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In recent years, nanoparticles have emerged as an important player in a broad range of applications, especially thanks to recent advances in their synthesis. The silver and copper nanoparticles are often used due to their antibacterial and fungicidal activities, and this article presents the results of the nanoparticle synthesis using electrical glow discharge generated directly in a volume of their salt solutions. Therefore, there is no influence of air (i.e. reactive nitrogen species) as it is usual in other commonly used approaches. Nanoparticles were prepared under various experimental conditions, and they were characterized by ultraviolet/visible spectrometry, dynamic light scattering, X-ray photoelectron spectroscopy, and high-resolution scanning electron microscopy. Particles were produced without any surfactant or stabilizing agent, and some of them showed higher resistance against agglomeration during their short-term (days) storage. The nanoparticle formation mechanism was confirmed by the fast camera imaging. Thus, the developed approach can be applied for simple environmentally friendly nanoparticle production for various applications.

This paper presents results on electric discharge generation by high frequency high voltage (15–100 kHz) in NaCl solutions with different initial conductivity (100–1300 mS cm-1), and compares them with DC discharge in the same electrode configuration. A batch plasma reactor in the pin-hole configuration contained a ceramic dielectric barrier separating two planar stainless steel electrodes; barrier thickness of 0.6 mm and pin-hole diameter of 0.6 mm was used. Lissajous charts were evaluated from electric measurements for different discharge phases (electrolysis, bubble formation and discharge regular operation). Breakdown moments for different solution conductivities were determined from discharge power evaluation as a function of applied frequency. Breakdown voltage amplitude was decreased by the increasing conductivity in both regimes while frequency and current decreased. Changes of physical parameters (temperature, solution conductivity and pH) as well as production of hydrogen peroxide at different solution conductivities were compared. Solution conductivity was increased in both discharge regimes and with the initial conductivity value. Solution temperature was increased by the discharge in both regimes and with the increasing initial conductivity, too. Solution pH dropped to acidic conditions when HF or DC positive regime was applied while it was enhanced by DC negative regime.

This work focuses on the antimycotic effects of the plasma gun as a potential tool for the treatment of superficial infections. Candida glabrata was chosen as a model microorganism. The preliminary tests have been done on the agar plates to establish the basic plasma parameters. To render this research more appropriate to the real application, more complex inoculation substrates, pork skin and 3D‐printed models of the dog ear canal have been used. The results of this work confirm the high efficiency of cold plasma in the inhibition of yeasts on different surfaces and will lead to further experiments. [ABSTRACT FROM AUTHOR]

Four different cold plasma sources were directly applied onto a 24h inoculum of Candida glabrata inoculated on agar plates, within the limits of in vitro experiment. Their effects were compared and evaluated with respect to the size and stability of the inhibition zones formed in the posttreatment cultivation. The results prove significant inhibitory cold atmospheric‐pressure plasma effects on the yeast C. glabrata. The overall inhibitory effects are directly proportional to the treatment time, the applied power, and the overall functioning of the plasma source and indirectly proportional to the initial cell concentration, although this factor was less significant compared to the other examined factors. The unipolar microwave torch was found to be the most effective in the inhibition of C. glabrata. [ABSTRACT FROM AUTHOR]

The pinhole discharge using a novel electrode configuration was generated in various water–ethanol mixtures. Proton transfer reaction time-of-flight mass spectrometry was used for the diagnostics of stable discharge products. The sampling was realized by nitrogen constant flow over the liquid surface. Mostly, aliphatic hydrocarbons were detected. The number of products and their concentrations was observed in the dependence on the changing experimental conditions: alcohol concentration in the solution, the electrodes polarity, and the discharge duration. More compounds were detected with the increasing alcohol concentration and in the case of the positive polarity of the pinhole electrode. [ABSTRACT FROM AUTHOR]

This study compares the effects of nonthermal plasma treatment on quinine water solutions for two configurations—the corona‐like discharge and the gliding arc discharge (GAD). Different electrolytes were added to the quinine solutions to modify the initial pH and enhance electrical conductivity for plasma discharge ignition directly in the liquid. A slightly higher quinine decomposition rate of 2.9 μg W−1 after 5 min of the treatment was achieved by GAD. From measured spectra, it was found that the absorption maximum at 332 nm was split into two separated peaks in the acidic and basic solution. The study of the time stability of quinine solutions has revealed quinine instability and that postpreparation time has influenced the plasma treatment effect. [ABSTRACT FROM AUTHOR]

Fourier‐transform infrared spectroscopy and proton‐transfer‐reaction–mass spectrometry are used in a complementary way to study gas‐phase processes during decomposition of ethanol in a microwave plasma torch. Decomposition products (C, C2 and simple hydrocarbons) reassemble into higher hydrocarbons and graphene nuclei and further grow into graphene nanosheets (GNS). Depending on microwave power, ethanol flow rate and molecular gas admixture, the material structure changes from amorphous to crystalline. The presence of C2n + 1Hy species was found to be responsible for the formation of defects in the GNS structure. O2 and H2 admixtures change the gas temperature axial profile and consequently modify reaction pathways influencing growth and production rate of GNS. Determination of reaction pathway selectivity enables us to predict whether high‐quality or defective GNS are produced. [ABSTRACT FROM AUTHOR]

Featured Application: A cold gaseous plasma torch generated in argon at low powers and atmospheric pressure is applicable in medicinal treatment where it could significantly decrease microbial skin or tissue contamination in a short time and with low operating costs. Recently, various cold plasma sources have been tested for their bactericidal and fungicidal effects with respect to their application in medicine and agriculture. The purpose of this work is to study the effects of a 2.45 GHz microwave generated plasma torch on a model yeast example Candida glabrata. The microwave plasma was generated by a surfatron resonator, and pure argon at a constant flow rate of 5 Slm was used as a working gas. Thanks to a high number of active particles generated in low-temperature plasma, this type of plasma has become highly popular, especially thanks to its bactericidal effects. However, its antimycotic effects and mechanisms of fungal inactivation are still not fully understood. Therefore, this study focuses on the antifungal effects of the microwave discharge on Candida glabrata. The main focus is on the measurement and evaluation of changes in inactivation effects caused by varying initial concentration of Candida glabrata cells, applied microwave power and exposure time. The discharge was applied on freshly inoculated colonies of Candida glabrata spread on the agar plates and its inhibitory effects were observed in the form of inhibition zones formed after the subsequent cultivation. [ABSTRACT FROM AUTHOR]

The inner surfaces of three samples (alumina and copper tubes, ozonizer) were treated by ozone. The surface reactions of oxygen and ozone were studied after this treatment. The surface reaction of gaseous molecular oxygen leads to fast ozone creation. The created ozone again reacts with the surface, which leads to its destruction. These reactions can be explained as surface reactions between adsorbed oxygen atoms and molecules or as surface reactions of these adsorbed species with gaseous species. [ABSTRACT FROM AUTHOR]

Featured Application: A cold gaseous plasma torch operating at low powers at atmospheric pressure, applicable in food treatment, could significantly decrease food surface microbial contamination without the use of harmful chemicals. Demand for food quality and extended freshness without the use of harmful chemicals has become a major topic over the last decade. New technologies are using UV light, strong electric field, ozone and other reactive agents to decontaminate food surfaces. The low-power non-equilibrium (cold) atmospheric pressure operating plasmas effectively combines all the qualities mentioned above and thus, due to their synergetic influence, promising results in fruit surface decontamination can be obtained. The present paper focuses on the applicability of the recently developed microwave surface wave sustained plasma torch for the treatment of selected small fruit. Optical emission spectroscopy is used for the determination of plasma active particles (radicals, UV light) and plasma parameters during the fruit treatment. The infrared camera images confirm low and fully applicable heating of the treated surface that ensures no fruit quality changes. The detailed study shows that the efficiency of the microbial decontamination of selected fruits naturally contaminated by microorganisms is strongly dependent on the fruit surface shape. The decontamination of the rough strawberry surface seems inefficient using the current configuration, but for smooth berries promising results were obtained. Finally, antioxidant activity measurements demonstrate no changes due to plasma treatment. The results confirm that the MW surface wave sustained discharge is applicable to fruit surface decontamination. [ABSTRACT FROM AUTHOR]

The paper presents the experimental study of the effect of ions of different mobilities (H + , Cl − , Li + and OH − ) in electrosprayed water solutions under atmospheric pressure conditions in air and in SF 6 background gas. Generally, at the atmospheric air conditions, the main difference between water electrospray (ES) in positive and in negative polarities is the shape and elongation direction of the water jets propagating from the charged nozzle. These phenomena can be associated with the movement of ions in water (i.e. the mobility of ions) or with the influence of the corona discharge and its ionic space charge. A comparison of HCl and LiOH water solutions with inversed mobility ratios of cations and anions showed that the mobility of ions inside the liquid is not an important parameter determining this difference between two ES polarities. The combined measurements in atmospheric air and SF 6 gas clearly showed that the only important factor determining the different shapes and propagations of the water jets for both polarities is the corona discharge and its ionic space charge. [ABSTRACT FROM AUTHOR]

The aim of this work is the application of low-temperature low-pressure hydrogen plasma on artificially prepared corrosion layers, so called plasma chemical reduction. It is necessary to use samples with artificially prepared corrosion layers because it is impossible to use the real artifacts for fundamental research. The bronze was chosen as a sample material. Formation of corrosion layers on the bronze samples was carried out in concentrated hydrochloric acid vapors with the addition of sand. The radio-frequency hydrogen plasma was generated in the flowing regime at a pressure of 160 Pa. Different values of supplied power were chosen as well as different discharge modes: continuous or pulsed mode with varied duty cycles. By the combination of supplied power and mode factors, we selected two values of effective power. The process of plasma chemical reduction was monitored by optical emission spectroscopy (OES) and simultaneously, the sample temperature was measured. Rotational temperatures were calculated from OH radicals spectra. Changes in the structure and elemental composition were determined using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). [ABSTRACT FROM AUTHOR]

In this work, several materials were studied as electrodes in a pinhole configuration of a DC plasma discharge to estimate their effect on the efficiency of the discharge, indicated by hydrogen peroxide production. Detection was carried out using a specific titanium reagent. This was combined with ICP-OES analysis of the final solutions to determine the difference between the amount of electrode material released during the discharge operation and electrolysis experiment carried out under the same conditions. It was found that from seven studied electrode materials, graphite gives the best results, while lower cost aluminum and titanium-zinc still work well. The most unsuitable materials were copper and brass; in these cases, no hydrogen peroxide was detected in the cathode part of the reactor. Results obtained by ICP analysis indicate that even in the case of brass, the absence of hydrogen peroxide is due to the presence of copper in the material. It probably affects both directly the phase of discharge creation and propagation and the decomposition reactions. [ABSTRACT FROM AUTHOR]

This paper presents results on electric discharge generation by high frequency high voltage (15-100 kHz) in NaCl solutions with different initial conductivity (100-1300 mS cm-1), and compares them with DC discharge in the same electrode configuration. A batch plasma reactor in the pin-hole configuration contained a ceramic dielectric barrier separating two planar stainless steel electrodes; barrier thickness of 0.6 mm and pin-hole diameter of 0.6 mm was used. Lissajous charts were evaluated from electric measurements for different discharge phases (electrolysis, bubble formation and discharge regular operation). Breakdown moments for different solution conductivities were determined from discharge power evaluation as a function of applied frequency. Breakdown voltage amplitude was decreased by the increasing conductivity in both regimes while frequency and current decreased. Changes of physical parameters (temperature, solution conductivity and pH) as well as production of hydrogen peroxide at different solution conductivities were compared. Solution conductivity was increased in both discharge regimes and with the initial conductivity value. Solution temperature was increased by the discharge in both regimes and with the increasing initial conductivity, too. Solution pH dropped to acidic conditions when HF or DC positive regime was applied while it was enhanced by DC negative regime. [ABSTRACT FROM AUTHOR]

Utilization of plasma activated water (PAW) for plant growing is mainly connected with the treatment of seeds and subsequent stimulation of their germination. A potential of PAW is its relatively simple and low-cost preparation that calls for studying its wider application in plant production. For this purpose, a pot experiment was realized in order to prove effects of the foliar PAW application on maize growth. The stepped PAW foliar application, carried out in 7-day intervals, led to provable decrease of chlorophyll contents in leaves compared to the distilled water application. The PAW application significantly increased root electrical capacitance, but it had no provable effect on weight of the aboveground biomass. Chlorophyll fluorescence parameters expressing the CO2 assimilation rate and variable fluorescence of dark-adapted leaves were provably decreased by PAW, but quantum yield of photosystem II electron transport was not influenced. A provably higher amount of nitrogen was detected in dry matter of plants treated by PAW, but contents of other macro- and micro-nutrients in the aboveground biomass of maize were not affected. Results of this pilot verification of the PAW application have shown a potential for plant growth optimization and possibility for its further utilization, especially in combination with liquid fertilizers. [ABSTRACT FROM AUTHOR]

Recently, the bactericidal and fungicidal effects of plasma-activated water (PAW) have been confirmed for its application in agriculture. Although the PAW application is beneficial in plant growth, no information is available about processes induced by PAW in soil. This paper gives the first experimental results about PAW's influence on selected physical and physical–chemical properties of soil. PAW was prepared using the dielectric barrier discharge (DBD) operating in the multistreamer mode at a frequency of 11 kHz. The total energy consumption was 60 J/ml. The obtained results show minimal changes in the natural water evaporation from the soil exposed to PAW, slower tap water absorption if a higher amount of PAW (16 doses per 10 ml to 90 g of the soil) is applied, as well as water retention in the soil of over 30%. The soil pH remains in the neutral range of values even at the highest applied PAW amount of 1.7 weight of soil, which represents the best conditions with respect to the plant growth. Thus, we can conclude that the PAW application, even at high amounts, has no negative influence on the physical and physical–chemical properties of soil and it can be safely applied in sustainable, environmentally friendly agriculture. [ABSTRACT FROM AUTHOR]

In this work, the potential of a microwave (MW)-induced atmospheric pressure plasma jet (APPJ) in film deposition of styrene and methyl methacrylate (MMA) precursors is investigated. Plasma properties during the deposition and resultant coating characteristics are studied. Optical emission spectroscopy (OES) results indicate a higher degree of monomer dissociation in the APPJ with increasing power and a carrier gas flow rate of up to 250 standard cubic centimeters per minute (sccm). Computational fluid dynamic (CFD) simulations demonstrate non-uniform monomer distribution near the substrate and the dependency of the deposition area on the monomer-containing gas flow rate. A non-homogeneous surface morphology and topography of the deposited coatings is also observed using atomic force microscopy (AFM) and SEM. Coating chemical analysis and wettability are studied by XPS and water contact angle (WCA), respectively. A lower monomer flow rate was found to result in a higher C–O/C–C ratio and a higher wettability of the deposited coatings. [ABSTRACT FROM AUTHOR]

Abstract: Water solutions of organic dye Direct Red 79 were treated by DC high voltage created by diaphragm discharge (input power up to 160W). Higher dye decoloration (60% after 40min) was observed in the anode part of the reactor by UV–VIS spectroscopy. Recorded absorption spectra showed shifts of absorption maximum to lower wavelength values that were related to the formation of stable degradation products. Absorption spectra obtained in the cathode part of the diaphragm reactor produced only negligible shifts of absorption maximum and the dye decomposition rate reached 25% after 80min of the treatment. HPLC-MS method revealed five main compounds in the anode part and another three ones in the cathode part. Analysis of identified products showed on the initial decomposition of one azo-group in the original dye molecule. Significant changes of solution properties during the diaphragm discharge were observed, too. Solution conductivity increased in both parts of the reactor. Solution pH dropped from the initial neutral value to acidic conditions (up to 3) in the anode part and to alkaline conditions (up to 10) in the cathode part. Changes were induced by formation of reactive species by the discharge and by electrochemical reactions on electrodes. [Copyright &y& Elsevier]