Reactive species produced by atmospheric pressure
plasma (APP) are useful in many applications including disinfection, pretreatment,
catalysis, detection and chemical synthesis. Most highly reactive species produced
by plasma, such as ·OH, 1O2 and
, are
short-lived; therefore, in-situ generation is essential to transfer plasma
products to the liquid phase efficiently. A novel microfluidic device that
generates a dielectric barrier discharge (DBD) plasma at the gas-liquid
interface and disperses the reactive species generated using microbubbles of ca.
200 µm in diameter has been developed and tested. As the bubble size affects the
mass transfer performance of the device, the effect of operating parameters and
plasma discharge on generated bubbles size has been studied. The mass transfer
performance of the device was evaluated by transferring the reactive species generated
to an aqueous solution containing dye and measuring percentage degradation of
the dye. Monodisperse microbubbles (polydispersity index between 2 - 7%) were
generated under all examined conditions but for gas flow rate exceeding a
critical value, a secondary break-up event occurred after bubble formation leading
to multiple monodisperse bubble populations. The generated microbubble size
increased by up to ~ 8% when the device was operated with the gas plasma in the
dispersed phase compared to the case without the plasma due to thermal
expansion of the feed gas. At the optimal operating conditions, initial dye
concentration was reduced by ~60% in a single pass with a residence time of 5-10
s. This microfluidic chip has the potential to play a significant role in
lab-on-a-chip devices where highly reactive species are essential for the
process. </p