Name: preparing silica aerogel monoliths via a rapid supercritical extraction method
Uploaded: 2014-02-28T14:15:00
Description: Watch this Scientific Journal Video about Preparing Silica Aerogel Monoliths via a Rapid Supercritical Extraction Method at JoVE.com

作者感谢本科生绿岛谢，为的气凝胶材料的物理特性，和奥德Bechu，用于测试程序草案。我们感谢联合学院工程实验室用于加工不锈钢模具。在联合学院气凝胶实验室已经由美国国家科学基金会（NSF MRI CTS-0216153，美国国家科学基金会芮CHE-0514527，美国国家科学基金会的MRI CMMI-0722842，美国国家科学基金会芮CHE-0847901，美国国家科学基金会芮DMR-1206631，和NSF MRI CBET补助-1228851）。这种材料是基于由美国国家科学基金会批准号CHE-0847901支持工作。

安全注意事项 ：安全眼镜或护目镜，应随时与解决方案和液压热压机的准备工作期间佩戴。当制备化学试剂的溶液，当将溶液倒入在热压模具实验室必须戴上手套。 TMOS，甲醇和浓氨和含有这些试剂的溶液，必须在通风橱内进行处理。超临界提取过程中释放的热的甲醇，因此，有必要既泄的油压式热压机，并确保有热压的通风路径内没有点火源。此外，我们建议安装在左右热压防护罩的。?...

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该RSCE法生产的单片二氧化硅气凝胶采用自动化，工艺简单一致的批次。如这里介绍的方法需要8小时的处理步骤。它可以加快加热和冷却步骤，使单片气凝胶在短短的3小时22，然而，当一8小时的过程应用中，气凝胶整料的更一致的批次的结果。的微小变化的过程中参数不影响所得气凝胶的物理性质，这表明该过程的鲁棒性22。 这里所用的前体配方导致单片二?...

氧化硅气凝胶材料具有低密度，高表面积和低的导热和导电性结合的纳米多孔结构，具有优良的光学性能。在一种材料这些特性的结合使得气凝胶有吸引力的大量应用1。在最近的一篇综述文章，Gurav 等 。详细描述二氧化硅气凝胶材料的现有的和潜在的应用，无论是在科研和工业产品2的发展。例如，二氧化硅气凝胶已被用作吸收剂，传感器，在低介电材料，作为存储介质为燃料，以及用于热绝缘应用2广泛。 气凝胶通常制作中，采用一个两步骤的过程。第一步骤涉及混合适当的化学前体，然后进行缩合和水解反应，以形成湿凝胶。为了准备硅胶，在水和含二氧化硅的前体之间的水解反应发生，在这种情况下，四甲酯（TMOS，硅（OCH 3）4），在酸或碱催化剂的存在下进行。 的Si（OCH 3）4 + H 2 O <img alt="箭头" fo:content-width=".2in" src="/files/ftp_upload/51421/arrow.jpg" width="20" />的Si（OCH 3）4-N（OH）N + N CH 3 OH TMOS是不溶于水。为了促进水解，这是必要的，包括其它溶剂，在这种情况下甲醇（MeOH中，CH 3 OH），并搅拌或超声处理的混合物。接着碱催化的缩聚反应的水解的二氧化硅物种之间发生： ，R 3的SiOH + HOSiR 3 <img alt="箭头" fo:content-width=".2in" src="/files/ftp_upload/51421/arrow.jpg" width="20" /> ，R 3的Si-O-SIR 3 + H 2 O ，R 3的SiOH + CH 3 </子&gt; 3 OSIR <img alt="箭头" fo:content-width=".2in" src="/files/ftp_upload/51421/arrow.jpg" width="20" /> ，R 3的Si-O-SIR 3 + CH 3 OH 缩聚反应导致的湿凝胶，由多孔的SiO 2固体基质，其中所述孔被填充在反应溶剂的副产物，在这种情况下的甲醇和水的形成。第二个步骤涉及干燥湿凝胶形成气凝胶：从孔而不改变固体基质中除去溶剂。干燥过程是气凝胶的形成是至关重要的。如果没有进行正确的脆弱纳米结构崩塌和干凝胶形成为在图1中示意性示出。 有三种基本方法用于干燥溶胶 - 凝胶的材料，以产生气凝胶：超临界萃取法，冷冻干燥和常压干燥。超临界萃取方法一空隙渡液 - 汽相线，使得表面张力的作用不会导致凝胶的纳米结构坍塌。超临界萃取方法可在高温（250-300℃），并用直接提取的缩合和水解反应3-7的醇溶剂的副产物的压力下进行。另外，可以执行一组的交流，并与液体二氧化碳，其具有低的超临界温度（〜31℃）代替醇的溶剂。提取然后可以在相对 ​​低的温度下进行8,9，尽管在高压下。冷冻干燥方法10,11首先冻结在低温下的湿凝胶，然后使溶剂直接升华成蒸气形式，又避免了交叉的液-汽相一致。环境压力的方法使用表面活性剂来降低表面张力作用或聚合物增强纳米结构，其次是湿凝胶的干燥在室温pressu重12-16。 在联合学院的快速超临界萃取（RSCE）过程是一步（前体气凝胶）方法17-19。该方法使用高温的超临界提取，这使得单片气凝胶的制备在小时，而不是天至通过其它方法需要几周。该方法利用一个密闭的金属模具和一个可编程的液压热压机。化学前体混合并直接倒入模具中，其放置的油压式热压机的压盘之间。热压被编程以关闭并应用的抑制力，以密封所述模具。热压然后以指定的速率加热所述模具的温度，T 高 ，高于溶剂的临界温度（参见图2的过程的曲线图）。在开始升温期间的化学反应形成凝胶和凝胶强化剂和年龄。当模具被加热的压力也上升，最终达到超临界压力。在到达T 高 ，热压住在一个固定的状态，而系统达到平衡。下一个热压力减小和超临界流体逸出，留下了热气凝胶。压然后冷却模具和其内容至室温。在该过程（其可以采取3-8小时）的端部压打开和单片气凝胶是从模具中取出。 这RSCE方法提供了比其他气凝胶制备方法显著优点。它速度快（&lt;8小时总数），而不是劳动密集型，通常只需要15-20分钟的准备时间后3-8小时的处理时间。它不需要溶剂交换，这意味着该过程中产生相对较少的溶剂废物。 在下面的章节中，我们描述了一个协议，用于通过联盟RSCE方法从母体混合物包括制订一套圆柱二氧化硅气凝胶巨石的D TMOS，甲醇和水以用作催化剂的水解和缩聚反应氨水（用TMOS：甲醇：H 2 O：的1.0:12:3.6:3.5×10 -3的NH 3的摩尔比）。我们注意到，该联盟RSCE方法可用于制备各种不同尺寸和形状的气凝胶，根据​​金属模具和油压式热压机使用。这RSCE方法也被用于从不同的前体配方20制备其它类型的气凝胶（二氧化钛，氧化铝等 ）。

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	<tbody>
		<tr height="61">
			<td height="61" style="height:61px;width:504px;">Tetramethylorthosilicate&#160; (TMOS)</td>
			<td style="width:252px;">Sigma Aldrich&#160;&#160; www.sigmaaldrich.com</td>
			<td style="width:252px;">218472-500G</td>
			<td style="width:336px;">98% purity, CAS 681-84-5&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;</td>
		</tr>
		<tr height="61">
			<td height="61" style="height:61px;width:504px;">Methanol&#160; (MeOH)</td>
			<td style="width:252px;">Fisher Scientific&#160; www.fishersci.com</td>
			<td style="width:252px;">A412-20</td>
			<td style="width:336px;">Certified ACS Reagent Grade, &#8805;99.8%</td>
		</tr>
		<tr height="61">
			<td height="61" style="height:61px;width:504px;">Ammonium Hydroxide (aqueous ammonia)</td>
			<td style="width:252px;">Fisher Scientific&#160; www.fishersci.com</td>
			<td style="width:252px;">A669S212</td>
			<td style="width:336px;">Certified ACS Plus, about 14.8N, 28.0-20.0 w/w%</td>
		</tr>
		<tr height="61">
			<td height="61" style="height:61px;width:504px;">Deionized Water</td>
			<td style="width:252px;">On tap in house</td>
			<td style="width:252px;"></td>
			<td style="width:336px;"></td>
		</tr>
		<tr height="61">
			<td height="61" style="height:61px;width:504px;">Flexible Graphite Sheet</td>
			<td style="width:252px;">Phelps Industrial Products</td>
			<td style="width:252px;">7500.062.3</td>
			<td style="width:336px;">1/16&#34; thick</td>
		</tr>
		<tr height="61">
			<td height="61" style="height:61px;width:504px;">Stainless Steel Foil</td>
			<td style="width:252px;">Various</td>
			<td style="width:252px;"></td>
			<td style="width:336px;">.0005&#34; thick, 304 Stainless Steel</td>
		</tr>
		<tr height="110">
			<td height="110" style="height:111px;width:504px;">High Temperature Mold Release Spray</td>
			<td style="width:252px;">Various&#160; (for example, CRC Industrial Dry PTFE Lube)</td>
			<td style="width:252px;"></td>
			<td style="width:336px;">Should be able to withstand high temperatures.</td>
		</tr>
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</table>

preparing silica aerogel monoliths via a rapid supercritical extraction method

一个程序的八个小时或更少的单片二氧化硅气凝胶通过一个快速的超临界萃取工艺的制作说明。该过程需要15-20分钟的准备时间，在此期间，液体前体的混合物制备并倒入金属模具的孔中，放置在油压式热压机的压板之间，然后热压内几个小时的处理。前体溶液由四甲酯的1.0:12.0:3.6:3.5×10 -3摩尔比（TMOS）：甲醇：水：氨。在模具中，多孔二氧化硅的溶胶 - 凝胶基质形成的各孔中。作为模具和其内容物的温度升高时，模具内的压力上升。后的温度/压力条件高于超临界点的矩阵（在此情况下，用甲醇/水混合物）的细孔内的溶剂，超临界流体被释放，单片气凝胶保持在模具的孔中。在此过程中使用的模具，2.2厘米直径的1.9厘米高的圆柱形巨石生产。通过这种快速方法形成气凝胶具有相当的性能（低堆积和骨架密度，高表面积，中孔形态）来制备的那些涉及任何附加的反应步骤或溶剂萃取等方法（即产生更多的化学废物冗长的进程）的快速超临界萃取法，也可应用到基于其它前体配方气凝胶的制造。

下面这里描述的结果在单片硅气凝胶一致的分批过程， 图4示出了通过该方法制备的典型的二氧化硅气凝胶的图像。每个气凝胶需要对井的形状和尺寸在加工模具与无收缩。这些图像表明，二氧化硅气凝胶是半透明的。 这些气凝胶的物理性质总结于表4中 。他们可以媲美二氧化硅气凝胶采用低温超临界萃取21。 图5相似的前体配方?...

Watch this Scientific Journal Video about Preparing Silica Aerogel Monoliths via a Rapid Supercritical Extraction Method at JoVE.com

Preparing Silica Aerogel Monoliths via a Rapid Supercritical Extraction Method

通过快速超临界萃取法制备二氧化硅气凝胶巨石

本文介绍了一种快速超临界萃取法制造二氧化硅气凝胶。通过利用一个密闭的模具和液压热压机，单片气凝胶可以在8小时以​​内进行。

A procedure for the fabrication of monolithic silica aerogels in eight hours or less via a rapid supercritical extraction process is described. The ...

Research

JoVE Journal

Chemistry

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Microwave-assisted synthetic techniques were used to quickly and reproducibly produce silica nanoparticle sols using an acid catalyst with nanoparticle ...

科研

化学

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Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where ...

A Straightforward Method for Glucosinolate Extraction and Analysis with High-pressure Liquid Chromatography (HPLC)

A Straightforward Method for Glucosinolate Extraction and Analysis with High-pressure Liquid Chromatography HPLC

简捷方法对硫甙的提取与分析用高压液相色谱法（HPLC）

Glucosinolates are a well-studied and highly diverse class of natural plant compounds. They play important roles in plant resistance, rapeseed oil ...

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The extraction and analysis of catecholamine neurotransmitters in biological fluids is of great importance in assessing nervous system function and ...

Fabrication and Testing of Catalytic Aerogels Prepared Via Rapid Supercritical Extraction

快速超临界萃取制备催化气凝胶的制备与试验研究

Protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms are presented. Three ...

Separation of Aldehydes and Reactive Ketones from Mixtures Using a Bisulfite Extraction Protocol

用亚硫酸氢萃取协议分离混合物中的醛和反应性酮

The purification of organic compounds is an essential component of routine synthetic operations. The ability to remove contaminants into an aqueous layer ...

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用 Bioinspired 法制备功能性二氧化硅

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直接溶液还原法快速合成金、钯、铂气凝胶的研究

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