NOVEL ADSORBENTS FOR PER- AND POLYFLUOROALKYL SUBSTANCES (PFAS):  MECHANISMS AND REGENERATION

Yuhao Tian

The extensive presence of a group of emerging contaminants, per- and polyfluoroalkyl substances (PFAS), in surface water, groundwater, even drinking water, has attracted great attention due to their extraordinary persistence and potential toxicity. Because of their unique properties, PFAS are exceptionally challenging to be removed from the water. To face this challenge, efficient treatment technology is needed. Current treatment technologies have limitations such as slow adsorption, high cost, and low regeneration efficiency. Therefore, this study aims to explore mechanisms governing the adsorption of PFAS and utilize those mechanisms for the design of novel and low-cost adsorbents with regeneration ability for removal of PFAS from contaminated water. Three hypotheses were proposed: 1) Electrostatic interaction is more important than hydrophobic effects for PFAS adsorption; 2) Adsorption and desorption of PFAS can be controlled by changing surface charges; 3) Increasing hydrophobicity of adsorbents can improve the performance for long-chain PFAS adsorption, but not for short-chain PFAS. To test these hypotheses, three materials (transition metal dichalcogenides (TMDC), polypyrrole (PPy) and lignin), were selected to run the designed experiments. TMDC can adsorb pharmaceuticals and personal care products (PPCP) effectively through hydrophobic effects, but not PFAS, suggesting stronger electrostatic repulsion between negatively charged TMDC and anionic PFAS. The adsorption of PFAS by PPy mainly comes from electrostatic attraction and hydrophobic effects. By introducing positively charged functional groups (amine groups) onto lignin, the adsorption of PFAS was improved significantly. Spent lignin-based adsorbents can be regenerated to almost 100% in less than 1 hour by changing the pH to 10. Results from adsorption of PFAS by several modified lignin materials with different hydrophobicity showed that increasing hydrophobicity could improve adsorption for all tested PFAS, except for PFBA, probably due to its shorter tails, which may reduce the hydrophobic effects. This study provided a comprehensive understanding of the fundamental mechanisms governing adsorption of PFAS and developed novel adsorbents with fast adsorption kinetics, high capacities and the ability to be regenerated effectively. These adsorbents are supposed to be able to remove other ionic organic contaminants similar to PFAS in the environment effectively.

NOVEL ADSORBENTS FOR PER- AND POLYFLUOROALKYL SUBSTANCES (PFAS): MECHANISMS AND REGENERATION

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