Water-silica gel interactions, X-ray diffraction study at room and low temperature

Area of Science:

• Materials Science
• Physical Chemistry
• Condensed Matter Physics

Background:

• Water exhibits unique properties when confined in porous materials.
• Understanding confined water structure is crucial for applications in catalysis, separation, and energy storage.
• Silica gel is a common nanoporous material used for water confinement studies.

Purpose of the Study:

• To investigate the structural modifications of water confined in silica gel.
• To analyze the influence of temperature on confined water structure.
• To elucidate the interplay between confinement effects and water-silica interactions.

Main Methods:

• X-ray diffraction experiments were conducted on silica gel powder hydrated at approximately 20%.
• Experiments were performed at room temperature and cooled down to 77 K.
• Analysis focused on structural changes, particularly at the second nearest neighbor distances.

Main Results:

• Significant structural modifications of confined water were observed.
• These changes were evident in the arrangement of water molecules, specifically at the second neighbor level.
• The observed structural alterations are temperature-dependent.

Conclusions:

• The structural modification of confined water is driven by a competition between the physical confinement within the silica gel pores and the chemical interactions between water and the silica surface.
• Temperature plays a critical role in modulating this competition and influencing the water structure.
• These findings provide insights into the fundamental behavior of water under nanoscale confinement.