Researchers at the UAE-based Masdar Institute, part of the Khalifa University of Science and Technology, have announced significant progress in their research in the field of optimized graphene-based membranes, which aim to make water filtration and desalination more efficient and sustainable.
The team worked to develop membranes made of layered reduced graphene-oxide sheets that are able to block the passage of salt ions in a membrane-based seawater desalination process. The spacing between the sheets is what ultimately affects the membrane’s efficacy, or its ability to filter impurities like salt ions while still permitting water molecules to pass through. The spaces between sheets must be just right – if they are too large and salt ions are not filtered out, and if they too small and even water molecules are unable to penetrate the membrane.
The ability to fine-tune the spacing size between layers is one of the most difficult challenges to developing efficient layered graphene membranes. Previous studies revealed that the optimal space between graphene sheets could be between 0.6nm and 0.7nm. Given this very narrow size range, a slight variation significantly affects the functionality of the membrane. The Masdar team believes that this research provides a needed tool which will help scientists better fine-tune the size of inter-layer spacing.
The researchers used atomic force microscopy (AFM) to probe the edges of each graphene sheet to obtain measurements of the exact height of the spaces between each sheet. They then combined these AFM measurements with statistical analysis to reveal the relationship between the amount of the chemical used to make layered reduced graphene oxide membranes, known as a reducing agent, and the resulting size of the spacing between each graphene layer.
Dr. Zou, leader of this study, is also leading a collaborative research project with The University of Manchester that aims to incorporate graphene into membranes for electrically-driven membrane desalination strategies, such as electrodialysis and capacitive deionization.