2019 journal article

Atmospheric pressure plasma activation of water droplets

Journal of Physics D: Applied Physics, 5.

By: J. Kruszelnicki, A. Lietz* & M. Kushner

author keywords: plasma activation water droplets; plasma chemistry; plasma-water interactions
UN Sustainable Development Goal Categories
6. Clean Water and Sanitation (OpenAlex)
Source: ORCID
Added: February 1, 2023

Low temperature plasma treatment of water is being investigated due to its use in pollution abatement, wound treatment and agriculture. Plasma produced reactive oxygen and nitrogen species (RONS) are formed in the gas phase and solvate into the liquid. Activation of the liquid is often limited by transport of these RONS to the liquid surface. Micrometer scale droplets immersed in the plasma have a large surface to volume ratio, which increases the interaction area for a given volume of water, and can increase the rates of transport from the gas to liquid. In this paper, results from 0 and 2D modeling of air-plasma activation of water micro-droplets are discussed. The solvation dynamics are sensitive to the Henry’s law constant (h) of each species, which describes its hydrophobicity (low h) or hydrophilicity (high h). The liquid densities of stable species with high h values (e.g. H2O2, HNOx) are sensitive to droplet diameter. For large droplets, hydrophilic species may deplete the gas-phase inventory of RONS before liquid-phase saturation is reached, limiting the total in-liquid density for species with high h. For smaller droplets, higher average in-droplet densities of these species can be produced. Liquid concentrations of stable species with low h (e.g. O3, N2O, H2) had a weak dependence on droplet size as droplets are quickly saturated and solvation does not deplete the gas phase. An analysis of this behavior is discussed using the well-stirred reactor (0D) approximation. Spatial non-uniformity of the plasma also has an impact on the solvation rates and kinetics. Gas phase depletion of high-h species leads to a decrease in solvation rates. Low-h species that saturate the surface of the droplets during plasma-on periods can quickly de-solvate in the afterglow.