Impact of dissolved ions on hydration layers at the solid-liquid interface of carbonates

界面水在地球化学、环境科学、防腐和催化等广泛领域发挥着关键作用。对表面组成和局部水结构的详细了解对于理解和预测界面化学过程是决定性的。虽然已经很好地确定，例如，从表面比谱研究中可以看出，界面处的局部水化结构通常不同于整体结构，但其详细排列仍然是一个深入研究的课题。直到最近，原子力显微镜（AFM）仪器才得到了进一步的发展，可以提供直接空间中固液界面局部有序的三维（3D）分子水平信息。这种技术现在提供了直接映射界面水化层的独特能力。在这个项目中，我们将使用最先进的3D水化层映射AFM来研究四个不同表面上的水化层。重点将放在三种不同的碳酸盐表面，即方解石、白云石和菱镁矿最稳定的解理面。除了与自然和技术过程高度相关外，这些表面还为系统研究改变单位细胞晶格尺寸对水化层结构的影响提供了理想的系统。作为第四种底物，化学和结构不同的氟化钙将作为一个突出的系统进行研究，可以与现有的非线性振动光谱研究相对照。人们普遍认为，溶解离子的存在可以改变水化层结构，然而，这种扰动的细节在很大程度上仍然是未知的。在本项目中，我们将阐明溶解离子对固液界面水化层结构的影响。我们将研究离子浓度（离子强度）和化学性质（单价和二价离子，不同的离子半径和极性）对界面水化层结构的影响。该项目将提供详细的、分子尺度的界面组成知识，包括固体表面、水合层和附加离子。这些实验见解，结合分子动力学模拟，将构成理解和预测基本界面过程的重要一步。

Interfacial water plays a key role in a large range of fields, including geochemistry and environmental science as well as corrosion protection and catalysis. The detailed knowledge of the surface composition and the local water structure is decisive for understanding and predicting interfacial chemistry processes.While it is well established, e.g., from surface-specific spectroscopy studies that the local hydration structure at an interface is commonly different from the bulk structure, the detailed arrangement remains a topic of intense research. Only very recently, atomic force microscopy (AFM) instrumentation has been further advanced to provide three-dimensional (3D), molecular-level information of the local ordering at the solid-liquid interface in direct space. This technique now offers the unique capability for directly mapping the hydration layers at the interface.In this project, we will investigate the hydration layers on four different surfaces using a state-of-the-art 3D hydration layer mapping AFM. The focus will be on three different carbonate surfaces, namely the most stable cleavage planes of calcite, dolomite and magnesite. Besides being highly relevant for natural and technical processes, these surfaces provide an ideal system to systematically study the influence of changing the unit cell lattice dimensions on the hydration layer structure. As a fourth substrate, chemically and structurally different calcium fluoride will be studied as a prominent system that can be benchmarked against existing nonlinear vibrational spectroscopy studies.It is generally accepted that the presence of dissolved ions can alter the hydration layer structure, however, the details of this perturbation are still largely unknown. In this project, we will elucidate the impact of dissolved ions on the hydration layer structure at the solid-liquid interface. We will investigate the influence of both concentration (ionic strength) and chemical nature (mono- and bivalent ions, different ionic radii and polarizabilities) of ions on the structure of the hydration layers at the interface.This project will provide detailed, molecular-scale knowledge of the composition of the interface, including the solid surface, hydration layers and additional ions. These experimental insights, combined with molecular dynamics simulations, will constitute an essential step forward for understanding and predicting fundamental interfacial processes.