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Non-thermal plasma is a promising technology for high purity nanomaterial synthesis in a fast, flexible and controllable process. Gliding arc discharge, as one of the most efficient non-thermal plasmas, has been widely used in gas treatment but rarely studied for the nanomaterial synthesis. In this study, a comparison study for carbon nanosheets synthesis including toluene dissociation and graphite exfoliation was investigated in a 2D gliding arc reactor at atmospheric pressure. The effects of gas flow rate, precursor concentration and power input on the structures of carbon nanosheets produced through the two synthesis routes were explored and compared. Amorphous carbon nanosheets were produced in both approaches with a few crystalline structures formation in the case of toluene dissociation. The thickness of carbon nanosheets synthesized from graphite exfoliation was less than 3 nm, which was thinner and more uniform than that from toluene dissociation. The flow rate of carrier gas has direct influence on the morphology of carbon nanomaterials in the case of toluene dissociation. Carbon spheres were also produced along with nanosheets when the flow rate decreased from 2 to 0.5 L/min. However, in the case of graphite exfoliation, only carbon nanosheets were observed regardless of the change in flow rate of the carrier gas. The generated chemical species and plasma gas temperatures were measured and estimated for the mechanism study, respectively. [ABSTRACT FROM AUTHOR]

The gliding arc discharge plasma reactors are known as a source of non-equilibrium plasma at atmospheric pressure. In the present study, generation of dominant reactive oxygen and nitrogen species in gaseous and liquid phase in water by the compact gliding arc device (mini-GAD) and corresponding bactericidal effects were investigated. Water and phosphate buffer solutions were used as model liquids. Mini-GAD is a strong source of nitrogen oxides (up to 800 ppm NO and 200 ppm NO2) that result in high concentrations of nitrites and nitrates in water solutions. The highest bactericidal efficacy towards Escherichia coli was achieved for non-buffered water solution. [ABSTRACT FROM AUTHOR]

The destruction of nitrous oxide in oxygen using plasma and post-plasma catalytic treatments was investigated experimentally in atmospheric-pressure dielectric barrier (DBD) and gliding arc (GAD) discharges. In the DBD, ~ 7% of the N2O is destroyed with ~ 70% selectivity to NOx whereas the GAD gives rise to greater conversion (~ 23%) with lower NOx selectivity (~ 30%). A gas-phase plasma kinetic model was developed and used to analyse the chemical reaction pathways involved in the plasma environment: in the room temperature DBD, the primary destruction process is reaction with O(1D), with the branching ratio to form 2NO versus N2 + O2 determining the product selectivity. On the other hand, in the hot GAD environment (~ 900 K), the reaction of ground-state O with N2O to form N2 + O2 becomes more important. The use of a catalytic bed after the DBD reactor resulted in significant enhancement of N2O conversion from 6.8 to 28.0%. A surface mechanism for the catalytic dissociation of N2O in the presence of O3 is proposed, whereby N2O reacts with the adsorbed atomic oxygen, released from ozone dissociation, to form N2 and NO in approximately equal proportions. [ABSTRACT FROM AUTHOR]

The aim of this work is the modeling of plasma-chemical reactions taking place between highly oxidizing gaseous species (OH, NO and derivatives), generated by Gliding Arc Discharge in Humid Air (GAD-HA), and organic pollutants in aqueous solution. Theses pollutants were chosen on the base of their volatility at atmospheric and ambient conditions: 1-Heptanol (highly volatile), phenol (moderately volatile) and para-chlorobenzoic acid, pCBA (poorly volatile). The mass transfer model of diffusion-convection was coupled to a proposed kinetic model in order to describe the phenomenology of the electrical process. The mass transfer model was obtained independently by stripping toluene and phenol molecules. The simplified kinetic model was proposed with the main reactions in gas and liquid phases mentioned in the literature. The only adjustable parameter of the model was the OH concentration in the plasma plume. For a concentration of OH of 24 ppm in the plasma plume, the model gives results in agreement with experimental results for the three model pollutants tested. The coupling of the experimental results and the simulation study allowed us to: (1) confirm that the main removal mechanism is different according to the nature of the pollutant and depends on the pollutant properties (reactivity, volatility), (2) calculate [OH], [ONOOH] and [NO]. The results of this work can be used to assist experiences in the plasma engineering field. [ABSTRACT FROM AUTHOR]

A warm plasma generated by gliding arc discharge, combining the advantages of both thermal and cold plasmas, is explored to synthesize TiO nanopowders for the first time. Air is used as the discharge gas and titanium tetraisopropoxide aerosol is carried by N into the plasma. X-ray diffraction and X-ray photoelectron spectroscopy characterizations confirm that the as-synthesized nanopowders are fully crystalline TiO. The weight fraction of anatase ( f) is higher than that of rutile and increases from 68.8 to 96.8 % by increasing specific energy input ( SEI) from 46 to 76 kJ/mol. The effect of SEI on specific surface area ( S) and BET-equivalent diameter ( d) of the nanopowders is investigated. The typically spheric morphology of the particles is observed by transmission electron microscopy (TEM) and the most probable d approaches the d. All the as-synthesized nanopowders show a high photocatalytic activity comparable to that of Degussa P25. [ABSTRACT FROM AUTHOR]

The present study explores a new method of synthesis of TiO nano-particles in an aqueous medium from TiCl precursor by non-thermal plasma in humid air as feeding gas obtained at atmospheric pressure. The precursor solution, TiCl is oxidized by strongly reactive species generated by gliding arc plasma (HO = 2.85 V/SHE) to produce titanium oxide powders. The synthesized powder was characterised by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, FTIR spectroscopy, nitrogen physisorption, and UV-Vis spectroscopy. The results obtained showed that the material consists of rod-shaped nanoparticles of rutile and anatase phases. The presence of TiO phases was confirmed by FTIR spectrum and textural analyses showed that the material is mesoporous with specific surface area of 158 m g. UV-Visible spectrum of the plasma-synthesized TiO sample showed that it absorbs in the UV-A region leading to effective use as a photocatalyst under visible light. [ABSTRACT FROM AUTHOR]

The respective roles of short and long-life oxidant species in the degradation of model organic pollutants in water have been investigated in a gas-liquid gliding arc plasma reactor. Three different model pollutants were treated in two configurations: direct discharge mode and spatial post discharge mode. In each case the pollutants were classified according to their ease of removal, from easier to more difficult to remove. The results were as follows: phenol >> 1-heptanol >> pCBA. The removal mechanisms also are different depending on the characteristics of the pollutant treated. Phenol (100 % of phenol was removed for energy density = 1.20 × 10 J/L) was supposed to react strongly with NO° radicals produced by the dissociation of NO in liquid phase. The degradation of 1-heptanol would proceed by desorption of the liquid phase to the gas phase, where oxidation occurs due to the plasma active short-lived species. In the case of pCBA, oxidation occurs in the liquid solution, but the degradation is low because of its low reactivity with species such as ozone and °NO and insufficient production of OH° radicals in the solution. [ABSTRACT FROM AUTHOR]

In this study, a technique of combining steam reforming with partial oxidation of CO-containing natural gas in a gliding arc discharge plasma was investigated. The effects of several operating parameters including: hydrocarbons (HCs)/O feed molar ratio; input voltage; input frequency; and electrode gap distance; on reactant conversions, product selectivities and yields, and power consumptions were examined. The results showed an increase in either methane (CH) conversion or synthesis gas yield with increasing input voltage and electrode gap distance, whereas the opposite trends were observed with increasing HCs/O feed molar ratio and input frequency. The optimum conditions were found at a HCs/O feed molar ratio of 2/1, an input voltage of 14.5 kV, an input frequency of 300 Hz, and an electrode gap distance of 6 mm, providing high CH and O conversions with high synthesis gas selectivity and relatively low power consumptions, as compared with the other processes (sole natural gas reforming, natural gas reforming with steam, and combined natural gas reforming with partial oxidation). [ABSTRACT FROM AUTHOR]

The aim of this research work was to evaluate the possibility of upgrading the simulated biogas (70 % CH and 30 % CO) for hydrogen-rich syngas production using a multi-stage AC gliding arc system. The results showed that increasing stage number of plasma reactors, applied voltage and electrode gap distance enhanced both CH and CO conversions, in contrast with the increases in feed flow rate and input frequency. The gaseous products were mainly H and CO, with small amounts of CH, CH and CH. The optimum conditions for hydrogen-rich syngas production using the four-stage AC gliding arc system were a feed flow rate of 150 cm/min, an input frequency of 300 Hz, an applied voltage of 17 kV and an electrode gap distance of 6 mm. At the minimum power consumption (3.3 × 10 W s/molecule of biogas converted and 2.8 × 10 W s/molecule of syngas produced), CH and CO conversions were 21.5 and 5.7 %, respectively, H and CO selectivities were 57.1 and 14.9 %, respectively, and H/CO (hydrogen-rich syngas) was 6.9. The combination of the plasma reforming and partial oxidation provided remarkable improvements to the overall process performance, especially in terms of reducing both the power consumption and the carbon formation on the electrode surface but the produced syngas had a much lower H/CO ratio, depending on the oxygen/methane feed molar ratio. The best feed molar ratio of O-to-CH ratio was found to be 0.3/1, providing the CH conversion of 81.4 %, CO conversion of 49.3 %, O conversion of 92.4 %, H selectivity of 49.5 %, CO selectivity of 49.96 %, and H/CO of 1.6. [ABSTRACT FROM AUTHOR]

new plasma-catalysis process of gliding arc discharge (GAD) plasma with zero-valent iron (ZVI) was examined. Because GAD plasma creates an acidic environment, solid iron releases ferrous ions which act as a catalyst for the decomposition of the hydrogen peroxide. A comparative study of the catalytic effects between Fe and Fe in GAD plasma was investigated. The decolorization reactions of Acid Orange 7 (AO7) followed pseudo-first-order kinetics. And the rate constants for the process of GAD with ZVI was increased by 30% and by 19%, respectively, compared with the process of GAD alone and the process of GAD with ferrous. The investigations of solution pH and hydrogen peroxide both demonstrated that the GAD plasma induced conditions are much suitable for advanced Fenton reactions. The corrosion of ZVI in GAD plasma can give continuous ferrous ions to sustain Fenton reaction. Also, ZVI was demonstrated to have favorable reusable feature. [ABSTRACT FROM AUTHOR]

The effect of stage number of multistage AC gliding arc discharge reactors on the process performance of the combined reforming and partial oxidation of simulated CO2-containing natural gas having a CH4:C2H6:C3H8:CO2 molar ratio of 70:5:5:20 was investigated. For the experiments with partial oxidation, either pure oxygen or air was used as the oxygen source with a fixed hydrocarbon-to-oxygen molar ratio of 2/1. Without partial oxidation at a constant feed flow rate, all conversions of hydrocarbons, except CO2, greatly increased with increasing number of stages from 1 to 3; but beyond 3 stages, the reactant conversions remained almost unchanged. However, for a constant residence time, only C3H8 conversion gradually increased, whereas the conversions of the other reactants remained almost unchanged. The addition of oxygen was found to significantly enhance the process performance of natural gas reforming. The utilization of air as an oxygen source showed a superior process performance to pure oxygen in terms of reactant conversion and desired product selectivity. The optimum energy consumption of 12.05 × 1024 eV per mole of reactants converted and 9.65 × 1024 eV per mole of hydrogen produced was obtained using air as an oxygen source and 3 stages of plasma reactors at a constant residence time of 4.38 s. [ABSTRACT FROM AUTHOR]

The effects of gas composition on hybrid gas–water gliding arc discharge plasma reactor have been studied. The voltage cycles are characterized by a moderate increase in the tension which is represented by a peak followed by an abrupt decrease and a current peak in the half period (10 ms). Emission spectrum measurements revealed that •OH hydroxyl radicals are present in the discharge with feeding any gas. The H2O2 concentrations reach 38.0, 15.0, 10.0, and 8.0 mg/l after 25 min plasma treatment with oxygen, argon, air, and nitrogen, respectively. O3 was produced when oxygen and air are used, but not when nitrogen and argon. The O3 concentration reached the highest value 1.0 mg/l after 25 min plasma treatment with oxygen feeding gas, but gradually decreased to 0.2 mg/l after that. With feeding nitrogenous gas, NO2 − and NO3 − byproducts were formed by the plasma chemical process. [ABSTRACT FROM AUTHOR]

In this research, the reforming of simulated natural gas containing a high CO2 content under AC non-thermal gliding arc discharge with partial oxidation was conducted at ambient temperature and atmospheric pressure, with specific regards to the concept of the direct utilization of natural gas. This work aimed at investigating the effects of applied voltage and input frequency, as well as the effect of adding oxygen on the reaction performance and discharge stability in the reforming of the simulated natural gas having a CH4:C2H6:C3H8:CO2 molar ratio of 70:5:5:20. The results showed marked increases in both CH4 conversion and product yield with increasing applied voltage and decreasing input frequency. The selectivities for H2, C2H6, C2H4, C4H10, and CO were observed to be enhanced at a higher applied voltage and at a lower frequency, whereas the selectivity for C2H2 showed an opposite trend. The use of oxygen was found to provide a great enhancement of the plasma reforming of the simulated natural gas. For the combined plasma and partial oxidation in the reforming of CO2-containing natural gas, air was found to be superior to pure oxygen in terms of reactant conversions, product selectivities, and specific energy consumption. The optimum conditions were found to be a hydrocarbons-to-oxygen feed molar ratio of 2/1 using air as an oxygen source, an applied voltage of 17.5 kV, and a frequency of 300 Hz, in providing the highest CH4 conversion and synthesis gas selectivity, as well as extremely low specific energy consumption. The energy consumption was as low as 2.73 × 10−18 W s (17.02 eV) per molecule of converted reactant and 2.49 × 10−18 W s (16.60 eV) per molecule of produced hydrogen. [ABSTRACT FROM AUTHOR]

The dependence of gliding arc gas discharge characteristics, including gas flow field, arc column motion and volatile organic compounds (VOCs) decomposition performance, on reactor configuration parameters was investigated based on numerical simulation and laboratory experimental findings. For a given supply voltage (10 kV) and a certain nozzle outlet diameter (1.5 mm), increasing the electrodes gap (1–4 mm) or decreasing vertical distance between electrode throat and nozzle outlet (25–10 mm) will increase the gas flow rate through the electrode throat, the gas velocity in the plasma region, the arc column velocity, the maximum attainable position of the arc column and the electrical power consumption, also, higher VOCs decomposition rate and lower specific energy requirement are observed according to the n-butane and toluene decomposition experiments. [ABSTRACT FROM AUTHOR]