Pyrite (001) Interface Chemistry is Controlled by a Sulfoxy Termination

Area of Science:

• Geochemistry
• Mineralogy
• Surface Science

Background:

• Pyrite (FeS2) is a prevalent sulfide mineral.
• The pyrite-water interface is critical for geochemical reactions and Earth cycles.
• Understanding pyrite surface structure is vital for geochemical modeling.

Purpose of the Study:

• To determine the atomic-scale structure of the pyrite (001)-water interface under low oxygen conditions.
• To identify surface species and their role in pyrite reactivity.

Main Methods:

• Crystal truncation rod (CTR) method.
• Ambient-pressure photoelectron spectroscopy (APPES).
• Density functional theory (DFT) calculations.

Main Results:

• Atomic structure of the pyrite (001)-water interface revealed.
• Dominant surface species identified as a sulfoxy group (S-O).
• Sulfoxy group readily protonates, influencing interfacial water and reaction energetics; iron sites remain unoxidized.

Conclusions:

• The identified sulfoxy group represents an initial step in pyrite oxidative dissolution.
• This interface structure may be stable in equilibrium with bulk pyrite under various reducing and acidic conditions.
• The findings are relevant to diverse experimental, industrial, and Earth environments.