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29. Water transport in Graphene Oxide laminates for membrane applications

Author

Lian, Boyue

Subjects
Molecular dynamic, Graphene oxide membrane, Nanofiltration
Abstract

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 a water adsorption rate five times higher than silica gel. In a novel solar-driven pervaporation process, utilising the solar adsorption capacity and the fast pervaporation water transport rate, GO laminates produced 6.45 kg m-2 day-1 of distilled water from a 35 g L-1 NaCl solution at a Gain Output Ratio of 0.63, which are both higher than a conventional solar still system..

Published
2020
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30. Water transport in Graphene Oxide laminates for membrane applications

Author

Lian, Boyue, Chemical Engineering, Faculty of Engineering, UNSW and Lian, Boyue, Chemical Engineering, Faculty of Engineering, UNSW

Abstract

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

Published
2020

33. Numerical and experimental investigation of a DC-powered RO system for Sri-Lankan villages.

Author

Li, Qiyuan, Zhang, Huili, Tan, Cheng, Lian, Boyue, García-Pacheco, Raquel, Taylor, Robert A., Fletcher, John, Le-Clech, Pierre, Ranasinghe, Buddhi, Senevirathna, Tharanga, and Leslie, Gregory

Subjects
*REVERSE osmosis, *ENVIRONMENTAL infrastructure, *WATER supply, *BLOOD proteins, *HUMIC acid, *SERUM albumin, *RURAL population
Abstract

High operation and maintenance costs, and 'last-mile' issues for populations not connected to municipal water infrastructure, have limited the utility of centralized reverse osmosis (RO) systems to alleviate water availability issues for rural communities. To address these challenges, a decentralized RO module which employs tubular RO membranes was designed and investigated. The system represents an appropriate technology because it requires minimal pretreatment and it fits in self-contained, low-profile suitcase. This compact desgin also incorporated innovative 3D printed static mixers to minimize salt concentration polarization and to improve performance. Since grid electricity may also be discontinuous in the target use cases, the system was tested with two direct current (DC) power solutions: a photovoltaics-battery configuration and an alternator-battery. The final prototype weighs less than 15 kg and was found to have a production capacity of ∼8 L/h, consuming ∼100 W of pumping power. Experiments of the prototype module revealed a 96% rejection rate of salt from a 1000–2000 ppm synthetic groundwater solution and a >99% rejection coefficient for bovine serum albumin protein and humic acid. From these performance metrics, it was estimated that 36 sets of this decentralized system (with a total CapEx of US$23,400) could provide drinking water for ∼600 rural households at a unit cost of water of 1 LKR/L (0.005 USD/L) in Sri Lanka. Overall, this study demonstrates how computational modeling and 3D printing can be leveraged to develop a compact and cost-effective decentralized RO package that could be rapidly deployed to water-stressed rural areas and in disaster relief applications. [Display omitted] • A plug-and-play, compact DC driven mobile RO desalination system was developed. • Both alternator-battery and solar PV- battery power solutions were designed and tested. • The system is less than 15 kg and can produce 8 L/h of water with 100 W of power. • Rejection of 96% for salt and >99% for both protein and humic acid was observed. • The levelized cost of water of water was found to be < 0.005 USD/L. [ABSTRACT FROM AUTHOR]

Published
2022
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