Blukis Roberts, Schindler Maria, Couasnon Thaïs, Benning Liane G
German Research Center for Geosciences, GFZ, Telegrafenberg, Potsdam 14473, Germany.
Langmuir. 2022 Jun 28;38(25):7678-7688. doi: 10.1021/acs.langmuir.2c00425. Epub 2022 Jun 16.
Saponite is a clay mineral of the smectite group that finds applications in the chemical industry as a catalyst or catalyst precursor as well as in nanocomposites used for structural or catalytic applications. Saponite of controlled composition, crystallinity, particle size, and morphology would be highly beneficial to industry; however, such materials are not found in a sufficiently pure form in nature. Synthetic methods to produce saponite with specific properties are currently lacking as the understanding of the mechanisms controlling its formation, crystalline properties and particle morphology, is limited. Understanding the saponite formation mechanism is crucial for the development of a highly tuned and controlled synthesis leading to materials with specific properties. Here, we report a new chemical reaction mechanism explaining the nucleation and kinetics of saponite growth at different pHs, at 95-100 °C, and under the influence of pH-modifying additives explored via a combination of X-ray scattering methods and infrared spectroscopy. Our results show that the main factor affecting the nucleation and growth kinetics of saponite is the pH, which has a particularly significant impact on the rate of initial nucleation. Non-uniform reactivity of the aluminosilicate gel also significantly affects saponite growth kinetics and causes a change in the rate-determining step as seen in graphical abstract. The most crystalline saponite is obtained when the nucleation is suppressed by a low initial pH (<7), but the reaction is performed at a higher pH of about 9. The stacking of the saponite sheets can be further improved by a separate postsynthesis treatment with an alkali (NaOH) solution. A simple, ambient pressure method for synthesizing a highly crystalline saponite is proposed that could be easily upscaled for industrial purposes.
皂石是蒙脱石族的一种粘土矿物，在化学工业中用作催化剂或催化剂前体，也用于结构或催化应用的纳米复合材料。具有可控组成、结晶度、粒径和形态的皂石对工业将非常有益；然而，这种材料在自然界中没有足够纯净的形式。由于对控制其形成、晶体性质和颗粒形态的机制的理解有限，目前缺乏生产具有特定性质皂石的合成方法。了解皂石的形成机制对于开发高度优化和可控的合成方法以获得具有特定性质的材料至关重要。在此，我们报告了一种新的化学反应机制，该机制解释了在95-100°C不同pH值下，以及在通过X射线散射方法和红外光谱相结合探索的pH调节添加剂影响下皂石生长的成核和动力学。我们的结果表明，影响皂石成核和生长动力学的主要因素是pH值，它对初始成核速率有特别显著的影响。如附图摘要所示，铝硅酸盐凝胶的不均匀反应性也显著影响皂石的生长动力学，并导致速率决定步骤的变化。当通过低初始pH值（<7）抑制成核，但在约9的较高pH值下进行反应时，可获得结晶度最高的皂石。通过用碱（NaOH）溶液进行单独的合成后处理，可以进一步改善皂石片层的堆叠。提出了一种简单的常压方法来合成高度结晶的皂石，该方法可以很容易地扩大规模用于工业目的。
