Morphological Analysis of Physically Reconstructed Silica Monoliths with Submicrometer Macropores: Effect of Decreasing Domain Size on Structural Homogeneity.
Morphological Analysis of Physically Reconstructed Silica Monoliths with Submicrometer Macropores: Effect of Decreasing Domain Size on Structural Homogeneity.
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具有亚微米大孔的物理重建二氧化硅整体的形态分析：减小域尺寸对结构均匀性的影响
DOI：
10.1021/la5046018
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发表时间：
2015
期刊：
影响因子：
--
通讯作者：
U. Tallarek
中科院分区：
文献类型：
--
作者：
D. Stoeckel;C. Kübel;M. O. Loeh;B. M. Smarsly;U. Tallarek
二氧化硅整料越来越多地用作分离和催化中的固定床载体，因为它们的双峰孔空间结构结合了优异的传质性能和大的表面积。为了优化它们的性能，必须建立形态和传输特性之间的定量关系，并且必须确定导致针对目标应用优化的期望形态的合成条件。然而，具体的合成参数对二氧化硅单块的结构性质的影响仍然知之甚少。一个重要的问题是，在不损害结构均匀性的情况下，大孔和域尺寸可以减小到何种程度。我们解决了这个问题与一组8个大孔-介孔二氧化硅整料的平均大孔尺寸（dmacro）为3.7和0.1 μm之间，制备后的既定路线，涉及溶胶-凝胶转变和相分离的定量形态数据。使用聚焦离子束扫描电子显微镜重建二氧化硅整体样品的大孔空间，然后基于弦长分布（CLDs）和孔网络的分支-节点分析分别对几何和拓扑性质进行定量评估。我们观察到一个显着增加的结构异质性，由减少的parameterkderived从拟合ak-γ函数的CLDs，whendmacroreaches亚微米范围。具有亚微米大孔的二氧化硅整料的结构均匀性受损可能源于溶胶-凝胶转变和相分离的竞争过程中的早期结构冻结。因此，通过改变溶胶-凝胶转变点将二氧化硅整料的形态特征降低到亚微米范围的常见方法是否能够成功是值得怀疑的。替代战略和更好地了解所涉及的竞争过程应该是未来研究的重点。
Silica monoliths are increasingly used as fixed-bed supports in separation and catalysis because their bimodal pore space architecture combines excellent mass transport properties with a large surface area. To optimize their performance, a quantitative relationship between morphology and transport characteristics has to be established, and synthesis conditions that lead to a desired morphology optimized for a targeted application must be identified. However, the effects of specific synthesis parameters on the structural properties of silica monoliths are still poorly understood. An important question is how far the macropore and domain size can be reduced without compromising the structural homogeneity. We address this question with quantitative morphological data derived for a set of eight macroporous–mesoporous silica monoliths with an average macropore size (dmacro) of between 3.7 and 0.1 μm, prepared following an established route involving the sol–gel transition and phase separation. The macropore space of the silica monolith samples is reconstructed using focused ion beam scanning electron microscopy followed by a quantitative assessment of geometrical and topological properties based on chord length distributions (CLDs) and branch-node analysis of the pore network, respectively. We observe a significant increase in structural heterogeneity, indicated by a decrease in the parameterkderived from fitting ak-gamma function to the CLDs, whendmacroreaches the submicrometer range. The compromised structural homogeneity of silica monoliths with submicrometer macropores could possibly originate from early structural freezing during the competitive processes of sol–gel transition and phase separation. It is therefore questionable if the common approach of reducing the morphological features of silica monoliths into the submicrometer regime by changing the point of sol–gel transition can be successful. Alternative strategies and a better understanding of the involved competitive processes should be the focus of future research.
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发表时间：
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影响因子：
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DOI：
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发表时间：
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期刊：
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