Anton Nikiforov

Influence of helium mole fraction distribution on the properties of cold atmospheric pressure helium plasma jets

The influence of helium mole fraction distribution in air on the cold atmospheric plasma jets excited by 1.5 kHz rectangular high voltage pulse is studied in this work. Computational fluid dynamics (CFD) with incorporation of large eddy simulation (LES) model is used to simulate the helium mole fraction distribution in air under the helium flow from laminar to turbulent regime with increasing helium outlet velocity. Numerical simulation results are combined with experimental results in order to determine the influence of helium distribution on the cold plasma jets. It reveals that the structure of the helium distribution caused by diffusion or by turbulent mixing in turbulent regime determines the characteristics of the cold plasma jets. On the other hand, the curves of plasma jet length (L) versus helium outlet velocity (V) at different jet diameters (D) are unified in a map of jet Reynolds number (Re = ρHe·V·D/μHe, where μHe is the helium viscosity constant) versus dimensionless plasma jet length (l = L...

Antimicrobial nano-silver non-woven polyethylene terephthalate fabric via an atmospheric pressure plasma deposition process

An antimicrobial nano-silver non-woven polyethylene terephthalate (PET) fabric has been prepared in a three step process. The fabrics were first pretreated by depositing a layer of organosilicon thin film using an atmospheric pressure plasma system, then silver nano-particles (AgNPs) were incorporated into the fabrics by a dipping-dry process, and finally the nano-particles were covered by a second organosilicon layer of 10-50 nm, which acts as a barrier layer. Different surface characterization techniques like SEM and XPS have been implemented to study the morphology and the chemical composition of the nano-silver fabrics. Based on these techniques, a uniform immobilization of AgNPs in the PET matrix has been observed. The antimicrobial activity of the treated fabrics has also been tested using P. aeruginosa, S. aureus and C. albicans. It reveals that the thickness of the barrier layer has a strong effect on the bacterial reduction of the fabrics. The durability and stability of the AgNPs on the fabrics has also been investigated in a washing process. By doing so, it is confirmed that the barrier layer can effectively prevent the release of AgNPs and that the thickness of the barrier layer is an important parameter to control the silver ions release.

Electrical and spectroscopic characterization of underwater plasma discharge inside rising gas bubbles

The generation of high-energetic species in plasma by discharge in liquids makes it suitable for applications such as water treatment. Effective reduction of input power and an increase in the process efficiency can be achieved by externally generated gas bubbles introduced in the liquid. Pulsed discharge in nitrogen, helium and argon bubbles in between a pin-to-plate electrode system submerged in a water solution has been investigated by electrical characterization and emission spectroscopy. A dynamic model for a bubble discharge, based on previously reported experiments and our measurements, is reported. Two types of bubble discharge are observed: a direct bubble discharge, with an immediate onset of a spark discharge inside the bubble, and a delayed bubble discharge, where spark discharge occurs after a delay time of typically several microseconds. The width of the H? Balmer line in the emitted spectra is dominated by Stark broadening and implies electron densities in the order of 1024 to 1025?m?3, which is relatively high in comparison with other low-temperature atmospherical plasmas. Also, the emitted spectra contain a continuum, originating from black-body radiation of the heated bubble gas, with black-body temperatures from 6000 to 9000?K. The dependence of the measured plasma characteristics on the experimental parameters is in agreement with our proposed model.

Measurement of OH radicals at state X 2 Π in an atmospheric-pressure micro-flow dc plasma with liquid electrodes in He, Ar and N 2 by means of laser-induced fluorescence spectroscopy

The density of OH radicals in ground state is measured by laser-induced fluorescence (LIF) spectroscopy in the core of a micro-flow discharge in He, Ar and N2 with a water electrode. The lines P2(6), P1(4) and P2(3) of the X 2 � (v �� = 0) to the A 2 + (v � = 1) transition are used for OH radical excitation. The density of the main quencher of OH radical in the core of the discharge is estimated based on the time decay of the LIF signal. It is revealed that the plasma core consists of a high amount of 8–10% of water vapour. The calculation of the absolute density of OH radical is carried out based on the model of LIF excitation including vibrational and translation energy transfer, and the results in different gases are presented for the discharge. (Some figures may appear in colour only in the online journal)

Removal of atrazine in water by combination of activated carbon and dielectric barrier discharge

Efficiency of modern wastewater treatment plants to remove or decompose persistent contaminants in low concentration is often insufficient to meet the demands imposed by governmental laws. Novel, efficient and cheap methods are required to address this global issue. We developed a new type of plasma reactor, in which atrazine decomposition by atmospheric dielectric barrier discharge (DBD) in dry air is combined with micropollutant adsorption on activated carbon textile and with extra bubbling of generated ozone. Investigation of reaction kinetics and by-product analysis shows that increasing input power with a factor 3.5 leads to deeper atrazine oxidation without significantly changing energy yield of atrazine removal. By-products of first and later generations are detected with HPLC-MS analysis in water and adsorbed on the activated carbon textile. Our reactor is compared in energy efficiency with reactors described in literature, showing that combination of plasma discharge with pollutant adsorption and ozone recycling is attractive for future applications of water treatment.

Influence of air diffusion on the OH radicals and atomic O distribution in an atmospheric Ar (bio)plasma jet

Treatment of samples with plasmas in biomedical applications often occurs in ambient air. Admixing air into the discharge region may severely affect the formation and destruction of the generated oxidative species. Little is known about the effects of air diffusion on the spatial distribution of OH radicals and O atoms in the afterglow of atmospheric-pressure plasma jets. In our work, these effects are investigated by performing and comparing measurements in ambient air with measurements in a controlled argon atmosphere without the admixture of air, for an argon plasma jet. The spatial distribution of OH is detected by means of laser-induced fluorescence diagnostics (LIF), whereas two-photon laser-induced fluorescence (TALIF) is used for the detection of atomic O. The spatially resolved OH LIF and O TALIF show that, due to the air admixture effects, the reactive species are only concentrated in the vicinity of the central streamline of the afterglow of the jet, with a characteristic discharge diameter of ~1.5 mm. It is shown that air diffusion has a key role in the recombination loss mechanisms of OH radicals and atomic O especially in the far afterglow region, starting up to ~4 mm from the nozzle outlet at a low water/oxygen concentration. Furthermore, air diffusion enhances OH and O production in the core of the plasma. The higher density of active species in the discharge in ambient air is likely due to a higher electron density and a more effective electron impact dissociation of H2O and O2 caused by the increasing electrical field, when the discharge is operated in ambient air.

Chemical Efficiency of

A dc underwater discharge generated in gas bubbles (air, Ar, He, and N2) in a NaH2PO4 · 2H2O solution is studied. It is shown that the maximal concentration of hydrogen peroxide produced in the discharge does not depend on gas composition. The energy efficiency of H2O2 production is, however, gas dependent, and the highest value of 2.95 g/kWh is obtained for air. The decomposition efficiency of the Direct Blue 106 dye, which is used as a model organic pollutant at an initial concentration of 20 mg/L, increases linearly with current in the investigated range (10-30 mA). A maximal dye decoloration of 65% is observed in a N2 discharge after 20 min of treatment at a current of 30 mA. Different mechanisms of dye decoloration by plasma are proposed and discussed.

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Hazardous micropollutants are increasingly detected worldwide in wastewater treatment plant effluent. As this indicates, their removal is insufficient by means of conventional modern water treatment techniques. In the search for a cost-effective solution, advanced oxidation processes have recently gained more attention since they are the most effective available techniques to decompose biorecalcitrant organics. As a main drawback, howev‐ er, their energy costs are high up to now, preventing their implementation on large scale. For the specific case of water treatment by means of electrical discharge, further optimi‐ zation is a complex task due to the wide variety in reactor design and materials, dis‐ charge types, and operational parameters. In this chapter, an extended overview is given on plasma reactor types, based on their design and materials. Influence of design and ma‐ terials on energy efficiency is investigated, as well as the influence of operational parame‐ ters. The collected data can be used for the optimization of existing reactor types and for development of novel reactors.

Production and Decomposition of Organic Compounds Under Action of DC Underwater Discharge in Gas Bubbles

This paper investigates the generation of a stable plasma phase in a liquid hydrocarbon (n-dodecane) by means of ultrasound (US) and radio-frequency (RF) or electromagnetic radiation. It is demonstrated for the first time that ultrasonic aided RF plasma discharges can be generated in a liquid. Plasma discharges are obtained for different gas mixtures at a pressure of 12?kPa and at low ignition powers (100?W for RF and 2.4?W?cm?2 for US). Direct carbon deposition from the liquid precursor on Cu, Ni, SiO2 and Si substrates has been obtained and no apparent compositional or structural difference among the substrate materials was observed. Characterization of the deposited solid phase revealed an amorphous structure. In addition, structural changes in the liquid precursor after plasma treatment have been analysed. Optical emission spectroscopy (OES) allowed the estimation of several plasma characteristic temperatures. The plasma excitation temperature was estimated to be about 2.3?2.4?eV. The rotational and vibrational temperatures of the discharge in n-dodecane with Ar as a feed gas were 1400?K and 6500?K, respectively. In Ar/O2 plasma, an increased rotational (1630?K) and vibrational temperature (7200?K) were obtained.

Electrical discharge in water treatment technology for micropollutant decomposition

Abstract In this work, degradation of the anthraquinonic dye Acid Blue 25 by non-thermal plasma at atmospheric pressure with and without photocatalyst is investigated. Titanium dioxide (TiO2) is used as a photocatalyst. The dye degradation by plasma in the presence of TiO2 is investigated as a function of TiO2 concentration, dye concentration and pH. The degradation rate is higher in acidic solutions with pH of 2 to 4.3, especially at pH 2, and decreases to 0.38 mg L-1 min-1 with the increase of pH from 2 to 5.65. A similar effect is observed in basic media, where a higher degradation rate is found at pH = 10.3. The degradation rate increases in the presence of TiO2 compared to the discharge without photocatalysis. The results show that the degradation of the dye increases in the presence of TiO2 until the catalyst load reaches 0.5 g L-1 after which the suppression of AB25 degradation is observed. The results indicate that the tested advanced oxidation processes are very effective for the degradation of AB25 in aqueous solutions. Graphical Abstract