Discharge Plasma System Research Articles

Assessing the Biological Safety of Atmospheric Cold Plasma Treated Wheat Using Cell and Insect Models.

Atmospheric cold plasma (ACP) is under investigation for an extensive range of biocontrol applications in food biosystems. However, the development of a novel intervention technology requires a thorough evaluation of the potential for negative effects and the implications for the human and animal food chains’ safety. The evaluations were performed using a contained, high-voltage, dielectric barrier discharge plasma system. The cytotoxicity of two types of food models—a liquid model (wheat model medium (WMM)) vs. a solid model (wheat grain extract (WGE)) was compared in vitro using the mammalian cell line CHO-K1. The residual toxicity of ACP treatment of grains for food purposes was assessed using the invertebrate model Tribolium castaneum, by feeding the beetles with flour produced from ACP-treated wheat grains. The cytotoxic effects and changes in the chemistry of the ACP-treated samples were more pronounced in samples treated in a liquid form as opposed to actual wheat grains. The feeding trial using T. castaneum demonstrated no negative impacts on the survivability or weight profiles of insects. Investigations into the interactions of plasma-generated species with secondary metabolites in the food matrices are necessary to ensure the safety of plasma for food applications.

Steel Wire Cleaning using Cold Plasma

Current galvanizing process used hydrochloric acid to remove oxide layer and mild acidic bath to remove oil on metal wire surface. These cleaning processes are compulsory before steel wire coated with zinc. These chemicals cleaning technique cause ecological harm and produce toxic waste. To consider of minimizing these problems, cold plasma was introduced for metal wire cleaning. Previous research already proves that cold plasma capable to remove oil by using dielectric barrier discharge (DBD) and remove oxide layer on copper by using RF plasma discharge. Therefore, in this research, the same plasma discharge system that is DBD was used to remove oil and oxide layer on steel wire. 8kV of voltage and air was used to generate plasma. By using copper and steel wire as electrode, it can remove oil around 82% and oxide layer around 54%.

Catalytic degradation of clothianidin with graphene/TiO2 using a dielectric barrier discharge (DBD) plasma system.

Clothianidin served as the model pollutant to investigate the performance and mechanism of pollutant removal by dielectric barrier discharge plasma (DBD) combined with the titanium dioxide-reduced graphene oxide (rGO-TiO2) composite catalyst. In this study, different ratios of titanium dioxide-graphene catalysts were loaded onto honeycomb ceramic plates via the sol-gel method, and the modified catalytic ceramic plates were characterized by XRD, SEM, FTIR, DRS, and energy dispersive X-ray. The results suggested that the rGO-TiO2 was well loaded on the surface of the honeycomb ceramic plates. According to the results of the characterization experiments and the degradation of the clothianidin solution with different proportions of the catalyst, 8wt% rGO-TiO2 was selected as the optimum ratio for degradation. Clothianidin degradation efficiency was significantly influenced by input power, clothianidin concentration, pH value, liquid conductivity, free radical quencher. Finally, six degradation products of clothianidin were identified by HPLC-MS, and the possible transformation pathways of clothianidin degradation were identified. Graphical abstract.

Experimental Investigation on Dust Vertical Coagulation Process in an Ethylene RF Discharge Plasma

The characteristics of dust coagulation process in gravitational direction are investigated in an ethylene RF (radio frequency) discharge plasma system. The experiment shows that dust particles can aggregate into the huge fractal structure (centimeter scale). The coagulation process is mainly characterized by the scattering laser intensity, the distribution of dust clouds, and the fractal dimension. In this experiment, the rotational characteristics of the huge fractal structure can be observed and investigated by the oscillation of the scattering spectrum. These results provide an experimental basis for the investigation of dust coagulations.

Plasma-catalytic degradation of ciprofloxacin in aqueous solution over different MnO2 nanocrystals in a dielectric barrier discharge system

The α-MnO2, β-MnO2 and γ-MnO2 samples were prepared by the hydrothermal method and were used for the degradation of ciprofloxacin (CIP) wastewater in a combined DBD-catalytic process. The physical and chemical properties of the samples were systematically studied by several analytical techniques including BET, XRD, SEM, HRTEM, XPS, and H2-TPR. The combination of DBD with α-MnO2 showed the highest CIP degradation efficiency, and the efficiency could reach 93.1% after 50 min, which was 10.8% and 18.1% higher, respectively, than those of β-MnO2 and γ-MnO2 catalysts in the plasma-catalytic system. According to the model of response surface methodology, the contribution of key experimental parameters on the CIP degradation decreased in the order: peak voltage > air flow rate > initial concentration > initial pH. The optimum operating parameters were peak voltage 17 kV, air flow rate 2.5 L min−1, an initial concentration 5 mg L−1 and an initial pH 6.9. The quenching experiments of active species showed that OH and O2− were critical to the CIP degradation. The generated O3 might be adsorbed by the α-MnO2 catalyst and resulted in more OH generation. The intermediate products of CIP degradation in DBD+α-MnO2 system were analyzed by LC-MS, and three possible degradation pathways were proposed. This research provides an insight into the use of the crystallographic structures in discharge plasma system for antibiotics in water.

Remediation of ciprofloxacin-contaminated soil by nanosecond pulsed dielectric barrier discharge plasma: Influencing factors and degradation mechanisms

Abstract The continuous release of antibiotics in soil environment poses a serious threat for soil and water quality and consequently human health. However, research efforts focused on the effective remediation of antibiotic-polluted soil are still very limited. In this study, a nanosecond pulsed dielectric barrier discharge (nsp-DBD) plasma system was used for the first time to remediate soil contaminated by ciprofloxacin which is one of the most widely used, persistent and genotoxic antibiotics. Various cold atmospheric plasma (CAP) operating parameters were investigated and optimized. The optimal moisture content and air flow rate were determined at 5% and 1.0 L min−1, respectively. Ciprofloxacin degradation increased with pulse voltage and pulse repetition rate and decreased with higher initial concentrations in the soil. At optimal conditions (pulse voltage 17.4 kV, pulse frequency 200 Hz), ciprofloxacin was completely degraded (~99%) in soil, at very short nsp-DBD treatment time (~3 min), with the corresponding energy efficiency being 4.6 mg/kJ. The relative distribution and identity of major ciprofloxacin degradants generated was determined by UPLC-MS analysis. This led to the generation of a degradation map that is consistent with hydroxyl radical-driven successive hydrogen atom abstractions and hydroxyl radical recombination events at the onset of the process followed by singlet oxygen mediated degradation. Interestingly, the degradation pattern observed under nsp-DBD conditions shares several aspects with the in-vivo metabolic profile of ciprofloxacin.

Application of electrical discharge plasma on the inactivation of Zygosaccharomyces rouxii in apple juice

Zygosaccharomyces rouxii is an osmotolerant yeast responsible for the quality degradation of apple juices. Cold plasma is a promising method for microbial inactivation. The primary purpose of this work was to study the influence of electrical discharge plasma treatment on hypertonic yeast inactivation in apple juice. The gas-phase surface discharge was triggered along a quartz tube in an electrical discharge plasma system, and then highly reactive species were bubbled into commercial apple juice artificially inoculated with yeast. The results showed that the yeast in the apple juice reached a 5.6 log10 reduction after the plasma exposure for 30 min at a 21 kV discharge voltage. Scanning electron microscopy showed that cell structure was damaged during plasma treatment. Plasma treatment caused a slight increase in pH, while the total soluble solids, titration acidity, and reducing sugar did not significantly change. After treatment, the apple juice brightness and hue values increased, the colour became yellower and lighter, and the main components of volatile compounds did not change significantly (p < 0.05). Plasma treatment can inactivate hypertonic yeast while maintaining the physicochemical properties of apple juice, including the retention of the volatile compounds in apple juice.

Performance of Capillary Plasma Source With Combustible Materials

Application of an energetic material (EM) in a liquid or gaseous form to electrothermal (ET) plasma discharge systems can provide an energetic plasma jet that has desirable parameters for launching applications. In this energetic ET concept, the EM is basically injected into the plasma source that is operated in an ablation-free regime. The discharge and EM combustion processes have been simulated using the ETFlowCom code, which is an in-house developed energetic ET plasma model. In this article, the ETFlowCom code is used to predict the energetic plasma jet parameters such as temperature, pressure, heat flux, and exit velocity. Different computational case studies have been conducted using a variety of EM mixtures. The simulation results show that the generated energetic plasma jet has the density on the order of 10271/m3, kinetic pressure on the order of hundreds of MPa, and an exit velocity that can reach up to 6 km/s. These parameters are found to be functions of the EM type and the mixing ratio as well. The jet parameters show strong potential for launching applicability.

High frequency discharge plasma induced plasticizer elimination in water: Removal performance and residual toxicity

Plasticizers are widely present in water and soil environment, and they can bring enormous threats to environmental safety and human health. A discharge plasma system driven by a high-frequency electric source was used to remove the plasticizer from wastewater; and dimethyl phthalate (DMP) was chosen as the representative of plasticizer. DMP elimination performance at various operating parameters, roles of active species in DMP degradation, DMP decomposition process, and its residual toxicity after decomposition were systematically investigated. The experimental results demonstrated that almost all of the DMP and 80.4% of the total organic carbon (TOC) were removed after 30 min of treatment. The DMP decomposition process fitted well with the first-order kinetic model. Relatively higher applied voltage, lower initial concentration, and alkaline conditions favored its decomposition. •OH was the decisive species for DMP decomposition, in addition to •O2− and 1O2; while the role of hydrated electrons was negligible. The analysis of DMP decomposition process showed that the molecular structures of the DMP were destroyed, and 3-hydroxy-dimethyl phthalate, monomethyl phthalate, and phthalic acid were detected. Furthermore, the residual toxicity after DMP decomposition was analyzed via seed germination and photobacterium bioassay.

Transition of low-temperature plasma similarity laws from low to high ionization degree regimes

Similarity laws are often employed when characteristics of two or more discharge plasma systems are compared. The classical similarity laws were previously validated and applied for weakly ionized plasma discharges. However, the classical similarity laws will not be valid for all plasma regimes. Especially for strongly ionized regimes, scaling laws are not well elaborated. In this study, transition characteristics of low-temperature plasma similarity laws are evaluated from low to high ionization degree regimes. The similarity relations of plasma density and ionization degree are obtained for geometrically similar gaps. The deviations from classical similarity laws are observed, which are gradually enlarged as the ionization increases from low to high degrees. The transition characteristics are affected by the significance of nonlinear reaction processes (such as three-body collisions), resulting in that the classical similarity relations hold up to a higher ionization degree at low pressure than that at high pressure. The time-dependent scaling characteristics of species densities and electron kinetic behaviors in geometrically similar gaps are also examined. The results are beneficial for utilizing the similarity laws in a wide range of ionization degree regimes, which is essential for correlating plasma characteristics in geometrical similar vessels of various scales.

Multi-catalysis of nano-zinc oxide for bisphenol A degradation in a dielectric barrier discharge plasma system: Effect and mechanism

As a widely used chemical material, bisphenol A (BPA) is often used to produce kinds of chemicals, which lead risk to the ecological environment and human health. Based on the multi-catalysis of the nano-ZnO and multi-effect (chemical and physical) formed in the dielectric barrier discharge plasma (DBDP) system, the synergistic elimination of the BPA in the DBDP system combined with nano-ZnO was evaluated. The obtained experimental results showed that the superior adding amount of the nano-ZnO was 50 mg/L and the synergistic system on the condition had the best effect for the BPA degradation (85.4%), which was 17% higher than that in the sole DBDP system. When O2 was bubbled into the reaction system, the degradation efficiency of the BPA in the synergistic system reached 100% after 20 min treatment. Compared with the alkaline solution, the acidic and weakly acidic solution could obtain higher treatment efficiency. OH and O2− had a vital role for the BPA elimination in the synergistic system. The intermediate products detected by LC-MS included 4-cumylphenol, 4-isopropenylphenol, 4-tert-butylphenol, propiophenone, 1-(4-hydroxyphenyl) ethanone, tert-butylbenzene, benzoquinone and 1, 4- dihydroxybenzene.

Multihole dielectric barrier discharge with asymmetric electrode arrangement in water and application to sterilization of aqua pathogens

To make aquaculture more environmentally and economically sustainable, novel water treatment technologies are urgently required. Therefore, in this study, a novel multihole dielectric barrier discharge (MH-DBD) plasma system submerged in water was investigated to sterilize aquaculture pathogens. The plumes from the DBD plasma directly contact water through multiple holes installed on an outer dielectric of an asymmetric coaxial DBD. The MH-DBD plasma in Vibrio harveyi sterilization showed inactivation performance higher than 2 log reduction, compared to coaxial DBD plasma without direct contact with water. From the plasma emission lines, we identified the chemically active species resulting from water dissociation. The aqua pathogens tested in the experiments were of five types containing Edwardsiella tarda, which causes lethal diseases in aquaculture populations; the MH-DBD plasma showed high sterilization performance over 6.5–7.5 log reduction under specific conditions. Consequently, we believe that the MH-DBD plasma can be an effective water treatment tool not only to sterilize fish pathogens in aquaculture but also to decontaminate waste water through plasma-based oxidation processes.

Dynamics of mutual harmonic synchronization between two coupled glow discharge plasma systems

The dynamics of harmonic synchronization between the anode glow oscillations of two mutually coupled glow discharge plasma systems are studied. The individual systems are operated in the regime where the frequencies of the anode glow oscillations increase linearly with an increase in the discharge voltage. In the experiments, the discharge voltage of one of the systems is kept fixed and that of the other increased progressively. A host of mutual synchronization phenomena is observed which includes a Devil's staircase progression of harmonic synchronization and frequency pulling and chaotic states. A systematic delineation of these experimental observations is presented, and some theoretical understanding is provided by the numerical simulation results of two coupled Van der Pol type equations.

Atmospheric-pressure plasma by remote dielectric barrier discharges for surface cleaning of large area glass substrates

A remote dielectric barrier discharge (RDBD) plasma system has been used to clean glass-surfaces under atmospheric pressure. To achieve a sustainable process, it is critical to optimize the parameters that affect the surface condition. Hence, the physical and chemical properties of the glass surface were investigated by changing the input voltage and the distance between the sample and electrodes. The optical emission spectroscopy (OES) characteristics were analyzed as a function of the gas concentration, and contact angles were measured before and after plasma treatments. The contact angle was reduced from 50 degrees (hydrophobic) to 5 degrees (hydrophilic) after the RDBD plasma treatment on the bare glass. The temperature of the samples was under 55 °C during the process without electrostatic charge. In this paper, we demonstrated the superior cleaning effectiveness of removing inorganic and organic contaminants on the glass surface using the RDBD without surface damage.

Application of gas phase surface discharge plasma with a spray reactor for Zygosaccharomyces rouxii LB inactivation in apple juice

Abstract The effects of the gas phase surface discharge plasma system with a spray reactor on yeast in 12, 36, and 60°Brix apple juice were evaluated. Results indicated that the number of Zygosaccharomyces rouxii LB cells in 0.5 L of 12°Brix apple juice was reduced by 5.60 log10 after discharge plasma treatment for 30 min. When the soluble solids content increased from 12 to 60°Brix, yeast inactivation was decreased by 2.55 log10. After treatment, the pH level of the apple juice only slightly increased, and the titratable acidity and concentration of reducing sugars remained unchanged. The total color differences between the plasma-treated and untreated samples in 12, 36, and 60°Brix apple juice were 9.53, 7.97, and 3.86. Meanwhile, the concentrations of alcohols, esters, aldehydes, and ketones—the main components of volatile compounds showed no significant change (p Industrial relevance Inactivation of microorganisms using nonthermal plasma technology can reduce food costs and minimize changes in food products and is therefore an alternative to heat-based technology. The proposed research showed that the gas phase surface discharge plasma treatment with a spray reactor can effectively reduce Zygosaccharomyces rouxii in apple juice. In addition, the effect of plasma treatment on the color and volatile compounds of the apple juice were determined. This study provided a technical support for the application of plasma technology in apple juice processing.

Synergistic effect in one-stage dielectric barrier discharge plasma and Ag/Al2O3 catalytic systems on C2H2-SCR of NOx

C2H2-SCR of NOx over one-stage dielectric barrier discharge (DBD) plasma system combined with Ag modified alumina catalyst at excess oxygen was carried out. NOx and C2H2 conversions and COx selectivity dependence on reaction temperature and discharge voltage were investigated systematically. At low temperatures, a synergistic effect of HC-SCR of NOx in one-stage DBD plasma and 2 wt% Ag/Al2O3 catalyst was clearly observed. The improvement on the NO+O2 co-adsorption and formation of more active nitrate species adsorbed on 2 wt% Ag/Al2O3 catalyst by plasma was analyzed by MS-TPD and TPSR methods.

Non-Thermal Plasma as a Unique Delivery System of Short-Lived Reactive Oxygen and Nitrogen Species for Immunogenic Cell Death in Melanoma Cells.

Breakthroughs in cancer immunotherapies have demonstrated considerable success, though not without limitations. Non‐thermal plasma (NTP) for cancer therapy has been emerging as a potential adjuvant treatment via induction of immunogenic cell death (ICD). Cancer cells undergoing ICD stimulate a patient's immune system to mount an anticancer response. While promising, the underlying mechanisms of NTP‐induced ICD must be closely examined. Here, the interaction between non‐thermal plasma and cancerous cells is studied. The short‐lived reactive oxygen and nitrogen species (e.g., hydroxyl radicals, atomic oxygen, nitric oxide) produced by plasma are the main effectors that elicit ICD in melanoma while, surprisingly, persistent species do not. This is demonstrated in vitro using a dielectric barrier discharge plasma system and is validated in a vaccination assay in vivo. Plasma generation of reactive species appears to be dictated by the total energy. Collectively, this work provides fundamental insight into plasma interactions with biological material. Furthermore, it lays the foundation for future development of NTP systems for clinical translation. The addition of plasma systems into the existing arsenal of cancer therapies opens the possibility for new combination strategies for safer and more robust control of cancer.

Enhanced catalytic performance of graphene-TiO2 nanocomposites for synergetic degradation of fluoroquinolone antibiotic in pulsed discharge plasma system

A hybrid graphene-TiO2 nanocomposites have been prepared by a facile hydrothermal method to improve the photocatalytic performance and applied for synergetic degradation of fluoroquinolone antibiotic in pulsed discharge plasma (PDP) system. The characterizations of the structure and morphology, chemical bonding state, optical property and electrochemical property show that the graphene-TiO2 nanocomposites can be hybridized successfully. Compared to the pure TiO2, the light absorption range can extend to visible light (<505 nm) and the recombination rate of electron–hole pairs declines apparently in the graphene-TiO2 samples. The degradation performance experiment manifests a significant enhancement of the removal efficiency of flumequine (FLU) when the graphene-TiO2 samples are added in the PDP system. The highest removal efficiency can reach 99.4% in PDP/graphene-TiO2 system with 5% graphene content, which is 23.7% and 34.6% higher than that in PDP/TiO2 system and sole PDP system, respectively. Correspondingly, the kinetic constant is 3.5 and 4.6 times higher than that in PDP/TiO2 system and sole PDP system, respectively. The radical species trapping test suggests that OH, h+ and O2− play the critical role for FLU degradation in PDP/graphene-TiO2 system. The graphene-TiO2 samples can further decompose the O3 and improve the generation of OH and H2O2. The degradation intermediates are determined by LC–MS and IC. The toxicity evolution of FLU reaction solutions is evaluated based on inhibition of photobacterium V. fischeri. Finally, the FLU degradation mechanism in the PDP/graphene-TiO2 system is proposed. This research would provide a novel insight into the application of graphene-based nanocomposites in PDP system as a promising remediation methodology for organic contaminants in water.

Characteristic behaviour of plasma fluctuations inside a plasma bubble in presence of a magnetic field due to the formation of a potential well

Experiments were carried out to observe the effect of a magnetic field and grid biasing voltage in presence of a plasma bubble in a magnetized, filamentary discharge plasma system. A spherical mesh grid of 80% optical transparency was negatively biased and introduced into the plasma for creating a plasma bubble. Diagnostics via an electrical Langmuir probe and a hot emissive probe were extensively used for scanning the plasma bubble. Plasma floating potential fluctuations were measured at three different positions of the plasma bubble. The instability in the pattern showed the dynamic transition from periodic to chaotic for increasing magnetic fields. Time scale analysis using continuous wavelet transform was carried out to identify the presence of non‐linearity from the contour plots. The mechanisms of the low‐frequency instabilities along with the transition to chaos could be qualitatively explained. Non‐linear techniques such as fast Fourier transform, phase space plot, and recurrence plot were used to explore the dynamics of the system appearing during plasma fluctuations. In order to demonstrate the observed chaotic phenomena in this study, characteristics of chaos such as the Lyapunov exponent were obtained from experimental time series data. The experimentally observed potential structure is confirmed with numerical analysis based on fluid hydrodynamics.

Design and Simulation of New Type Reactor in the Wastewater Treatment System Based on Discharge Plasma

The organic pollutants in the wastewater are difficult to treat effectively. The traditional method cannot meet the demand of the degradation rate and the treatment efficiency at the same time. The electro-hydraulic discharge provides a new method for the disposal of the industrial organic wastewater. The working principle of the wastewater treatment system based on discharge plasma is introduced. As the reactor is one of the most important components of the wastewater treatment system based on discharge plasma, the effect of the needle-plate and traditional barrel-type reactor is analyzed. After the solid-liquid-gas (SLG) three-state reactor for the high-voltage-pulsed discharge plasma system is put forward, the working principle of the SLG three-state reactor is introduced. A simulation model of the reactor based on the finite-element method is built. The effect of the voltage, the radius, and the relative permittivity of the solid packing to the electric field distribution is analyzed based on the numerical calculation. The conclusion that SLG three-state reactor of the wastewater treatment system based on the high-voltage-pulsed discharge plasma has a better effect than two-state reactors can be drawn. Furthermore, the high voltage is better for the partial discharge and the generating of the plasma. Meanwhile, small radius and relative permittivity of the solid packing are beneficial to the partial discharge of the reactor.