Development of a Novel, Cellulose Sponge Based Sorbent for PFAS Adsorption

Abstract

Per and polyfluoroalkyl substances are a category of synthetic emerging contaminants that have become a global concern due to their ability to bioaccumulate and their association with various health effects. Modern water treatment practices are unable to adequately and economically remove PFAS molecules present in influent waters. The state-of-the-art method for sequestering PFAS from water is the use of granular activated carbon (GAC). GAC, along with most other commercially available sorbents, faces many issues when implemented on a large scale for PFAS adsorption. Most adsorption matrices, particularly GAC, rely on non-specific adhesion of molecules into fine pores that exist on a sorbent surface to capture the suspended contaminant molecules. PFAS molecules are comparatively larger than other suspended organic contaminants normally treated with GAC and end up clogging the pore openings of the sorbent matrix. This effectively reduces the surface area of GAC to remove residual contaminants in water, leading to premature breakthrough of contaminants through the process. At this point under normal circumstances the GAC would be regenerated, which involves heating the material to remove the adsorbed contaminants in order to reuse the sorbent for further use cycles. GAC contaminated with PFAS however cannot be regenerated under standard regeneration conditions because PFAS molecules adhere with incredible strength activated carbon. As a result, temperatures upward of eight hundred degrees Celsius are required to regenerate PFAS laden GAC, which is an insurmountable task for most water treatment facilities. Specific adsorption of PFAS molecules presents a significant challenge that requires fine tuning of the molecular properties of a sorbent surface in order to adsorb the variable types of PFAS 12 molecules present in differing water supplies. Surface composition also requires optimization of binding strength for each PFAS molecule to ensure feasible regeneration of the sorbent material. In this dissertation, the adhesion of multiple PFAS molecules was studied on three molecularly tailored siloxane films under variable conditions to understand the factors that contribute most to the adhesion strength of PFAS to surfaces. The same siloxane films were then deposited onto cellulose sponges as a three-dimensional scaffold to examine their impact on PFAS adsorption and desorption.