THE DEVELOPMENT OF TEMPERATURE AND PH RESPONSIVE HYDROGELS AND MEMBRANES FOR SELECTIVE SORPTION OF PERFLUOROORGANICS AND NANOPARTICLE INTEGRATED CATALYTIC DEGRADATION OF PCB

The functionalization and use of responsive and catalytic polymeric membranes and materials were explored for contaminant capture and degradation. While membranes have a wide variety of uses across multiple industries, the inclusion of materials that are temperature and pH responsive in the membrane pore domain yields a wide range of applications and possibilities for water treatment. Temperature and pH responsive polymers, as well as controlled nanostructured materials, were synthesized in membrane pores for advanced adsorption-desorption and catalytic treatment of emerging organic contaminants in water. In this study, supported by the NIEHS, poly-N-isopropylacrylamide (PNIPAm) was used as a model thermo-responsive polymer, while perfluorochemicals (PFCs) and polychlorinated biphenyls (PCBs) are used as model emerging water contaminants. A stimuli-responsive membrane-based adsorptive-desorptive system was developed by incorporating PNIPAm and poly-methyl methacrylate (PMMA) into a PVDF membrane structure and quantified through in-situ characterizations. Furthermore, a novel membrane system was developed for enhanced degradation of emerging halo-organics that is both stimuli-responsive and catalytic due to the incorporation of Fe-Pd nanoparticles into the polymeric membrane matrix. By incorporating a thermo-responsive polymer into a membrane platform, temperature was used to control permeability, hydrophilicity, and pollutant partitioning. Solubility parameters of the model contaminants and of the thermo-responsive polymer in its different conformational states were determined. This was used to develop a fundamental understanding of the interaction between the polymer domain and halo-pollutant domain in order to conduct reversible temperature swing adsorption through manipulation of external stimuli. In doing so, PNIPAm’s temperature-responsive behavior and hydrophilic/hydrophobic transition was leveraged for reversible adsorption and desorption of perfluoro-organics from water. Adsorption of perfluorooctanoic acid (PFOA) onto PNIPAm hydrogels yielded adsorption capacities lower than commercially used adsorbents. However, the initial rates of 28 mg/g/h and 41 mg/g/h for adsorption and desorption, respectively, and the ability to reversibly desorb with ease through external temperature manipulation make the use of stimuli-responsive polymeric membranes an exciting avenue for the development of advanced adsorbents that can be easily regenerated. Temperature swing adsorption-desorption of pollutants using the thermo-responsive membrane was demonstrated and quantified. The incorporation of stimuli-responsive polymers as well as reactive bimetallic nanoparticles into membrane pores enabled the development of an advanced stimuli-responsive catalytic membrane for enhanced halo-organic degradation. Iron nanoparticles were used due to iron’s ability to react with water and form hydrogen species, unlike other reactive metal-based nanoparticles that would require a hydrogen source, with Palladium as a reaction catalyst. By adding stimuli-responsive polymers into the catalytic membrane matrix, temperature variations were used to selectively control adsorption and diffusion of model halo-organic contaminants into the membrane’s catalytic domain. Chloro-organic degradation in batch and convective flow mode was achieved via the reductive pathway and modeled using advanced material characterization. The effect of temperature on the reaction process was evaluated as a means of increasing contaminant degradation efficiency by using the conformational change of the thermo-responsive polymer. Convective flow degradation of PCB-1 using the PNIPAm-PMMA-functionalized membranes with immobilized Fe-Pd nanoparticles yielded first-order kSA values of 0.13 L/m2/g, 0.28 L/m2/g, 0.72 L/m2/g, and 1.36 L/m2/g at 15 ºC, 25 ºC, 35 ºC, and 45 ºC, respectively, with an activation energy of 60 kJ/mol. Batch degradation of PCB-1 resulted in first-order kSA values of 0.12 L/m2/h and 0.35 L/m2/h at 25 °C and 35 °C, respectively. Stimuli-responsive, functionalized polymeric membranes for reversible contaminant adsorption with high initial rates provide a very exciting technology for the removal of toxic organic contaminants from water