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One-pot synthesis of the reduced-charge montmorillonite via molten salts treatment
Applied Clay Science ( IF 5.6 ) Pub Date : 2020-03-01 , DOI: 10.1016/j.clay.2019.105429
Qiuzhi He , Runliang Zhu , Qingze Chen , Yanping Zhu , Yixuan Yang , Jing Du , Jianxi Zhu , Hongping He

Abstract Layer charge is a critical factor determining the structural characteristics and physicochemical properties of clay minerals, and fixing small cations (e.g., Li+) into the tetrahedral/octahedral sheets of clay minerals is a feasible way for reducing their layer charges. However, conventional methods for preparing reduced-charge clay minerals are usually quite complex and time-consuming. Herein, a facile one-pot treatment method for preparing reduced-charge clay minerals was successfully developed using molten salts. In particular, montmorillonite (Mt) was mixed with mono LiNO3 or LiNO3-NaNO3 mixture, which was then heated above the melting points of salts. The obtained results showed that the cation exchange capacity (CEC) of Mt decreased evidently after being treated with molten LiNO3, and the CEC value was reversely related to the heating time. The X-ray diffraction results demonstrated that Mt layers collapsed upon treatment with molten LiNO3. On the other hand, the partial replacement of LiNO3 by NaNO3 could restrict the collapse of Mt layers, as the larger ionic radius of Na+ (than Li+) helped in maintaining the interlayer spaces of Mt during the process of charge reduction. As indicated by the Fourier transform infrared spectroscopy, the structural OH stretching vibration shifted to a higher wavenumber (from 3623 to 3632 cm−1) after the molten LiNO3 treatment, which suggested that some Li+ ions migrated into the hexagonal cavities in the tetrahedral sheets of Mt, and the new band at 3670 cm−1 indicated that some Li+ ions even further migrated into the octahedral vacancies of Mt. The locations of fixed Li+ ions were further confirmed by the X-ray photoelectron spectroscopy characterization. Due to the migration of Li+ ions into the layers of Mt, the Li1s peak shifted to lower binding energy. The above results showed that the molten salt treatment might be a cost-effective and environmentally friendly approach for synthesizing reduced-charge clay minerals, and using mixed molten salts can help in maintaining the interlayer structure.

中文翻译:

熔盐处理一锅法合成减荷蒙脱石

摘要 层电荷是决定粘土矿物结构特征和理化性质的关键因素,将小的阳离子(如Li+)固定在粘土矿物的四面体/八面体片中是降低其层电荷的可行方法。然而,制备低电荷粘土矿物的常规方法通常非常复杂和耗时。在此,成功开发了一种使用熔盐制备降低电荷粘土矿物的简便的一锅处理方法。特别是,将蒙脱石 (Mt) 与单 LiNO3 或 LiNO3-NaNO3 混合物混合,然后将其加热至盐的熔点以上。所得结果表明,Mt经熔融LiNO3处理后阳离子交换容量(CEC)明显降低,CEC 值与加热时间呈负相关。X 射线衍射结果表明 Mt 层在用熔融 LiNO3 处理后坍塌。另一方面,用 NaNO3 部分替代 LiNO3 可以限制 Mt 层的坍塌,因为 Na+(比 Li+)更大的离子半径有助于在电荷减少过程中保持 Mt 的层间空间。傅里叶变换红外光谱表明,在熔融的 LiNO3 处理后,结构 OH 伸缩振动向更高波数移动(从 3623 到 3632 cm-1),这表明一些 Li+ 离子迁移到四面体片中的六边形空腔中。 Mt 和 3670 cm-1 处的新带表明一些 Li+ 离子甚至进一步迁移到 Mt 的八面体空位中。X 射线光电子能谱表征进一步证实了固定 Li+ 离子的位置。由于 Li+ 离子迁移到 Mt 层中,Li1s 峰转移到较低的结合能。上述结果表明,熔盐处理可能是一种具有成本效益且环境友好的合成低电荷粘土矿物的方法,并且使用混合熔盐有助于保持层间结构。
更新日期:2020-03-01
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