(371d) Development of Nanostructured Polyelectrolyte-Based Membranes with Enhanced Permeability and Ion Rejection

Perchlorate ion is a recently found groundwater contaminant which has affected almost 15 million people in United States. Perchlorate-containing salts are commonly used as components of rocket propellants and explosives, which explains the predominance of this ion in defense and military areas. The presence of perchlorate in drinking water causes interference in the normal hormonal activities of the thyroid gland. Removal of this ion can be effectively brought about by commercial reverse osmosis (RO) membranes. However the high pressure requirement of a typical RO process owing to the inherently low water permeabilities of RO membranes leads to high operating costs. Nanofiltration (NF) membranes on the other hand have higher water permeabilities but lower rejections than RO membranes. Our research focusses on the surface modification of existing NF membranes using Layer-by-layer (LbL) assembly in order to fabricate highly perm-selective membranes. LbL is an aqueous based thin film deposition technique which involves the layering of alternately charged polyelectrolytes on a substrate to form nanothin films. The method allows enormous versatility in terms of its fabrication parameters; the tuning of which allows optimization of the membrane performance. The types of polyelectrolytes used, the pH used during their deposition and the number of bilayers deposited are a few of the several tunable parameters available for designing these nanostructured films. These polyelectrolyte-based films when deposited on a NF membrane can serve as nanothin charged barriers to the passage of ions. The most optimized system is expected to have higher permeability than a commercial RO membrane but with equivalent rejection capabilities. All membranes are tested in a cross-flow membrane setup and the perchlorate concentrations are quantified using LC-MS/MS technique.