Mechanisms leading to plasma activated water high in nitrogen oxides

• Published in: Physica scripta Vol. 98; no. 4; pp. 45619 - 45630
• Main Authors: Matějka, F, Galář, P, Khun, J, Scholtz, V, Kůsová, K
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01-04-2023
• Subjects: mechanisms of nanoparticles surface modifications; non-thermal plasma; plasma activated water; plasma-liquid phase interaction
• ISSN: 0031-8949; 1402-4896
• DOI: 10.1088/1402-4896/acc48e

Abstract
Plasma activated water (PAW) is a unique highly reactive medium, traditionally used in medicine and agriculture because of its decontamination and disinfection abilities. Recently, we have shown that this medium can also be beneficial for tailoring the surface chemistry of semiconductor nanostructures if its composition is tuned to contain a high concentration of nitrogen-related species (HiN:PAW). However, pathways leading to the production of HiN:PAW remained unclear, which we address in this article. By monitoring the composition of the produced PAW and the concentration of selected species in the discharge under different activation geometries and discharge conditions, we identify the activation geometries favourable for the production of HiN:PAW using two phenomenological factors, a barrier parameter
P
and a maximum effective radius of the vessel
r
max
. A key point is the presence of a barrier area in the discharge reactor, which forms as a result of the favourable activation geometry and a discharge with prevailing more reactive atomic species. This area acts as a partial barrier between the discharge and the surrounding air atmosphere, limiting, but still allowing a flow of source N
2
molecules from the surrounding atmosphere. The minimal and ideal build-up times of 10 and 30 min, respectively, for the discharge to stabilize are also reported. Using the reported experimental settings, we were able to produce HiN:PAW containing a mixture of various reactive species beneficial for the surface modification of nanoparticles, with the NO
3
−
to H
2
O
2
ratio of at least 20 × 10
3
: 1, in contrast to approximately 1:1 under more traditional conditions.