Investigation of the Synergy between Atmospheric Plasma and Graphene-Oxide-Based Materials for Perfluorooctanoic Acid Degradation

Cold atmospheric plasmas offer promise for the treatment of water contaminated by per- and polyfluoroalkyl substances (PFAS). One approach to improve these treatments combines plasma with various heterogeneous materials, searching for new catalytic routes or for benefits associated to physical phenomena like sorption. Here a 32-pin electrode was used to generate pulsed (M-SPD, Multipin-Self Pulsing Discharge) and corona (MCD, Multipin Corona Discharge) discharges, and test them in combination with graphene oxide (GO), reduced graphene oxide (rGO) and boron-doped reduced graphene oxide (B-rGO). Preliminary tests on the degradation of perfluorooctanoic acid (PFOA) in water, identified beneficial effects by these materials, the M-SPD/B-rGO system being the most effective one. Further research focussed on this system, to evaluate the effect of B-rGO on the velocity and products of plasma-induced PFOA degradation, using argon or air as plasma feed gas. The amount of PFOA adsorbed on the material during the treatment was also determined. Both with argon and air plasma, significantly lower concentrations of residual PFOA were found in the presence of catalyst than with plasma only. For example, after 5 min treatment of a 1∙10^{− 6} M PFOA solution, residual PFOA with and without catalyst was, respectively, 32% and 17% for air plasma and 51% and 32% for argon plasma. Moreover, the fraction of PFOA adsorbed on the material was also efficiently degraded during the treatment. Both features make the plasma plus B-rGO treatment a promising option for stream processing of PFOA-contaminated water. Defluorination was 32% after 30 min treatment of a 1∙10^{− 5} M PFOA solution.