Complete electrocatalytic defluorination of perfluorooctane sulfonate in aqueous solution with nonprecious materials

Abstract

Perfluorooctane sulfonate (PFOS) was completely defluorinated in aqueous electrocatalysis with laser-made [NiFe]-layered double hydroxide nanocatalysts immobilized on hydrophilic carbon fiber paper anodes. All materials were nonprecious, as needed for globally scalable remediation technologies for per- and poly-fluoroalkyl substances (PFAS). Pulsed electrolysis of 0.50 or 0.05 mM PFOS in aqueous 8.0 M LiOH solution assisted by ultraviolet light irradiation enhanced electrical energy and capital expense efficiency compared to existing techniques. Electrocatalytic defluorination occurred within the anode microenvironment, as evidenced by pulsed electrolysis vs continuous chronoamperometry data and electrolyte agitation experiments. We observed adsorbed PFOS and surface-bound OOH in X-ray photoelectron spectra of post-electrocatalysis anodes, corroborating that electrocatalytically regenerated reactive oxygen species defluorinated PFOS within the anode microenvironment. High concentrations of lithium ions and high basicity were essential for efficient defluorination, which also worked for perfluorooctanoic acid (PFOA), albeit more efficiently for PFOS, presumably due to advanced oxidation processes by sulfate radicals near the anode that assisted defluorination.