Ion Transport through Atomically Thin Cap74illaries

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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.