Changes in Structure, Morphology, Porosity, and Surface Activity of Mesoporous Halloysite Nanotubes Under Heating
Changes in Structure, Morphology, Porosity, and Surface Activity of Mesoporous Halloysite Nanotubes Under Heating
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DOI：
10.1346/ccmn.2012.0600602
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发表时间：
2012-12
影响因子：
2.2
通讯作者：
P. Yuan;Daoyong Tan;F. Annabi-Bergaya;Wenchang Yan;Mingde Fan;Dong Liu;Hongping He
中科院分区：
文献类型：
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作者：
P. Yuan;Daoyong Tan;F. Annabi-Bergaya;Wenchang Yan;Mingde Fan;Dong Liu;Hongping He
本研究的目的是调查的结构，质地和加热下的管状埃洛石，这是重要的埃洛石作为功能材料的应用程序，但很少受到关注相比，高岭石的表面性质的变化。将纯化的埃洛石样品在不同温度下加热至1400°C，然后通过X射线衍射、电子显微镜、傅里叶变换红外光谱、热分析和氮吸附进行表征。埃洛石的热分解过程包括三个主要步骤。在500-900°C的脱羟基过程中，最初分别处于四面体和八面体片中的二氧化硅和氧化铝逐渐分离，导致长程有序的损失。第二步在1000-1100 ℃下生成纳米（5-40 nm）γ-Al_2O_3。第三步是在1200 ~ 1400°C形成莫来石状相，在1400°C形成方石英。加热温度<900°C时，埃洛石的粗管状形貌和中孔性基本保持不变。在1000°C下煅烧导致管状纳米颗粒变形。在较高温度下煅烧导致进一步的扭曲，然后破坏管状结构。首次揭示了在原来的四面体和八面体片层断裂和无序化过程中，管外表面羟基的形成。这些羟基对于有机硅烷（γ-氨丙基三乙氧基硅烷）的接枝改性具有活性，这表明埃洛石在陶瓷材料或新型粘土聚合物纳米复合材料中作为填料的一些非常有前途的潜在用途。
The objective of the present study was to investigate changes in the structural, textural, and surface properties of tubular halloysite under heating, which are significant in the applications of halloysite as functional materials but have received scant attention in comparison with kaolinite. Samples of a purified halloysite were heated at various temperatures up to 1400°C, and then characterized by X-ray diffraction, electron microscopy, Fourier-transform infrared spectroscopy, thermal analysis, and nitrogen adsorption. The thermal decomposition of halloysite involved three major steps. During dehydroxylation at 500–900°C, the silica and alumina originally in the tetrahedral and octahedral sheets, respectively, were increasingly separated, resulting in a loss of long-range order. Nanosized (5–40 nm) γ-Al2O3 was formed in the second step at 1000–1100°C. The third step was the formation of a mullite-like phase from 1200 to 1400°C and cristobalite at 1400°C. The rough tubular morphology and the mesoporosity of halloysite remained largely intact as long as the heating temperature was <900°C. Calcination at 1000°C led to distortion of the tubular nanoparticles. Calcination at higher temperatures caused further distortion and then destruction of the tubular structure. The formation of hydroxyl groups on the outer surfaces of the tubes during the disconnection and disordering of the original tetrahedral and octahedral sheets was revealed for the first time. These hydroxyl groups were active for grafting modification by an organosilane (γ-aminopropyltriethoxysilane), pointing to some very promising potential uses of halloysite for ceramic materials or as fillers for novel clay-polymer nanocomposites.