Unimpeded permeation of water through helium-leak-tight graphene-based membranes

TL;DR

This study demonstrates that graphene oxide membranes are completely impermeable to gases and vapors but allow water to permeate at extremely high rates due to low-friction flow through nanoscale capillaries, with other molecules blocked by capillary narrowing or clogging.

Contribution

It reveals a unique selective permeability of graphene oxide membranes, enabling unimpeded water flow while blocking other molecules, due to nanoscale capillary behavior.

Findings

Water permeates at least 10^10 times faster than helium.

Membranes are impermeable to gases, vapors, and most molecules.

Permeability is due to low-friction flow in nanoscale capillaries.

Abstract

Permeation through nanometer pores is important in the design of materials for filtration and separation techniques and because of unusual fundamental behavior arising at the molecular scale. We found that submicron-thick membranes made from graphene oxide can be completely impermeable to liquids, vapors and gases, including helium, but allow unimpeded permeation of water (H2O permeates through the membranes at least 10^10 times faster than He). We attribute these seemingly incompatible observations to a low-friction flow of a monolayer of water through two dimensional capillaries formed by closely spaced graphene sheets. Diffusion of other molecules is blocked by reversible narrowing of the capillaries in low humidity and/or by their clogging with water.