Development of experimental methods to measure osmosis-driven water flux and molecular transport across nanoporous graphene membranes

Abstract

Graphene, an atomically thin planar lattice of sp2 bonded carbon atoms with high strength and impermeability, has drawn attention as a promising next generation high flux separation membrane. Molecular dynamics simulations predicted graphene's potential for exhibiting both high flux and selectivity as water desalination and gas separation membranes. Measurement of diffusive transport of water and molecules demonstrated the feasibility of harnessing graphene as a nanofiltration membrane with high selectivity. However, experimental investigation on convective flow of water and ions/molecules in liquid phase across nanopores in graphene has been confined due to difficulties in fabricating large area defect-free graphene membranes and complexity in experiment design considerations for convectively driven flow. In this thesis, I present experimental methodologies to measure water and molecular transport driven by osmotic pressure gradient across large area graphene membranes. Measured water flux and salt/organic molecules selectivity consistent with predictions from molecular dynamics simulations and continuum models. Combined with multi-scale graphene defect sealing process, this work shows that forward osmosis presents a facile and reliable platform for measuring transport of water and filtration of ions/molecules across nanopores introduced to centimeter scale single-layer graphene membrane.