Speaker: Prof Slaven Garaj
Abstract Details: The curious behavior of water and ions in constrictions with dimensions comparable to the size of ions is of particular interest for many applications, including filtration membranes, single-biomolecule analysis, supercapacitors, etc. The nanofluidic behavior of such structures depends on their dimensionality: ranging from the edge-enhanced ionic current in 0D graphene nanopores [1,2], anomalous ionic flow in 1D nanotubes, to frictionless water transport in 2D graphene  and graphene-oxide nanochannels [4, 5]. Â We set to investigate ionic flow in graphene-based nanostructures, including scalable GO membranes, and model systems consisting of individual graphene channels only about 1 nm in height. By measuring mobility of a wide selection of aqueous salts ions in channels of GO membranes , we demonstrated that the dominant mechanisms for the ion rejection are (a) size exclusion due to compression of the ionic hydration shell in narrow channels; and (b) electrostatic repulsion due to the membrane surface charge. Â Armed with the insight into the physical mechanism governing the ionic flow, we are able to engineer new membranes with decreased the ionic cut-off size and increased charge selectivity. At the end, I will present some new results leading to promising applications in desalination and electrodialysis.
 Garaj, S. et al. Graphene as a subnanometre trans-electrode membrane. Nature 467, 190 (2010).
 Garaj, S. et al. Molecule-hugging graphene nanopores. Proc Natl Acad Sci USA 110, 12192 (2013).
 Radha, B. et al. Molecular transport through capillaries made with atomic-scale precision. Nature 538, 222 (2016).
 Nair, R. R. et al. Unimpeded Permeation of Water Through Helium-Leakâ€“Tight Graphene-Based Membranes. Science 335, 442 (2012).
 Hong, S. et al. Scalable Graphene-Based Membranes for Ionic Sieving with Ultrahigh Charge Selectivity. Nano Lett. 17, 728 (2017).
About the Speaker: Slaven Garaj is Assistant Professor at the Departments of Physics and of Biomedical Engineering at the National University of Singapore, as well as a member of the NUS Centre for Advanced 2D Materials and NUSNNI-Nano Core. He is also a Singapore NRF Fellow (2012).
Slaven explores nanoscale phenomena emerging at the interface of solid-state devices and soft-matter systems. He is interested in behaviour of water molecules and ions in atomic-scale confinements; control and analysis of individual biomolecules using physical methods; and electrical and structural properties of 2D materials. The research is often guided by the desire to address a real technological challenges and includes: ultra-fast, inexpensive DNA sequencing using physical methods; nanopore devices for detection, fingerprinting and sequencing of individual proteins; electrical sensors based on 2D materials; 2D materials as next-generation membranes for filtration and water desalination.
Slaven received his PhD from Swiss Federal institute of Technology Lausanne (EPFL), Switzerland, in the field of solid-state physics. He continued his research career at Harvard University, working at the intersection of nano-electronics and biophysics, particularly by developing novel methods for electrical (4th generation) DNA sequencing based on nanopores. Throughout his career, his different research projects attracted general public attention and were featured in international media and professional magazines (such as BBC News, New Scientist, Technology Review, MRS Bulletin, etc).