Generation and delivery of free hydroxyl radicals using a remote plasma

Abstract

We demonstrate a new gas-based OH• generation source using a low power RF-driven atmospheric pressure plasma configured to deliver the radical flux into the far effluent region, well away from interference from other plasma factors such as electric fields, currents, and UV radiation. Using He – H2O gas chemistry isolated from the laboratory air, the plasma generated flux contains OH• and other radicals including H•, O and HO2 as well as H2O2 which, along with OH•, was found to vary with H2O vapour content and absorbed power density. Peak flux values were 2.3 nmol s-1 and 0.23 nmol s-1 for H2O2 and OH• respectively at a distance of 50 mm from the plasma, with 790 ppmv H2O and a power density of ~ 108 W m-3. The maximum OH• flux density was 4.5 x 1019 m-2 s-1 falling to 1.7 x 1019 m-2 s-1 at 110 mm, equivalent to generation rates of 74 mM s-1 and 28 mM s-1. Despite high OH• recombination rates at the plasma exit, the escaping flux is still significant, indicating a viable delivery capability to downstream targets. Its performance with regard to OH• generation rates compares well with traditional OH• generation techniques such as radiolysis, advanced oxidation processes and enhanced Fenton-chemistry approaches where OH• production rates are sub-mM s-1. Delivering precisely quantifiable OH• fluxes provides new opportunities for scientific studies and technological opportunities in cell biology, atmospheric chemistry, protein unfolding and systematic dose studies for plasma-based and other OH• related potential medical treatments.

Degradation of 2,4-dinitrotoluene in aqueous solution by dielectric barrier discharge plasma combined with Fe–RGO–BiVO4 nanocomposite

“…However, given that other variables have been maintained at their center point levels (Fe–RGO–BiVO 4 dosage = 0.5 g L −1 , Voltage = 21kV, Reaction time = 20 min and pH = 7), when a particular level was reached, the pollutant concentration surpassed the oxidation capacity of DBD/Fe–RGO–BiVO 4 process which leads to reduced removal efficiency 37 , 39 . This could be due to the saturation of the catalyst surface by 2,4-DNT molecules, reduction of conductivity and consequently decrease of plasma discharge in the reaction solution, which ultimately reduced the production of reactive species like radicals 40 . In fact, the DBD/Fe–RGO–BiVO 4 process produces a certain number of reactive species that can’t compete with higher concentrations of 2,4-DNT, and so-called reactive species dilution occurs.…”

Kinetic model of grating-like DBD fed with flowing humid air

“…First, the 'pseudo-1D plug flow' approximation was applied, namely, the transport of species in the direction vertical to the main airflow was not considered. This approach is common in reports regarding APPJs [38,39]. The feasibility of this approximation will be discussed in section 3.2.4.…”