Li Yun, Chen Meng, Liu Chanjuan, Song Hongzhe, Yuan Peng, Zhang Baifa, Liu Dong, Du Peixin
CAS Key Laboratory of Mineralogy and Metallogeny, Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Institutions of Earth Science, Chinese Academy of Sciences (CAS), Guangzhou 510640, China.
University of Chinese Academy of Sciences, Beijing 100049, China.
Langmuir. 2020 Apr 7;36(13):3323-3335. doi: 10.1021/acs.langmuir.0c00183. Epub 2020 Mar 16.
Molecular dynamics simulations were used to investigate the effects of the external surface of a 2:1 clay mineral with different charge amounts and charge locations on CH hydrate formation. The results showed that 5, 56, 56, and 56 were formed away from the clay mineral surface. The surface of the clay mineral with high- and low-charge layers was occupied by Na to form various distributions of outer- and inner-sphere hydration structures, respectively. The adsorbed Na on the high-charge layer surface reduced the HO activity by disturbing the hydrogen bond network, resulting in low tetrahedral arrangement of HO molecules near the layer surface, which inhibited CH hydrate formation. However, more CH molecules were adsorbed onto the vacancy in the Si-O rings of a neutral-charge layer to form semicage structures. Thus, the order parameter of HO molecules near this surface indicated that the arrangement of HO molecules resulted in a more optimal tetrahedral structure for CH hydrate formation than that near the negatively charged layer surface. Different nucleation mechanisms of the CH hydrate on external surfaces of clay mineral models were observed. For clay minerals with negatively charged layers (i.e., high and low charge), the homogeneous nucleation of the CH hydrate occurred away from the surface. For a clay mineral with a neutral-charge layer, the CH hydrate could nucleate either in the bulk-like solution homogeneously or at the clay mineral-HO interface heterogeneously.
采用分子动力学模拟研究了不同电荷量和电荷位置的2:1型黏土矿物外表面对CH水合物形成的影响。结果表明，在远离黏土矿物表面处形成了5、56、56和56。高电荷层和低电荷层黏土矿物的表面分别被Na占据，形成了外层和内层水化结构的各种分布。高电荷层表面吸附的Na通过扰乱氢键网络降低了HO活性，导致层表面附近HO分子的四面体排列较少，从而抑制了CH水合物的形成。然而，更多的CH分子吸附到中性电荷层Si - O环中的空位上形成半笼状结构。因此，该表面附近HO分子的序参表明，与带负电荷层表面附近相比，HO分子的排列为CH水合物形成提供了更优化的四面体结构。观察到黏土矿物模型外表面CH水合物的不同成核机制。对于带负电荷层的黏土矿物（即高电荷和低电荷），CH水合物的均相成核发生在远离表面处。对于具有中性电荷层的黏土矿物，CH水合物可以在本体状溶液中均相成核，也可以在黏土矿物 - HO界面异相成核。
