Perfluoroalkyl substances (PFASs) are emerging as water contaminants of growing environmental concern. Porous silica adsorbents with organic functional groups were tailored to remove PFASs from contaminated groundwater. Surface chemistry in a well-defined porous organosilica was used to better understand the prerequisites for PFAS adsorption. One of the unique features of the adsorbents was their ability to swell in order to expand pore size and therefore improve the kinetics of adsorption. Four classes of organosilica adsorbents were synthesized using a base-catalyzed sol-gel method: i) hydrophobic aryl rich, ii) fluoroalkyl modified, iii) quaternary amine modified, and iv) adsorbents with varying amounts of all three functional groups. Characterization of adsorbents was done using swelling capacity tests, surface area-pore volume analysis (using a nitrogen adsorption-desorption method), and Fourier-transform infrared spectroscopy. Kinetic adsorption and adsorption isotherm measurements were performed for PFOS, PFOA, and PFBA (perfluorobutanoic acid) in deionized water and at elevated ionic strength (50 mM NaCl). Generally, higher swelling capacity and larger surface area-pore volume was correlated with increased PFAS adsorption. Specific ratios of hydrophobic aryl rich, fluoroalkyl, and quaternary amine groups were found to have optimal adsorption. Although quaternary amine adsorbents tested had lower surface area-pore volume, PFAS adsorption was found to be more effective under low ionic strength conditions due to the electrostatic interaction between the positively-charged quaternary amines and the negatively-charged PFASs.

Development and characterization of organosilica adsorbents tailored for removal of perfluoroalkyl substances from water

2019 Fall National Meeting

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