Visualising the molecular alteration of the calcite (104) – water interface by sodium nitrate

Abstract

The reactivity of calcite, one of the most abundant minerals in the earth’s crust, is determined by the molecular details of its interface with the contacting solution. Recently, it has been found that trace concentrations of NaNO3 severely affect calcite’s (104) surface and its reactivity. Here we combine molecular dynamics (MD) simulations, X-ray reflectivity (XR) and in situ atomic force microscopy (AFM) to probe the calcite (104) – water interface in the presence of NaNO3. Simulations reveal density profiles of different ions near calcite’s surface, with NO3− able to reach closer to the surface than CO32− and in higher concentrations. Reflectivity measurements show a structural destabilisation of the (104) surfaces’ topmost atomic layers in NaNO3 bearing solution, with distorted rotation angles of the carbonate groups and substantial displacement of the lattice ions. Nanoscale AFM results confirm the alteration of crystallographic characteristics, and the ability of dissolved NaNO3 to modify the structure of interfacial water was observed by AFM force spectroscopy. Our experiments and simulations consistently evidence a dramatic deterioration of the crystals’ surface, with potentially important implications for geological and industrial processes.

Can Point Defects in Surfaces in Solution be Atomically Resolved by Atomic Force Microscopy?

“…Thanks to recent advances in AFM technology, it is now possible to obtain images or movies containing isolated imperfections in a periodic structure [16,17]. However, these experimental studies have not been able to interpret what they have observed, due to the lack of knowledge regarding the imaging mechanism.…”

In Situ Atomic Force Microscopy Studies on Nucleation and Self-Assembly of Biogenic and Bio-Inspired Materials

“…For example, Voitchovsky and Schmidt et al investigated calcite (104)-water interface in the presence of NaNO 3 [175]. In situ AFM images confirmed the alteration of crystallographic characteristics, and AFM force spectroscopy indicated the ability of dissolved NaNO 3 to modify the structure of interfacial water.…”

Self-assembly of small molecules at hydrophobic interfaces using group effect

“…High-resolution amplitude modulation atomic force microscopy (AFM) in liquid 23 is used to explore in situ the sub-nanometre details of the resulting interfacial molecular assemblies. When operated in solution and at small amplitude, the technique can routinely provide molecular-level details of the interface, 24,25 including of solvation structures 26,27 and stable supramolecular assemblies. 21 The AFM results include simultaneously acquired topographic and phase images of the interface.…”