Hydration of bilayered graphene oxide

Area of Science:

• Materials Science
• Nanotechnology
• Physical Chemistry

Background:

• Graphene oxide (GO) membranes exhibit remarkable selectivity for water permeation and humidity-dependent gas separation.
• Understanding the hydration behavior of GO is essential for optimizing its performance in these applications.

Purpose of the Study:

• To investigate the hydration mechanism of single graphene oxide (GO) layers as a function of relative humidity (RH).
• To determine the interlayer distance changes in GO upon hydration and differentiate between monolayer water insertion and gradual layer thickening.

Main Methods:

• Utilized scanning force microscopy (SFM) to measure the step height of single GO layers on bilayer GO substrates.
• Quantified the change in interlayer distance with increasing relative humidity from 2% to approximately 80% and upon immersion in liquid water.

Main Results:

• The interlayer distance of single GO layers gradually increased by approximately 1 Å with increasing RH up to 80%.
• Immersion in liquid water further expanded the interlayer distance by an additional 3 Å.
• Hydration up to 80% RH involves continuous incorporation of water molecules into GO layers, while liquid water insertion occurs as monolayers.

Conclusions:

• The hydration of GO is a continuous process of water molecule incorporation into individual GO layers, not solely interstratification.
• GO bilayers and few-layer GO membranes are suitable for selective water transport, similar to multilayered materials.
• The findings provide direct evidence for the mechanism of water interaction with GO at the single-layer level.