is about 470 m²/g and the thermal conductivity of the silica aerogel prepared with E-40 is 0.014 w m^–1 K^–1 at room temperature and 1 atm.     

Preparation of Alumina Aerogel Films by Low Temperature CO2 Supercritical Drying Process

Alumina aerogel thin films were formed by a new synthesis route. Sols were prepared by the Yoldas process. Gels were formed by sol evaporation in a few hours. Films were prepared by dip coating glass or alumina substrates into both the sols and the gels. Aerogel films with special morphology were produced for the first time by exchanging the film solvent with acetone after the dip coating, followed by supercritical drying. The morphology of the films, studied by SEM and TEM, consists of fiber-like network of round chains (≈0.1 μm thick), and pores (0.1–0.5 μm in diameter). It is shown that the fibers contain a homogeneous arrangement of sol particles, 2–4 nm in size. Formation of this microstructure can be attributed to phase separation in the alumina-water-acetone system in a 2D film geometry. A conceptual model for the film development is proposed.     

添加环氧丙烷法常压干燥制备ZrO2气凝胶

以无机锆盐硝酸氧锆(ZrO(NO3)2·5H2O)为前驱体,1,2-环氧丙烷(PO)为凝胶促进剂,甲酰胺(FA)为干燥控制化学添加剂(DCCA),采用溶胶-凝胶法并通过常压干燥制备了轻质二氧化锆(ZrO2)气凝胶,利用差热分析(DTA)、扫描电镜(SEM)、N2吸附/脱附等测试技术对所制得的ZrO2气凝胶进行了表征.结果表明:添加环氧丙烷常压干燥制得的ZrO2气凝胶具有纳米尺寸的多孔网络结构,表观密度可低至202.08 kg·m-3,比表面积可高达645.0 m2·g-1,与超临界干燥效果相当.环氧丙烷因其环氧原子的强亲核性和不可逆的开环反应,可促进凝胶化,并通过环氧丙烷的量控制反应过程和凝胶状态.     

常压干燥法制备Al2O3块状气凝胶

以无机铝盐Al(H2O)9(NO3)3为前驱体，甲酰胺作为干燥控制化学添加剂(DCCA)，1,2-环氧丙烷作为凝胶网络诱导剂，通过溶胶-凝胶法制备氧化铝凝胶；在常压条件下对凝胶进行干燥，得到乳白色、半透明、轻质、块状氧化铝气凝胶.初步探讨了在凝胶制备和陈化过程中增强凝胶网络结构强度的途径和机理.     

超临界干燥法制备Fe2O3-SiO2气凝胶

以正硅酸乙酯（TEOS）和硝酸铁为原料,采用溶胶-凝胶法和超临界干燥工艺制备了Fe2O3-SiO2气凝胶,研究了Fe2O3-SiO2醇凝胶的形成条件的影响,并对所得气凝胶样品结构特性进行了初步表征．所得气凝胶样品是由直径约8nm的胶体粒子构成的低密度、高孔隙率的块状非晶固态材料．     

超临界流体干燥法合成超微二氧化锡

采用溶胶－凝胶法制备出胶体，利用超临界流体干燥技术合成出高比表面，纳米级ＳｎＯ＿２超细粉体，用ｘ－射线衍射，透射电镜和比表面及孔分布测试等分析了ＳｎＯ＿２的结构，形貌及比表面。     

Studies on Highly Porous Hybrids Prepared by a Novel Fast Gellation Process Under Ambient Pressure

Supercritical drying of hydrolyzed alkoxysilanes is a typical method for making aerogels that exhibit over 75% porosity. Recent works demonstrated the possibility to prepare, under ambient pressure, aerogel-type of highly porous materials. However, multiple step process is being required for surface modification of pore walls to avoid collapsing effect caused by drying shrinkage. We wish to describe in here a novel fast, single step sol-gel route for the preparation of ultra high porous materials. Commercially available hydrogensilsesquioxane was used as precursor in this approach, leading through a simple, single step process to gels within minutes and thus without any further surface modification needed. Systematic studies of this novel fast gellation process were carried out through careful variation of experimental conditions to gain porosity control and enable improved design of this class of ultra high porous monolithic materials.     

常压干燥制备酚醛树脂基炭气凝胶研究进展

以间苯二酚-甲醛为代表的酚醛树脂基炭气凝胶是一种轻质、多孔、非晶态的纳米炭材料,在催化、吸附、电化学和隔热等领域中有广阔的应用前景.但是复杂且高成本的超临界干燥工艺极大地限制了炭气凝胶的工业化制备及其应用,因此常压干燥工艺成为目前研究最为广泛的炭气凝胶制备技术之一.本文综述了酚醛树脂基炭气凝胶常压干燥制备过程的四种结构...     

纳米颗粒的超临界干燥法制备及用于醋酸乙烯蒸气的催化发光检测

利用乙醇超临界流体干燥技术 (SCFD)(280 ℃× 7.0 MPa×30 min)制备了纳米MgO及Y2O3颗粒,发现其对一些有害气体的催化发光强度远高于普通干燥技术制备的纳米MgO及Y2O3.设计了一种以SCFD技术合成的纳米MgO为敏感材料,催化发光检测醋酸乙烯蒸气的传感器.此传感器具有很高的灵敏度及优异的选择性,在温度279 ℃、波长425 nm、空气流速为160 mL/min的最佳条件下,催化发光强度与醋酸乙烯蒸气浓度在1.8～1800 mg/m3内呈良好的线性关系,检出限为0.7 mg/m3.当浓度相同的丙酮、乙醛、乙酸乙酯、乙酸、甲醛、氨水、乙醇、苯和甲醇蒸气通过此传感器时,除乙醇引起3.56%的干扰外,其它气体基本不干扰醋酸乙烯的测定.应用本方法可快速测定车间空气中的醋酸乙烯.     

Loading of Bacterial Cellulose Aerogels with Bioactive Compounds by Antisolvent Precipitation with Supercritical Carbon Dioxide

Bacterial cellulose aerogels overcome the drawback of shrinking during preparation by drying with supercritical CO₂. Thus, the pore network of these gels is fully accessible. These materials can be fully rewetted to 100% of its initial water content, without collapsing of the structure due to surface tension of the rewetting solvent. This rehydration property and the high pore volume of these material rendered bacterial cellulose aerogels very interesting as controlled release matrices. Supercritical CO₂ drying, the method of choice for aerogel preparation, can simultaneously be used to precipitate solutes within the cellulose matrix and thus to load bacterial cellulose aerogels with active substances. This process, frequently termed supercritical antisolvent precipitation, is able to perform production of the actual aerogel and its loading in one single preparation step. In this work, the loading of a bacterial cellulose aerogel matrix with two model substances, namely dexpanthenol and L-ascorbic acid, and the release behavior from the matrix were studied. A mathematical release model was applied to model the interactions between the solutes and the cellulose matrix. The bacterial cellulose aerogels were easily equipped with the reagents by supercritical antisolvent precipitation. Loading isotherms as well as release kinetics indicated no specific interaction between matrix and loaded substances. Hence, loading and release can be controlled and predicted just by varying the thickness of the gel and the solute concentration in the loading bath.     

耐高温核/壳结构TiO2/SiO2复合气凝胶的制备及其光催化性能

以钛酸四丁酯为源, 采用苯胺-丙酮原位生成水溶胶-凝胶法, 在乙醇超临界干燥过程中用部分水解的钛醇盐和硅醇盐对TiO₂凝胶进行超临界修饰制备了具有核/壳纳米结构的块体TiO₂/SiO₂复合气凝胶. 制备的复合气凝胶具有优异的机械性能, 其杨氏模量可达4.5 MPa. 复合气凝胶同时具有极好的高温热稳定性. 经过1000 ℃热处理后, 线性收缩由纯TiO₂气凝胶的31%降至复合气凝胶的10%, 且比表面积由纯TiO₂气凝胶的31 m²·g^-1提升至复合气凝胶的143 m²·g^-1. 此外, 该复合气凝胶经1000 ℃热处理后具有优异的光催化降解亚甲基蓝的性能. 其优异的光催化性能得益于TiO₂/SiO₂复合气凝胶1000 ℃处理后高的比表面积和小的颗粒尺寸. 优良的耐热性能、力学性能和光催化性能使获得的具有核/壳纳米结构的TiO₂/SiO₂复合气凝胶在光催化领域具有良好的应用前景.     

Optimization of Ethanol Supercritical Fluid Extraction of Medicinal Compounds from St. John's Wort by Central Composite Design

Extraction of medicinal compounds from St John's Wort was performed using supercritical ethanol. The supercritical fluid extraction parameters were optimized via response surface methodology which included a central composite design. The independent variables were extraction temperature (ranging from 300°C to 340°C), extraction times (ranging from 60 to 120 min), and plant concentration (ranging from 8% to 12%). The response was the St John's Wort extract yield. The extraction temperature was the most significant factor which affects St John's Wort yields according to statistical results. The coefficient of determination was estimated to be 0.98 which indicates the effectiveness of the model and its adaptability to the experimental data. The extract of St John's Wort was comprised of a wide array of compounds including phenols, acids, acid esters, and alkanes. The most prominent components of the extract of St. John's Wort in terms of their relative concentrations were linoleic acid ethyl ester, oleic acid ethyl ester, hexadecanoic acid ethyl ester, and nonacosane.     

超临界干燥方法对甲烷燃烧催化剂LaMnAl11O19结构及活性的影响

 摘要：用水热合成法制备了锰取代的六铝酸盐催化剂，并比较了超临界干燥法和普通烘箱干燥法对催化剂结构及甲烷燃烧反应活性的影响．DTA－MS结果表明，超临界干燥过程中，催化剂前驱物中的表面铝羟基部分被乙氧基取代．这种表面修饰作用可保持铝分散的均匀性，使催化剂前驱物中碳酸锰和碳酸镧的分解温度明显降低，且氢氧化铝的脱水温度维持在较适宜的范围内；焙烧后，易形成六铝酸盐相．甲烷燃烧反应结果表明，用超临界干燥方法制得的催化剂对甲烷燃烧反应的催化活性明显高于用普通烘箱干燥方法制得的催化剂．