Adsorption, Diffusion and Structure Formation of Water on Calcite: Fundamental Processes in Wetting of an Omnipresent Mineral Surface
Final Report Abstract
Calcite, the most stable modification of calcium carbonate, constitutes the most abundant carbonate in the Earth’s crust. As such, it is at the heart of a multitude of processes, e.g., within the carbonate equilibrium. Consequently, calcite is involved in buffering the oceans’ pH value and central for future strategies for carbon storage. Likewise, calcite is relevant in technological applications, e.g., within water desalination and incrustation inhibition. These examples have in common that the calcite surface is in contact with water. Thus, the properties of the mineral and its interaction with the environment cannot be described properly without recognizing the role of adsorbed water. The main goal of the project was to elucidate fundamental steps in the interaction of water with calcite, including adsorption, diffusion and structure formation of water on calcite under ultrahigh vacuum (UHV) conditions. Perhaps the most important finding of the project is the verification of a (2x1) surface reconstruction of calcite (10.4) and the demonstration of its impact on the adsorption and desorption of water onto / from calcite. Our atomic force microscopy (AFM) results show that exclusively one of the two adsorption sites present on the surface is occupied at low coverages. Only if more than half a monolayer is deposited, the second adsorption site is adopted. Density functional theory (DFT) calculations suggest that dosing more than 0.5 monolayer is associated with lifting of the reconstruction. Our temperature-programmed desorption (TPD) experiments reveal a characteristic peak shape that further corroborates this picture. The TPD data can be fitted with a two-site model and exchange between the two sites with energies that agree excellently with the energies obtained from the DFT calculations. The insights gained for the UHV situation studied in this project now serve as a benchmark for future investigations carried out at the solid-liquid interface. To this end, we will study the interface of calcite with bulk water using three-dimensional AFM. For the calibration, drift-correction and further analysis of these data, a fast and reliable software is needed. An open-source software was developed within this project, which is now publicly available for the analysis of scanning probe microscopy data.
Publications
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Crucial impact of exchange between layers on temperature programmed desorption. Physical Chemistry Chemical Physics, 23(34), 18314-18321.
Dickbreder, Tobias; Bechstein, Ralf & Kühnle, Angelika
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Water on Calcite (10.4) and K-Feldspar (001) – Adsorption Structure and Desorption Kinetics – Dissertation Universität Bielefeld
Tobias Dickbreder
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How water desorbs from calcite. Physical Chemistry Chemical Physics, 25(18), 12694-12701.
Dickbreder, Tobias; Lautner, Dirk; Köhler, Antonia; Klausfering, Lea; Bechstein, Ralf & Kühnle, Angelika
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unDrift: A versatile software for fast offline SPM image drift correction. Beilstein Journal of Nanotechnology, 14, 1225-1237.
Dickbreder, Tobias; Sabath, Franziska; Höltkemeier, Lukas; Bechstein, Ralf & Kühnle, Angelika
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Water adsorption lifts the (2 × 1) reconstruction of calcite(104). Physical Chemistry Chemical Physics, 26(32), 21365-21369.
Heggemann, Jonas; Aeschlimann, Simon; Dickbreder, Tobias; Ranawat, Yashasvi S.; Bechstein, Ralf; Kühnle, Angelika; Foster, Adam S. & Rahe, Philipp
