Long-lived species in plasma-activated water generated by an AC multi-needle-to-water discharge: effects of gas flow on chemical reactions

Abstract

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.

Deposition of charged aerosols by E × B enhanced low‐temperature plasma jet array

“…The measurement by aerosol spectrometer suggested the total aerosol density (diameter: 0.25–10 μm) was 1.5 × 10 9 /m 3 at the humidity of 50%, which was much lower than the ion density (15.8 × 10 12 –1.5 × 10 12 /m 3 ) shown in Figure 8, therefore, aerosols had ample opportunities to be charged. [ 15,19,35 ] The diffusion of ions to aerosols’ surface facilitated the charging of aerosols, so lots of aerosols were charged through the diffusion charging mechanism. Different from the neutral aerosols, which can only collide with each other through the thermophoretic and diffusionphoretic forces, the charged aerosols can induce the image charges in adjacent neutral aerosols, and the consequent image charge forces were the short‐range attractive and long‐range repulsive charge.…”

“…The negligible difference between plasma only case and B enhancement case is attributed to the limited increase of ion B enhancement, whereas the deposition of the E × B enhancement group was 24% more than that of the B enhancement and 108% more than the natural deposition, which confirms the contribution of higher ion density and the subsequent higher collision rate of charged aerosols generated by E × B enhancement. [ 8,15,35–37 ]…”

Focused Plasma- and Pure Water-Enabled, Electrode-Emerged Nanointerfaced NiCo Hydroxide–Oxide for Robust Overall Water Splitting

“…As shown in Figure S2, there are many active species (e.g., N 2 , N 2 + , Ar, OH, O 2 + , and H) formed in the plasma jet. 23,24,31 Noted that the emission lines at 265.5, 314.8, 336.0, 357.3, and 477.3 nm (Figure S2a) are attributed to the ionized N 2 arising from the ambient air. 25 The emission signals at 307.8, 380.1, 406.6, and 429.1 nm are derived from OH, N 2 + , H, and O 2 + , respectively, and the spectrum near 550 and 617.8 nm including the region of 700− 800 nm in Figure S2b is dominated by Ar peaks, as well as the detected O line at 774 nm.…”

Recent advances towards aqueous hydrogen peroxide formation in a direct current plasma–liquid system

“…If the discharge plasma is operated in ambient air, nitrogen oxides are usually generated in the gas phase and then dissolved in the solution to form nitrate (NO 3 − ) and nitrite (NO 2 − ) [46, 47]. It has been frequently reported that hydrogen peroxide (H 2 O 2 ) is observed in the aqueous solution after the plasma treatment [5, 48, 49]. In some cases, peroxynitrous acid (ONOOH), an unstable isomer of nitric acid (HNO 3 ) with a powerful oxidising ability, is also generated in the solution using Equation () [50, 51].…”