Surface Discharge Plasma Research Articles

Effect of plasma on ochratoxin degradation and raisin properties

This study aimed to investigate the efficacy of gas-phase surface discharge plasma in degrading ochratoxin A (OTA) and assess the impact on the quality of raisins. The plasma discharge voltage was found to significantly influence the degradation rate, with residual percentages of 28.69% and 16.38% after 10 min of treatment with 15 and 18 kV plasma, respectively. No ochratoxin was detected after 10 min of 21 kV plasma treatment. The degradation rate of OTA in raisins slowed down, and the complete degradation took 15 min. Liquid chromatography–tandem mass spectrometry/mass spectrometry analysis revealed that OTA was degraded into nontoxic phenylalanine. Importantly, plasma treatment did not significantly affect the moisture, titratable acidity, total sugar, ascorbic acid, color parameters, or aroma of raisins (P ≥ 0.05). Therefore, gas-phase surface discharge plasma treatment proved effective in degrading OTA in raisins while preserving their quality.

Red mud and foundry sand industry wastes for reducing NOx in plasma activated diesel exhaust

Solid waste in association with plasma was explored as an alternate to commercial catalyst/adsorbents. We have demonstrated reuse of foundry sand and red mud wastes for adsorption of gaseous pollutant from plasma treated diesel exhaust. A novel dielectric barrier discharge reactor with dual metal film is designed to explore the oxidation potential of surface discharge plasma effect onto the exhaust. The metal film was subjected to high voltage pulse/AC energization to assess the effect of plasma in oxidising NO to NO2. A separate reactor filled with industry wastes was cascaded with plasma reactor to test its efficacy in NO2 adsorption. It was observed that some amount of NO was also reduced owing to some visible light-enabled photocatalytic activity. About 85 % NOx (oxides of nitrogen) reduction was observed with red mud waste compared to half of that with foundry sand.

Control of the flame and flow characteristics of a non-premixed bluff body burner using dielectric barrier discharge plasma actuators

Reducing emissions and improving combustion are necessary steps to reach greener combustion systems. In this study, the effect of employing an annular plasma actuator mounted on the surface of a bluff body in a non-premixed burner is numerically investigated. Activating the plasma actuator induces an ionic wind near the surface of the bluff body that modifies the flow features. While the previous relevant studies were mainly focused on volume dielectric barrier plasma discharges, this study investigates the influences of surface plasma discharges. Also, the effect of plasma actuator position, fuel-to-air velocity ratio, and the size of the bluff body are investigated. The characteristics of the flow and temperature fields, the mass fraction of carbon monoxide and carbon dioxide inside the burner in the presence, and the absence of a plasma actuator are analyzed. Also, spatial mixing deficiency (SMD) is used to evaluate the plasma actuator's influence on the reactants' mixing. The results show that among various configurations of annular plasma actuators, positioning the plasma actuator on the bluff body surface acting upwards near the air duct, strengthens the external recirculation region which leads to a favorable change in the characteristics of the flame inside the burner. With the activation of the plasma actuator, the spatial mixing deficiency (SMD) values decrease by an average of 12.75%, showing improvement in mixing, and the flame becomes more uniform compared to the baseline case leading to the reduction of CO concentration. In addition, the root of the flame is strengthened and the height of the body of the flame measured from the bluff body surface is reduced by about 43%. For both low and high fuel-to-air velocity ratios, the presence of a plasma actuator leads to a positive effect on the flame structure. For a high fuel-to-air velocity ratio, the external recirculation area has a favorable size. The created flame is elongated and the root of the flame is entirely away from the burner. When the plasma actuator is active, it causes the flame to get closer to the burner tip. For various diameters of the bluff body, the plasma actuator showed reasonable capability in altering the flame behavior. For larger bluff body diameters, the plasma actuator strengthens both recirculation zones, especially the external recirculation zone, leading to a uniform and shorter flame.

Synergistic degradation of malachite green by water surface plasma combined with Fe2+/PMS

Water surface plasma (WSP) discharge technology coupling with Fe2+ and peroxymonosulfate (PMS) was investigated for the degradation of malachite green (MG) dye wastewater. The effects of Fe2+ dosage, PMS dosage, input voltage and solution initial conductivity on the degradation of MG were investigated. When the Fe2+ dosage was 125 μM, PMS dosage was 0.5 mM and input voltage was 16 kV, the degradation performance and reaction rate of MG reached 96.3% and 0.219 min−1 within the discharge time of 15 min. When increasing the initial conductivity from 31.1 μS/cm to 1000 μS/cm, degradation efficiency of MG decreased from 97.9% to 94.1% with the decrease of only 3.8% and degradation rate declined by only 0.074 min−1.

Flotation separation of pyrite from arsenopyrite by surface discharge plasma modification

Low-temperature plasma has not been reported to be applied to pulp system although it has been proved to be an effective method for the selective modification of minerals. In this research, surface dielectric barrier discharge (SDBD) low-temperature plasma was introduced into the pulp through a bubble generator, and its modification mechanism on arsenopyrite and pyrite was investigated. SDBD plasma exhibited an excellent selectivity where the concentration of hydrophilic oxidation products on the surface of plasma-modified pyrite was much less than arsenopyrite. The introduction of plasma into the pulp resulted in a longer residence time of the pulp chemistry of arsenopyrite in the stable oxidation region than that of pyrite. Plasma modification significantly enhanced the oxidation degree of the defect area on the surface of arsenopyrite, which resulted in the decrease of its hydrophobicity and thereby hindered the adsorption of collector and the oxidation of xanthate ions into dixanthogen. Since its environmently-friendly property, SDBD plasma modification has a broad application prospect in the flotation separation of polymetallic sulfide ores.

Functionally Gradient Coatings from HfC/ HfTaC2 to Ti: Growth Process, Basic Mechanical Properties and Wear Behavior

HfC and HfTaC2 coatings with gradient composition manufactured by double-cathode glow discharge plasma surface metallurgy technology were designed to improve the wear resistance of TA15 titanium alloy. The deposition mechanism of plasma and diffusion mechanism of atoms were investigated, and the growth process of coatings was revealed. The mechanical properties comprising microhardness and elastic modulus were investigated via first-principles calculations and experimental verification. The results reveal that the wear resistance of HfC and HfTaC2 coatings with abrasive wear mechanism is always better than that of the substrate with abrasive wear, adhesive wear and oxidation wear mechanism. The volume wear rates of the coatings are reduced by 90%–97% compared with the substrate, and that of HfTaC2 coatings are reduced by 29.9%–45.5% compared with HfC coatings. Furthermore, V-shaped cross section profiles of wear scars formed on HfC coatings, and U-shaped on HfTaC2 coatings, which is attributed to the addition of tantalum which causes HfC to form a sufficient solid solution, a 0.187–0.030 Å elongation of Ta-C bond length and 0.039–0.051 Å shortening of Hf-C bond length led to the unit cell shrinkage and the Bragg lattice changes from face-centered cubic to face-centered square lattice; accordingly, hardness and wear behavior were further improved.

The addition of hydrogen peroxide and the incorporation of fluorides by surface plasma jointly promote the bactericidal effects of plasma-treated water

The antibacterial ability of plasma-treated water (PTW) is affected by many factors, such as the type of equipment and operating conditions. These factors hinder the application of plasma technology, making it necessary to develop new methods that could prepare PTW with high efficiency for disinfection. In this study, a surface discharge plasma with a dielectric layer of polytetrafluorethylene (PTFE) was used to treat 110 mM H2O2 solution to prepare plasma-treated H2O2 solution (PTH). The bactericidal ability of PTW was evaluated by the inactivation of methicillin-resistant S. aureus (MRSA). The results show that the PTH treated by surface plasma for 3 min inactivated more than 6.3 orders of magnitude MRSA. Importantly, bubbles were produced when the MRSA suspension was incubated with the untreated H2O2 solution, while no bubbles were observed when the suspension was incubated with the PTH. Further experiments show the amounts of bubbles produced in this process were negatively correlated with the bactericidal effects. The concentrations of several reactive species in PTH were measured for antibacterial mechanism analysis and provided a clue that the synergism among hydrogen peroxide, peroxynitrite, as well as unstable reactive fluorides, derived from the gaseous fluorides from the etching of the PTFE dielectric, might play a key role in the bactericidal process. This work provides a new strategy to produce potent disinfectants with low irritation for the disinfection of the environment, object surfaces, and body surfaces.

Metabolomics of Pseudomonas aeruginosa Treated by Atmospheric-Pressure Cold Plasma

With increasing drug resistance of Pseudomonas aeruginosa, a new sterilization method is needed. Plasma has been shown to be an effective method of sterilization, but no researchers have studied the effect of plasma on bacterial metabolism. In this paper, we studied the emission spectrum, liquid phase active particles, and other physical and chemical properties of a portable plasma device. Pseudomonas aeruginosa were then treated with activated water generated by surface plasma discharge. Using gas chromatography time-of-flight mass spectrometry (GC-TOF-MS) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, we obtained the differential metabolite pathways. The results showed that, after plasma activated water treatment, the carbohydrate metabolism of the bacteria was inhibited and the metabolic processes of protein and amino acid decomposition were enhanced. Therefore, water activated by atmospheric-pressure cold plasma can significantly change bacterial metabolites, thus promoting bacterial death.

Extrusion of a nanosecond surface discharge plasma near a dielectric ledge

The presence of a dielectric ledge along the pulse discharge propagation led to a redistribution of the pulsed surface (plasma sheets) discharge glow. Discharge glow on the surface without the ledge, was uniform and lasted no more than 200 ns. Two plasma channels with increased glow intensity were observed near the rectangular ledge placed in the discharge area. The duration of these longitudinal plasma channels increased and lasted for about 0.9 μs (at a voltage of 25 kV and a density of 0.03 – 0.18 kg/m3 ). A nine-frame nanosecond camera recorded the evolution of the plasma glow. The dynamics of the flow induced by the pulse surface discharge was recorded using a high-speed shadow imaging during 40-50 μs after the ignition of the discharge.

Modeling the effect of initial cell concentration and soluble solids on the plasma inactivation of yeast in apple juices

Atmospheric cold plasma is a powerful and profitable microbial decontamination technology in the food industry. The microbial load and food matrix have a great influence on the plasma inactivation effect. This study aimed to quantify the effects of initial cell concentration and soluble solids on the inactivation of yeast in apple juice by gas-phase surface discharge plasma. A computer simulation model was developed to predict the inactivation process using commercial finite element software, COMSOL Multiphysics, and the model was verified by experiments. Studies have shown that the inactivation of yeast was affected by the initial cell concentration and soluble solids. These effects were quantified by fitting equations and used as model inputs. The simulation model predicted the D-value of plasma inactivation of yeast under different discharge voltages and apple juice volume, which was verified in experiments. Therefore, the established model can be used for plasma development to predict how the food matrix affects the inactivation process, thereby providing useful and practical tools for amplifying the commercial application of plasma.

Using cold atmospheric plasma treated-air for COVID-19 disinfection in cold-chain environment

This study applied surface discharge plasma treated-air to deactivate the pseudovirus with the SARS-CoV-2S protein in a cold-chain environment. The results of experiments show that the capability of infection of either the dried or the wet COVID-19 pseudovirus are inhibited after exposure to plasma treated-air regardless of whether it is attached to flakes of plastic or a copper sheet. Moreover, various plasma-generated reactive species provide it with an advantage over conventional ozone in deactivating the wet pseudovirus in a cold-chain environment. Our findings provide a potential disinfecting strategy to combat the spread of SARS-CoV-2 through cold-chain systems.

Simultaneous production of low molecular weight chitosan and reducing sugar via high molecular chitosan depolymerization by surface discharge plasma

Chitosan is widely used in antibacterial, hypolipidemic, and anticancer fields, and the preparation of low molecular weight chitosan with excellent solubility and hydrophilicity is beneficial for its application. In this study, simultaneous production of low molecular weight chitosan and reducing sugars via chitosan depolymerization by surface discharge plasma was developed. More than 95% of the chitosan with an initial molecular weight of 682.5 kDa was depolymerized after 60 min of treatment, with the reducing sugar yield of 23.7%. ·OH, O2·-, and 1O2 played important roles in chitosan depolymerization; they preferentially attacked the amorphous structure of chitosan, resulting in breakage of the intra- and intermolecular hydrogen bonds and β-(1,4) glycosidic bonds, thereby forming low molecular weight chitosan. More electrons and hydrogen atoms would be provided by prepared low molecular weight chitosan due to the decreased intra- and intermolecular hydrogen bonds, and a high biological activity was finally attained. Overall, discharge plasma could be used as an effective technique for chitosan depolymerization, which widens its potential applications.

Plasma-Activated Water Promotes Wound Healing by Regulating Inflammatory Responses

Infection can hinder the process of wound healing, so it is important to begin antibacterial treatment quickly after a wound forms. Plasma activated water (PAW) can inactivate a variety of common wound infection bacteria. In this study, we compared the effects of PAW prepared with portable surface discharge plasma equipment and medical alcohol on wound healing in a mouse full-thickness skin wound model. The effectiveness of wound healing processes in mice was ranked accordingly: PAW treatment group > medical alcohol treatment group > control group. In order to further understand the mechanism of PAW in promoting wound healing, we tested the expression levels of the pro-inflammatory factors interleukin (IL)-1β and IL-6, the anti-inflammatory factor IL-10, and vascular endothelial growth factor (VEGF). The results showed that PAW promoted the release of pro-inflammatory factors and anti-inflammatory factors from the wounds in mice, which allowed the mice in the treatment group to transition out of the inflammatory period early and enter the next stage of wound healing. The expression level of VEGF in the wounds of mice in the PAW treatment group was higher, which indicates that the microvessels around the wound in the PAW treatment group proliferated faster, and thus the wound healed faster. PAW biosafety experiments showed that PAW did not significantly affect the appearance, morphology, or tissue structure of internal organs, or blood biochemical indicators in mice. In general, PAW prepared via portable devices is expected to become more widely used given its convenience, affordability, and lack of side effects in promoting wound healing.

The bactericidal effects of plasma-activated saline prepared by the combination of surface discharge plasma and plasma jet

Plasma-activated water (PAW), as a derivative of cold atmospheric pressure plasma, can inactivate bacteria and greatly expand the application of plasma technology. Commonly used PAW is activated by a plasma device, plasma jet, or surface discharge plasma. PAW prepared by some methods, such as a plasma jet with low frequency, exhibits little bactericidal effect and cannot be applied for use in disinfection or sterilization. Therefore, developing strategies to improve the bactericidal effects of PAW is necessary. Here, the air was first activated by a surface discharge device with a ceramic dielectric under two modes—the ozone mode and nitrogen oxide mode—and then incorporated with helium as the working gas for the plasma jet, which was used to prepare the plasma-activated saline (PAS). The concentrations of long-lived NO2 − and NO3 − and the short-lived 1O2 in the PAS activated by the nitrogen oxide mode and plasma jet were highest. The amount of ONOO− in the PAS activated by the combination was lower than the amount in the PAS activated only by the plasma jet. The PAS activated by the combination of nitrogen oxide mode and plasma jet exhibited the strongest bactericidal effect, which was consistent with the intracellular reactive oxygen species levels. The scavenger analysis demonstrated that 1O2 and ONOO− play essential roles in bacterial inactivation. These results indicate a new strategy for the preparation of PAW with strong bactericidal ability for application in environmental disinfection.

Emerging Technologies for Degradation of Dichlorvos: A Review

Dichlorvos (O,O-dimethyl O-(2,2-dichlorovinyl)phosphate, DDVP) is a widely acknowledged broad-spectrum organophosphorus insecticide and acaracide. This pesticide has been used for more than four decades and is still in strong demand in many developing countries. Extensive application of DDVP in agriculture has caused severe hazardous impacts on living systems. The International Agency for Research on Cancer of the World Health Organization considered DDVP among the list of 2B carcinogens, which means a certain extent of cancer risk. Hence, removing DDVP from the environment has attracted worldwide attention. Many studies have tested the removal of DDVP using different kinds of physicochemical methods including gas phase surface discharge plasma, physical adsorption, hydrodynamic cavitation, and nanoparticles. Compared to physicochemical methods, microbial degradation is regarded as an environmentally friendly approach to solve several environmental issues caused by pesticides. Till now, several DDVP-degrading microbes have been isolated and reported, including but not limited to Cunninghamella, Fusarium, Talaromyces, Aspergillus, Penicillium, Ochrobium, Pseudomonas, Bacillus, and Trichoderma. Moreover, the possible degradation pathways of DDVP and the transformation of several metabolites have been fully explored. In addition, there are a few studies on DDVP-degrading enzymes and the corresponding genes in microorganisms. However, further research relevant to molecular biology and genetics are still needed to explore the bioremediation of DDVP. This review summarizes the latest development in DDVP degradation and provides reasonable and scientific advice for pesticide removal in contaminated environments.

Evaluation of microbial species inactivation and purification of pond sewage by a custom‐built air surface discharge plasma

AbstractThe presence of the hazardous microbial species in pond sewage is a serious threat to the aquatic environment and human health, and an effective purification method is urgently needed. Here, we reported the evaluation and purification effect of sewage by a custom‐built air surface discharge plasma. Results show that the most sensitive bacterial flora mainly includes Cyanobium, Candidatus, and Proteobacteria, based on inactivation map by the DNA sequence. The inactivation of microbial species by plasma treatment would reach beyond 5‐log reduction and the water turbidity would be effectively improved. Identification of the significance of reactive oxygen and nitrogen species with scavengers indicates that the purification effect is closely linked to the key agents ONOO− and H2O2. This study would contribute to an in‐depth insight into decontamination and provide a potential alternative for sewage purification.

Degradation of pharmaceutical contaminants by bubbling gas phase surface discharge plasma combined with g-C3N4 photocatalysis

The feasibility of using gas phase surface discharge with microporous bubbling combined with g-C3N4 photocatalysis for the degradation of pharmaceutical contaminants was evaluated.

Nanosecond discharges in a non-stationary flow around an obstacle

The purpose of the work is to study the effect of a pulsed surface discharge (plasma sheet) on the transverse flow upon its initiation in an unsteady gas-dynamic flow in a channel with an obstacle on the wall. Also a comparison with the effect of a pulsed volume discharge under similar conditions was studied. The dynamics of the blast waves propagating from the separation zone behind the obstacle after self-localization of the discharge plasma there is investigated.

The secondary ionization wave and characteristic map of surface discharge plasma in a wide time scale

The surface discharge is the elementary process in a broad range of low temperature plasma applications. Variation of voltage profiles with different time scales leads to the redistribution of deposited energy as well as electro-hydrodynamic forces of surface discharges, while the mechanism and scaling law is still unknown. On the basis of theoretical and numerical analysis, we show that a secondary surface ionization wave forms during the voltage rising slope when electron density decreases to a critical level while the voltage is still rising. A characteristic map of energy and electro-hydrodynamics force in time scales between 1 ns and 0.1 s at atmospheric pressure is proposed, opening the door towards the target-directed design of surface discharges.

Etching Characteristics of SixNy Film on Textured Single Crystalline Silicon Surface Using Ar/CF4 and He/CF4 Surface-Discharge Plasma

In this study, we investigated the characteristics of electrode grooves formed by etching silicon nitride (SixNy) films using surface-discharge plasma under Ar/CF4 and He/CF4 gases on the basis of differences in the widths of the electrode grooves etched on the SixNy film. The widths of the grooves etched using Ar as the carrier gas were narrower than those etched using He, and the etching speed achieved using Ar was higher than that achieved using He. Furthermore, the electrode groove created by surface-discharge plasma gradually widened as etching time and applied voltage increased.