Molecular Dynamics Simulations Reveal that Water Diffusion between Graphene Oxide Layers is Slow

Area of Science:

• Materials Science
• Physical Chemistry
• Nanotechnology

Background:

• Graphene oxide (GO) membranes offer potential for advanced water filtration and desalination.
• Controlling selective molecular transport through GO membranes is crucial for their application.
• Understanding water behavior within GO interlayers is essential for optimizing membrane performance.

Purpose of the Study:

• To investigate water intercalation and transport within stacked graphene oxide layers.
• To correlate molecular dynamics simulations with experimental findings on GO membrane hydration.
• To elucidate the mechanisms governing water diffusion in hydrated GO.

Main Methods:

• Molecular dynamics simulations of water in GO interlayers across various hydration levels (1-23.3 wt.%).
• Experimental synthesis and characterization of hydrated graphene oxide membranes.
• Analysis of interlayer spacing, mass changes, and water diffusion dynamics.

Main Results:

• Hydration increased GO interlayer spacing from 0.8 nm to 1.1 nm (simulated) and 0.7 nm to 0.8 nm (experimental).
• Water diffusion through GO layers is significantly slower (order of magnitude) than in bulk water due to hydrogen bonding.
• Water molecules predominantly bind to hydroxyl (OH) groups, forming clusters spanning different GO regions and holes.

Conclusions:

• Slow interlayer diffusion in GO membranes is attributed to strong hydrogen bonding and sorption effects.
• The presence of holes in GO membranes may create shorter transport paths than previously assumed.
• Sorption of water is a critical rate-limiting step for water transport in graphene oxide membranes.