Plasma-activated water (PAW) represents a promising green antibacterial agent for biomedical and agricultural applications. In this study, a novel AC multi-needle-to-water discharge device was developed to investigate the effects of gas flow on the generation and chemical composition of PAW. It is shown that the concentrations of NO 3 − and N(III) ( NO 2 − and HN O 2 ) in the PAW both increased with an extension of the plasma-processing time and a reduction of the gas-flow rate. The absorption of gas-phase products carried by the gas flow from the discharge chamber was found to be beneficial for the generation of both NO 3 − and N(III) in the PAW at a gas flow rate of 20–60 L h−1, yet their concentrations were still lower than those without any feeding gas. As opposed to NO 3 − or N(III), the H 2 O 2 concentration in the plasma-activated phosphate buffer solution (PAPBS) increased under stronger gas flows and was almost unaffected by absorption in PAPBS. The pH value of PAW increased at higher gas flow rates. A comparison of the N(III) in PAW and PAPBS reflects the effects of the reactions of NO 2 − and H 2 O 2 in the two different working liquids. To quantify the effects of gas flow on the discharge characteristics, gas temperatures were calculated from the optical emission spectra and were proven to be flow-independent near the discharge channel. Fourier transform infrared (FTIR) measurements of the gaseous products during the discharge, and further analysis of possible reaction pathways indicated that by controlling the gas flow in the multi-needle-to-water discharge system, the concentration of long-lived species in PAW could be tuned, which might favor the generation of ONOOH . These findings contribute to a better understanding of effective electric discharge-related mechanisms for enhancing the biochemical and chemical activities of PAW.
To gain insights into the mechanisms of the plasma chemical product interactions, the dynamic changes of the surface dielectric barrier discharge (SDBD) products are experimentally related to the reduced electric...
Nitrogen oxide-generating dielectric barrier discharge plasma is shown to effectively inhibit microorganisms and maintain fruit freshness. Physical and biological mechanisms of the plasma-electrified fungicidal effects suggest that plasma-generated NO
To gain insight into the interaction mechanism among the gaseous products of atmospheric pressure air plasma, using a surface dielectric barrier discharge as the study object, the dynamic processes of characteristic products (nitric oxide NO and ozone O<sub>3</sub>) concentrations were measured by in-situ Fourier infrared spectroscopy and UV absorption spectroscopy, respectively; the real energy density of the plasma was calculated by Lissajous figure and ICCD optical image; and the gas temperature was obtained by fitting the emission spectrum of the second positive band of the nitrogen molecule. The results showed that the real energy density and gas temperature were highly positively correlated with the applied voltage and frequency. Higher applied voltages and frequencies could lead to lower peak absorbance of O<sub>3</sub> and higher absorbance of NO, and accelerate the conversion of the products from O<sub>3</sub>-containing state to O<sub>3</sub>-free state. The microscopic mechanism of the product changes was revealed by analyzing the effects of the real energy density and gas temperature on the major generation and quenching chemical reactions of the characteristic products. The analysis pointed out that there are two major reasons for the disappearance of O<sub>3</sub>, the quenching effect of O and O/O<sub>2</sub> excited state particles on O<sub>3</sub> as well as the quenching effect of NO on O<sub>3</sub>. And the mechanism of O<sub>3</sub> disappearance accelerates with the increase of energy density and gas temperature are following: as the real energy density increases, it means that the energy injected into the discharge region is boosted, which intensifies the collision reaction to produce more energetic electrons as well as reactive oxygen and nitrogen particles. Since the discharge cavity is gas-tight, the rapid generation of O leads to a rapid increase in the ratio of O to O<sub>2</sub>, which accelerates the decomposition of O<sub>3</sub>; besides, the gas temperature was raised due to the intensification of the collision reaction. Whereas the gas temperature could change the rate coefficients of the chemical reactions involving the excited state particles of nitrogen and oxygen to regulate the production and quenching of the products. The increase of gas temperature has a negative effect on O<sub>3</sub>. The higher the gas temperature is, the lower the rate of O<sub>3</sub> generation reaction is, but the higher the rate of dissociation is, which was thought to be the endogenous cause of the rapid disappearance of O<sub>3</sub>. In contrast, the rise in gas temperature could significantly elevate the reaction rate of NO production and decrease its dissociation rate. This contributes to the faster production of massive NO, resulting in an accelerated quenching process of NO to O<sub>3</sub>, which could be considered as the exogenous cause of the rapid disappearance of O<sub>3</sub>. In a word, based on the analysis above, it contributes to a better understanding of the physico-chemical processes in atmospheric pressure low-temperature plasma.
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