Water transport in Graphene Oxide laminates for membrane applications

This thesis used experimental observations, coupled with numerical techniques, to provide new insights on the inter-relationship between environmental conditions, interlayer (d-) spacing and water transport through Graphene Oxide (GO) laminates. In situ X-ray diffraction measurements during the drying of hydrated GO laminates captured the coexistence of two d-spacings at 1.16 nm and 0.87 nm, indicating that environmental conditions can affect the phase of water in GO. Molecular dynamic (MD) simulations showed diffusion and pore flow transport behaviours of water at these two GO d-spacings respectively. The slip length obtained from the velocity profile of the water pore flow in GO was found to range from 0.44 nm to 79 nm and was highly dependent on the distribution of hydroxyl functional groups on the pristine carbon.During the filtration of a 5 g L-1 NaCl solution, a non-incremental change in rejection from 5% to 99% was observed at feed temperatures between 30 degree C and 34 degree C indicating a mechanistic change of water transport from pore flow to diffusion. By modifying GO with alkylamines with different carbon chain lengths, the precise GO d-spacing at which the water phase change occurred was narrowed down to between 1.06nm to 1.16nm. Modifications of the Hagen-Poiseuille equation to include a slip length of approximately 60 to 70 nm, determined by molecular dynamic simulation, coupled with an estimate for laminate tortuosity of 11.3, determined by fitting Knudsen equation to experimental observation, enables a good agreement between theory and experiment. These studies distinguished the different water transport mechanisms for GO at varying environmental conditions and examined the viability of conventional transport theories, which can guide future theory development.Applying this knowledge, GO laminates were tested in a desiccation application and showed high water adsorption capacity of 0.58 g g-1 with a low regeneration temperature of 40 degree C and