Plasma-droplet interaction study to assess transport limitations and the role of ⋅OH, O⋅,H⋅,O2(a 1Δg),O3, He(23 S) and Ar(1s 5) in formate decomposition
- 1 November 2021
- journal article
- research article
- Published by IOP Publishing in Plasma Sources Science and Technology
- Vol. 30 (11), 115003
- https://doi.org/10.1088/1361-6595/ac2676
Abstract
Plasmas interacting with liquid microdroplets are gaining momentum due to their ability to significantly enhance the reactivity transfer from the gas phase plasma to the liquid. This is, for example, critically important for efficiently decomposing organic pollutants in water. In this contribution, the role of ⋅OH as well as non-⋅OH-driven chemistry initiated by the activation of small water microdroplets in a controlled environment by diffuse RF glow discharge in He with different gas admixtures (Ar, O2 and humidified He) at atmospheric pressure is quantified. The effect of short-lived radicals such as O⋅ and H⋅ atoms, singlet delta oxygen (O2(a 1Δg)), O3 and metastable atoms of He and Ar, besides ⋅OH radicals, on the decomposition of formate dissolved in droplets was analyzed using detailed plasma diagnostics, droplet characterization and ex situ chemical analysis of the treated droplets. The formate decomposition increased with increasing droplet residence time in the plasma, with ∼70% decomposition occurring within ∼15 ms of the plasma treatment time. The formate oxidation in the droplets is shown to be limited by the gas phase ⋅OH flux at lower H2O concentrations with a significant enhancement in the formate decomposition at the lowest water concentration, attributed to e−/ion-induced reactions. However, the oxidation is diffusion limited in the liquid phase at higher gaseous ⋅OH concentrations. The formate decomposition in He/O2 plasma was similar, although with an order of magnitude higher O⋅ radical density than the ⋅OH density in the corresponding He/H2O plasma. Using a one-dimensional reaction–diffusion model, we showed that O2(a 1Δg) and O3 did not play a significant role and the decomposition was due to O⋅, and possibly ⋅OH generated in the vapor containing droplet-plasma boundary layer.Funding Information
- Fusion Energy Sciences (DE-SC-0020232)
- Army Research Office (W911NF-20-1-0105)
- National Science Foundation (PHY 1903151)
This publication has 95 references indexed in Scilit:
- Generation and loss of reactive oxygen species in low-temperature atmospheric-pressure RF He + O2 + H2O plasmasJournal of Physics D: Applied Physics, 2012
- Electronic quenching of OH(A) by water in atmospheric pressure plasmas and its influence on the gas temperature determination by OH(A–X) emissionPlasma Sources Science and Technology, 2009
- Continuum-plasma solution surrounding nonemitting spherical bodiesPhysics of Plasmas, 2009
- New Plasma Techniques for Polymer Surface Modification with Monotype Functional GroupsPlasma Processes and Polymers, 2008
- Dielectric Barrier Discharge at Atmospheric Pressure as a Tool to Deposit Versatile Organic Coatings at Moderate Power InputPlasma Processes and Polymers, 2007
- Cross Sections for Electron Collisions with Water MoleculesJournal of Physical and Chemical Reference Data, 2005
- Continuum radiation in a high pressure argon–mercury lampPlasma Sources Science and Technology, 2004
- Critical Review of rate constants for reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals (⋅OH/⋅O− in Aqueous SolutionJournal of Physical and Chemical Reference Data, 1988
- Two-photon excitation of thelevel in H and D atomsPhysical Review A, 1981
- Determination of rate constants of reaction and lifetimes of singlet oxygen in solution by a flash photolysis techniqueJournal of the American Chemical Society, 1973