Efficient water desalination is vital to sustaining the quality of life for populations living without access to sufficient freshwater resources as well as treating the wastewater produced from industrial activities before reuse or being discharged to the environment.  In this work, we utilize the flexibility of the layer-by-layer (LbL) assembly process to create composite thin films comprised of cross-linkable polyelectrolytes and silicate clay nanoparticles to serve as a substitute for the polyamide selective layer in commercially-available reverse osmosis (RO) membranes.  The spray layer-by-layer (spray-LbL) assembly process enables the deposition of large, asymmetric thin films with intercalated clay platelets orders of magnitude faster than possible through traditional dip-LbL processing.  The composite thin films were deposited on polyethersulfone nanofiltration (NF) membranes, with composition and physical properties fine-tuned by manipulating the assembly conditions such as spray time and pH of the film components, the number of layers deposited, and the time and temperature of the post-deposition heat treatment.  Films were characterized with ATR-FTIR and TGA to determine the efficacy of the cross-linking treatment as well as the clay content.  Using mathematical modeling on data collected from a dead-end permeation cell, permeability coefficients for water and salt through selective layers of varying film composition were calculated.  At operating pressures up to 300 psi (20.7 bar) and both brackish and seawater desalination conditions, the water permeability coefficient calculated for these composite thin films was found to be an order of magnitude greater than what was observed for a commercially-available polyamide selective layer.  Over the same range of operating pressures, the composite thin films rejected up to 93.3% of aqueous NaCl.  These experimental results confirm the viability of using composite polyelectrolyte-clay thin films as an alternative selective layer.

Spray-assembled composite polyelectrolyte-clay thin films as selective layers in RO membranes

247th National Meeting (2014)

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