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Schematic illustrations of four different experimental setups used for plasma generation. (a) Type I: the plasma jet is in direct contact with the solution surface, (b) type II: the afterglow gas of helium plasma is mixed with oxygen gas in the chamber, (c) type III: the afterglow gas of helium plasma is mixed with oxygen gas in the glass tube, and (d) type IV: oxygen gas is in contact with helium plasma in the tube.
Image of plasma at tee joint in the type IV setup shown in Fig. 1(d).
Electron spin resonance (ESR) spectra of sample solution after plasma processing at room temperature. (a), (b), (c), and (d) correspond to types I, II, III, and IV, respectively. Most of the observed signals are attributed to the two spin adducts of O2 −· and OH·. These signals can be distinguished by the peaks in the central part; the solid triangles indicate the O2 −· adduct and the solid diamonds indicate the OH· adduct.13 Microwave power was 4 mW in all measurements.
ESR spectra of solution after plasma processing in type III for different oxygen flow rates: (a) 0.5 slm and (b) 1.5 slm. Arrow markers indicate the signal of the OH· adduct.
Summary of characteristics and results for four different plasma sources.
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