Thermal behavior of kaolinite-urea intercalation complex and molecular dynamics simulation for urea molecule orientation
Thermal behavior of kaolinite-urea intercalation complex and molecular dynamics simulation for urea molecule orientation
复制标题
高岭石-尿素插层复合物的热行为及尿素分子取向的分子动力学模拟
DOI：
10.1007/s10973-014-3646-1
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发表时间：
2014-07-01
影响因子：
4.4
通讯作者：
Frost, Ray L.
中科院分区：
文献类型：
--
作者：
Liu, Qinfu;Zhang, Shuai;Frost, Ray L.
用热重-差示扫描量热法(TG-DSC)、X射线衍射仪(XRD)和傅立叶变换红外光谱(FTIR)研究了高岭石-尿素插层复合体的热行为。此外，还用分子动力学模拟方法研究了尿素分子在高岭石分子筛中的相互作用模式。TG-DSC曲线在136℃、210-270℃和500℃有三个主要的质量损失，分别归因于(1)表面吸附尿素的熔融、(2)插层尿素的脱除和(3)脱层高岭石的脱羟基。在218、250和261摄氏度的三个DSC吸热峰与具有三种不同分布结构的插层尿素的连续去除有关。根据尿素的偶极矩向量与高岭石基面的夹角，三种尿素模型可描述为：(1)A类，偶极矩向量与高岭石基面几乎平行；(2)B类，偶极矩向量指向硅四面体，其与高岭石基面的夹角在20A~40A度之间；(3)C型，偶极矩向量几乎垂直于高岭石基面。分子动力学模拟结果验证了尿素分子的三种分布结构。此外，用TG-DSC研究了高岭土-尿素插层复合体的热行为，并用FTIR和X射线衍射仪进行了分析。
The thermal behavior of kaolinite-urea intercalation complex was investigated by thermogravimetry-differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), and fourier transform infrared spectroscopy (FTIR). In addition, the interaction mode of urea molecules intercalated into the kaolinite gallery was studied by means of molecular dynamics simulation. Three main mass losses were observed at 136 A degrees C, in the range of 210-270 A degrees C, and at 500 A degrees C in the TG-DSC curves, which were, respectively, attributed to (1) melting of the surface-adsorbed urea, (2) removal of the intercalated urea, and (3) dehydroxylation of the deintercalated kaolinite. The three DSC endothermic peaks at 218, 250, and 261 A degrees C were related to the successive removals of intercalated urea with three different distribution structures. Based on the angle between the dipole moment vector of urea and the basal surface of kaolinite, the three urea models could be described as follows: (1) Type A, the dipole moment vector is nearly parallel to the basal surface of kaolinite; (2) Type B, the dipole moment vector points to the silica tetrahedron with the angle between it and the basal surface of kaolinite ranging from 20A degrees to 40A degrees; and (3) Type C, the dipole moment vector is nearly perpendicular to the basal surface of kaolinite. The three distribution structures of urea molecules were validated by the results of the molecular dynamics simulation. Furthermore, the thermal behavior of the kaolinite-urea intercalation complex investigated by TG-DSC was also supported by FTIR and XRD analyses.