Tuning the structure and orientation of hexagonally ordered mesoporous channels in anodic alumina membrane hosts: A 2D small-angle X-ray scattering study
Tuning the structure and orientation of hexagonally ordered mesoporous channels in anodic alumina membrane hosts: A 2D small-angle X-ray scattering study
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DOI：
10.1002/anie.200503301
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发表时间：
2006-01-01
影响因子：
16.6
通讯作者：
Bein, T
中科院分区：
文献类型：
--
作者：
Platschek, B;Petkov, N;Bein, T
周期性介孔材料在过去的十年中吸引了相当大的关注，因为它们作为催化剂载体和纳米反应器，或作为具有吸引人的光电性能的纳米结构材料的主体的有前途的应用。[1，2]这些应用中的许多将受益于某些介观结构的优先对准的有序阵列的布置。蒸发诱导自组装（EISA）方法已被确立为制备具有单取向介观结构域的薄膜的有效方法。[3，4]然而，最常获得的膜显示平行于基底表面排列的六边形有序通道。[5]最近，在阳极氧化铝膜（AAM）的规则的较大通道内合成介孔材料已经被探索，目的是实现对介孔系统的形态的更大控制。[6]第一种方法，通过溶胶-凝胶合成路线，使用三嵌段共聚物聚环氧乙烷100-b-聚聚环氧丙烷（环氧乙烷）100（PEO 100 PPO 65 PEO 100或PluronicF-127）作为结构导向剂，导致具有两种不同取向的2D六边形介观结构，发现这两种不同取向取决于纳米颗粒的浓度而以不同的比率共存。表面活性[7]在一种情况下，中孔的长轴与AAM通道的长轴对齐（柱状取向）。在另一种情况下，观察到介观结构的圆形取向。类似的（独立的）不寻常的中间相结构已知存在于通过溶剂热方法制备的十六烷基三甲基溴化铵（CTAB）模板材料中，并已被命名为“circulites”或圆形晶体。[8，9]有效的EISA方法也可用于通过施加通常用于沉积介孔二氧化硅膜的涂布溶液来制备AAM介孔复合材料。当使用阳离子CTAB作为模板，部分有序的介孔材料与对齐，柱状介孔仅在附近的氧化铝壁，得到表现出有前途的行为作为分子分离器。[10]使用三嵌段共聚物PEO 20 PPO 70 PEO 20（Pluronic 123或P123）作为模板，导致具有同心或螺旋介孔和球形介孔单链的惊人的介孔结构，这取决于直径小于100 nm的氧化铝纳米通道施加的限制条件。[11]相比之下，当在较大Anopore通道中的溶胶-凝胶方法中使用相同的模板（P123）时，报道了柱状中孔。[12]然而，当在相同的表面活性剂/二氧化硅的比例略有不同的协议中使用的溶胶-凝胶合成路线，具有混合取向的六方中间相。[13]在使用P123模板的相关研究中研究了老化过程中水蒸气的存在。[14在这种情况下，在较高的水压下，圆形取向优于柱状取向;这种选择性归因于凝胶化速率的增加。多个介孔二氧化硅相也已通过顺序加载技术被包括在AAM通道中。[16]从以上讨论的研究，很明显，化学计量和反应条件的细微变化可以导致中孔的顺序和形态的显著变化。为了更好地理解机制和随意调整这些有趣结构的能力，我们在此提出了一种结合2D小角X射线散射（SAXS）和透射电子显微镜（TEM）的研究，它表明高度有序的六方结构。
Periodic mesoporous materials have attracted considerable attention during the last decade because of their promising applications as catalyst supports and nanoreactors, or as hosts for nanostructured materials with appealing optoelectronic properties.[1, 2] Many of these applications will benefit from arrangements of preferentially aligned, ordered arrays of certain mesostructures. The evaporation-induced self-assembly (EISA) method has been established as an efficient process for the preparation of thin films with mono-oriented mesostructured domains.[3, 4] However, the most frequently obtained films display hexagonally ordered channels that are aligned parallel to the surface of the substrate.[5] Recently, the synthesis of mesoporous materials within the regular, larger channels of anodic alumina membranes (AAMs) has been explored, with the aim of attaining greater control over the morphology of the mesoporous system.[6] A first approach, through a sol–gel synthesis route using the triblock copolymer poly (ethylene oxide) 100-b-poly (propylene oxide) 65-b-poly (ethylene oxide) 100 (PEO100PPO65PEO100 or PluronicF-127) as a structure-directing agent, resulted in 2D hexagonal mesostructures with two different orientations that were found to coexist at different ratios depending on the concentration of the surfactant.[7] In one case, the long axes of the mesopores were aligned with the long axes of the AAM channels (columnar orientation). In another case, a circular orientation of the mesostructure was observed. Similar (freestanding) unusual mesophase structures are known to exist in cetyltrimethylammonium bromide (CTAB)-templated materials prepared by solvothermal methods and have been named “circulites” or circular crystals.[8, 9] The efficient EISA method can also be used to prepare AAM mesoporous composite materials by applying coating solutions that are typically used for the deposition of mesoporous silica films. When using cationic CTAB as a template, partially ordered mesoporous materials with aligned, columnar mesopores only in the vicinity of the alumina walls were obtained that showed promising behavior as molecular separators.[10] Use of the triblock copolymerPEO20PPO70PEO20 (Pluronic123 or P123) as a template resulted in striking mesostructures with concentric or helical mesopores and single chains of spherical mesopores, depending on the confinement conditions imposed by alumina nanochannels with diameters of less than 100nm.[11] In contrast, columnar mesopores were reported when the same template (P123) was used in the sol–gel approach in larger Anopore channels.[12] However, when a slightly different protocol at the same surfactant/silica ratio was used in the sol–gel synthesis route, hexagonal mesophases with mixed orientations resulted.[13] The presence of water vapor in the ageing process was investigated in a related study using the P123 template.[14, 15] In this case, the circular orientation was favored over the columnar one at higher water pressure; this selectivity was attributed to the increased rate of gelation. Multiple mesoporous silica phases have also been included in AAM channels through sequential loading techniques.[16] From the studies discussed above, it is clear that subtle changes in stoichiometry and reaction conditions can lead to striking changes in the order and morphology of the mesopores. With an aim to better understand the mechanism and the ability to tune these intriguing structures at will, we present herein a combined 2D small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) study, which shows that highly ordered hexagonal …