Crystal Growth of Smectite: A Study Based on the Change in Crystal Chemistry and Morphology of Saponites with Synthesis Time
Crystal Growth of Smectite: A Study Based on the Change in Crystal Chemistry and Morphology of Saponites with Synthesis Time
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蒙皂石晶体生长：基于皂石晶体化学和形貌随合成时间变化的研究
DOI：
10.1021/acsearthspacechem.9b00194
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发表时间：
2020
影响因子：
3.4
通讯作者：
Zhu Jianxi
中科院分区：
文献类型：
--
作者：
Zhang Chaoqun;Petit Sabine;He Hongping;Villieras Frederic;Razafitianamaharavo Angelina;Baron Fabien;Tao Qi;Zhu Jianxi
蒙脱石是一种广泛分布于地壳中的2：1型膨胀性粘土矿物。其独特的结构和性能使其在许多领域有着广泛的应用。然而，它们的生长过程和机制仍不完全清楚。在本研究中，我们试图从晶体化学和形态学的角度来理解这种生长过程和模式。通过在自生压力下在220 °C下水热处理起始材料0.25至30天来合成蒙脱石。起始材料由在150 °C下合成1天的具有相同摩尔重量的Mg-和Ni-蒙脱石前体的混合物获得。通过X射线衍射分析和傅里叶变换红外（FTIR）光谱，将起始材料以及进一步合成的样品鉴定为蒙脱石、皂石型。起始材料的FTIR光谱仅显示ν Mg3 OH和ν Ni 3OH带。在起始材料的水热处理（220 °C）之后，出现ν Mg 2NiOH和ν Ni 2 MgOH谱带，并且随着延长的处理而相对增加，表明在皂石的八面体片中出现相邻的Mg-Ni，并且因此新形成的皂石的结晶具有混合组成。氩气吸附和扫描透射电子显微镜（STEM）的结果是一致的，并表明，合成的皂石的平均粒径增加了一个短的持续时间，并往往保持停滞从14至30天。Mg和Ni的分布和颗粒尺寸的演变从氩吸附和STEM暗示以下：（i）的八面体阳离子的分布往往是随机的;（ii）氩吸附和STEM的组合提供了一个强有力的证据，为颗粒尺寸的增加;和（iii）晶体生长通过表面控制的生长层的横向延伸进行。实验结果表明耦合FTIR，氩气吸附，和STEM在照亮的晶体化学和形态在蒙脱石的晶体生长过程的早期阶段的可行性和有效性。
Smectites are 2:1 type swelling clay minerals widely distributed in the earth’s crust. The unique structures and properties endow them with various applications in many fields. However, their growth process and mechanism are still not completely understood. In this study, we tried to understand this growth process and pattern from the perspective of crystal chemistry and morphology. Smectites were synthesized by the hydrothermal treatment of starting materials at 220 °C under autogenous pressure from 0.25 to 30 days. The starting materials were obtained from the mixtures of Mg- and Ni-smectite precursors synthesized at 150 °C for 1 day with identical molar weights. The starting materials, as well as further synthesized samples, are identified as smectites, saponite-type, by X-ray diffraction analysis and Fourier transform infrared (FTIR) spectroscopy. The FTIR spectra of the starting materials exhibited the νMg3OH and νNi3OH bands only. After the hydrothermal treatment (220 °C) of the starting materials, the νMg2NiOH and νNi2MgOH bands appear and relatively increase with the prolonged treatment, indicating the appearance of neighboring Mg–Ni in the octahedral sheet of saponite and thus the crystallization of the newly formed saponite with a mixed composition. Argon adsorption and scanning transmission electron microscopy (STEM) results are consistent and indicate that the mean particle size of the synthesized saponites increases for a short duration and tends to remain stagnant from 14 to 30 days. The evolution of Mg and Ni distribution and of the particle size from argon adsorption and STEM imply the following: (i) the distribution of the octahedral cations tends to be random; (ii) the combination of argon adsorption and STEM offers a powerful evidence for the increase of particle size; and (iii) crystal growth proceeds via a lateral extension of the layers by surface-controlled growth. The experimental results indicate the viability and effectiveness of coupling FTIR, argon adsorption, and STEM in illuminating the crystal chemistry and morphology at the early stage of the crystal growth process of smectite.