Discharge Air Plasma Research Articles

Dissipation of Pesticide Residues on Grapes and Strawberries Using Plasma-Activated Water

In this study, we present a novel atmospheric air plasma discharge for the generation of plasma-activated water (PAW), with the aim of reducing pesticide residues on fresh fruit. For this purpose, a large discharge volume pin-to-plate cold plasma reactor was employed. The pesticide-spiked grapes and strawberries were processed with varying PAW concentrations to study their efficacies for pesticide degradation combined with an evaluation of any induced changes in key nutritional and quality attributes. The results suggest that the reduction of chlorpyrifos was 79% on grapes and 69% on strawberries while that of carbaryl was 86% on grapes and 73% on strawberries, respectively. The degradation of pesticides in PAW is due to the generation of metastable reactive species including nitrates, nitrites, and hydrogen peroxide. The high oxidation potential and acidic environment of this PAW are proposed as important actors for pesticide dissipation. In addition to the effective pesticide reductions obtained, there were no significant changes in the key physical attributes (color and firmness) of the treated samples and only slight changes in the ascorbic acid levels observed for both strawberries and grapes. This study points to the effective potential of PAW for chemical decontamination of fruit while maintaining important quality and nutritional parameters.

Comparing Acid Red B Dye Decolorization by Glow and Spark Discharge Plasma in Atmospheric Pressure Air

We examined the decolorization of Acid Red B (ARB) in glow/spark discharge plasma (GDP/SDP). It is found that the decolorization of ARB was observably higher in GDP than in SDP. After 16 min treatment, ARB decolorization rate reached 97.16% with the energy efficiency of 7.16 kg/kW-h in GDP, and 92.76% with 0.84 kg/kW-h energy efficiency in SDP. The average yield of plasma oxidants were 1.73 kg/kW-h in GDP, and 0.14 kg/kW-h in SDP. Some factors, which probably affect the decolorization of ARB aqueous solution, such as hydroxyl radical and ultraviolet radiation etc. were investigated. The results showed that plasma oxidation, especially hydroxyl radical might be main factors accounting for ARB decolorization.

Синтез заполненных карбидом вольфрама многостенных углеродных нанотрубок в атмосферной плазме дугового разряда постоянного тока

Показана возможность синтеза многостенных углеродных нанотрубок в плазме дугового разряда постоянного тока, инициированного в открытой воздушной среде. Процесс синтеза реализован в полости графитового катода, в которой в качестве катализатора присутствует порошок вольфрама. Применяемый метод реализуется за счет генерации газообразного оксида углерода СО, экранирующего реакционную зону от кислорода воздуха, предотвращая окисление продуктов синтеза. Согласно данным рентгеновской дифрактометрии синтезированные порошковые материалы содержат более чем 85 об. % углеродных кристаллических фаз с графитоподобной структурой, а также содержат кубическую фазу вольфрама, две фазы карбида вольфрама WC и W2C. Согласно результатам просвечивающей электронной микроскопии продукт синтеза содержит углеродные нанотрубки, особенностью которых можно считать относительно большое количество слоев (до ~50 шт.) при диаметре до ~100 нм и длине до ~1.5 мкм. При этом внутри углеродных нанотрубок идентифицируются кристаллические объекты, соответствующие по структуре карбиду вольфрама WC.

Sterilization of Microorganisms Contaminated Surfaces and its Treatment with Dielectric Barrier Discharge Plasma.

Dielectric barrier discharge (DBD) is a promising method of producing non-thermal plasma, which is widely used in variety of industrial and biological applications including disinfection/sterilization. Plasma sterilization offers a faster, less toxic and versatile alternative to conventional sterilization techniques. 45 kV, 50 kHz high voltage high-frequency power supply was designed for generating DBD plasma. Experimental studies were conducted using DBD plasma on growth control in algae, breakdown of complex phenols for chemical wastewater treatment and generation of UV, ozone and other reactive species using DBD plasma discharges in ambient air. A portable DBD plasma-based sterilization system is developed for fighting the Covid-19 pandemic. Quartz tube is used as a dielectric medium between copper foil—SS electrodes and 17 kV, 30 kHz pulse is applied across it, which produces intense DBD across SS mesh. This system can sterilize and disinfect the microorganism contaminated surfaces, garments and used disposable protective gears with UV, ozone and short-lived molecules of metastable states and excited chemical species of nitrogen and oxygen produced during the DBD plasma discharges in ambient air.

Antibiotics Degradation and Bacteria Inactivation in Water by Cold Atmospheric Plasma Discharges Above and Below Water Surface

Cold atmospheric plasma discharges in air above air–water surface interface and discharges inside water with injection of air bubbles, show interesting properties for water purification. Water parameters during plasma treatment get different values depending on discharge schemes. Detailed measurements of water parameters during plasma applications as pH, oxidation–reduction potential, total dissolved solids and conductivity are essential in understanding micropollutants degradation mechanisms in water. E. coli bacteria in water have been eliminated faster by plasma discharges produced in water than in air above it. Degradations of two antibiotics oxytetracycline hydrochloride (OTC) and doxycycline hyclate (DXC) in water solution are faster for plasma generated below solution surface than above it with appearance of one degradation product for OTC and two for DXC along plasma treatment time. Degradations are enhanced in the solution after 200 h following plasma treatment for the two antibiotics. H2O2 concentration can give a good indication of plasma effectiveness on different pollutants as it is a relatively stable compound. For water purification, contributions of two factors have to be identified namely water acidity with certain pH value and concentrations of reactive species generated in water. For plasma discharges inside water with air bubbles the most pronounced effect is the increasing value of H2O2 generated in water, while for plasma discharges above water the effect of water acidity induced by low pH is more dominant regarding pollutants degradations.

Comparison of Direct and Indirect Effect of Spark Discharge Plasma and UV Lamp Radiation on Water and an Aqueous Solution of Methyl Orange

The oxidation of methyl orange (MO) under the influence of radiation from spark discharge plasma in air and a low-pressure mercury lamp is studied. Two modes of sample processing are compared: the action of radiation on an aqueous solution of MO (mode 1, direct action) and the action of radiation on water, after which the water is mixed with a solution of MO (mode 2, indirect action). The radiation energy of the mercury lamp is ten times greater than the energy of radiation from spark discharge, but the yield of MO oxidation under the action of the mercury lamp is 100 times lesser than the yield under the action of spark discharge radiation. This is due to the difference in the spectrum of radiation and the operating regime (continuous and pulsed). The yields of MO oxidation under the action of spark discharge plasma radiation for modes 1 and 2 are the same and amount to 1.2–1.3 1/(100 eV). This means that active species are first produced in water and then interact with the dissolved substance, indirect mechanism takes place. Under the action of radiation from a mercury lamp, the oxidation yield in mode 2 is zero within the limits of experimental errors, direct mechanism takes place.

Understanding of the Spark Effect of Electron Collision by a Capacitive Discharge Ignition in a Constant Volume Combustion Chamber

This work is to investigate the physical effect of plasma discharge in atmospheric air using a capacitive discharge ignition (CDI) system. Also, to specifically investigate the kernel effects of CDI system, this work represents the different characteristics including the spark ignition, electric current, integral energy, spark propagation, flame growth, and kernel distribution comparing with the conventional spark ignition. In the experimental setup, the system is composed of a constant volume combustion chamber (CVCC), spark plug, transformer, capacitor device, mass flow controllers, regulators, high-speed camera, and LabVIEW software and cDAQ. The experiment carried out a wide range as the following conditions: J type spark plug, central type electrode, 1.0 mm plug gap, atmospheric air of initial pressure, 292 K of room temperature, 0.75 ms of spark duration, 420 V of CDI voltage, and 12.5 V of initial transformer voltage. As a result, the spark flame kernel of 400V CDI is increased by MEHV comparing with the conventional spark and the improved effect can be seen in 50 μs. Consequently, the plasma effect of MEHV based on CDI system has a linear characteristic regarding spark kernel growth by capacitance energy comparing with the conventional spark.

Effects of DBD air plasma treatment on the enhancement of black gram (Vigna mungo l.) seed germination and growth

Effects of black gram (vigna mungo L.cv. Barimash 3) seed treatments with 400 torr dielectric barrier discharge (DBD) air plasma on seed surface morphology, seed germination, seedling growth and antioxidant enzyme activities in the roots, shoots and leaves were investigated. The plasma discharge voltage, frequency, electrode spacing, gas temperature and power were 5kV, 4.5kHz, 60mm, 310K and 45W, respectively. The seeds were treated for the duration ranging from 20 to 180 s. Seed germination rate, seedling growth, total chlorophyll content, total soluble protein and sugar concentrations in the seedlings grown from the treated seeds were found to increase 13.67%, 37.13%, 37.26%,53.60% and 51.71%, respectively, with respect to control. This study reveals that the DBD air plasma was involved in the enhancement of nitrogen complex in the seed coat of black gram which upregulated the protein through nitrogen conversion that was ultimately responsible for the increased seed germination and seedling growth of black gram.

Effect of various electrolytes and other wastewater constituents on the degradation of volatile organic compounds in aqueous solution by pulsed power plasma technology

SO4˙− radicals were produced in sulfate containing solution by plasma discharge in air, which enhanced the degradation of chlorobenzene, chloroform, toluene and MIBK.

Ultrasound generated by alternating current dielectric barrier discharge plasma in quiescent air

Dielectric barrier discharge (DBD) driven by an alternating current (AC) high-voltage power supply, also called silent discharge, has been known for more than a century since Siemens first proposed the term DBD in 1857, and penetrates into our daily lives. In our traditional view, AC-DBD is considered as an ozone generator for disinfection, an electronic emitter for depollution of gas streams, a jet actuator for flow control, and so on. However, the acoustic effect of AC-DBD is always neglected. Here, we demonstrate that an asymmetrical DBD plasma actuator which was powered by sinusoidal AC waveforms with an AC voltage of 16 kVp–p at a high voltage frequency of a few kHz can generate ultrasound in quiescent air by using a pressure-field microphone and a high accuracy phase-lock image Schlieren technique. The frequency of this induced ultrasound is approximately 100 kHz which is much higher than the sin high voltage frequency of a few kHz. It is the first time that ultrasound created by the AC-DBD is observed. This finding provides a comprehensive understanding of AC-DBD and might open up possibilities for novel industrial applications of AC-DBD by using the induced ultrasonic energy. In addition, according to the experimental results, a hypothesis is proposed on the formation mechanism of ultrasound generated by the AC-DBD plasma actuator.

Uniform atmospheric pressure plasmas in a 7 mm air gap

Homogeneous penetration of atmospheric pressure uniform air plasma (APUAP) into thin gaps is highly warranted for multipurpose processing of materials. Here, we report APUAP generation in a 7 mm discharge gap with ambient air as the working gas, well beyond the presently maximum achievable 4 mm. Driven by a short pulse high voltage power, a 7 mm wide and 60 mm long uniform air plasma sheet is generated. The discharge is robust and the uniformity is not affected by the complex and variable components of ambient air, as is the case for most plasma discharges in air. Ultrafast photography shows that, different from previous reports, the discharge initiates in the whole air gap simultaneously and brightens quickly with the fast rise of the pulsed voltage. The generation of uniform plasma is mainly attributed to the high density of seed electrons and the reduced number density of molecules in air. Moreover, the achievable gas temperature of up to 1300 K indicates that this type of plasma is suitable for processing of a broad range of materials.

SYNTHESIS OF TUNGSTEN CARBIDE-FILLED MULTIWALLED CARBON NANOTUBES BY DC ARC DISCHARGE PLASMA IN AMBIENT AIR

In this paper, the possibility of synthesizing multiwalled carbon nanotubes (CNTs) by DC arc discharge plasma in ambient air is shown. The synthesis takes place in a graphite cathode with a crucible shape using tungsten powder as a catalyst. In the non-vacuum synthesis method the CO atmosphere is generated in the reaction zone during the arcing, preventing the products of the synthesis from oxidation. According to the X-ray diffraction analysis (XRD), the synthesized product includes more than 85 vol % of carbon crystalline phases with a graphite-like structure, a cubic tungsten phase, and two phases of tungsten carbide WC and W2C. The transmission electron microscopy data shows that the product of the synthesis contains CNTs with a relatively large number of walls (up to ~50 pcs) (MWCNTs) with a diameter of up to ~100 nm and a length of up to ~1.5 μm. It was found that crystalline objects corresponding in structure to WC tungsten carbide are identified inside CNTs.

Humidification effect of air plasma effluent gas on suppressing conidium germination of a plant pathogenic fungus in the liquid phase

AbstractIncrease of the water flow rate into atmospheric pressure air discharge plasma for humidification can significantly improve suppressing conidium germination of a plant pathogenic fungus in the liquid phase by its effluent gas exposure. The role of the introduced water includes enhancement of hydrogen supply to the plasma and cooling of the plasma effluent gas. The hydrogen‐containing precursors for antibacterial species generation are experimentally increased. The gas cooling by the latent heat assists dinitrogen pentoxide density in the gas phase, a suggested precursor for antibacterial species generation near the liquid surface. This suggested near‐surface reaction is a second‐order reaction, generally requiring lower precursors concentrations and leading to less residues, thus it can be an important process for agricultural applications.

Electric field evolution in a diffuse ionization wave nanosecond pulse discharge in atmospheric pressure air

The time-resolved electric field in a nanosecond pulse discharge plasma in atmospheric pressure air is measured using the Electric Field Induced Second Harmonic (E-FISH) diagnostic. The electric field is placed on an absolute scale by calibration against a Laplacian field. At relatively low peak voltages, when the plasma is generated only near the pin high-voltage electrode, the electric field is measured ahead of the ionization wave during the entire voltage pulse, exhibiting a strong field enhancement compared to the Laplacian field, by about an order of magnitude. As the peak voltage is increased and the ionization wave traverses the laser beam, the electric field is measured both ahead of the wave and behind the ionization front, where the field drops rapidly due to the charge separation and plasma self-shielding. When the wave reaches the grounded electrode, the discharge transitions into a conduction phase in which the potential is redistributed within the gap. The electric field in the vicinity of the pin then increases again, following the applied voltage waveform for the rest of the pulse. The effective time resolution of the present measurements is 150 ps. Based on the single shot data, we find that the peak electric field in the wave front is moderately influenced by the applied voltage and varies between 160 and 210 kV cm−1. This study demonstrates the viability of the E-FISH diagnostic for this class of atmospheric pressure discharges and paves the way for future in-depth studies of this particular problem.

Characterization of Various Air Plasma Discharge Modes in Contact with Water and Their Effect on the Degradation of Reactive Dyes

Plasma in- or in-contact-with liquid is an emerging technology that has high potential for use in liquid treatment applications. Due to the simultaneous production of highly reactive species, plasmas can efficiently eliminate pollutants that are difficult to remove using conventional methods. In this study, we investigate an AC-driven air plasma in contact with water, generated using five discharge modes. Modes 1, 2, and 3 are run at air-gap distance of 1, 3, and 3.5 mm, respectively, at a repetition rate of 10 kHz (sinusoidal waveform). Water polarity alternates between cathode and anode in modes 1 and 2, whereas mode 3 produces anode polarity only. Mode 4 is similar to mode 1, but with a repetition rate of 5 kHz, while mode 5 is similar to mode 3, but without the high-voltage preceding discharge when water is anode. The electrical characteristics of each discharge mode are presented in detail, and variations in water properties (namely water acidity and conductivity) are also discussed. The effect of discharge mode on the degradation rate of methylene blue (MB), a standard pollutant, is also investigated. Modes 1, 2, and 4 exhibit comparable MB degradation efficiencies, indicating insignificant dependence neither on air-gap distance or number of discharges. The difference between the efficiencies obtained using modes 3 and 5 suggests a substantial effect of the electric field applied between two successive discharges.

Silicon and germanium nanostructures formed by spark discharge plasma

Formation of semiconductor nanostructures on the surface of single crystalline silicon and germanium wafers by spark discharge plasma in air was investigated. The prepared nanostructures were analyzed by means of the scanning and transmission electron microscopy and optical spectroscopy of the photoluminescence and Raman scattering. The formed nanostructures exhibit a fractal-like morphology with interconnected nanocrystals of 2-200 nm sizes that is explained by repeated processes of spark ablation and subsequent condensation. While the size and morphology of the nanostructure depend on power sources of the spark discharge, short interaction times of spark discharge plasma and target determine a relatively low efficiency of the chemical oxidation of germanium and silicon, as well as low ionic temperatures of the plasma.

Impact of energetic neutral nitrogen atoms created by glow discharge air plasma on the physico-chemical and rheological properties of kithul starch

The changes in physico-chemical and rheological properties of kithul starch by the impact of energetic neutral nitrogen atoms produced by the glow discharge air plasma with novel technique were analysed. Here, treatment was carried out at different power levels (5 W & 15 W) and treatment time (30 min & 60 min). Decrease in amylose and moisture content and increase in swelling index and solubility of plasma treated kithul starch were observed. Fourier transform infrared spectra of plasma treated starch showed variation in the peaks corresponding to CH2 and OH groups. Relative crystallinity significantly (p ≤ 0.05) decreased after plasma treatment. Scanning electron microscopy showed severe damages on the starch granular surface by the effect of energetic neutral nitrogen atoms. Pasting properties increased and thermal properties showed significant (p ≤ 0.05) changes after plasma treatment. Storage modulus (G′) and loss modulus (G″) reduced at higher levels of plasma power and it indicated to its weak gel formation.

A Convenient Method to Realize Large-Area APGD for Wool Surface Modification

In this paper, a method of realizing large-area atmospheric pressure glow discharge (APGD) plasma in ambient air was investigated. The dielectric barrier discharge (DBD) type was adopted, and the electrode arrangement of a tubular array was designed to achieve large-area APGD (about $1000 \times 60$ mm $^{2}$ ). Optical emission spectroscopy (OES) was used to identify active particles and calculate gas temperature. The results show that the seed electrons can react with N2, O2, and H2O in the air to produce N2 (C-B), N2+, OH, and O3. The gas temperature was calculated to be 410 K–514 K, which is suitable for low-added-value materials treatment. The homogeneity of the plasma temperature was also verified by an infrared camera. Furthermore, a prototype for the wool surface modification was also investigated. The scanning electron microscope (SEM) micrographs and wettability test were adopted, which shows that the plasma can damage the squamae of the natural wool to improve the wettability greatly without burning the wool fiber.

Flotation of low rank coal using dodecane after pretreatment by dielectric barrier discharge (DBD) air plasma

Non-polar oils are commonly used as collectors for coal flotation but they are generally lack of collecting efficiency to low rank coals even at a high dosage. In this study, dodecane, a representative of the non-polar oily collectors, was treated by dielectric barrier discharge (DBD) air plasma and the product was employed in the flotation of a low-rank coal slime, attempting to improve its flotation performance. Results show that the dodecane treated by DBD air plasma led to a high concentrate yield and combustible material recovery. The mechanism underpinning the observed effect was investigated using gas chromatograph-mass spectrometer (GC–MS), Fourier transform infrared spectroscopy (FTIR) and contact angle measurements. The effect of UC (untreated collector) and TC (treated collector) on coal and gangue were detected, respectively. It was found that abundant polar substances were produced after the air plasma treatment. The functional groups including OCO and OH enhanced the adsorption of collectors onto the oxygenated surface sites of the coal and gangue, and thus increased the hydrophobicity of coal and gangue. According to the contact measurements, the increase of coal in hydrophobicity is stronger than that in gangue, as evidenced by their measured contact angle of organic matter increasing from 78.23° to 95.82°, and gangue increasing from 75.11° to 83.22° after conditioning with the TC. This implies that oily collectors after air plasma treatment is effective to improve low rank coal flotation performance, which may have great potential for industrial applications.

Influence of the pH value on the degradation of an azo dye of methyl orange by air discharge plasma

Treatment of methyl orange (MO) synthetic wastewater by air discharge plasma was investigated, and the solution's pH value was found to be a key parameter of influencing the treatment efficiency. The results indicate that lower pH value can induce production of high reactive species, NO+ and peroxynitrous acid, which can contribute to the MO decomposition. When the appropriate amount of Fe2+ ions is present in the MO solution, the MO decomposition can be promoted by Fenton's reaction (Fe2+ reacts with H2O2 produced from the plasma–liquid interaction). Furthermore, the lower pH value is also beneficial for the Fenton's reaction by avoiding an appearance of Fe(OH)3 precipitate that can reduce the treatment efficiency.