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Title: Membrane fabrication and membrane fouling for low salinity water by reverse osmosis
Author: Jiang, Zhiwei
ISNI:       0000 0004 7228 8904
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2017
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Polyamide nanofilms made at the aqueous-organic interface have been developed for a few decades, yet understanding the formation mechanism and measurement of the active thickness of the nanofilms is still a challenge. To overcome this lack of knowledge, ultrathin and smooth polyamide nanofilms with thickness less than 10nm were made from the controlled interfacial polymerization on a sacrificial layer or at the free interface. The nanofilms were robust and defect free, and could be incorporated into composite membranes and used in reverse osmosis. By controlling the reaction conditions, the nanofilms bent up at the interface to create a crumpled texture, resulting in higher permeable area for water passage. This provides strong evidence that the active thickness of the polyamide nanofilms is one order of magnitude lower than the observed thickness of the undulated structure. The water permeance was further enhanced by solvent activation which provides a structural change in the polymer network to create more free volume for faster water diffusion. The intrinsic water permeability of the nanofilm was studied by manipulating the thickness from ~5 to 16nm while keeping the surface smooth. The absorption and diffusion rate was enhanced for the nanofilms below ~8nm which increased the intrinsic permeability from a constant value to 40% higher. Fouling tests were conducted with a protein as the model foulant for both smooth and rough membranes, for which the observed flux decline was similar. Rather than surface morphology, the initial permeance of the membranes was shown to be the dominating factor influencing the extent of fouling.
Supervisor: Livingston, Andrew Sponsor: British Petroleum Company ; Imperial College London
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral