这项工作得到了酸气诱导能源材料演变理解与控制中心（UNCAGE-ME）的支持，该中心是由美国能源部科学办公室基础能源科学资助的能源前沿研究中心，获得 #DE-SC0012577奖。J.S. 承认，本材料基于美国国家科学基金会研究生研究奖学金（Grant No.DGE-2039655 中。本材料中表达的任何意见、发现、结论或建议均为作者的观点，并不一定反映美国国家科学基金会的观点。

1. 样品制备
<ol><li>样品合成<ol><li>将 0.35 mM 对苯二甲酸和 0.35 mM ZrCl4 溶于 4 mL 二甲基甲酰胺 （DMF） 中。密封在PTFE衬里中，在120°C下加热24小时。冷却至室温。</li>
		<li>以120× g 离心溶液30分钟。倒出剩余的液体，让粉末在环境空气中干燥过夜。</li>
	</ol></li>
	<li>样品装载<ol><li>测量空样品管的质量。将30-50mg MOF UiO-66加载到样品管中。测量新质量。</li>
	</ol></li>
	<li>激活<ol><li>将样品管连接到样品制备系统，用 0.5 英寸 O 形圈固定密封件。将管子放入加热罩内。</li>
		<li>将温度控制器设置为指定的激活温度，此处为 120 °C，并等待温度稳定。 注意:在真空下，活化温度应高于合成溶剂（或用于溶剂交换的溶剂）的沸点。</li>
		<li>打开将系统连接到真空的阀门，等待压力稳定。等待指定的激活时间，24小时。</li>
		<li>从加热罩上取下管子，让样品冷却至室温。用氮气回填样品管。从制备系统中取出试管。</li>
		<li>取活化样品和试管的质量。如公式 4（方程 4）中所述计算活化样品的质量。 （样品质量）=（活化样品和试管的质量）-（空样品管的质量）（式4）</li>
	</ol></li>
</ol>2. 实验文件设置
<ol><li>创建示例文件<ol><li>打开仪器软件，单击 "文件"，然后单击 "新建样品"。在 "样品描述 "选项卡下，输入样品名称、样品质量和样品密度。</li>
	</ol></li>
	<li>输入分析参数<ol><li>打开 "分析条件" 选项卡，然后选择吸附气体（氮气）和分析条件 （BET）。</li>
		<li>选择 "可用空间 "按钮。输入可用空间是由仪器测量、由用户输入还是计算。如果要测量自由空间，请在测量前输入疏散持续时间。</li>
		<li>选择在测量过程中是否降低氮气杜瓦瓶，以及系统是否对样品除气进行测试。如果要输入可用空间，请同时指定环境可用空间和分析可用空间。单击 "确定"。 注意:在 77 K 时，氦气会被困在微孔内。对于微孔材料，可以在N2 吸附分析后测量氦自由空间。</li>
		<li>选择 p0和 T。输入 p0 是由 po 管测量、由用户输入还是计算。通常，吸附物的P0 由仪器测量。输入分析温度 （77K） 和 p0 值（如果适用）。单击 "确定"。</li>
		<li>选择 回填。选择在分析之前和之后是否回填样品。如果选择其中任何一个，请选择回填气体 （N2） 的标识。单击 "确定"。</li>
		<li>在 "等温线集合 "部分中，选择 "目标压力"。单击 "压力"，然后以 0.005 的间隔输入介于 0 和 1 之间的 p/p0 的等温线压力值，然后单击 "确定"。单击 "选项" 并输入 5% 的相对压力公差。单击 "确定"。</li>
		<li>打开 "报告选项" 选项卡，然后选择要报告的数据分析图。单击 "另存为"，为文件命名，然后选择文件夹目标。</li>
	</ol></li>
</ol>3. 进行吸附测量
<ol><li>物理设置<ol><li>将样品管滑入等温套管中。将样品管连接到吸附仪器上，用 O 形圈固定密封件。</li>
		<li>使用适当的安全/个人防护设备用液氮填充杜瓦瓶。将杜瓦瓶放在样品下方的升降机上。如果使用 p0 管，请连接它并确保在电梯升起后将其配置为位于杜瓦瓶内。</li>
		<li>关闭屏蔽门。</li>
	</ol></li>
	<li>运行实验<ol><li>在仪器软件中，单击仪器名称，然后单击 样品分析。</li>
		<li>单击 "浏览"，然后选择示例文件。确保分析编号与加载样品的端口编号相匹配。单击 "开始"。</li>
	</ol></li>
</ol>4.氮气吸附测量
<ol><li>吸附:将氮气注入样品管，直到达到第一个目标压力（±压力公差范围）。让样品保持平衡，直到压力在指定的平衡时间内稳定。重复此操作，直到达到氮气的饱和压力。</li>
	<li>解吸:打开真空阀解吸氮气，直到达到第一个解吸目标压力（±压力公差范围）。让样品保持平衡，直到压力在指定的平衡时间内稳定。重复此操作，直到样品中的氮被完全解吸。</li>
	<li>用指定的回填气体 （N2） 回填样品管。如果在输入分析参数时选择了该选项，仪器将自动回填试管。 注:吸附装置示意图如 图1所示。</li>
</ol>5. 数据分析
<ol><li>收集完所有数据点后，选择" 文件"，然后选择 "导出"，然后选择试验文件。输入文件目标并将文件另存为电子表格。单击 "确定"。</li>
	<li>使用等温线数据创建 BET 图，根据公式 1，x 轴为p /p 0，y 轴为 （p/p0）/[n（1-p/p0）]。<ol><li>要将 BET 方法应用于给定的等温线，请取膝盖的线性范围。对于介孔材料，这通常在 0.05-0.30 的 P/P0 范围内，而对于微孔材料，它取自 0.005-0.03 的 P/P0 范围。</li>
		<li>确保线性范围符合下面讨论的 Rouquerol 标准。有一些工具可用于自动检测 MOF 材料13 的线性范围。线性范围为: 斜率 = （C-1）/（nmC） Y 截距 = 1/nmC</li>
		<li>使用 BET 图的斜率和 y 截距的值来计算 BET 常数 （C） 和单层容量 （nm）</li>
		<li>使用单层容量和吸附物特性，使用公式 3 中给出的关系来计算总表面积。</li>
	</ol></li>
</ol>

使用氮孔隙度法表征金属有机框架

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提交人没有相互竞争的经济利益。

适用性和局限性 BET方法需要几个关键假设:（1）表面是平面和均匀的，（2）表面是均匀的，所有吸附位点在能量上都是相同的（3）吸附物形成单层。因此，BET可能不适用于无孔材料、表面结构复杂（表面部位类型不同、表面形貌不规则、能量差异较大的部位）或不表现出单层吸附行为的材料。与假设条件的较大偏差可能会影响比表面积计算的准确性。与BET一样，BJH方法也假设均匀吸附和均匀的表面，以及刚性的圆柱形孔隙。因此，它也可能不适用于具有复杂表面或透气结构的材料20。此外，由于孔隙度测量需要访问孔隙空间，因此计算值将不考虑闭合孔隙体积。
BET 和 BJH 方法都应谨慎使用微孔材料。BJH不考虑流体-表面相互作用或孔隙内吸附物分子之间的相互作用，这两者在较小的孔隙中变得更加明显。因此，BJH仅限于介孔和小大孔。由于微孔通常表现出孔隙填充行为，因此很难找到执行 BET 计算所需的等温线的线性区域21。
这两种方法的另一个限制是它们对样品制备方法的敏感性。样品需要以分割形式存在，例如粉末或薄膜，这可能很难均匀制备。这可能会在测量中引入误差，并使可重复性变得困难。表面积和孔隙体积也可能受到样品制备方法和条件的影响，例如材料合成技术、活化方法/条件或干燥温度/时间22。
替代方法的意义 氮是 BET 和 BJH 数据的标准吸附剂，因为它具有四极矩 - 其中氮分子的取向取决于吸附剂的表面化学性质，允许形成单层 - 并且成本低17.然而，氩气和二氧化碳23 也可以利用，特别是对于微孔结构。氩气具有化学惰性，是一种对称的单原子分子;然而，77 K 低于其三相点，因此体参比状态值得怀疑，并且氩单层的结构在很大程度上取决于吸附剂17 的表面化学性质。
由于BET和BJH并非普遍适用，因此应考虑其他测量表面积和孔隙体积的方法。Langmuir 图、t 图或 Horvath-Kawazoe 方法可用于分别确定微孔表面积、孔体积和孔径分布。非局部密度泛函理论 （NLDFT） 建模也是孔径分布的一种选择，对于微孔特别有利，因为它考虑了流体密度相对于孔径的变化。汞孔隙度法可用于确定孔隙率和孔隙体积，但必须考虑该技术的可及范围，因为它不能渗透到微孔中。计算方法可用于计算理论表征指标，并提供与实验结果的比较点，这对于具有闭合孔隙的材料很有用。尽管BJH产生孔径分布，但它不能解释不均匀的分布或完全表征孔隙之间的连通性。其他表征，如SEM、TEM24或XRD，可用于更全面地了解多孔材料的结构。即使材料不能完全用BET或BJH表示，它们仍然可以用作材料之间的定性比较。氮气孔隙率法与其他技术相结合，是一种非常有用的工具。12

表面积和孔隙体积的相关性 多孔材料的准确表征对于了解其潜在应用至关重要。表面积和孔隙体积是重要的定量指标，可深入了解各种应用中的金属有机框架 （MOF） 性能，包括气体吸附、分离、催化和传感1。
MOF的表面积是一个参数，用于量化可用于与客体分子相互作用的表面量，并可能影响其在各种应用中的性能2,3。在气体吸附应用中，MOF的表面积反映了结合位点的可用性和亲和力，这与其分离性能直接相关4。在催化应用中，MOF表面积会影响活性位点的数量及其对反应物分子的可及性，从而影响其催化活性5。活性位点的数量和可及性在传感应用中也很重要，因为与活性位点的更多访客互动会导致灵敏度（和潜在的选择性）的提高6。表面积也会影响MOF在极端条件下的稳定性，因为表面积越大，表面缺陷的数量就越多7。
MOF的孔隙体积是量化多孔结构内空隙空间量的参数。它被定义为MOF中孔隙的总体积，其中包括开放（可触及）和闭合（不可接近）的孔隙。MOF的孔体积会影响其在各种应用中的性能，包括气体吸附、分离和催化。与表面积一样，MOF的孔隙体积与其气体吸收和储存能力以及允许客体分子到达吸附或催化位点的能力直接相关8。
使用氮吸附确定表面积和孔隙体积 表面积和孔隙体积通常使用气体吸附技术进行测量，最常见的是氮吸附。在Brunauer-Emmett-Teller（BET）分析中，氮被选为吸附物，因为它具有四极矩，其中氮分子的取向取决于吸附剂的表面化学性质，从而形成单层。氮吸收与压力的关系图可用于获得有关MOF表面和孔径的信息。材料表面积和总孔容可以使用吸附数据9计算。这里详述的方法的总体目标是获得氮吸附数据，并使用该数据来计算MOF表面积和孔隙体积。
BET方法10 是一种广泛使用的用于确定多孔材料比表面积的技术，其原理是气体在固体表面上的吸附是表面积、气体分子的性质和系统的函数。在给定的压力范围内，将已知量的吸附气体（如氮气）引入样品材料中，并在每个压力增量下测量吸附到表面上的气体量。该数据用于通过关联吸附物吸收、压力和单层容量来计算比表面积，由 BET 方程9 表示:
<img alt="Equation 1" src="/files/ftp_upload/65716/65716eq01.jpg" style="margin: auto;"> （等式1;式1）
哪里: p = 吸附物的平衡压力 （Pa） p0 = 吸附物饱和压力 （Pa） n = 吸附物吸收量 （m3/g） nm = 单层容量 （m3/g） C = BET 常数（无单位）
单层容量与总表面积的关系如下:
<img alt="Equation 2" src="/files/ftp_upload/65716/65716eq02.jpg" style="margin: auto;"> （等式 2;式 2）
哪里: St = MOF总表面积（m2） nm = 单层容量 （m3/g） NAv = 阿伏伽德罗数（分子/摩尔） scs = 吸附物分子的横截面积 （m2/分子） V摩尔 = 吸附物摩尔体积 （m3/mol）
Barrett-Joyner-Halenda （BJH） 方法11 是一种利用解吸数据来计算总孔隙体积的常用方法。与BET方法一样，将已知量的吸附气体（通常是氮气）引入样品中。然后逐渐降低吸附物的分压，并测量每个步骤中解吸的气体体积。假设每个孔隙中的解吸首先发生在毛细管体积中，然后是吸附层厚度的减小，BJH 方程将解吸的体积与吸附层厚度、孔径和孔隙体积相关联。这种关系可以用 BJH 孔径分布图来表示，该图绘制了孔径与孔隙体积的关系图。分布与孔径相积分，以确定总孔隙体积。BJH 方程12 写为:
<img alt="Equation 3" src="/files/ftp_upload/65716/65716eq03.jpg" style="margin: auto;"> （等式3;式3）
哪里: n = 解吸步骤（无单元） vn = 排空毛细管冷凝水的孔隙体积 （m3） ΔVn = 从孔隙中去除的吸附物体积 （m3） Δtn = 吸附层厚度的变化 （m） A = 参与解吸的孔隙的表面积 （m2） Rn = BJH 常数取决于平均孔径（无单位） c = BJH 常数，取决于平均吸附层厚度（无单位）

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			<td>Helium</td>
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			<td>Ultra-High Purity Gaseous N2</td>
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			<td>302-61001-02</td>
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			<td>061-00030-00</td>
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			<td>Terephthalic Acid (H2BDC)</td>
			<td>Sigma Aldrich</td>
			<td>185361</td>
			<td></td>
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		<tr>
			<td>ZrCl4</td>
			<td>&#160;Sigma Aldrich</td>
			<td>221880</td>
			<td>Zirconium(IV) chloride, &#8805;99.5% trace metals basis</td>
		</tr>
	</tbody>
</table>

determining surface areas and pore volumes of metal-organic frameworks

金属有机框架 （MOF） 的表面积和孔体积可以深入了解其结构和潜在应用。这两个参数通常使用氮吸附实验的数据来确定;用于执行这些测量的商用仪器也随处可见。这些仪器将计算结构参数，但必须了解如何选择输入数据以及计算方法何时适用于样品MOF。本文概述了使用 Brunauer-Emmett-Teller （BET） 方法和 Barrett-Joyner-Halenda （BJH） 方法分别计算表面积和孔隙体积。示例计算是在具有代表性的 MOF UiO-66 上执行的。虽然广泛适用于MOF，但除了适当的样品制备外，样品材料和吸附数据还必须满足某些标准，才能使计算结果被认为是准确的。还讨论了这些方法的假设和局限性，以及MOF孔隙空间表征的替代和补充技术。

遵循协议后，可以分析获得的等温线，并推导出关键的材料特性。氮吸附实验的结果为给定吸附剂的表面积、孔隙体积和孔隙结构提供了关键信息。该实验的目的是研究使用氮吸附来测量纳米多孔MOF（UiO-66）的表面积和孔体积。UiO-66 是一种典型的锆基 MOF，具有高比表面积和显着的稳定性。虽然许多MOF具有较弱的热稳定性、机械稳定性和化学稳定性，但由于氧化锆立方八面体金属节点，UiO-66非常坚固，允许在BDC连接子配位中具有12个延伸点。该结构由 7.5 Å 四面体保持架和 12 Å 八面体保持架14,15 组成。
无缺陷的 UiO-66 表现出 1 型等温线形状16。1 型等温线表示具有相对较小的外表面的微孔固体。在1型等温线中吸附的量迅速接近极限值，表明氮的吸收由吸附物可触及的微孔体积控制，而不是由内表面积控制。低 P/P0 时的急剧吸收表明吸附剂和吸附物17 之间的窄微孔中存在强烈的相互作用。滞后环在 1 型等温线中并不常见，因为它们出现在多层物理吸附范围内，并且与孔隙中的毛细管冷凝有关。在低 P/P0 范围内，吸附剂上氮的单层形成与吸附剂的表面积有关，而接近统一的 P/P0 处的孔隙填充与材料的总孔隙体积17 有关。
BET方法的应用通常是在吸附仪器软件中完成的。但是，分析和计算可以很容易地手动完成，也可以使用其他计算程序和方法进行，这些程序和方法可以适应以给出关键结果。要将BET模型应用于获得的氮等温线，有两个关键步骤。首先，必须将氮等温线转化为 BET 图，并从中推导出 BET 单层容量。接下来，根据单层容量和通过选择分子横截面积17的适当值来计算BET表面积。这通常在氮气吸附仪器软件中完成。 图 2 显示了 UiO-66 获得的氮等温线。等温线为 1 型，表示微孔结构和氮单层形成。在高相对压力下的急剧台阶，导致轻微的 2 型等温线，表明 UiO-66 中由于缺陷工程而形成多层以及较大的介孔或大孔。在高相对压力下观察到的滞后表明较大的介孔和大孔形成。 表 1 显示了从 BET 分析中获得的值。
使用 BET 方法时，Rouquerol 标准必须成立。Rouquerol 标准规定，必须获得对变换后的 BET 数据的线性拟合，如果方法在适当的分析范围内，则 C 值应始终为正，Rouquerol 变换必须随着相对压力的增加而增加，并且单层容量必须在用于 BET 参数的数据范围内18.要将 BET 方法应用于给定的等温线，必须取膝关节的线性范围。对于介孔材料，这通常在 0.05-0.30 的 P/P0 范围内，而对于许多微孔材料，它通常取自 0.005-0.03 的 P/P0 范围。然而，实际的线性范围通常受到更多限制，因为它取决于材料和分析温度。因此，线性范围的选择将需要定性评估，类似于 表1 中显示的参数（正C和接近统一的相关系数表示适当的分析范围）。同样，线性范围内必须有足够数量的实验数据点（至少 10 个）才能进行可靠的分析。这些考虑因素也表明了BET方法的固有局限性。C 是一个常数，与形成单层的相对压力有关。C 是一个度量，用于定义单层未覆盖的表面部分，因为 BET 方法假设统计单层形成。因此，C值越大，表面覆盖度越高，单层形成越均匀。当 C 值小于 2 时，等温线为 3 型或 5 型，BET 不适用。当 C 小于 50 时，单层和多层形成有明显的重叠。系数 C 至少为 80 表示单层吸附完成并开始多层吸附的尖锐等温线拐点。参数C大于150通常与狭窄微孔的填充或高能表面位点17的吸附有关。
UiO-66 是一种微孔 MOF，通常表现出缺陷，可以增加表面积并改善某些所需的吸附性能，但会导致较低的稳定性和结晶度15。有缺陷的 UiO-66 框架可以具有 1000-1800 m2/g 的 BET 表面积和 0.40-0.90 cm3/g 的孔隙体积，具体取决于缺陷工程的程度15,16。
对于测得的 UiO-66，当使用线性 P/P0 范围 0.01-0.05 时，BET 表面积为 1211 m2/g，C 值为 457。模拟的无缺陷 UiO-66 的理论表面积为 1200 m2/g14。在 1 型等温线中，如 UiO-66 所示，BET 表面积应被视为表观表面积，因为 BET 模型不能确认 BET 单层容量17 的有效性。测得的表面积落在UiO-66的预期范围内，与C值相结合，表明微孔结构具有均匀的单层形成和孔隙填充。
通常以 0.80-0.95 的 P/P0 分析材料的孔隙体积。如果材料中存在大孔，则氮吸附等温线在P/P0 接近统一时不会几乎水平，因此无法评估总孔隙体积17。在这种情况下测量的孔隙体积仅是微孔和中孔的孔隙体积。
在P/P0 为0.80时测得的UiO-66的孔隙体积为0.86 cm3/g。UiO-66的理论孔隙体积为0.77 cm3/g15。测得的 UiO-66 样品的孔隙体积较高，很可能是由于 UiO-66 结构中存在缺陷。存在缺陷，而不是只有微孔，导致更大的中孔或大孔，从而产生更大的孔隙体积。氮等温线的形状证实了这一点，在高相对压力下，氮等温线急剧增加和滞后，以及 1-2 型等温线形状。
通常，测得的给定材料的BET表面积和孔隙体积将在给定范围内。研究表明，氮吸附等温线和表面积测量的重复性在文献中差异很大19.这是由于所选 BET 范围的变化、材料缺陷、放弃重复实验以及模型的内在特征。BET表面识别（BETSI）程序等工具可用于根据扩展选择标准自动选择线性范围，从而明确评估BET表面积。尽管BET模型是材料表征的标准，但它并不是为了在微孔材料中吸附而开发的。这是由于单层覆盖和理想化吸附行为的思想13。BET模型假设吸附均匀，表面均匀。这些假设可能不适用于具有非均质表面或非常小孔的材料，因此，必须针对每种给定材料评估 BET 模型的应用。
氮吸附实验和分析结果表明，成功形成了具有轻微缺陷的UiO-66微孔晶体结构。计算出的表面积和孔体积落在文献15,19 中报道的范围内，从而得出结论，如果给定的假设和条件适用，BET 模型可以应用于 MOF UiO-66，并且可以转化为其他纳米多孔材料。
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/65716/65716fig01.jpg"> 图1:吸附仪器示意图。 密封的样品管连接到压力传感器、真空和自由空间/分析气源。 <a href="https://www.jove.com/files/ftp_upload/65716/65716fig01large.jpg" target="_blank">请点击这里查看此图的较大版本.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/65716/65716fig02.jpg"> 图 2:UiO-66 在 77 K 下的氮吸附和解吸等温线。 MOF UiO-66在77 K下的氮等温线，其中BET表面积为1211 m2/g，孔体积为0.86 cm3/g。 请 <a href="https://www.jove.com/files/ftp_upload/65716/65716fig02large.jpg" target="_blank">点击这里查看此图的较大版本.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always"><tbody><tr><td>BET专区</td>
			<td>1211 米2/克</td>
		</tr><tr><td>坡</td>
			<td>0.0035 克/厘米3 STP</td>
		</tr><tr><td>Y-截距</td>
			<td>0.000008 克/厘米3 STP</td>
		</tr><tr><td>C</td>
			<td>457</td>
		</tr><tr><td>单层容量</td>
			<td>278 厘米3/克 STP</td>
		</tr><tr><td>分子横截面积</td>
			<td>0.1620纳米2</td>
		</tr><tr><td>相关系数</td>
			<td>0.9999</td>
		</tr></tbody></table>表 1:表格显示了在 77 K 下对 UiO-66 进行 BET 分析获得的值。 该表包括从BET分析中获得的MOF UiO-66的P/P 0 范围为0.01-0.05的关键值的摘要。正 C 和 y 截距以及 0.9999 的相关系数表明选择了可接受的线性区域进行 BET 分析。

Watch this Scientific Journal Video about Characterizing Porous Materials for Aiding the Development of Robust Metal-Organic Frameworks with Adsorption Behavior at JoVE.com

作者聚焦:表征多孔材料以帮助开发具有吸附行为的稳健金属有机框架 

本文介绍了使用氮孔隙法表征金属有机框架，以 UiO-66 为代表材料。

确定金属有机骨架的表面积和孔隙体积

The surface area and pore volume of a metal-organic framework (MOF) can provide insight into its structure and potential applications. Both parameters are ...

我们的团队专注于合成和表征多孔材料，用于集水、空气净化和二氧化碳捕获等应用。我们真正感兴趣的是了解孔的大小、体积、连通性和化学性质如何影响吸收性能，然后利用这些见解为我们的材料设计工作提供信息。因此，稳健的表征技术至关重要。表征是任何多孔材料研究的一个重要方面。X 射线衍射、气体吸收技术和热分析技术是表征的顶级方法。这些也可用于研究结构稳定性，这是用于实际应用的任何材料的关键特征。表面积和孔隙体积是多孔材料的两个最重要的特性。这些特性可以使用市售仪器进行测量，这些仪器使用既定的方法和软件进行操作。氮作为吸收物价格低廉、容易获得且安全。测量快速可靠。

determining-surface-areas-and-pore-volumes-of-metal-organic-frameworks

Research

JoVE Journal

Chemistry

Determining Surface Areas and Pore Volumes of Metal-Organic Frameworks

6.5K 次观看.  Georgia Institute of Technology. 我们的团队专注于合成和表征多孔材料，用于集水、空气净化和二氧化碳捕获等应用。我们真正感兴趣的是了解孔的大小、体积、连通性和化学性质如何影响吸收性能，然后利用这些见解为我们的材料设计工作提供信息。因此，稳健的表征技术至关重要。表征是任何多孔材料研究的一个重要方面。X 射线衍射、气体吸收技术和热分析技术是表征的顶级方法。这些也可用?...

视频: 作者聚焦:表征多孔材料以帮助开发具有吸附行为的稳健金属有机框架 

Preparation of Hydrophobic Metal-Organic Frameworks via Plasma Enhanced Chemical Vapor Deposition of Perfluoroalkanes for the Removal of Ammonia

Plasma enhanced chemical vapor deposition (PECVD) of perfluoroalkanes has long been studied for tuning the wetting properties of surfaces. For high surface area microporous materials, such as metal-organic frameworks (MOFs), unique challenges present themselves for PECVD treatments. Herein the protocol for development of a MOF that was previously unstable to humid conditions is presented. The protocol describes the synthesis of Cu-BTC (also known as HKUST-1), the treatment of Cu-BTC with PECVD of perfluoroalkanes, the aging of materials under humid conditions, and the subsequent ammonia microbreakthrough experiments on milligram quantities of microporous materials. Cu-BTC has an extremely high surface area (~1,800 m2/g) when compared to most materials or surfaces that have been previously treated by PECVD methods. Parameters such as chamber pressure and treatment time are extremely important to ensure the perfluoroalkane plasma penetrates to and reacts with the inner MOF surfaces. Furthermore, the protocol for ammonia microbreakthrough experiments set forth here can be utilized for a variety of test gases and microporous materials.

Herein the procedures for plasma enhanced chemical vapor deposition of perfluoroalkanes on microporous materials such as metal-organic frameworks to enhance their stability and hydrophobicity are described. Furthermore, breakthrough testing of milligram quantities of samples is described in detail.

增强型氟烷烃的化学气相沉积等离子通过疏水金属 - 有机骨架的制备氨的去除

Plasma enhanced chemical vapor deposition (PECVD) of perfluoroalkanes has long been studied for tuning the wetting properties of surfaces. For high ...

科研

化学

Synthesis and Characterization of Functionalized Metal-organic Frameworks

Metal-organic frameworks have attracted extraordinary amounts of research attention, as they are attractive candidates for numerous industrial and technological applications. Their signature property is their ultrahigh porosity, which however imparts a series of challenges when it comes to both constructing them and working with them. Securing desired MOF chemical and physical functionality by linker/node assembly into a highly porous framework of choice can pose difficulties, as less porous and more thermodynamically stable congeners (e.g., other crystalline polymorphs, catenated analogues) are often preferentially obtained by conventional synthesis methods. Once the desired product is obtained, its characterization often requires specialized techniques that address complications potentially arising from, for example, guest-molecule loss or preferential orientation of microcrystallites. Finally, accessing the large voids inside the MOFs for use in applications that involve gases can be problematic, as frameworks may be subject to collapse during removal of solvent molecules (remnants of solvothermal synthesis). In this paper, we describe synthesis and characterization methods routinely utilized in our lab either to solve or circumvent these issues. The methods include solvent-assisted linker exchange, powder X-ray diffraction in capillaries, and materials activation (cavity evacuation) by supercritical CO2 drying. Finally, we provide a protocol for determining a suitable pressure region for applying the Brunauer-Emmett-Teller analysis to nitrogen isotherms, so as to estimate surface area of MOFs with good accuracy.

Synthesis, activation, and characterization of intentionally designed metal-organic framework materials is challenging, especially when building blocks are incompatible or unwanted polymorphs are thermodynamically favored over desired forms. We describe how applications of solvent-assisted linker exchange, powder X-ray diffraction in capillaries and activation via supercritical CO2 drying, can address some of these challenges.

功能化的合成与表征金属 - 有机骨架

Metal-organic frameworks have attracted extraordinary amounts of research attention, as they are attractive candidates for numerous industrial and ...

Surface Functionalization of Metal-Organic Frameworks for Improved Moisture Resistance

Metal-organic frameworks (MOFs) are a class of porous inorganic materials with promising properties in gas storage and separation, catalysis and sensing. However, the main issue limiting their applicability is their poor stability in humid conditions. The common methods to overcome this problem involve the formation of strong metal-linker bonds by using highly charged metals, which is limited to a number of structures, the introduction of alkylic groups to the framework by post-synthetic modification (PSM) or chemical vapour deposition (CVD) to enhance overall hydrophobicity of the framework. These last two usually provoke a drastic reduction of the porosity of the material. These strategies do not permit to exploit the properties of the MOF already available and it is imperative to find new methods to enhance the stability of MOFs in water while keeping their properties intact. Herein, we report a novel method to enhance the water stability of MOF crystals featuring Cu2(O2C)4&#160;paddle-wheel units, such as HKUST (where HKUST stands for Hong Kong University of Science &#38; Technology), with the catechols functionalized with alkyl and fluoro-alkyl chains. By taking advantage of the unsaturated metal sites and the catalytic catecholase-like activity of CuII ions, we are able to create robust hydrophobic coatings through the oxidation and subsequent polymerization of the catechol units on the surface of the crystals under anaerobic and water-free conditions without disrupting the underlying structure of the framework. This approach not only affords the material with improved water stability but also provides control over the function of the protective coating, which enables the development of functional coatings for the adsorption and separations of volatile organic compounds. We are confident that this approach could also be extended to other unstable MOFs featuring open metal sites.

Robust functional catechol coatings were produced in one step by direct reaction of the material known as HKUST with synthetic catechols under anaerobic conditions. The formation of homogeneous coatings surrounding the entire crystal is ascribed to the biomimetic catalytic activity of Cu(II) dimers on the external surface of the crystals.

金属-有机框架的表面功能化改善防潮性能

Metal-organic frameworks (MOFs) are a class of porous inorganic materials with promising properties in gas storage and separation, catalysis and sensing. ...

Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks (MOFs)

Substrate size discrimination by the pore size and homogeneity of the chiral environment at the reaction sites are important issues in the validation of the reaction site in metal-organic framework (MOF)&#8211;based catalysts in an enantioselective catalytic reaction system. Therefore, a method of validating the reaction site of MOF-based catalysts is necessary to investigate this issue. Substrate size discrimination by pore size was accomplished by comparing the substrate size versus the reaction rate in two different types of carbonyl-ene reactions with two kinds of MOFs. The MOF catalysts were used to compare the performance of the two reaction types (Zn-mediated stoichiometric and Ti-catalyzed carbonyl-ene reactions) in two different media. Using the proposed method, it was observed that the entire MOF crystal participated in the reaction, and the interior of the crystal pore played an important role in exerting chiral control when the reaction was stoichiometric. Homogeneity of the chiral environment of MOF catalysts was established by the size control method for a particle used in the Zn-mediated stoichiometric reaction system. The protocol proposed for the catalytic reaction revealed that the reaction mainly occurred on the catalyst surface regardless of the substrate size, which reveals the actual reaction sites in MOF-based heterogeneous catalysts. This method for reaction site validation of MOF catalysts suggests various considerations for developing heterogeneous enantioselective MOF catalysts.

Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks MOFs

Here, we present a protocol for active site validation of metal-organic framework catalysts by comparing stoichiometric and catalytic carbonyl-ene reactions to find out whether a reaction takes place on the inner or outer surface of metal-organic frameworks.

使用气性金属-有机框架 （MoF） 开发异构异构选择性催化剂

Substrate size discrimination by the pore size and homogeneity of the chiral environment at the reaction sites are important issues in the validation of ...

Synthesis of Single-Crystalline Core-Shell Metal-Organic Frameworks

Because of their designability and unprecedented synergistic effects, core-shell metal-organic frameworks (MOFs) have been actively examined recently. However, the synthesis of single-crystalline core-shell MOFs is very challenging, and thus a limited number of examples have been reported. Here, we suggest a method of synthesizing single-crystalline HKUST-1@MOF-5 core-shells, which is HKUST-1 at the center of MOF-5. Through the computational algorithm, this pair of MOFs was predicted to have the matched lattice parameters and chemical connection points at the interface. To construct the core-shell structure, we prepared the octahedral- and cubic-shaped HKUST-1 crystals as a core MOF, in which the (111) and (001) facets were mainly exposed, respectively. Via the sequential reaction, the MOF-5 shell was well-grown on the exposed surface, showing a seamless connect interface, which resulted in the successful synthesis of single-crystalline HKUST-1@MOF-5. Their pure phase formation was proved by optical microscopic images and powder X-ray diffraction (PXRD) patterns. This method presents the potential of and insights into the single-crystalline core-shell synthesis with different kinds of MOFs.

Here, we demonstrate a protocol for the two-step synthesis of single-crystalline core-shells using a non-isostructural metal-organic framework (MOF) pair, HKUST-1 and MOF-5, which have well-matched crystal lattices.

单晶核壳金属有机骨架的合成

Because of their designability and unprecedented synergistic effects, core-shell metal-organic frameworks (MOFs) have been actively examined recently. ...

A Technical Guide for Performing Spectroscopic Measurements on Metal-Organic Frameworks

Metal-organic frameworks (MOFs) offer a unique platform to understand light-driven processes in solid-state materials, given their high structural tunability. However, the progression of MOF-based photochemistry has been hindered by the difficulty in spectrally characterizing these materials. Given that MOFs are typically larger than 100 nm in size, they are prone to excessive light scatter, thereby rendering data from valuable analytical tools like transient absorption and emission spectroscopy nearly uninterpretable. To gain meaningful insights of MOF-based photo-chemical and physical processes, special consideration must be taken toward properly preparing MOFs for spectroscopic measurements, as well as the experimental setups that garner higher quality data. With these considerations in mind, the present guide provides a general approach and set of guidelines for the spectroscopic investigation of MOFs. The guide addresses the following key topics: (1) sample preparation methods, (2) spectroscopic techniques/measurements with MOFs, (3) experimental setups, (3) control experiments, and (4) post-run stability characterization. With appropriate sample preparation and experimental approaches, pioneering advancements toward the fundamental understanding of light-MOF interactions are significantly more attainable.

Here, we use a polymer stabilizer to prepare metal-organic framework (MOF) suspensions that exhibit markedly decreased scatter in their ground-state and transient absorption spectra. With these MOF suspensions, the protocol provides various guidelines to characterize the MOFs spectroscopically to yield interpretable data.

对金属有机骨架进行光谱测量的技术指南

Metal-organic frameworks (MOFs) offer a unique platform to understand light-driven processes in solid-state materials, given their high structural ...

从多主题膦接头合成低价 MOF

Experimental Approaches for the Synthesis of Low-Valent Metal-Organic Frameworks from Multitopic Phosphine Linkers

Metal-organic frameworks (MOFs) are the subject of intense research focus due to their potential applications in gas storage and separation, biomedicine, energy, and catalysis. Recently, low-valent MOFs (LVMOFs) have been explored for their potential use as heterogeneous catalysts, and multitopic phosphine linkers have been shown to be a useful building block for the formation of LVMOFs. However, the synthesis of LVMOFs using phosphine linkers requires conditions that are distinct from those in the majority of the MOF synthetic literature, including the exclusion of air and water and the use of unconventional modulators and solvents, making it somewhat more challenging to access these materials. This work serves as a general tutorial for the synthesis of LVMOFs with phosphine linkers, including information on the following: 1) the judicious choice of the metal precursor, modulator, and solvent; 2) the experimental procedures, air-free techniques, and required equipment; 3) the proper storage and handling of the resultant LVMOFs; and 4) useful characterization methods for these materials. The intention of this report is to lower the barrier to this new subfield of MOF research and facilitate advancements toward novel catalytic materials.

作者聚焦:从多主题膦接头合成低价金属有机框架的实验方法  

Here, we describe a protocol for the synthesis of low-valent metal-organic frameworks (LVMOFs) from low-valent metals and multitopic phosphine linkers under air-free conditions. The resulting materials have potential applications as heterogeneous catalyst mimics of low-valent metal-based homogeneous catalysts.

多位膦接头合成低价金属有机骨架的实验方法

Metal-organic frameworks (MOFs) are the subject of intense research focus due to their potential applications in gas storage and separation, biomedicine, ...

氧化还原活性 MOF 固态电化学的磁力表征

Magnetometric Characterization of Intermediates in the Solid-State Electrochemistry of Redox-Active Metal-Organic Frameworks

Electrochemical energy storage has been a widely discussed application of redox-active metal-organic frameworks (MOFs) in the past 5 years. Although MOFs show outstanding performance in terms of gravimetric or areal capacitance and cyclic stability, unfortunately their electrochemical mechanisms are not well understood in most cases. Traditional spectroscopic techniques, such as X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS), have only provided vague and qualitative information about valence changes of certain elements, and the mechanisms proposed based on such information are often highly disputable. In this article, we report a series of standardized methods, including the fabrication of solid-state electrochemical cells, electrochemistry measurements, the disassembly of cells, the collection of MOF electrochemical intermediates, and physical measurements of the intermediates under the protection of inert gases. By using these methods for quantitatively clarifying the electronic and spin state evolution within a single electrochemical step of redox-active MOFs, one can provide clear insight into the nature of electrochemical energy storage mechanisms not only for MOFs, but also for all other materials with strongly correlated electronic structures.

作者聚焦:氧化还原活性金属有机框架固态电化学中中间体的磁力表征  

Ex situ magnetic surveys can directly provide bulk and local information on a magnetic electrode to reveal its charge storage mechanism step by step. Herein, electron spin resonance (ESR) and magnetic susceptibility are demonstrated to monitor the evaluation of paramagnetic species and their concentration in a redox-active metal-organic framework (MOF).

氧化还原-活性金属-有机骨架固态电化学中中间体的磁力表征

Electrochemical energy storage has been a widely discussed application of redox-active metal-organic frameworks (MOFs) in the past 5 years. Although MOFs ...