Products, Reactive Species and Mechanisms of Pfoa Degradation in a Self-Pulsing Discharge (Spd) Plasma Reactor

Cold Plasma for Green Advanced Reduction/Oxidation Processes (AROPs) of Organic Pollutants in Water**

“…[12,34,37,38] The prevailing role of plasma electrons in attacking PFOA, thus initiating its degradation in the SPD reactor, is consistent with the results of a recent optical emission spectroscopy study which highlighted a correlation between the efficiency of PFOA degradation in solution and the density of electrons within the plasma at the liquid interface. [40] Hydroxyl radicals, however, do appear to be involved in subsequent steps of the complex process [40] which achieves the fast and complete degradation of PFOA with only trace amounts of organic carbon byproducts remaining in the treated solution. These byproducts are mainly perfluoroalkyl carboxylic acids homologues of reduced chain length, formed in an orderly sequence and in turn decomposed as sketched in Scheme 1.…”

“…A detailed mechanistic scheme was recently proposed to account for these intermediate products as well as for those of minor side reactions resulting in hydro-defluorination and hydroxy-defluorination of PFOA and of its lower homologues. [40] Interestingly, while complete degradation of perfluoroalkyl carboxylic acids from C8 to C5 could be achieved in both the SPD and RAP reactors, the shorter chain homologues including notably perfluorobutanoic acid (PFBA) appeared to be extremely refractory also to prolonged treatment. This behavior is evident in Figure 6(a) which reports the time evolution of reactant and intermediate products in an experiment in which a 1×10 À 5 M PFOA solution was treated in the RAP reactor.…”