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Abstract Plasmas in contact with liquids can degrade organic molecules in a solution, as reactive oxygen and nitrogen species produced in the plasma solvate into the liquid. Immersing small droplets (tens of microns in diameter) in the plasma can more rapidly activate the liquid compared to treating a large volume of liquid with a smaller surface-to-volume ratio. The interactions between a radio frequency glow discharge sustained in He/H2O and a water droplet containing formate (HCOO−aq) immersed in and flowing through the plasma were modeled using a zero-dimensional global plasma chemistry model to investigate these activation processes. HCOO−aqinteracts with OHaq, which is produced from the solvation of OH from the gas phase. The resulting HCOO−aqconcentrations were benchmarked with previously reported experimental measurements. The diameter of the droplet, initial HCOO−aqconcentration, and gas flow rate affect only the HCOO−aqconcentration and OHaqdensity, leaving the OH density in the gas phase unaffected. Power deposition and gas mixture (e.g. percentage of H2O) change both the gas and liquid phase chemistry. A general trend was observed: during the first portion of droplet exposure to the plasma, OHaqprimarily consumes HCOO−aq. However, O2−aq, a byproduct of HCOO−aqconsumption, consumes OHaqonce O2−aqreaches a critically large density. Using HCOO−aqas a surrogate for OHaq-sensitive contaminants, combinations of residence time, droplet diameter, water vapor density, and power will determine the optimum remediation strategy.
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Generation of Reactive Species in Water Film Dielectric Barrier Discharges Sustained in Argon, Helium, Air, Oxygen and Nitrogen
Activation of liquids with atmospheric pressure plasmas is being investigated for envi-ronmental and biomedical applications. When activating the liquid using gas plasma produced species (as opposed to plasmas sustained in the liquid), a rate limiting step is transport of these species into the liquid. To first order, the efficiency of activating the liquid is improved by in-creasing the ratio of the surface area of the water in contact with the plasma compared to its vol-ume – often called the surface-to-volume ratio (SVR). Maximizing the SVR then motivates the plasma treatment of thin films of liquids. In this paper, results are discussed from a computa-tional investigation using a global model of atmospheric pressure plasma treatment of thin water films by a dielectric barrier discharge (DBD) sustained in different gases (Ar, He, air, N2, O2). The densities of reactive species in the plasma activated water (PAW) are evaluated. The resi-dence time of the water in contact with the plasma is increased by recirculating the PAW in plasma reactor. Longer lived species such as H2O2aq and NO3−aq accumulate over time (aq de-notes an aqueous species). DBDs sustained in Ar and He are the most efficient at producing H2O2aq, DBDs sustained in argon produces the largest density of NO3−aq with the lowest pH, and discharges sustained in O2 and air produce the highest densities of O3aq. Comparisons to experi-ments by others show agreement in the trends in densities in PAW including O3aq, OHaq, H2O2aq and NO3−aq, and highlight the importance of controlling desolvation of species from the activated water.
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- Award ID(s):
- 1902878
- PAR ID:
- 10175604
- Date Published:
- Journal Name:
- Journal of Physics D: Applied Physics
- ISSN:
- 0022-3727
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1088/1361-6463/aba21a
