Periodic Reporting for period 1 - n-AQUA (Nanoscale water: A Quantum Understanding of Angstrom-scale transport)
Reporting period: 2023-04-01 to 2024-09-30
Many of the challenges facing mankind revolve around water. These challenges range from a straightforward lack of clean water to finding more efficient ways to generate hydrogen from water. Current water-related technologies are highly inefficient. They require large amounts of energy, and technology improvement is often incremental and typically occurs through trial and error. The reasons for those technological limitations lie in our limited understanding of water. To improve water-related technologies, we need to understand this crucial liquid in particular at the nanoscale. Nanoscale effects are critical: Water purification and desalination processes rely on membranes with nanopores where only water molecules fit through; water splitting into hydrogen and oxygen is inherently a molecular-level, nanometer process. At the nanoscale, classical descriptions of water as a simple liquid with a certain density and viscosity break down: water behaves in completely unexpected ways, flowing differently, for instance. Such discoveries hold great technological promise: can we use the properties of nanoscale water to improve water purification/desalination and hydrogen production? This pressing fundamental water question can only be addressed using an interdisciplinary scientific approach: there is no single discipline that can provide an answer. N-aqua aims to combine different experimental and theoretical approaches from world-leading experts to force breakthroughs in this crucial field. The proposed research has the potential to enable world-changing novel technologies in the water-energy nexus.
We have made significant progress in determining both the structure of water under Nanoconfinement, and have elucidated friction mechanisms for water flowing under confinement. Specifically, we have determined where the transition occurs from water "feeling" two interfaces to water being truly confined. Our new experiments amount to the first quantitative experimental test of surface effects versus confinement effects. We find that confinement does not set in until sub-nanometer confinement is reached. For water containing salt, we have established that the interface is depleted from ions: at the surface, there is a few-molecules thin layer that contains pure water, and it is not until deeper into the solution that ions appear.
The impact of the finding that true confinement does not set in until sub- nanometer length scales implies that the properties of nanoconfined water can be finely tuned by tuning the interaction of water with the confining material. This means that the properties of water desalination and purification membranes, that typically have porous in the nanometer range can be fully tuned by the chemistry of the surfaces. The ion depletion at the surface of water can possibly be used for desalination purposes, since those first few water layers are pure water.