Date of Award

August 2022

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Engineering

First Advisor

Yin Wang

Committee Members

Jin Li, Qian Liao, Shangping Xu, Woojin Chang

Abstract

ABSTRACTADSORPTION OF PER- AND POLYFLUOROALKYL SUBSTANCES ON FUNCTIONALIZED MINERALS: EFFECTS OF MODIFIER PROPERTY AND MINERAL STRUCTURE

by Qianqian Dong

The University of Wisconsin-Milwaukee, 2022Under the Supervision of Professor Yin Wang

Per-and polyfluoroalkyl substances (PFAS) are a large group of manmade chemicals widely used in various consumer and industrial products. The adverse effect of PFAS exposure includes bioaccumulation, organ damage and birth defects. Although the primary feedstock perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) has been phased out since the 2000s, PFAS are worldwide detectable in water bodies due to the historical production, accumulation and endless substitution of long-chain PFAS in the environment. Removal of PFAS represents a special challenge for water/wastewater treatment because of their diverse structures and unique physicochemical properties such as high-water solubility and high stability of the C-F bond. Therefore, it is urgent to find a cost-effective way to deal with PFAS contamination. Compared to the destructive approaches, adsorption is a safe and economical way to treat PFAS through physical separation. Clay mineral-based adsorbent shows great potential in PFAS removal due to its environmental friendliness, small particle size, layered structure, cation exchangeability and abundant active grafting sites. Ionic liquid, as a green solvent, has not been studied for the PFAS removal through the intercalation with clay minerals. Ionic liquid and silane with various functional groups and chain lengths can be used for clay modification through ionic exchange or post-grafting reactions. Enlarging the surface area of clay minerals with exfoliation could provide more active sites for post-grafting. The covalent bond between silane and clay minerals also benefits the regeneration and reuse of spent adsorbents. Besides, clay minerals such as montmorillonite and vermiculite possess different structures and compositions which play important roles in adsorption. Overall, the objective is to develop organically functionalized clay materials with high adsorption capacity, fast adsorption kinetics and good regeneration ability for PFAS removal. The effect of organic modifier composition, clay mineral structure, PFAS structure and clay/modifier ratio are systematically investigated. This dissertation entails (1) the review of current technology on PFAS treatment including destructive and non-destructive methods, (2) the development and characterization of ionic liquid-modified montmorillonite with enhanced adsorption of PFOA and PFOS and the elucidation of the impact of ionic liquid chain length on PFOA and PFOS removal, (3) the characterization and comparison of ionic liquid-modified clays prepared using various clay substrates for the adsorption of eight representative PFAS, (4) and removal of perfluoroalkyl acids (PFAAs) and precursors with silylated clay: efficient adsorption and enhanced reuse.

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