Molecular Self-Assembly Versus Surface Restructuring During Calcite Dissolution.

Area of Science:

• Geochemistry
• Materials Science
• Physical Chemistry

Background:

• Organic additives influence mineral-water interfaces by self-assembly or surface restructuring.
• Calcium-complexing azo dyes are known to interact with mineral surfaces.

Purpose of the Study:

• Investigate the impact of azo dyes on calcite dissolution and surface morphology.
• Compare the effects of Eriochrome Black T and Eriochrome Black A on calcite (10.4).

Main Methods:

• High-resolution atomic force microscopy (AFM) in aqueous solution.
• Controlled experiments varying pH and dye isomers.

Main Results:

• Pronounced surface restructuring of calcite observed with both azo dye isomers, irrespective of pH.
• Restructuring involves stabilization of step edges, altering interface morphology.
• Ordered molecular stripe formation occurred only with Eriochrome Black A within a narrow pH window (~3.6).

Conclusions:

• Surface restructuring induced by azo dyes is robust against pH and molecular conformation changes.
• Ordered molecular self-assembly requires precise control over molecular properties like conformation and deprotonation state.
• Calcite surface morphology is significantly altered by calcium-complexing azo dyes.