Gas–Liquid Chemical Reactions with Nanosecond Pulses: Role of Frequency and Pulse Delivery Modes

The effects of changes in the mode of delivery of nanosecond pulses in a gas–liquid plasma reactor on the formation of hydrogen peroxide, H₂O₂, and, as an indicator for ·OH radicals, the decoloration of methylene blue, MB, were determined for pulse delivery by (a) increasing frequency with uniform pulses (5–50 kHz), (b) variation of the time between bursts of pulses (burst period), (c) changing the inner burst frequency (1 over the time between the pulses in the burst), and (d) variation of number of pulses in a burst (N-cycles). H₂O₂ peroxide formation was not affected by the method of pulse delivery in the range of parameters studied here and all data followed an approximately linear increase in H₂O₂ production rate with discharge power. In contrast, the MB decoloration rate was affected by the burst modes. In terms of discharge power, the MB decoloration rate was highest for the uniform pulse mode; however, the linear trend in increase of MB decoloration with power when the burst period was varied, suggest that at higher power the burst mode may be more effective than the uniform pulsing. Consideration of the per pulse decoloration with energy per pulse and with number of pulses suggest that the burst mode can affect reactions differently from applying a uniform pulse.