Chemistry of the Positive and Negative Electrical Discharges Formed in Liquid Water and Above a Gas–Liquid Surface

Abstract

The physical processes and chemical reactions that take place inside different temperature plasma zones in water are only partially understood. The present study uses the emission spectroscopy and hydrogen peroxide measurements as indicators of the processes that take place on the gas-liquid boundary and inside plasma. Based on the hydrogen peroxide measurements with negative and positive high-voltage polarities as a function of solution conductivity, it was concluded that the main difference between positive polarity plasma and negative polarity plasma lies in the active radical concentration inside plasma. Data suggested that in the positive polarity electrical discharge the hydrogen peroxide concentration depends on the solution pH, whereas in the negative polarity discharge, it depends on the solution conductivity. Also, only in the negative polarity discharge do some of the electrons that are emitted from the high voltage electrode diffuse into the bulk where they react with the solutes.

Assessment of Damage of Glutathione by Glow Discharge Plasma at the Gas–Solution Interface through Raman Spectroscopy

“…Water molecules in solution are ionized and activated by collision with these positive ions under the acceleration of cathode drop near the solution surface, followed by formation of primary free radicals, including hydroxyl radical, aqueous electron, hydrogen radical, and so on. [5,[17][18][19] e…”

“…It not only originated from the dissociation of water molecules, but also from the neutralization of aqueous electron by hydrogen ion in acid solution as in our experimental conditions (pH 3.1). [18,61] Littman et al have examined the products of aqueous phase reactions between hydrogen radical and cysteine and found that the cystine was the main product in acid or neutral solution. [62] The formation mechanism was explained satisfactorily by reaction (3).…”

“…[8,[12][13][14][15][16] As a form of advanced oxidation-reduction processes (AORP), discharge plasma can induce the generation of large number of oxidative and reductive free radicals, such as hydroxyl radical, hydrogen radical, aqueous electron, and so on. [17][18][19] Most applications of this technique are dependent on the reactions of the dissolved materials/pollutants with the generated chemical reactive species. For example, as for the environmental application, the generated reactive species can be used directly to degrade or remove pollutants from solution, [5][6][7][8] or to modify the physicochemical properties of absorbents.…”

Kinetics and Mechanism of Cr(VI) Reduction in a Water Cathode Induced by Atmospheric Pressure DC Discharge in Air

“…High voltage (up to 4 kV) was applied between liquid electrolyte cathode and steel anode placed at a distance of 10 mm, h, above the solution surface. The given polarity of a discharge was chosen since it is well known that the discharges with a liquid cathode provide a higher chemical activity [11]. The anode was made from mechanically sharpened stainless steel wire (radius of curvature is *100 lm).…”

Degradation of microcystin-LR in water by glow discharge plasma oxidation at the gas–solution interface and its safety evaluation

“…This leads to formation of chemically active species, ultraviolet radiation and shock waves. Lots of active molecular such as hydrogen, oxygen, hydrogen peroxide and active radicals such as hydroxyl radical, hydroperoxyl radical, oxygen radical and hydrogen radical are produced Thagard et al, 2009). Among these active species, hydroxyl radical ( OH) plays an important role in the degradation of organic pollutants in wastewater.…”