(521da) Electrochemical Removal of Perfluoroalkyl Substances from Water By Adsorption and Comprehending Reductive Defluorination

Perfluoroalkyl substances (PFAS) are unique in nature because of their strong C − F bonds (485 kJ/mol) which make them intractable towards thermal, chemical, and biological degradation^1–2. Due to their persistent nature, they have been identified as organic pollutants of significant concern with potential hazardous effect to environment, wildlife, and human beings. Despite the rapid advances, the current treatment technologies for perfluoroalkyl and polyfluoroalkyl substances removal are not yet practical due to limited effectiveness, convenience, and high operational costs. Electrochemical adsorption onto an electrode surface and subsequent (electro)catalytic reductive defluorination are promising alternatives for the removal and destruction (respectively) of PFAS from water and wastewater. However, little is known about the thermodynamics of PFAS binding or of the mechanism of the defluorination.

In this work cyclic voltammetry is used to electrochemically measure the adsorption strength of different perfluoro-alkyl acids with increasing (perfluoroalkyl) chain-length on a Pt (111) single crystal electrode. By deconvoluting cyclic voltammograms further information is extracted to demonstrate how binding energy, adsorption type (chemisorption vs physisorption ratio) and orientation (lying flat or upright on the surface) varies with increasing chain-length for these PFAS molecules. The effects of PFAS concentration and electrolyte pH are additionally considered. By understanding the binding strength, mechanism, and configuration of these PFAS molecules as a function of their size and concentration as well as electrolyte pH, process conditions that would enable the PFAS removal process have been identified. Further, as adsorption is (likely) the first step in reductive defluorination, we can also begin to understand the mechanism of this complex reaction.

Reference:

1. Chen, Z. et al. Efficient Reductive Destruction of Perfluoroalkyl Substances under Self-Assembled Micelle Confinement. Environ Sci Technol 54, 5178–5185 (2020).
2. Duchesne, A. L. et al. Remediation of PFAS-Contaminated Soil and Granular Activated Carbon by Smoldering Combustion. Environ Sci Technol 54, 12631–12640 (2020).