TUNABLE NANOCOMPOSITE MEMBRANES FOR WATER REMEDIATION AND SEPARATIONS

OF DISSERTATION TUNABLE NANOCOMPOSITE MEMBRANES FOR WATER REMEDIATION AND SEPARATIONS Nano-structured material fabrication using functionalized membranes with polyelectrolytes is a promising research field for water pollution, catalytic and mining applications. These responsive polymers react to external stimuli like temperature, pH, radiation, ionic strength or chemical composition. Such nanomaterials provide novel hybrid properties and can also be self-supported in addition to the membranes. Polyelectrolytes (as hydrogels) have pH responsiveness. The hydrogel moieties gain or lose protons based on the pH, displaying swelling properties. These responsive materials can be exploited to synthesize metal nanoparticles in situ using their functional groups, or to immobilize other polyelectrolytes and biomolecules. Due to their properties, these responsive materials prevent the loss of nanomaterials to the environment and improve reactivity due to their larger surface areas, expanding their range of applications. The present work describes different techniques used to create nanocomposites based on poly(vinylidene fluoride) (PVDF) hollow fiber and flat sheet membranes, both thick sponge-like and thin. Due to their hydrophobicity, hollow fiber membranes were hydrophilized by a water-based green process of cross-linking polyvinylpyrrolidone (PVP) onto their surface. Commercial hydrophilic and hydrophilized lab-prepared membranes were subsequently functionalized with a poly(acrylic acid) (PAA) hydrogel through free radical polymerizations. This work advanced membrane functionalization, specifically flat sheet membranes, from lab-scale to full-scale by modifications of the polymerization procedures. The hydrogel functionalized membranes by redox polymerization showed an expected responsive behavior, represented by permeability variation at various pH values (4.0 ≤ pH ≤ 9.0), from 53.9 to 3.4 L/(m·h·bar) and a change in effective pore size from 222 to 111 nm, being 3800 L/(m·h·bar) and 650 nm the former permeability and pore size values of the non-functionalized membrane. Then, throughout a double ion exchange of sodium/iron and a subsequent reduction, bimetallic Fe/Pd nanoparticles were synthesized in-situ. Similarly, it was possible to use the reacted accelerants of the redox polymerization to synthesize Fe nanoparticles. These hydrogel-membrane systems with Fe/Pd nanoparticles were studied throughout the reduction of trichloroethylene (TCE). This work has demonstrated an effective improvement in TCE reduction by the variation of the supporting membrane types and the functionalization (polymerization and nanoparticle synthesis) processes. The TCE normalized dechlorination rates (ksa) are 3 times greater and 8 times for hollow fiber and sponge-like flat sheet membranes, respectively, than previous studies. For membrane supported Fe/Pd nanoparticles by redox functionalization, the dechlorination rates are similar to previous works in flat sheet membranes; and for the redox polymerized hydrogel, the dechlorination rates are the highest results with 1.3 times greater than the rates of solution-phase nanoparticles and 10 times the rate values of the membranes. All supports showed nonsignificant nanoparticle loss (up to 1%). Up to 80% of reduction was achieved within 2 hours with chloride production near to stoichiometric values (3:1), demonstrating absence of intermediates. As an extension of the membrane functionalization, it was possible to immobilize Outer membrane protein F precursor (OmpF) from Escherichia coli within the PVDF membrane pore structure, using layer-by-layer (LbL) assembly of polyeletrolytes. This LbL technique allows to reuse the membranes numerous times, having reproducibility and greater selective rejections of uncharged (organic species) over charged solutes (small ions) than similar functionalized membranes without OmpF: 1.7 times and 2.0 times higher for Organic/CaCl2 and Organic/NaCl, respectively. Additionally, the permeability of OmpFmembranes is almost double of the non-OmpF: 2.6 to 1.5 L/(m·h·bar).