Nozomi Takeuchi1,Shanshan Qing1,Kiyotaka Okada2,Takao Namihira2,Douyan Wang2
Tokyo Institute of Technology1,Kumamoto University2
Nozomi Takeuchi1,Shanshan Qing1,Kiyotaka Okada2,Takao Namihira2,Douyan Wang2
Tokyo Institute of Technology1,Kumamoto University2
Perfluorooctane sulfonic acid (PFOS: C<sub>8</sub>F<sub>17</sub>SO<sub>3</sub>H), a type of perfluoro compound, has been widely used for numerous commercial applications, such as water-proofing materials and fire-extinguishing foam owing to its excellent properties as a surfactant and its high stability. However, PFOS and its salts were listed as persistent organic pollutants in the Stockholm Convention because of their high toxicity and resistance to degradations. Therefore, the production and utilization of these compounds has been restricted. Numerous research groups, including ours, have investigated the decomposition of PFOS and perfluorocarboxylic acids (PFCAs: C<i><sub>n</sub></i>F<sub>2<i>n</i>+1</sub>COOH, <i>n</i> = 1–7) using various types of plasma in contact with liquid. In this study, decomposition of PFOS was conducted using two types of plasma: plasma generated within gas bubbles and nanosecond pulsed discharge plasma generated with fine droplets, and the decomposition rate and efficiency were compared with those by other plasmas in literature.<br/>First, effects of several parameters for generation of plasma within Ar gas bubbles on the decomposition characteristics were investigated. Although the rates of decomposition and defluorination increased with the number of energetic species generated by the plasma and discharge duration, the energy efficiency decreased. This was probably due to the lack of PFOS molecules on the plasma–solution surface where decomposition reactions occurred. Hence, a nanosecond pulsed discharge plasma generated with fine droplets of PFOS solution was applied. Effective interactions between highly energetic electrons and PFOS molecules with a short duration were achieved, resulting in more energy-efficient PFOS decomposition. Establishment of such reaction field is the key to realize an efficient decomposition system for PFOS.<br/>This work was partly supported for Joint Research by the Institute of Industrial Nanomaterials, Kumamoto University.