(371f) Understanding Water Sorption and Transport in Graphene-Based Membranes from First-Principles Based Atomistic Modeling

Graphene-like materials (GLMs) have gained significant attention for many applications because of their interesting features. One of interesting feature of graphene sheets is their layered structure. The planar (2D) structure makes GLMs possible to form an ultra-thin laminated structure which is suitable for use as a separation membrane. Many researchers have attempted to apply ultra-thin graphene-based membranes to various separation processes including water purification and gas separation. However, graphene-based membranes have a large drawback since the interlayer space of graphene sheets is too small for even small molecules to pass. To overcome this problem, researchers have used graphene oxide (GO), the oxidized form of graphene, as hydroxyl groups on the basal plane may increase the interlayer space while also attracting polar molecules such as water. Finally, as water molecules can permeate into the GO membranes, they can be utilized for desalination and CO₂ separation. However, the permeability of GO membranes tends to be too low for their practical application. There has been a substantial experimental effort to improve their permeability, but only limited fundamental studies have been undertaken to understand the factors influencing the sorption and diffusion of gaseous species in GO-based membranes.

In this talk, we will present our recent findings from intensive molecular simulations regarding the molecular mechanisms of water sorption and transport in GO sheets with layered structures, especially the influences of relative humidity, OH group content and distribution, and GO geometry. We will focus on discussing (i) how the amount and dynamics of intercalated water varies under different conditions of humidity, temperature, and GO structure and (ii) the effects of intercalated water on the separation of a target gas from a mixture of gases. The improved understanding helps the design of more efficient GO-based membranes for gas separation.