Controlling water clusters under confinement in a graphene oxide matrix

Abstract

Porous materials hold water in two forms: surface-bound water and clustered water. The pore size and wall chemistry are important in determining the water clustering. Graphene oxide (GO) is unique because its dynamic pores, in the form of sub-nanometer interlayer spaces, can expand upon water intercalation. In this work, we investigate the water-cluster formation using temperature-dependent water sorption isotherms complemented with chemical analysis. We have demonstrated that the size of water clusters is largely independent of the oxidative state of the wall surfaces, for C: O ratio $\approx 2.5-5.1$. However, crosslinking the GO sheets with an amine binder severely quenches the water clustering even though the primary sites are well populated. The critical cluster size around an adsorbed water molecule diminishes from $\approx 1.6$ to 0.1 for the crosslinked system. We attribute this effect to a restricted expansion of the spacing between the graphene oxide sheets and a dense network of linkages in the space between the sheets.