Role of Pinhole Defects in Enhancing Water Transport through Graphene Oxide Laminates

Laminates made of graphene oxide nanosheets (GO) have emerged as promising materials for separation applications due to their high water permeance and salt rejection. However there is no clear consensus on the origin of ultrafast water transport through these laminates. Some studies have attributed this to the presence of a network of graphene capillaries in GO nanosheets. However, some other studies have attributed this to presence of pinhole defects in sheet interiors, which reduce the effective length that water needs to travel before progressing deeper into the laminate. To determine the primary pathway responsible for water permeance, we synthesized GO nanosheets with two orders of magnitude difference in lateral sizes and compared water permeance through laminates made by pressure-assisted deposition of these sheets. We found that water permeance through these laminates is identical despite such massive differences in lateral sizes of sheets. Furthermore we simulated water flow through these laminates using an interconnected nanochannel network model. Our simulations in tandem with the experimental data indicate that trans-sheet flow through pinhole defects in GO must be the dominant water transport pathway – as opposed to a circuitous, lateral pathway around the sheets.