Ultrathin, rigid graphene oxide-based membranes for molecular separation

Abstract

Separation consumes a huge amount of energy which increases the production cost and causes a large carbon footprint. Membranes have attracted great attention for mixture separation and are a promising candidate for replacing some energy-intensive thermal separation processes in the industry. Currently, polymeric membranes are dominant membranes and are available commercially. However, a trade-off between the selectivity and the permeance/permeability of the polymeric membranes always exists. Other issues with polymeric membranes, which greatly hinders their applications, are thermal and mechanical stability and the stability in harsh chemical environments, such as in organic solvents. To overcome these challenges, it is highly desirable to develop ultrathin, stable, and rigid membranes with molecular-sized pores to overcome these adversities. My research is focused on the rational design of ultrathin membranes using two-dimensional material – Graphene Oxide (GO) as a building block. This choice of building block provides an opportunity to make ultrathin membranes, which helps to overcome the upper-bound of the selectivity/permeance tradeoff. Previous studies in our lab demonstrated the growth of dense hybrid coatings via Molecular Layer Deposition (MLD) occurring on hydroxyl rich substrates. GO with a high propensity of hydroxyl groups at the edges and the structural defects have been strategically used along with the MLD technique. MLD on lamellar stacking of GO has shown to seal the gaps between adjacent flakes in a way so that we can stitch them into a continuous layer that acts as an ultrathin membrane. The propensity of hydroxyl groups along the intrinsic in-plane pores/structural defects of GO provides a possibility of tuning the pore size of these membranes with altering MLD cycles. These stable stitched GO membranes utilize MLD modified in-plane pores of the GO flakes to separate hydrocarbon molecules with size differences as small as 2.5 Å. Because of the appropriate pore size, these membranes may be a promising candidate for its use in the petroleum industry for the separation of smaller, straight-chain hydrocarbons with lower octane numbers from branched hydrocarbons and aromatics from the exiting stream of the catalytic reformer to boost octane number and increase the efficiency of the reformer.