Increased demand for highly selective and energy-efficient separations processes has stimulated substantial interest in emerging two-dimensional (2D) nanomaterials as a potential platform for next-generation membranes. However, persistently poor separation performance continues to hinder the viability of many novel 2D-nanosheet membranes in desalination applications. In this study, we examine the role of the lamellar structure of 2D membranes on their performance. Using self-fabricated molybdenum disulfide (MoS₂) membranes as a platform, we show that the separation layer of 2D nanosheet frameworks not only fails to demonstrate water-salt selectivity but also exhibits low rejection toward dye molecules. Moreover, the MoS₂ membranes possess a molecular weight cutoff comparable to its underlying porous support, implying negligible selectivity of the MoS₂ layer. By tuning the nanochannel size through intercalation with amphiphilic molecules and analyzing mass transport in the lamellar structure using Monte Carlo simulations, we reveal that small imperfections in the stacking of MoS₂ nanosheets result in the formation of catastrophic microporous defects. These defects lead to a precipitous reduction in the selectivity of the lamellar structure by negating the interlayer sieving mechanism that prevents the passage of large penetrants. Notably, the imperfect stacking of nanosheets in the MoS₂ membrane was further verified using 2D X-ray diffraction measurements. We conclude that developing a well-controlled fabrication process, in which the lamellar structure can be carefully tuned, is critical to achieving defect-free and highly selective 2D desalination membranes.

中文翻译：

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层状二维二硫化钼（MoS2）膜的选择性和分离性能与纳米片堆叠行为的关系。

对高度选择性和高能效分离工艺的需求不断增长，激发了人们对新兴的二维（2D）纳米材料作为下一代膜的潜在平台的浓厚兴趣。然而，持续不良的分离性能继续阻碍许多新型2D纳米片在脱盐应用中的可行性。在这项研究中，我们检查了二维膜的层状结构对其性能的作用。使用自制的二硫化钼（MoS ₂）膜作为平台，我们表明2D纳米片框架的分离层不仅不能表现出水盐选择性，而且对染料分子的排斥性低。此外，MoS ₂膜具有与其下层多孔载体相当的分子量截留值，这意味着MoS ₂层的选择性可忽略不计。通过插入两亲性分子来调节纳米通道的尺寸并使用蒙特卡洛模拟分析层状结构中的质量传递，我们揭示出MoS ₂纳米片堆叠中的小缺陷会导致灾难性的微孔缺陷的形成。这些缺陷通过否定防止大渗透剂通过的层间筛分机制，导致层状结构的选择性急剧下降。值得注意的是，MoS ₂中纳米片的堆叠不完全使用2D X射线衍射测量进一步验证膜。我们得出的结论是，开发一种可控的制造工艺（其中可以仔细调整层状结构）对于实现无缺陷且高度选择性的2D脱盐膜至关重要。