Advanced Filtration Membranes for the Removal of Perfluoroalkyl Species from Water

Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are two perfluoroalkyl substances that have been shown to result in several adverse health effects, including birth defects, kidney/testicular cancer, as well as liver and thyroid damage. The surfactant nature of PFOS and PFOA in water makes these compounds extremely difficult to remove from drinking water. In this paper, an efficient method to remove PFOS and PFOA from drinking water using linear fluorinated silane-functionalized aluminum oxide hydroxide (γ-AlOOH) nanowhiskers was developed. Filters functionalized with linear fluorinated silanes containing 13-17 fluorine atoms were able to remove >90% of the PFOS/PFOA at a very high flux of 1223 L/m²·h. However, due to the hydrophobicity of these linear fluorinated silanes, high pressure drop was also noted across the membrane thickness during the filtration process. To reduce the back-pressure drop, linear fluorinated silanes with appended hydrophilic poly(ethylene glycol) units were synthesized, and it was further demonstrated that the new hydrophilic linear fluorinated silane dramatically reduced the pressure drop of the γ-AlOOH filter while maintaining 99.9% PFOS and PFOA reduction. Adsorption tests were performed to understand the removal mechanism.