Precise and Ultrafast Molecular Sieving Through Graphene Oxide Membranes

TLDR

Graphene-based materials possess well‑defined nanometer pores and low‑friction water flow, making them attractive for filtration and separation. The study investigates permeation through micrometer‑thick graphene oxide laminates prepared by vacuum filtration. The laminates are formed by vacuum filtration of graphene oxide suspensions, creating a network of nanocapillaries that open in water and selectively accept species that fit. In the dry state the laminates are vacuum‑tight, but in water they act as molecular sieves blocking solutes with hydrated radii >4.5 Å, while smaller ions permeate thousands of times faster than simple diffusion, attributed to a capillary‑like high pressure inside graphene capillaries.

Abstract

Graphene-based materials can have well-defined nanometer pores and can exhibit low frictional water flow inside them, making their properties of interest for filtration and separation. We investigate permeation through micrometer-thick laminates prepared by means of vacuum filtration of graphene oxide suspensions. The laminates are vacuum-tight in the dry state but, if immersed in water, act as molecular sieves, blocking all solutes with hydrated radii larger than 4.5 angstroms. Smaller ions permeate through the membranes at rates thousands of times faster than what is expected for simple diffusion. We believe that this behavior is caused by a network of nanocapillaries that open up in the hydrated state and accept only species that fit in. The anomalously fast permeation is attributed to a capillary-like high pressure acting on ions inside graphene capillaries.