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.
Electrochemical processes are capable of removing PFASs from water by the direct electron transfer oxidation. For example, electro-oxidation of PFOS at boron-doped diamond (BDD) anode forms short-chain fluorinated polymers, which are further converted to defluorinated products at prolonged electrolysis time. However, the energy consumption of the process is too high for the process to be applied in water and wastewater treatment, around 15-40 kWh/m3/order.
In this project, we are developing novel anode materials based on carbon and metal-based nanomaterials, for electrochemical removal of PFASs from water. We are focused on two main groups of materials: 1) TiO2 nanotube array (NTA)-based anodes, and 2) graphene sponge electrodes. Graphene sponge electrodes are of particular interest for PFAS removal as they are a porous, three-dimensional material that is highly hydrophobic, offers a high surface area for PFAS sorption and electrosorption, and given their excellent electrocatalytic activity, ensures efficient loss of electrons from the PFAS and their complete oxidation.