بهبود عملکرد و خواص ضد فیلم نازک کامپوزیت غشاء و فرآیندهای غشایی برای فن آوری های جداسازی آب
Abstract: Membrane-based water separation processes utilize semi-permeable membranes to retain dissolved solids and contaminants. Deployment of these technologies for desalination and wastewater reuse has the potential to sustainably increase the supply of potable, agricultural, and industrial water. Despite considerable development of semi-permeable membranes in the last decades, several design obstacles hampering their progress have yet to be overcome. Specifically, major membrane improvements are currently sought with respect to their performance and productivity, as well as their resistance to fouling. This dissertation research aims at the advancement of semi-permeable membranes by rational optimization of their design to: (i) understand and improve their transport properties and (ii) reduce fouling by organic molecules and delay biofouling by microorganisms. In particular, thin-film composite polyamide membranes for both reverse osmosis and forward osmosis processes are the main target of the investigation. The structural and physicochemical properties of thin-film composite membranes are both characterized and tailored through implementation of original techniques and novel functionalization protocols. The membrane structure and morphology are rationally modified to enhance the mass transport within the support layer. The influence of fabrication conditions on support layer formation and on its final structure is elucidated. The intricate interrelationship among the performance of the different layers of the composite membrane is highlighted and a new protocol is developed to characterize the transport properties of membranes deployed in forward osmosis processes. Novel approaches to impart targeted properties to the active surface of thin-film composite membranes are also proposed. The functionalization is achieved by exploiting the inherent moieties of the polyamide layer to irreversibly bind nanomaterials with desired properties. An experimental method to determine the concentration of negatively-charged functional groups at the polyamide surface is initially developed, utilizing uranyl acetate and toluidine blue O dye as probes. In one instance, covalent bonds between these polyamide moieties and antimicrobial single-walled carbon nanotubes are formed. The presence of surface-bound biocidal material is confirmed by experiments using E. coli cells that demonstrate an enhanced bacterial cytotoxicity for the functionalized membranes, which can delay the onset of membrane biofouling during operation. In other experiments, superhydrophilic silica nanoparticles are tightly tethered to the membrane surface to produce a highly hydrophilic and wettable membrane. Reduced organic fouling and lower foulant-membrane interactions are observed for the hydrophilic membranes. The reduced fouling of the functionalized membranes is attributed to the bound hydration layer at the surface that creates a barrier for foulant adhesion. This dissertation research has direct implications for improving the performance of membrane-based separation processes by increasing membrane productivity, and by reducing and delaying their fouling and biofouling. The proposed characterization and functionalization platforms also show potential for use on other surfaces and materials.