Perfluorinated compounds (PFCs) such as Perfluorooctanoic acid (PFOA) and Perfluorooctane sulfonate (PFOS) have gained much attention due to their environmentally persistent and bioaccumulative nature. Our novel remediation approach involves the use of temperature responsive polymer which goes through hydrophilic/hydrophobic transition near LCST (Lower Critical Solution Temperature). The use of responsive polymeric materials in order to not only remove PFCs from water through adsorption mechanisms, but also to controllably and reversibly desorb the PFCs near ambient temperature (to highly concentrated form) by a small change of the environmental conditions. Poly-N-isopropylacrylamide (PNIPAm) has been widely studied as a lower critical solution temperature (LCST) polymer that exhibits a phase transition from a hydrophilic state to a hydrophobic state at its LCST of 32°C. By increasing temperature, property changes in the polymer chains affect hydrogen bonding with water molecules, thereby causing the chains to collapse in an aqueous environment. The goal is to determine the effectiveness of using PNIPAm to repeatedly adsorb and desorb PFOA and PFOS, and to concentrate solutions, using its responsive characteristics. The equilibrium adsorption isotherms as well as the adsorption and desorption kinetics are quantified around PNIPAm’s LCST. With PNIPAM hydrogel, initial PFOA sorption rate of about 28 mg/g gel/h was observed above LCST. A Pseudo second order kinetic adsorption model is used to find experimentally determined adsorption rate constant values. Using the equilibrium isotherm data and the adsorption rate constant values, temperature swing adsorption and desorption can be predicted, and PFOA/PFOS solutions can ultimately be concentrated. The interaction properties between PNIPAm and the PFCs are explored in order to quantify relation between interaction parameters and adsorption capacity. For pore functionalized membranes, responsive permeability (1.6 LMH/bar below LCST, 29 LMH/bar above LCST). The presentation will include: (1) PNIPAm hydrogels (100 – 500 nm size) synthesis and <i>in situ </i>polymerization of Nipam in membrane pores, results of responsive behavior, (2) fast PFOA sorption and desorption kinetics, (3) high level concentration of dilute PFOA in water to highly concentrated form through further regenerant solution processing by GO nanofiltration membrane.

Thermo-responsive polymer hydrogel and pore functionalized membrane for temperature swing sorption and desorption of PFOA

2019 Spring National Meeting

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