Abstract The modification of natural zeolites via ion exchange is an efficient technique used to improve their performances and tune their properties for specific applications. In this study, a natural levyne-Ca intergrown with erionite was fully exchanged by Ag+ and its structure [with idealized chemical composition Ag6(Si,Al)18O36·18H2O] was investigated by combining a theoretical and experimental approach. Single-crystal X-ray difraction data demonstrated that Ag-levyne maintained the R3m space group, characteristic of the natural levyne. Ag ions distribute over partially occupied sites along the threefold axis and, differently from the pristine material, at the wall of the 8-membered ring window of the lev cavity. The lack of ~30% of Ag ions that could not be located by the structural refinement is ascribed to the strong disorder of the extraframework occupants. The structural results obtained by Molecular Dynamics simulations are in overall agreement with the experimental data and showed that, on average, Ag+ is surrounded by ~2 H2O and 1 framework oxygen at distances between 2.43 and 2.6 Å. Molecular Dynamics trajectories indicate that the occurrence of silver inside the D6R cage depends on the water content: silver occupancy of D6R cages is estimated to be 83, 30, and 0% when the structure contains 3, 2.5, and 2 H2O per Ag ion, respectively. The cation-exchange process, as demonstrated by scanning electron microscopy and energy-dispersive spectroscopy (SEM-EDS) spectrometry, affects the intergrown erionite as well. A structural characterization of the Ag-erionite phase (with dimension <100 μm) was possible by means of a CuKα micro-focus source: structure solution pointed to P63/mmc space group, indicating no change with respect to natural erionite. In agreement with previous studies, K ions in the cancrinite cage could not be exchanged, whereas Ag+ is found in the eri cavity.

中文翻译：

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Ag 交换的 levyne 与毛沸石共生的晶体结构：单晶 X 射线衍射和分子动力学模拟

摘要 通过离子交换对天然沸石进行改性是一种有效的技术，可用于改善其性能并针对特定应用调整其性质。在这项研究中，与毛沸石共生的天然 levyne-Ca 被 Ag+ 完全交换，并通过理论和实验相结合的方法研究了其结构 [具有理想的化学成分 Ag6(Si,Al)18O36·18H2O]。单晶 X 射线衍射数据表明 Ag-levyne 保持了 R3m 空间群，这是天然 levyne 的特征。Ag 离子沿三重轴分布在部分占据的位置上，并且与原始材料不同，分布在 lev 腔的 8 元环窗口的壁上。通过结构改进无法定位的约 30% 的银离子的缺乏归因于框架外居住者的强烈无序。分子动力学模拟获得的结构结果与实验数据总体一致，表明平均而言，Ag+ 被 ~2 H2O 和 1 骨架氧包围，距离在 2.43 和 2.6 Å 之间。分子动力学轨迹表明，D6R 笼内银的出现取决于水含量：当结构中每个 Ag 离子包含 3、2.5 和 2 个 H2O 时，D6R 笼的银占有率估计为 83、30 和 0%，分别。如扫描电子显微镜和能量色散光谱 (SEM-EDS) 光谱所证明的，阳离子交换过程也会影响共生毛沸石。Ag-毛沸石相（尺寸 <100 μm）的结构表征可以通过 CuKα 微焦点源进行：结构解指向 P63/mmc 空间群，表明相对于天然毛沸石没有变化。与先前的研究一致，钙燧石笼中的 K 离子不能交换，而 Ag+ 则在 eri 腔中发现。