Quantification of plasma produced OH radical density for water sterilization

Abstract

The interactions between plasma-generated excited particles and water play an integral role in sustainable degradation of pharmaceutical compounds, improving aerobic respiration of activated sludge, and efficient removal of microorganisms from water, and are fundamental to the intentional transfer of reactivity from plasmas to biological solutions for such medical applications as cancer treatment and wound healing. The physical and chemical mechanisms that govern this transfer of reactivity are complex, and include concomitant generation and consumption of species in the gas and liquid phases, and at the interface. As such, it is challenging to predict the quantities of biologically-active radicals and molecules in liquid phase from gas phase measurements alone. Rapid and accurate quantification of reactive species, such as OH radicals and H 2 O 2 molecules within the liquid phase and their link to specific biological effects is therefore critical for medical applications of plasmaactivated solutions. Using a simple, low-cost method for trapping and stabilization of OH radicals by means of salicylic acid, this work seeks to provide further insights into the physics and chemistry of generation of OH radicals within the liquid phase, and integrate these findings with decontamination outcomes for four commonly used processing gases.

Direct Treatment of Liquids Using Low-Current Arc in Ambient Air for Biomedical Applications

“…As shown in Figure 6, the optical emissions from the N 2 second positive system (C 3 Π → B 3 Π) at 316, 337, 357, 380, and 405 nm; the N 2 + first negative system (B 2 Σ u + → X 2 Σ g +) at 391.4 nm; and the OH emissions from the transition of A 2 Σ+ → X 2 Π at 309 nm were clearly observed for AALCA [44]. Evaporation of the liquid discussed above could be the source of OH radicals, which could be produced by electron impact dissociation of water molecules [14]. Despite the presence of hydrogen from evaporated water, hydrogen emission lines (e.g., H α and H β ) were not observed in the spectra.…”

“…The observed concentrations were two orders of magnitude higher than those of 5 mL DI water treated for 1 min with commercially available NEAPPJ operated with He (0.37 mg/L of H2O2, 0.18 mg/L of NO2 − , and 0.06 mg/L of NO3 − ). Additionally, considerably small concentrations of RONS in water treated using NEAPPJ (up to 890 µg/L of H2O2, up to 180 µg/L of NO2 − , and up to 410 µg/L of NO3 − ) [20][21][22]45,46] and custom plasma jets operated with air or addition of air (up to 9.3 mg/L of H2O2, up to 4 mg/L of NO2 − , and up to 5.5 mg/L of NO3 − ) [14,28,47,48] were reported elsewhere, confirming the high efficiency of the developed AALCA as compared with commonly used nonequilibrium plasma jets.…”

“…Recently, treatment of liquids using various atmospheric pressure plasmas has attracted much attention owing to its wide range of possible applications, such as synthesis of nanocarbons and nanoparticles, sterilization of microorganisms, growth enhancement of plants, plasma farming, cancer therapy, and water purification [1][2][3][4][5][6][7][8][9][10][11][12][13]. Typically, low-temperature nonequilibrium atmospheric pressure plasma jets (NEAPPJs) or dielectric barrier discharges (DBDs) are used for activation of liquids by plasma [5,[12][13][14][15][16]. However, in both the case of atmospheric pressure plasma jet (APPJ) and DBD, the production rate of reactive oxygen and nitrogen species (RONS), which play key roles in bactericidal effect and plant growth promotion, is low and irradiation of the liquid takes a long time (from several minutes to hours) due to the low density of the plasma [5,[12][13][14][15][16][17][18][19][20][21].…”

“…Typically, low-temperature nonequilibrium atmospheric pressure plasma jets (NEAPPJs) or dielectric barrier discharges (DBDs) are used for activation of liquids by plasma [5,[12][13][14][15][16]. However, in both the case of atmospheric pressure plasma jet (APPJ) and DBD, the production rate of reactive oxygen and nitrogen species (RONS), which play key roles in bactericidal effect and plant growth promotion, is low and irradiation of the liquid takes a long time (from several minutes to hours) due to the low density of the plasma [5,[12][13][14][15][16][17][18][19][20][21]. Moreover, in most cases, plasma is generated using pure gases (e.g., argon, helium, or oxygen) at a high voltage, so a substantial amount of electrical energy is required to sustain the discharge and only a limited volume (typically several milliliters) of medium can be treated at one time [4,7,17,[19][20][21][22].…”

Mode transition and plasma characteristics of nanosecond pulse gas–liquid discharge: Effect of grounding configuration

“…Atmospheric pressure gas–liquid discharges have been widely applied in materials processing, water purification, and biomedicine, in great part due to the abundance of reactive chemical species . In these applications, the chemical activity of gas–liquid discharge plasma is crucial, and many efforts have been made to better serve the applications.…”