Zhang Shuai, Liu Qinfu, Gao Feng, Ma Rujia, Wu Zeguang, Teppen Brian J
College of Geoscience and Surveying Engineering, China University of Mining & Technology (Beijing), Beijing 100083, People's Republic of China.
Department of Plant, Soil, and Microbial Sciences, Michigan State University, East Lansing, Michigan 48824, United States.
Appl Clay Sci. 2018 Jun 15;158:204-210. doi: 10.1016/j.clay.2018.03.032. Epub 2018 Apr 4.
The evolution of basal spacing and interfacial structure of kaolinite-N-methylformamide (NMF) complexes during the intercalation process were difficult to obtain using experimental methods. In present study, a series of kaolinite-NMF complex models with various numbers of NMF molecules in the interlayer space were constructed to mimic the progressive stage of the intercalation process of kaolinite intercalated by NMF. The MD simulations were performed on these models to explore the evolution of basal spacing and interfacial structure of kaolinite-NMF complexes during the intercalation process. It was found that the basal spacing of complex was stabilized at 11 Å during the intercalation process, where the molecular plane of NMF oriented at small angles with respect to the interlayer surface with the C=O groups and N-H bonds pointing toward the octahedral and tetrahedral surfaces, respectively, due to the hydrogen bonding interactions. The basal spacing can be enlarged to larger values with the prerequisite of overcoming the energy barrier. With the increase of basal spacing during the intercalation process, the NMF were rearranged as a pillar with the molecular planes orienting at higher angles with respect to the interlayer surface, and then developed to disordered bilayer structure. For the interfacial interaction of kaolinite-NMF complex, both the octahedral surface and tetrahedral surface showed binding affinity to the NMF, which is the driving force for the intercalation of NMF in kaolinite. The octahedral surface displays stronger binding affinity to the NMF in terms of the H-bonds and energetics compared to the tetrahedral surface partially due to the highly active surface hydroxyl groups. The present study provides insight into the basal spacing evolution, and interfacial structure and interaction of kaolinite-NMF complexes, which can enhance the understanding of kaolinite intercalated by small molecules.
在插层过程中，高岭石 - N - 甲基甲酰胺（NMF）复合物的基面间距和界面结构的演变难以通过实验方法获得。在本研究中，构建了一系列层间空间中含有不同数量NMF分子的高岭石 - NMF复合物模型，以模拟NMF插层高岭石插层过程的渐进阶段。对这些模型进行分子动力学（MD）模拟，以探索插层过程中高岭石 - NMF复合物的基面间距和界面结构的演变。研究发现，在插层过程中复合物的基面间距稳定在11 Å，由于氢键相互作用，NMF的分子平面相对于层间表面以小角度取向，其中C = O基团和N - H键分别指向八面体和四面体表面。在克服能垒的前提下，基面间距可以扩大到更大的值。随着插层过程中基面间距的增加，NMF重新排列成柱状，分子平面相对于层间表面以更大角度取向，然后发展为无序的双层结构。对于高岭石 - NMF复合物的界面相互作用，八面体表面和四面体表面都对NMF表现出结合亲和力，这是NMF插层高岭石的驱动力。与四面体表面相比，八面体表面在氢键和能量方面对NMF表现出更强的结合亲和力，部分原因是其表面羟基具有高活性。本研究深入了解了高岭石 - NMF复合物的基面间距演变、界面结构和相互作用，有助于增强对小分子插层高岭石的理解。
