Decoding ultrafast water transport in graphene oxide.

Area of Science:

• Materials Science
• Nanotechnology
• Physical Chemistry

Background:

• Graphene oxide (GO) membranes exhibit rapid water transport, but the underlying mechanisms remain debated.
• Understanding water diffusion is crucial for applications in separation and filtration.

Purpose of the Study:

• To comprehensively investigate water transport mechanisms in GO membranes.
• To elucidate the role of nano-confinement, surface interactions, and membrane geometry on water diffusion.

Main Methods:

• Sorption and permeation experiments across a full relative humidity (RH) range.
• Varied membrane thicknesses and flake sizes to probe diffusion pathways.
• Thermodynamic correction to Fickian diffusion coefficients to determine Maxwell-Stefan diffusion coefficients (DMS).

Main Results:

• In-plane water diffusion is significantly faster than out-of-plane diffusion (D2D/Dout ~ 10^2), attributed to pinholes on GO basal planes.
• Maxwell-Stefan diffusion coefficient (DMS) increases with interlayer spacing, indicating reduced wall friction.
• DMS is lower than bulk water self-diffusion, characteristic of hydrophilic nanoporous systems.

Conclusions:

• High water permeation rates in GO membranes result from substantial sorption capacity, despite modest molecular mobility (DMS).
• Pinholes on GO flakes play a critical role in facilitating rapid in-plane water transport.
• Findings reconcile the observed high flux with fundamental transport parameters in confined systems.