Martin Clupek

GENERATION OF CHEMICALLY ACTIVE SPECIES BY ELECTRICAL DISCHARGES IN WATER

Pulse positive streamer corona discharges in water solution with a different conductivity have been investigated in reactors with the needle-plate and coaxial electrode geometry. A special composite anode was used in the coaxial geometry. With such an anode hundreds of streamers were generated at each voltage pulse. Production of H, O and OH radicals by the discharge was proved by emission spectroscopy and formation of H2O2 and degradation of phenol was demonstrated by chemical methods. Assuming that the broadening of the line profile was caused by the dynamic Stark effect, plasma with an electron density over 1018 cm-3 was generated during the initial phase of voltage pulse in the both reactors in spite of the very different electrode geometry and wave-forms of voltage pulses. Production of OH radicals was most effective at solution conductivity below .

Aqueous-phase chemistry and bactericidal effects from an air discharge plasma in contact with water: evidence for the formation of peroxynitrite through a pseudo-second-order post-discharge reaction of H2O2 and HNO2

The formation of transient species (OH?, NO2?, NO radicals) and long-lived chemical products (O3, H2O2, , ) produced by a gas discharge plasma at the gas?liquid interface and directly in the liquid was measured in dependence on the gas atmosphere (20% oxygen mixtures with nitrogen or with argon) and pH of plasma-treated water (controlled by buffers at pH 3.3, 6.9 or 10.1). The aqueous-phase chemistry and specific contributions of these species to the chemical and biocidal effects of air discharge plasma in water were evaluated using phenol as a chemical probe and bacteria Escherichia coli. The nitrated and nitrosylated products of phenol (4-nitrophenol, 2-nitrophenol, 4-nitrocatechol, 4-nitrosophenol) in addition to the hydroxylated products (catechol, hydroquinone, 1,4-benzoquinone, hydroxy-1,4-benzoquinone) evidenced formation of NO2?, NO? and OH? radicals and NO+ ions directly by the air plasma at the gas?liquid interface and through post-discharge processes in plasma-activated water (PAW) mediated by peroxynitrite (ONOOH). Kinetic study of post-discharge evolution of H2O2 and in PAW has demonstrated excellent fit with the pseudo-second-order reaction between H2O2 and . The third-order rate constant k?=?1.1???103?M?2?s?1 for the reaction was determined in PAW at pH 3.3 with the rate of ONOOH formation in the range 10?8?10?9?M?s?1. Peroxynitrite chemistry was shown to significantly participate in the antibacterial properties of PAW. Ozone presence in PAW was proved indirectly by pH-dependent degradation of phenol and detection of cis,cis-muconic acid, but contribution of ozone to the inactivation of bacteria by the air plasma was negligible.

Generation of ozone by pulsed corona discharge over water surface in hybrid gas–liquid electrical discharge reactor

Ozone formation by a pulse positive corona discharge generated in the gas phase between a planar high voltage electrode made from reticulated vitreous carbon and a water surface with an immersed ground stainless steel plate electrode was investigated under various operating conditions. The effects of gas flow rate (0.5–3 litre min−1), discharge gap spacing (2.5–10 mm), applied input power (2–45 W) and gas composition (oxygen containing argon or nitrogen) on ozone production were determined. Ozone concentration increased with increasing power input and with increasing discharge gap. The production of ozone was significantly affected by the presence of water vapour formed through vaporization of water at the gas–liquid interface by the action of the gas phase discharge. The highest energy efficiency for ozone production was obtained using high voltage pulses of approximately 150 ns duration in Ar/O2 mixtures with the maximum efficiency (energy yield) of 23 g kW h−1 for 40% argon content.

Ultraviolet radiation from the pulsed corona discharge in water

Quantitative analysis of ultraviolet radiation from the pulsed corona discharge in water with needle-plate electrode geometry (~1?3?J?pulse?1) was performed using the potassium ferrioxalate actinometry. Photon flux J190?280 and radiant energy Q190?280 of the UV light emitted from the discharge at spectral region 190?280?nm was determined in dependence on the applied voltage (17?29?kV, positive polarity) and the solution conductivity (100?500??S?cm?1). The intensity of the UV radiation strongly increased with increasing water conductivity and applied voltage. Depending on the applied voltage the determined photon flux varied by more than two orders of magnitude within the range of solution conductivities 100?500??S?cm?1. It was found that photon flux from the discharge may be directly related to the discharge pulse mean power Pp as J190?280 = 44.33 (quanta?pulse?1). A significant role of UV radiation in the production of hydrogen peroxide and bacterial inactivation by the corona discharge in water has been identified. As the solution conductivity increased the yield of H2O2 produced by the discharge decreased due to increasing photolysis of H2O2 accounting for up to 14% of the total decomposition rate of H2O2. As regards bactericidal effects, it was estimated that the UV radiation contributes about 30% to the overall inactivation of Escherichia coli.

Efficiency of ozone production by pulsed positive corona discharge in synthetic air

We have studied the efficiency of ozone production by pulsed positive corona discharge in coaxial wire-cylinder geometry at atmospheric pressure. A corona discharge was generated by short (~150 ns) high voltage pulses applied between a silver coated copper wire anode and stainless steel cylinder cathode in synthetic air. A pyrex probe and Teflon tube was used for collecting discharge products and an ozone concentration was monitored outside of the discharge chamber by a non-dispersive UV absorbtion technique. The production of ozone was investigated as a function of energy density (10-4-3×10-1 Wh l-1) delivered to the discharge volume by combining the discharge frequency (0.1-10 Hz) and airflow rate (1-32 l min-1). From ozone concentration measurements we have evaluated the ozone production, yield and production energy cost. The ozone production yield and cost vary in the range of 15-55 g kWh-1 and 35-110 eV/molecule.

Degradation of phenol by underwater pulsed corona discharge in combination with TiO2 photocatalysis

Non-thermal plasma-induced degradation of phenol by pulsed high-voltage discharge generated in water using point to plane geometry of electrodes was investigated in the presence of photocatalytically active TiO2. The phenol removal attributed directly to the effects of plasma chemical activity of the discharge was enhanced in the presence of TiO2. At the same time, higher formation of 1,4-benzoquinone as the main primary aromatic by-product and increased accumulation of hydrogen peroxide in the solution were found. The main effect of TiO2 addition was in the utilizing of ultraviolet radiation from the plasma resulting in the photocatalytical formation of OH radicals on the surface of TiO2 particles and, thus, in the increase of the yield of OH radicals available for phenol degradation.

Excitation of ) and ) states in a pulsed positive corona discharge in , - and -NO mixtures

Time resolved multichannel emission spectroscopy has been applied to study emission in the 200-500 nm spectral range produced by a pulsed positive corona discharge. The discharge was driven in coaxial geometry by an HV power supply (100 kV/1 kA) at atmospheric pressure in nitrogen, and in and mixtures. Emission of NO- (-) and 2.PG (-) bands has been studied in order to trace the development of and electronic states during both discharge and post-discharge periods. Analysis of spectroscopic data indicates an evolution of the electron mean energy during the discharge pulse in the range 20-1 eV and post-discharge kinetics of the NO and electronic states which is predominantly controlled by , v = 0,1) metastable species.

Pulsed Electrical Discharge in Water Generated Using Porous-Ceramic-Coated Electrodes

A special metallic electrode covered by a thin layer of porous ceramic prepared by the technology of thermal plasma spraying has been developed and used for the generation of large-volume nonthermal plasma in water. Images of multichannel pulsed electrical discharge generated in water at the composite electrode as a function of solution conductivity are presented.

Localized damage of tissues induced by focused shock waves

A novel method for generation of focused shock waves has been developed. A cylindrical pressure wave, created by a high-voltage multichannel discharge in water with an increased electrical conductivity, is focused by a metallic parabolic reflector. The discharge is formed on a composite anode consisting of a cylindrical stainless steel electrode covered by a thin porous ceramic layer. In such an arrangement at the applied voltage of 30 kV, a large number of short discharge channels distributed homogeneously on the anode surface is initiated. Each discharge channel creates a semi-spherical pressure wave, and by superposition of all of the waves, a cylindrical pressure wave propagating from the anode is formed. The cylindrical pressure wave is focused by a metallic parabolic reflector (cathode) and near the focus it is transformed into a strong shock wave. The focal volume is 2.5 mm in diameter and 32 mm long. We have demonstrated that the focused shock waves destroy human red blood cells (erythrocytes) very efficiently. Interaction of the focused shock waves with fresh potatoes that have high water content have been used to assess the mechanical effects of the waves. The 6-cm-thick slab of potato was placed next to the focal region and exposed to 10 shocks at 30 kV. The experiment demonstrated that only the focal region inside the potato had been damaged and no damage was seen between the potato surface and the focal region. Local injury of animal liver tissues exposed to the shock waves were observed in vitro. Livers of three rabbits have been exposed in vivo. Histological analysis of the exposed tissues revealed injuries and hemorrhages at the focal region of the shock waves.

Time and space resolved analysis of N 2 (C 3 Π u ) vibrational distributions in pulsed positive corona discharge

Time- and space-resolved emission spectroscopy was applied to study the N2(C 3 � u → B 3 � g) and NO(A 2 � + → X 2 � r) emission induced by pulsed positive primary streamers in coaxial geometry generated in high-purity