Poly- and perfluoroalkyl substances (PFASs) are a large group of persistent chemicals that have been used in industrial processes and commercial products for over 60 years. For example, perfluorooctanesulfonic acid (PFOS) is one of the most persistent, toxic and bioaccumulative contaminants from the EU Directive 2013/39/EU list of priority substances. PFOS and related chemicals are refractory to currently applied advanced chemical oxidation processes (e.g., ozonation, UV/H2O2). Available technologies for the removal of PFASs from water - activated carbon, ion exchange and reverse osmosis - are inefficient for more toxic, short-chain perfluorinated compounds, and are highly affected by the background organic matter. More importantly, these technologies do not destroy the contaminants but merely transfer them to another medium.
Graphene sponge electrodes developed in the ELECTRON4WATER project have demonstrated to be capable of C-F bond cleavage and PFAS defluorination. In our first proof of concept study (Duinslaeger and Radjenovic, Water Res 2022), we demonstrated that the fluoride radical and/or HF released by the C-F bond cleavage remain incorporated in the graphene structure at very low, trace levels. Thus, electrochemical oxidation at graphene sponge anode results in PFAS defluorination and a treated effluent free of fluoride. This capacity of graphene sponge anodes to break the C-F bond is remarkable when considering that at the same time, this material does not oxidize chloride, thus enabling the treatment of brackish, PFAS-rich streams without increasing their toxicity (e.g., reverse osmosis brine, landfill leachate). We are currently investigating continuous electrochemical degradation of PFAS at graphene sponge anodes doped with different two-dimensional (2D) materials at pre-pilot scale, using commercial plate-and-frame reactors.
