Plasma Chemistry and Plasma Processing (v.38, #5)

Cold atmospheric pressure plasma is widely used in research for biomedical applications and is a promising therapy to selectively eradicate cancer cells. However, fundamental information related to the plasma modification of biomolecules in aqueous solution remains elusive. In this work, we studied the chemical basis of tryptophan (Trp) oxidation using an Ar plasma jet and investigated the effects of plasma-treated tryptophan (PTT) on cell viability. The results show that the main product of the Trp of plasma induced oxidation is a mixture of hydroxyl derivatives and hydroperoxides in aqueous form. The products result primarily from the hydroxyl radical (·OH) attacking the Trp, which can be explained by the interaction with both the aromatic and the pyrrole rings. We observed that the PTT has a different proliferation effect between the growth of the B16 melanoma cells and the L929 fibroblast cells. The experimental results indicated that the effect of the PTT is dose-dependent in the B16 cells, ranging from cell proliferation to cytotoxic damage with apoptosis. Furthermore, we examined the intracellular changes in hydrogen peroxide (H2O2) and superoxide radicals ($${ ext{O}}_{2}^{{ar{ cdot }}}$$ O2·¯ ) following the Trp-derived treatment using the fluorescence probe method. Rigorous identification of the reactive oxygen species (ROS) produced by PTT in cells as $${ ext{O}}_{2}^{{ar{ cdot }}}$$ O2·¯ and H2O2 helped establish the cellular source of ROS. It is shown that the intracellular H2O2 might originate from the activation of NADPH. These results suggested that the amino acid and protein hydroperoxides may play a crucial role in the action of plasma on the biologic target.
Keywords: Cold atmospheric plasma jet; Tryptophan; Oxidized products; Plasma medicine

Hemoglobin as a Diagnosing Molecule for Biological Effects of Atmospheric-Pressure Plasma by Se Hoon Ki; Somin Sin; Jae-Ho Shin; Young Wan Kwon; Myoung Won Chae; Han Sup Uhm; Ku Youn Baik; Eun Ha Choi (937-952).
The studies with proteins are necessary to understand the biological effects of atmospheric pressure plasma (APP). Among proteins, those with transient metal ions play key roles in many biological events and they are very sensitive to environmental redox states. Iron-containing hemoglobin (Hb) is investigated in this study, after APP treatments under two environmental gas conditions of pure N2 and N2 + O2 mixture. Monitoring the intensity change for absorption spectra could lead to a quantitative assessment of the effect of discharge plasma on Hb. Redox states of Hb are classified into five states including O2-bound Hb (oxy-Hb), deoxy-Hb, met-Hb, NO-bound Hb (NO-Hb), and hemichrome. Chemically generated reactive species and some scavengers are applied to understand the chemical reactions. Our experimental results confirm the complex chemical reactions of APP and suggest the possible use of Hb as a model protein for the visualization of APP biological effects.
Keywords: Atmospheric pressure plasma; Hemoglobin; Reactive oxygen species (ROS); Reactive nitrogen species (RNS); ROS/RNS scavengers

Effects of the Pulse Polarity on Helium Plasma Jets: Discharge Characteristics, Key Reactive Species, and Inactivation of Myeloma Cell by Zhijie Liu; Dehui Xu; Chunxi Zhou; Qingjie Cui; Tongtong He; Zeyu Chen; Dingxin Liu; Hailan Chen; Michael G. Kong (953-968).
In this paper, we report the effects of the pulse polarity on the plasma jet’s discharge characteristics, particularly, on the production of the reactive oxygen and nitrogen species (RONS) and the inactivation efficiency of myeloma cells, for the purpose of identifying and elucidating the correlation between the dose of RONS and cell viability. Experimental results reveal that the positive plasma jet has a longer length than that for negative plasma jet with the equivalent pulse power. The positive pulse plasma jet would produce higher production of the excited reactive species (OH(A), N2(C), N2 +(B), He(3s3S), O(3p5P)), the positive ions (N+, O+, N2 +, O2 +), and the aqueous species O2 , OH, and ONOO, while negative plasma jet would generate higher concentration of the negative ions (OH, O2 , NO2 , NO2 ) and the aqueous species NO2 and NO3 . Additionally, the myeloma cells treated by positive plasma jet results in more cell apoptosis and more CD95 expression compared to negative plasma jet, indicating the impact for the cell apoptosis is more significant in the cellular response to the positive plasma jet. By comparing and analyzing the different doses of RONS to the responses of myeloma cells under positive and negative pulse plasma jet, our findings suggest the cell viability has a positive correlation with the concentration of the concentration of ONOO and the concentration ratio of H2O2 to NO2 , implying the high concentrations for ONOO and H2O2 might be responsible for the inactivation of myeloma cancer cells.
Keywords: Plasma jet; Pulse polarity; Reactive oxygen and nitrogen species; Myeloma cells; Inactivation efficiency

Effect of Cold Atmospheric Pressure Plasma on Maize Seeds: Enhancement of Seedlings Growth and Surface Microorganisms Inactivation by Anna Zahoranová; Lucia Hoppanová; Juliana Šimončicová; Zlata Tučeková; Veronika Medvecká; Daniela Hudecová; Barbora Kaliňáková; Dušan Kováčik; Mirko Černák (969-988).
Cold atmospheric pressure ambient air plasma generated by Diffuse Coplanar Surface Barrier Discharge (DCSBD) was investigated for inhibition of native microbiota and potentially dangerous pathogens (Aspergillus flavus, Alternaria alternata and Fusarium culmorum) on the maize surface. Moreover, the improvement of germination and growth parameters of maize seeds was evaluated. Maize (Zea mays L.; cv. Ronaldinio), one of the most important cultivated crops worldwide, was selected as the research material. Electrical measurements confirmed the high volume power density (80 W cm−3) of DCSBD plasma. Non-equilibrium plasma state evaluated using optical emission spectroscopy showed values of vibrational and rotational temperature (2700 ± 300) K and (370 ± 75) K, respectively. Changes on the plasma treated seeds surface were studied by water contact angle measurement, scanning electron microscope analysis and Fourier transform infrared spectroscopy. A complete devitalisation of native microbiota on the surface of seeds was observed after a short treatment time of 60 s (bacteria) and 180 s (filamentous fungi). The plasma treatment efficiency of artificially contaminated maize seeds was estimated as a reduction of 3.79 log (CFU/g) in F. culmorum after a 60-s plasma treatment, 4.21 log (CFU/g) in A. flavus and 3.22 log (CFU/g) in A. alternata after a 300-s plasma treatment. Moreover, the obtained results show an increase in wettability, resulting in a better water uptake and in an enhancement of growth parameters. The investigated DCSBD plasma source provides significant technical advantages and application potential for seed surface finishing without the use of hazardous chemicals.
Keywords: Cold atmospheric pressure plasma; Maize seed; Inactivation; Filamentous fungi; Germination enhancement

Stimulation of the Germination and Early Growth of Tomato Seeds by Non-thermal Plasma by Monica Măgureanu; R. Sîrbu; Daniela Dobrin; Mihai Gîdea (989-1001).
The influence of non-thermal plasma on tomato seeds has been investigated using a fluidized bed dielectric barrier discharge generated in air. It was found that plasma-treated seeds germinate faster than untreated ones. Plasma slightly enhanced germination rate and considerably influenced growth parameters. Seedling length and weight are significantly higher than those of untreated seeds. The influence of plasma exposure is more visible on the plant roots, which are substantially longer and more branched. An increase in weight of 20–40% was observed for the plants grown from treated seeds as compared to the control ones. The best results are obtained for relatively short plasma exposure, while too long treatment appears to be detrimental to the seeds.
Keywords: Non-thermal plasma; Dielectric barrier discharge; Fluidized bed; Seed germination; Plant growth; Tomato seeds

Microwave Plasma Jet in Water: Characterization and Feasibility to Wastewater Treatment by Ahmad Hamdan; Jing-Lin Liu; Min Suk Cha (1003-1020).
Plasma–liquid interactions have gained escalated interests over the last decade due to their potentials in many applications. The simultaneous generation of physicochemical phenomena of interest promotes itself to the top of the promising technologies for liquid processing. Here, we study the physics of a microwave plasma jet (MWPJ) submerged into water and its feasibility to wastewater treatment. We investigate the plasma and bubble dynamics using high-speed imaging. The effects of the argon flow rate, additive gas, and microwave power on the dynamics are examined highlighting the retreating behaviors of plasma channels due to the losses of electrons and power caused by nearby water surface. The addition of N2 (< 5%) to Ar flow results in an oscillatory motion of the foremost edge of the plasma channel. We characterize the submerged MWPJ using a time- and space-averaged optical emission spectroscopy. We found the dominant OH (A–X) molecular band and atomic Ar lines with pure Ar flow indicating the effective dissociation of water. Meanwhile, the addition of N2 leads to an intense emission of NH (A–X) molecular band. Finally, we assess the submerged MWPJ as a viable method for water purification based on the degradation of methylene blue (popular model compound). We find a significant improvement in the efficiency by adding 1–3% of N2 to the Ar, which should be attributed to a combined effects of NH radicals, having high redox potential, and the backward reactions of H2O2 to form OH radicals with NO and NO2.
Keywords: Microwave plasma; Plasma in water; Water treatment; High-speed imaging; Optical emission spectroscopy

Removal of Oil Products from Water Using a Combined Process of Sorption and Plasma Exposure to DBD by Andreiy A. Gushchin; Vladimir I. Grinevich; Grigoriy I. Gusev; Elena Yu. Kvitkova; Vladimir V. Rybkin (1021-1033).
The paper presents the results of studies of a combined process involving the sorption of engine oil on a sorbent (diatomite) followed by regeneration of the sorbent by plasma-oxidative destruction of oil in DBD of atmospheric pressure in oxygen. The process parameters (gas flow rate, sorbent mass, power, treatment time), which provide the possibility of fivefold regeneration of the sorbent and 100% degree of oil decomposition, are revealed. It was found that the kinetics of oil degradation obeys the pseudo-first kinetic order equation with a rate constant of 0.017 s−1. The energy efficiency of the decomposition was 0.169 molecules of oil per 100 eV of input energy. It is shown that treatment of the sorbent for 5 min leads to the complete decomposition of oil. The products of oil decomposition are carboxylic acids, aldehydes and CO2. Complete removal of acids and aldehydes requires the time of about 40 min. The possible participation of ozone in the oxidative degradation of oil is discussed.
Keywords: Oxygen DBD; Kinetics; Engine oil; Decomposition; Sorption

Inactivation of Shewanella putrefaciens by Plasma Activated Water by Zhihua Qi; Enqiang Tian; Ying Song; Eduard A. Sosnin; Viktor S. Skakun; Tingting Li; Yang Xia; Yao Zhao; XueSong Lin; Dongping Liu (1035-1050).
Plasma activated water (PAW) generated by atmospheric-pressure air microplasma arrays is a solution containing a variety of reactive species. Here we investigate the effects of different applied voltage and water-activated time on bactericidal activities against Shewanella putrefaciens (S. putrefaciens). Our measurements showed that the sterilization efficiency of S. putrefaciens by PAW could be up to 2.0 Log Reduction. Scanning electron microscopy image and DNA concentration measurement showed that the S. putrefaciens cells were damaged and deformed due to the PAW treatment. The physicochemical properties of PAW treated by different applied voltage and water-activated time were evaluated, including pH value, initial PAW temperature, and the concentrations of plasma-activated species, such as H2O2, NO3, NO2, and O3. Analysis indicates that the sterilization efficiency of S. putrefaciens treated by PAW was mainly determined by H2O2 concentration and pH value of PAW. This study provides a basis for the PAW potential applications in the disinfection of rotten food.
Keywords: Plasma activated water; Inactivation; Hydrogen peroxide; Nitrate; S. putrefaciens

This work was carried out based on the principles of biological effectiveness and environmental acceptability of the International Maritime Organization (IMO). The non-native red tide organisms Prorocentrum donghaiense and Scrippsiella trochoidea were selected to examine ·OH inactivation to meet the IMO standard of ballast water discharge (< 10 cells/mL). The effective quantum yield of photosystem II of algal chlorophyll rapidly decreased to zero within a contact time of only 6 s. Under scanning electron microscope (SEM) observation, the algal cells treated with the ·OH inactivation dose still had an intact shape and did not release cellular material, and thus, there are no risks associated with oceanic environmental safety. The potential disinfection byproducts (DBPs) from discharged ship’s ballast water at high salinity (33.7 PSU) treated at a maximum TRO dose of 2.41 mg/L were analyzed by 5-day storage experiments. The results indicated that the contents of bromate, trihalomethanes (THMs), haloacetic acids (HAAs) and haloacetonitriles (HANs) were below the WHO drinking water standards. Therefore, discharged ship’s ballast water with ·OH inactivation is safe for oceanic environments.
Keywords: Non-native red tide organisms; ·OH inactivation; SEM observation; Potential DBPs; Oceanic environmental safety

A High-Efficiency Double Surface Discharge and Its Application to Ozone Synthesis by Meng Li; Bin Zhu; Yan Yan; Tie Li; Yi-Min Zhu (1063-1080).
Surface discharge with the flat plate configuration tends to generate a uniform and high-density plasma during ozone synthesis, but suffers from relatively low energy yield at high ozone concentration. Here we report that a double surface discharge reactor can produce, at the same input power, two uniform plasma zones that locate two sides of the thin dielectric layer simultaneously, which results in a high ozone energy yield at high ozone concentration. Discharge characteristics confirm that reducing dielectric thickness and discharge gap favors the achievement of high plasma-density and energy efficiency. The optical emission spectroscopy diagnosis suggests that the double surface discharge with thinner dielectric thickness and narrower discharge gap possesses much higher electron density, as well as higher excitation temperature and low rotational temperature, which is responsible for the excellent performance in ozone synthesis. The optimal parameters of 0.25 mm dielectric thickness and 2 mm discharge gap enable ozone synthesis to proceed with an energy yield of 295.2–108.7 g/kWh at ozone concentration of 11.1–48.3 g/Nm3 and exhibit a good stability during a 4-h test. This performance surpasses the performance of many other typical discharge processes for ozone synthesis.
Keywords: Atmospheric plasma; DBD; Surface discharge; Ozone synthesis; Optical emission spectroscopy

We studied the combined effect of the pulse or sinusoidal driving voltage and magnetic field on electrical characteristics and ozone production of a dielectric barrier discharge in air. These effects were studied for both polarities of the pulse. We found that the pulse polarity, as well as the magnetic field, affects discharge ozone production only for higher powers. The discharge driven by sinusoidal voltage produces higher ozone concentration than the discharge driven by voltage pulses of negative polarity. The discharge driven by the voltage pulses of negative polarity produces higher ozone concentrations than the discharge driven by positive voltage pulses. Ozone production yield for the voltage pulses of negative polarity is similar to that of sinusoidal driving voltage. For the positive polarity of voltage pulses, the yield is lower. Magnetic field slightly increases the concentration of ozone produced by the discharge and ozone production yield only for the discharge driven by positive voltage pulses. For the discharge driven by the sinusoidal voltage or by the pulses of the negative polarity magnetic field has only small effect on the concentration of ozone produced by the discharge.
Keywords: Dielectric barrier discharge; Pulse voltage; Magnetic field; Ozone

Numerical Simulation of Metal Vapour Behavior in Double Electrodes TIG Welding by X. Wang; Y. Luo; G. Wu; L. Chi; D. Fan (1095-1114).
Metal vapour from the weld pool in double electrodes tungsten inert gas welding is taken into account by a unified numerical model including the arc plasma and the weld pool. The thermodynamic properties and transport coefficients of the arc plasma are dependent on both the local temperature and the mass fraction of the metal vapour. A second viscosity approximation is used to describe the diffusion coefficient of the metal vapour in the arc plasma. The temperature and the flow fields of both the arc plasma and the weld pool are calculated together with the metal vapour concentration. The simulated results are presented for the cases of 3 and 9 mm electrode separation, respectively. It is shown that the metal vapour behavior is much different in these two cases. In the case of 3 mm electrode separation, the metal vapour above the mass fraction of 0.2% is concentrated just above the weld pool surface, while in the case of 9 mm electrode separation, the metal vapour is diffused to the most region of the arc plasma for the same range of mass fraction. In addition, the arc plasma temperature as well as the heat flux at the weld pool is constricted by the presence of the metal vapour. The constricted heat flux at the weld pool results in an increase in the temperature of the weld pool about 100 K or less but a slight shrinkage of the weld pool shape.
Keywords: Metal vapour; Double electrodes; Welding; Numerical simulation

A New Spark Plug to Improve the Performances of Combustion Engines: Study and Analysis of Unburned Exhaust Gases by Dragos Astanei; François Faubert; Stéphane Pellerin; Bogdan Hnatiuc; Maxime Wartel (1115-1132).
The ignition sparks provided by the conventional spark plug do not always ensure a fast and complete combustion of the hydrocarbon-air mixture. For this reason, we offer a new type of plug with a double spark using two simultaneous discharges generated by a pulsed high voltage-power supply. This work presents the comparison of two spark plugs, a classical one and a double spark plug, by analyzing the unburned hydrocarbon gases from the exhaust pipe of the engine. For a first gasoline engine, we measure the oxygen concentration in the exhaust gases with a lambda probe and the unburned hydrocarbon by the use of GC–MS coupled with SPME extraction technique. We can observe a clear decrease of total unburned hydrocarbon (THC). For a second motor test bench, powered with propane, we complete measures in function of air/fuel ratio of the THC, NOx, CO2 and CO. These results confirm that we obtained a better combustion especially for leaner mixtures.
Keywords: GC–MS; SPME; Unburned exhaust gases; THC, CO, CO2, NOx ; Ignition improvement; Air/fuel ratio

Combined Diffusion Coefficients in CO2 Thermal Plasmas Contaminated with Cu, Fe or Al by Yang Liu; Linlin Zhong; Aijun Yang; Xiaohua Wang; Mingzhe Rong; Junhui Wu (1133-1149).
Our work aims at the computation of combined diffusion coefficients in CO2–metal (Cu, Fe, Al) mixtures at a temperature interval of 2000–30,000 K at 0.1 MPa and aims at the investigation of the impact of the concentration and nature of metal vapor (Cu, Fe, Al) on diffusion phenomena. The combined diffusion coefficients have four components, more specifically, combined ordinary diffusion coefficient, combined electric field diffusion coefficient, combined temperature diffusion coefficient and combined pressure diffusion coefficient due to the gradients of the species densities, applied electrical field temperature and pressure. The results indicate that, for Cu and Fe, the combined diffusion coefficients are quite identical under the condition of same metal concentrations (1 and 10% mass concentration). Compared with Cu and Fe under the same metal concentrations (1 and 10%), Al results in a larger enhancement of combined electric field and ordinary diffusion coefficients while smaller enhancement of combined temperature diffusion coefficients. All the combined diffusion coefficients exhibit an upward trend with metal concentrations except for combined electric field, temperature and pressure diffusion coefficients. These three mentioned coefficients are attenuated by the metal vapor above the certain concentration such as, in the case of combined temperature diffusion coefficients, 70% Cu, 70% Fe and 50% Al for CO2–Cu, CO2–Fe and CO2–Al mixtures respectively. Namely, compared with Cu and Fe, less quantity of Al is required to achieve the maximum of combined diffusion coefficients. Maximum peaks for the combined coefficients are shifted to the higher temperature with increasing metal concentrations.
Keywords: Plasma arc; Diffusion coefficients; CO2 ; Metal

The antimicrobial coating on plasma treated packaging polymer materials are potential and alternative techniques for extending the post harvest life of fresh fruits and vegetables. The present work is to evaluate the shelf life time of post harvest grapes stored in different plasma (air, argon and oxygen) treated and chitosan coated polystyrene (PS) petri plates at atmospheric condition (room temperature 28 °C). The plasma treatments were used to activate the inert PS film surface to enhance the adhesion of chitosan coating. Plasma treatments on the PS film changed the chemical and morphological properties were investigated by ATR-FTIR, EDS and FE-SEM analyses. The contact angle measurement conforms that the air, argon and oxygen plasma treatments greatly enhanced the hydrophilicity of PS and the greater decrease was found in oxygen plasma treatment. Further, the chitosan was immobilised onto PS surface utilizing dip coating and it was characterized by contact angle, ATR-FTIR and FE-SEM evaluations. XPS result indicates the chitosan was efficiently immobilized on the PS film. Subsequently the shelf life time and weight loss (%) was calculated for table grapes stored in the air, argon and oxygen plasma treated with chitosan coated PS. The result suggests that oxygen plasma treatment along with chitosan coating on PS demonstrates the active packaging to extend the self-life time of grapes than the other PS.
Keywords: DC glow discharge; Polystyrene; Chitosan; Roughness; Hydrophilicity