Cs-137 is a radionuclide fission product that poses a significant risk to life, making it crucial to develop effective methods for its separation and sequestration from nuclear waste streams. Zeolitic structures have emerged as promising materials. This work examines the influence of structure, exchange site energetics, and formation enthalpies of nascent and cation-exchanged Faujasite-X, -Y, and -HY zeolites in terms of their Cs-exchange selectivity. Their interplay was quantified with the application of high-temperature calorimetry, adsorption isotherms, X-ray diffraction and density functional theory (DFT) calculations. Greater efficacy of Cs exchange was demonstrated for the Na-substituted Fau-Y (NaY) zeolite than that of the Fau-X (NaX) and Fau-HY (Na-HY) zeolites. This is explained by a higher amount of Na in un-exchangeable sites in the case of NaX and a lower stability in NaY that favors the ionic exchange with Cs. Moreover, Cs incorporation in the structure increases the stability of each kind of zeolite. Correspondingly, structure and DFT analyses demonstrated site-exchange thermodynamic favorability as well as the contribution from cage cell, which resulted in an energy landscape far more conducive to Cs incorporation for NaY than either NaX or Na-HY.

中文翻译：

---

FAU-沸石 Cs+ 交换的微观结构、吸附位点能量学和形成焓控制

Cs-137 是一种放射性核素裂变产物，对生命构成重大风险，因此开发有效的方法将其从核废料流中分离和封存至关重要。沸石结构已成为有前途的材料。这项工作研究了初生和阳离子交换八面沸石-X、-Y 和-HY 沸石的结构、交换位点能量和形成焓对其 Cs 交换选择性的影响。通过应用高温量热法、吸附等温线、X 射线衍射和密度泛函理论 (DFT) 计算，对它们的相互作用进行了量化。 Na 取代的 Fau-Y (NaY) 沸石比 Fau-X (NaX) 和 Fau-HY (Na-HY) 沸石具有更高的 Cs 交换效率。这是因为 NaX 的不可交换位点中的 Na 含量较高，而 NaY 的稳定性较低，有利于与 Cs 的离子交换。此外，结构中的Cs掺入增加了每种沸石的稳定性。相应地，结构和 DFT 分析证明了位点交换热力学的有利性以及笼形细胞的贡献，这导致能量景观比 NaX 或 Na-HY 更有利于 NaY 的 Cs 掺入。