Randrianandraina Joharimanitra, Badawi Michael, Cardey Bruno, Grivet Manuel, Groetz Jean-Emmanuel, Ramseyer Christophe, Anzola Freddy Torrealba, Chambelland Caroline, Ducret Didier
Laboratoire Chrono-Environnement UMR 6249, Université de Bourgogne Franche-Comté, 16 route de Gray, F-25030 Besançon Cedex, France.
Phys Chem Chem Phys. 2021 Sep 14;23(34):19032-19042. doi: 10.1039/d1cp02624k. Epub 2021 Aug 24.
The very wide range of applications of LTA zeolites, including the storage of tritiated water, implies that a detailed and accurate atomic-scale description of the adsorption processes taking place in their structure is crucial. To unravel with an unprecedented accuracy the mechanisms behind the water filling in NaA, we have conducted a systematic ab initio molecular dynamics investigation. Two LTA structural models, the conventional Z4A and the reduced one ZK4, have been used for static and dynamic ab initio calculations, respectively. After assessing this reduced model with comparative static DFT calculations, we start the filling of the α and β cages by water, molecule by molecule. This allowed us to thoroughly study the interaction of water molecules with the zeolite structure and between water molecules, progressively forming H-bond chains and ring patterns as the cage is being filled. The adsorption energies could then be calculated with an unprecedented accuracy, which showed that the interaction of the molecules with the zeolite weakens as their number increases. By these methods, we have been able to highlight the primary role of Na cations in the interaction of water with zeolite, and inversely, the role of water in the displacement of cations when it is sufficiently solvated, allowing the passage between the α and β cages. This phenomenon is possible thanks to the inhomogeneous distribution of water molecules on the cationic sites, as shown by our AIMD simulations, which allows the formation of water clusters. These results are important because they help in understanding how the coverage of cationic sites by water will affect the adsorption of other molecules inside the Na-LTA zeolite.
LTA 沸石的应用范围非常广泛，包括储存氚水，这意味着对其结构中发生的吸附过程进行详细准确的原子尺度描述至关重要。为以前所未有的精度揭示 NaA 中水分子填充的机制，我们进行了系统的从头算分子动力学研究。分别使用了两种 LTA 结构模型，传统的 Z4A 和简化的 ZK4，用于静态和动态从头算计算。在用比较静态 DFT 计算评估了这个简化模型之后，我们开始逐个水分子地向 α 和 β 笼中填充水。这使我们能够深入研究水分子与沸石结构之间以及水分子之间的相互作用，随着笼子被填充，逐渐形成氢键链和环状结构。然后可以以前所未有的精度计算吸附能，结果表明分子与沸石的相互作用随着其数量的增加而减弱。通过这些方法，我们能够突出 Na 阳离子在水与沸石相互作用中的主要作用，反之，当水充分溶剂化时，水在阳离子置换中的作用，这使得水能够在 α 和 β 笼之间通过。正如我们的 AIMD 模拟所示，由于水分子在阳离子位点上的不均匀分布，这种现象是可能的，这允许形成水簇。这些结果很重要，因为它们有助于理解水对阳离子位点的覆盖将如何影响 Na-LTA 沸石内部其他分子的吸附。
