This project seeks to obtain proof-of-concept that energy requirements can be significantly decreased and enhance the reliability and cost-effectiveness of the thermal destruction of per- and polyfluoroalkyl substances (PFAS) in solid matrices (e.g., impacted soils and spent sorbents used to remove PFAS from groundwater) by leveraging the catalytic functionality of common transition metals (e.g., Fe(III), Cu(II)). The mechanistic hypothesis is that the ionic head groups of the PFAS of greatest regulatory concern (e.g., carboxylate and sulfonate) chemisorb on the cationic transition metal, which acts as a redox center facilitating electron transfer from the PFAS molecule (at least those of greatest regulatory concern) and initiates bond scission at unprecedentedly low temperatures (possibly <200 ºC). Specifically, this project will address the following objectives:

• Demonstrate a catalytic effect of Fe(III) and Cu(II) in the thermal degradation of PFAS of greatest regulatory concern leading to enhanced mineralization (demonstrated by fluorine mass balances), and significantly decreased energy requirements for PFAS destruction (i.e., lower temperature and treatment time). Since clays are common soil components whose metal content can be easily controlled, ion-exchanged bentonite (with/without transition metals) will be used to obtain proof-of-concept.
• Apply molecular modeling with density functional theory (DFT) in concert with adsorption experiments to gain a molecular-level predictive understanding of PFAS adsorption and degradation on Fe(III) and Cu(II) catalytic sites.

Proof-of-concept will also include testing “real-world” impacted soils amended with up to 10% (wt.) ion-exchanged bentonite from the above studies to confirm that amendments with properly coordinated transition metals can significantly decrease the temperature needed to treat soils impacted with mixtures of PFAS.

Thermal-catalytic PFAS destruction will be conducted in benchtop reactors (with liquid traps for collecting PFAS decomposition products) at unprecedentedly mild temperatures that preserve soil fertility, which would be irreversibly damaged by clay dehydroxylation or soil organic matter combustion at the high temperatures of common incineration approaches. This would retain the soil’s value for restoration efforts. Initial tests will focus on how PFAS degradation (i.e., fate and reaction rates) is affected by the catalytic properties of transition metals in soil components (e.g., clays) or metal-modified clay amendments. State-of-the-art analytical methods (thermogravimetry with online mass and infrared spectroscopy and ion chromatography to obtain F mass balances and quantify extent of defluorination) will be used and DFT computations to advance molecular-level understanding of the mechanisms governing thermal-catalytic destruction of PFAS in metal-containing, solid matrices.

Demonstration of PFAS destruction via the thermal-catalytic treatments will enable the development of more energy-efficient, faster, and less costly soil remediation and sorbent regeneration processes. By requiring lower temperatures, the improved processes will provide higher impacted soil throughput with lower energy requirements, while reliably meeting the treatment objectives. The new mechanistic insight generated by this project will inform the development of amendments for solid matrices treatment. This project also represents pioneering steps toward developing an integrated sorption-thermal-catalytic “trap-and-zap” system, where novel catalytic sorbents (e.g., metal-modified zeolites) remove, concentrate and thermally destroy PFAS. This would be useful to treat off-gas emissions from commercial incinerators. By leveraging existing technology infrastructure and earth-abundant materials, this project facilitates scalability for field applications. (Anticipated Project Completion - 2026)