Ultra-thin graphene-based membranes for hydrogen purification

Hydrogen is emerging as a versatile raw material and energy vector. However, current hydrogen production methods rely on fossil fuels, leading to greenhouse gas emissions and contributing to global warming. Carbon capture technologies are being explored as a potential solution to this issue. One approach for carbon capture and storage (CCS) is to use membranes, which are perm-selective barriers that, in this specific case, can allow for the separation of hydrogen from carbon dioxide. Polymeric membranes, in particular, are becoming increasingly important thanks to their great versatility and processability. However, there is a limitation in separation performance known as the Robeson upper bound, which means that as permeability increases, selectivity decreases. Mixed matrix membranes (MMM) have been introduced to integrate polymeric materials with organic or inorganic fillers that have excellent separation properties. Low dimensional materials, such as graphene and its derivatives, have emerged as promising fillers due to their high permeability and selectivity. Two types of graphene-based membranes are possible: nanoporous graphene and multilayered graphene-based membranes. This thesis work is focused on graphene oxide (GO) multilayered membranes. Polyimides, specifically Matrimid, are used as polymeric support onto which GO multilayered coating is deposited by means of dipping Layer by Layer (LbL) technique. By carrying out permeation tests, effect of temperature, GO concentration, thermal reduction, number of bilayers and deposition of the coating on one side only have been investigated. Furthermore, since several factors have an influence on the LbL assembly, a standardization procedure has been started in order to improve reproducibility and scalability of the process. Overall, GO nanocomposite membranes result to be highly effective in gas separations and offer many insight and potential to be exploited in the production of competitive systems.