Ion Transport through Atomically Thin Cap74illaries

我建议研究离子通过主要尺寸为几埃的毛细管传输时的尺寸效应。离子筛分在许多自然系统(亚纳米离子通道在细胞膜中发挥重要作用)和许多技术中都是极其重要的，包括海水淡化、化学分离、透析、生物分析等。到目前为止，创建这种大小的人工通道、根据需要调整它们的性质并研究它们的功能还只是一个遥远的目标。传统上，分子筛和多孔聚合物膜用于离子和分子筛分，但大尺寸分布和对智能膜的追求推动了这一领域的研究。尽管在过去几十年里取得了所有进步，包括使用纳米管和先进的纳米光刻技术，但这一目标甚至无法实现，因为设备尺寸在有限的几何尺寸和有限的材料数量上很少达到真正的纳米级。这是一项艰巨的挑战，但也是从事这一迷人研究领域的核心原因，我想通过使用2D原子晶体来应对这一挑战。2D原子晶体非常吸引人，通过范德华异质结构组装，通过选定的材料调整其特性，提供了一条制造“按设计的器件”的途径。如果从大块晶体中移除单个原子平面，留下选定高度的平坦空隙，那么这个微小的空隙在操纵流体、液体、气体、粒子和离子方面可以提供如此多的东西。这不仅是纳米流体领域的突破性技术进步，而且重要的是，拟议的毛细管为研究最终受限空间中的离子传输的基本科学现象提供了一个平台。这一提议的主要目的是(1)深入研究通过这些毛细管的本征离子传输，包括空间效应的作用，离子进出效应，特别是当离子的大小与毛细管大小相当时，‘量子’限制对毛细管内离子周围水化壳层的影响等。这种深入分析之所以可能，是因为所提议的毛细管在原子上是干净的，涉及的表面电荷很少，不像以前研究的由后者主导的实验系统(例如纳米管)。(2)从离子通过这些狭缝传输的基本原理中获得洞察，将构建智能毛细管，其中离子可以通过垂直电场进行操纵。该项目将由曼彻斯特大学凝聚态物理组、石墨烯/2D材料研究的先驱物理学院和国家石墨烯研究所执行。在密歇根大学，石墨烯小组遍布物理、化学、计算机科学、材料和生命科学学院的许多学院，拓宽了智能毛细管可能的目标应用范围，使该项目真正成为跨学科的。我们的埃级毛细管制造方法为设计和复杂的工程提供了极大的灵活性、重复性和可能性，如方案中所述。特别是，我们的制造工艺为已经激动人心的纳米流体的大领域提供了一个新的方向，但并不局限于一个领域。通过解决一个核心问题，即了解固有的离子传输，以及克服利用奥级受限空间进行尺寸选择性离子分离的主要障碍，我的研究将影响包括海水淡化在内的广泛领域和技术，为未来具有深远社会和经济意义的应用铺平道路。

I propose to study the size effect in ion transport through capillaries with principal dimensions of few angstroms (Å). Ion sieving is of extreme importance in many natural systems (sub-nm ion channels perform important functions in cellular membranes) and in many technologies including desalination, chemical separation, dialysis, bio-analytics, etc. It has so far been only a distant goal to create artificial channels of this size, tune their properties as required and investigate their functioning. Traditionally, zeolites and porous polymer membranes are used for ionic and molecular sieving but the large size distribution and quest for smart membranes has driven the research in this area. Despite all the progress during the last decades, including the use of nanotubes and advanced nanolithography techniques, this goal could not be even approached, with device dimensions rarely reaching the true nanoscale in a limited number of geometries and with a limited number of materials. This is a formidable challenge, but also a central reason to engage in this fascinating area of research and I want to address this challenge by the use of 2D-atomic crystals. 2D-atomic crystals are highly fascinating and offer a route to the fabrication of "devices-by-design" through van der Waals heterostructure assembly with their properties tuned via chosen materials. If individual atomic planes were removed from a bulk crystal leaving behind flat voids of a chosen height; the tiny empty space has so much to offer in terms of manipulation of fluids, liquids, gases, particles and ions.Not only is this a groundbreaking technological advancement of the field of nanofluidics but also importantly the proposed capillaries offer a platform for studying fundamental scientific phenomenon of ionic transport in ultimately confined spaces. The key aims of this proposal are (1) investigation of in-depth intrinsic ion transport through these capillaries, including the role of steric effects, ion entry-exit effects especially when the size of ion is comparable to the capillary size, effect of 'quantum' confinement on the hydration shells surrounding the ions inside capillaries, etc. Such in-depth analysis is possible only because the proposed capillaries are atomically clean and involve little surface charge, unlike the previously studied experimental systems (e.g., nanotubes) dominated by the latter. (2) Gaining insights from the fundamentals of ion transport through these slits, smart capillaries will be constructed where the ions can be manipulated by a perpendicular electric field. The project will be executed at the University of Manchester (UoM) in condensed matter physics group, school of physics which has pioneered graphene/2D-materials research and National Graphene Institute. At the UoM, the graphene group is spread across many schools in the faculty of physics, chemistry, computer science, materials and life sciences, widening the scope of the possible target applications of the smart capillaries and making the project truly interdisciplinary. Our fabrication approach of angstrom-scale capillaries offers a great flexibility, reproducibility and possibility for design and sophisticated engineering, as described in the proposal. In particular, our fabrication procedures provide a new direction for the already exciting large field of nanofluidics but are not limited to only one area. By tackling a core issue i.e., understanding the intrinsic ion transport, alongside overcoming the primary obstacle to exploiting Å-scale confined spaces for size-selective ion separation, my research will impact across a broad range of fields and technologies including desalination, paving the way to future applications of far-reaching social and economic importance.