How Water Binds to Microcline Feldspar (001)

Area of Science:

• Geochemistry and Materials Science
• Surface Science
• Mineral Physics

Background:

• Microcline feldspar (KAlSi3O8) is crucial for Earth's ecological balance, influencing carbon, potassium, and water cycles.
• Understanding microcline's surface interactions with water is key to comprehending CO2 sequestration, soil formation, and ice nucleation.

Purpose of the Study:

• To elucidate the atomic structure of microcline's lowest-energy surface.
• To investigate the interaction between the microcline surface and water molecules at the atomic scale.

Main Methods:

• Utilized ultrahigh vacuum (UHV) investigations including noncontact atomic force microscopy (NC-AFM) and X-ray photoelectron spectroscopy (XPS).
• Performed density functional theory (DFT) calculations to complement experimental findings.

Main Results:

• An ordered array of hydroxyls (–OH groups) bonded to silicon (Si) or aluminum (Al) forms on the cleaved microcline surface at room temperature.
• The differing proton affinities of Si-OH and Al-OH groups dictate the adsorption and orientation of initial water molecules.

Conclusions:

• The atomic-level surface structure and hydroxyl group characteristics of microcline significantly influence water adsorption.
• These findings provide fundamental insights into water condensation processes on mineral surfaces, relevant to geochemical cycles.