SUMMARY

Unraveling the transport mechanisms of water and salt is critical for the fabrication of advanced membranes. The aims of this research proposal are focused on identifying and quantifying the modes of transport of water and salt in inorganic and organic-based membranes. I propose to accomplish this with the aid of advanced characterization techniques to identify key microstructural environments and transport modalities within the membrane. I will examine three types of membranes used in water treatment applications: polyamide-based reverse osmosis (RO) membranes, reduced graphene oxide (rGO) nanofiltration membranes, and Nafion-based cation (proton) exchange membranes (CEM). I will use nuclear magnetic resonance (NMR) spectroscopy and benchtop diffusion cells to extract water and salt diffusion coefficients. I will pair this with small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), and transmission electron microscopy (TEM) to probe membrane microstructural properties. With 1H and 23NA NMR, I aim to track the water and salt dynamics of all three membranes. I specifically aim to probe the translational and rotational diffusion of proton and salt within the membrane. Preliminary data acquired on polyamide RO membranes suggest that there are two states of confinement for mobile water in the RO membrane. Similarly, in the hydrated Nafion membranes, two states of water mobility are identified. Future work aims to quantify the diffusion in the various states and to examine how diffusion varies with changes in microstructure. In the case of Nafion, I plan to examine how water diffusion changes as a catalyst (TiO2) is added to the membrane, as this has relevance in further understanding a new class of membrane termed bipolar membranes. Finally, SAXS and DLS will be used to quantify morphological changes in rGO nanosheets by acquiring critical shape measurements as organic dye molecules are introduced for the purpose of tuning selectivity in water treatment.