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We report on the synthesis of ternary SiGeSn nanocrystals (NCs) produced via nonthermal plasma synthesis from silane (SiH4), germane (GeH4), and tetramethylstannane (Sn(CH3)4) precursor sources. Detailed structural, chemical, and vibrational analyses show that all three elements are incorporated both on the NC surface and within the NC core. Incorporation of Sn into the NC core is realized using a secondary injection of SiH4 and GeH4 precursor gases in the after-glow region of the plasma, which kinetically traps Sn in the core. We demonstrate compositional tunability of the SiGeSn NCs in which the Si and Ge ratios can be varied broadly at low Sn concentrations. We also show tunability of the Sn content up to ∼2 atomic percent as revealed by ICP-MS analysis. More generally, this report demonstrates how nonthermal plasma synthesis can be used to produce metastable ternary nanostructured alloys involving thermodynamically insoluble constituents.

In this work, the reaction mechanism in non-thermal plasma enabled methane conversion driven by different sources, i.e., microwave discharge, nanosecond pulsed dielectric barrier discharge, and spark discharge, is investigated. The behavior of reactive species is monitored using the optical emission spectroscopy (OES), while the final gaseous products are analyzed with gas-chromatograph (GC). A zero-dimensional (0D) reaction kinetics model is established to reveal the underlying reaction processes. By changing pressure, different plasma modes (diffuse and filamentary) are achieved and the relative emission intensity of different species and distribution of gaseous productions are manipulated. It is found that there is a strong correlation between the intensity-ratio of C2 A→X and CH A→X, gas temperature, and the relative concentration of C2 products in different discharge forms, i.e., higher intensity ratio of C2/CH is associated with higher gas temperature and more unsaturated hydrocarbon products. Assisted with the 0D reaction kinetics model, the relationship between the intermediate species and final products is illustrated. Based on the investigation in this work, it is proposed that intensity-ratio of OES can be widely adapted as a non-intrusive and real-time process monitoring in the plasma-enabled methane conversion.

Outbreaks of airborne infectious diseases such as measles or severe acute respiratory syndrome can cause significant public alarm. Where ventilation systems facilitate disease transmission to humans or animals, there exists a need for control measures that provide effective protection while imposing minimal pressure differential. In the present study, viral aerosols in an airstream were subjected to non-thermal plasma (NTP) exposure within a packed-bed dielectric barrier discharge reactor. Comparisons of plaque assays before and after NTP treatment found exponentially increasing inactivation of aerosolized MS2 phage with increasing applied voltage. At 30 kV and an air flow rate of 170 standard liters per minute, a greater than 2.3 log reduction of infective virus was achieved across the reactor. This reduction represented ~2 log of the MS2 inactivated and ~0.35 log physically removed in the packed bed. Increasing the air flow rate from 170 to 330 liters per minute did not significantly impact virus inactivation effectiveness. Activated carbon-based ozone filters greatly reduced residual ozone, in some cases down to background levels, while adding less than 20 Pa pressure differential to the 45 Pa differential pressure across the packed bed at the flow rate of 170 standard liters per minute.

Catalytic conversion of CO2 to renewable chemicals and fuels is a promising approach to mitigate issues associated with climate change and energy supply deficiency. Hybrid non-thermal plasma (NTP) and catalysis systems, that is, NTP catalysis systems, enable the activation of stable CO2 molecules under relatively mild conditions in comparison with conventional thermal catalysis, and are promising for the energy-efficient conversion of CO2. This review presents the state-of-the-art development of NTP catalysis of CO2 conversion, including CO2 splitting and CO2 hydrogenation and reforming, with the focus on mechanistic insights developed forcatalytic CO2 conversion. Additionally, the role of intrinsic catalyst composition and structure in determining the selectivity of CO2 conversion under NTP conditions is also discussed in light of the need for rational design of catalysts for NTP catalysis. Finally, a perspective on future challenges and opportunities in the development of next-generation catalysts for NTP catalysis and the advanced hybrid NTP catalysis process for practical industrial applications are discussed.

An atmospheric, dielectric-barrier discharge µ-plasmatron was designed, fabricated, and applied to synthesize a methylated organometallic complex. The design comprises counter-current flow to packed-bed microstructures to facilitate gas–liquid and plasma–liquid mixing. Micropillars arranged in a staggered configuration served as a porous media for the optimum 2D mixing of components that replenish plasma-liquid interfaces. Longitudinal dispersion was characterized through residence time distribution (RTD) measurements. The experimental RTD data were then described by an axial dispersion model with a time delay parameter. Levenspiel number (lv) indicating the intensity of axial dispersion was estimated in the range of 20.1–374, indicating that a dispersion model should be accounted for in plasma-assisted reaction kinetics development. Stable plasma excitation of methane-helium gas mixtures was observed within the 2D porous media, by in-situ optical emission spectra, while applying an alternating high voltage across the dielectric barrier. This novel technique made it possible to confirm in-situ formations of methyl radicals. Interestingly, the porous media served as a static mixer as no discrete plasma streamers were observed. To investigate its utility, an example homogeneous cobalt catalyst was injected into the µ-plasmatron and methylated. Our findings potentially introduce a new plasma-assisted reactor design and methodology for the synthesis of methylated cobaloxime.

This work explores the use of an atmospheric pressure, low temperature, cold non-thermal plasma (obtained by dielectric barrier discharge (DBD)) to achieve a water-gas shift (WGS) reaction (CO + H2O H2 + CO2). This work establishes the use of a DBD to generate hydroxyl radicals that initiate and enhance the WGS reaction at low temperatures. The effect of the steam to CO molar ratio (MR) and the gas residence time on the CO conversion (X CO) to H2 is studied. The results show that, at an MR of 20, with 2600 ms of gas residence time and a plasma power of 70 W, a maximum CO conversion of 63 ± 4 can be achieved with an H2 concentration of 48 ± 2 mol in the product. Preliminary studies of reaction pathways for the enhanced hydrogen formation confirm the role of C formed from the CO2 dissociation. A reaction mechanism for the plasma WGS reaction is proposed and the hydrogen yield is calculated. © 2020 IOP Publishing Ltd.

(−)-Epigallocatechin gallate (EGCG), which is the most abundant bitter polyphenol in green tea (Camellia sinensis) leaves, is generally unstable under oxidative conditions. In this study, the efficient dimerization of EGCG was successfully achieved without changes in stereochemistry by treatment with nonthermal dielectric barrier discharge (DBD) plasma. The stereochemically pure dimers 2 and 3 connected by a methylene linkage exhibited significantly enhanced melanogenesis inhibitory activities compared to the parent EGCG and the active compounds 2 and 3 suppressed cellular tyrosinase, tyrosinase-related protein (TRP)-1, and TRP-2 expression in B16F10 melanoma cells, which could be considered one of the mechanisms of action. These results indicate a new method for efficient dimerization of stereochemically active depigment agent induced by DBD plasma treatment.

The interest in plasma-activated water (PAW) has been greatly increasing during the last few years due to its potential applications in biological and medical sciences, as well as in agriculture and food industry. The effect of PAW is caused by the reactive oxygen and nitrogen species (RONS) generated in the liquid exposed to plasma. This work reviews recent research on the formation of reactive nitrogen species (RNS) in aqueous solutions treated by non-thermal plasma. The most important chemical reactions leading to the production of these active species in the gas and liquid phase, as well as their chemistry in the liquid, correlated with their lifetime are addressed. The literature data on the most important long-lived RNS in PAW (nitrite and nitrate) and the short-lived ones (peroxynitrite and peroxynitrate) are reviewed. The reported results show that their concentrations strongly depend on the type of electrical discharge, gas composition, liquid properties and treatment conditions, and thus tuning the PAW composition over a relatively wide range can be achieved. Results on the possible application of PAW in agriculture are also reviewed. The role of RNS in this area is related to their participation in various signalling pathways in plants, which regulate metabolic processes, plant development, response to stress, etc, and thus can finally lead to enhanced germination and/or faster germination process and increase in plant growth.

We performed time-resolved characterization of plasma-photocatalytic removal of nitric oxide (NO) in a ceramic foam packing double dielectric barrier discharge (DBD) reactor using mid-infrared laser absorption spectroscopy (LAS). Non-thermal plasma (NTP) was generated in the porous ceramic foam coated with mesoporous TiO2 thin film. Real-time NO monitoring was performed using a quantum cascade laser (QCL) at 5.26 µm combined with a custom-designed multipass gas cell, leading to a sub-ppm detection limit at 0.1-s measurement time. By analyzing the feed gas of 90 ppm NO/1% O2 balanced in N2, the plasma treatment without TiO2 photocatalyst had no effect on NO removal when the discharge power was below 45 W. In comparison, the NTP-TiO2 system achieved an efficiency of 49% for NO removal even at the relatively low discharge power of 18 W. The synergy between NTP and TiO2 photocatalyst effectively promotes the NO removal at low plasma discharge powers. However, we also observed a negative effect of TiO2 photocatalyst on NO removal at a relatively high discharge power of 135 W.

Interaction between dielectric barrier discharge (DBD) and porous catalyst in dry methane reforming (CH4 + CO2 = 2H2 + 2CO) was studied. Coke formation behavior and coke morphology, as well as material conversion and selectivity, over the cross-section of porous pellets was investigated comprehensively by SEM analysis, Raman spectroscopy and pulsed reforming diagnosis, showing DBD and porous pellet interaction is possible only in the interfacial region (the external surface of the pellet): neither generation of DBD nor the diffusion of plasma generated reactive species in the internal micropores is possible. Coke formation and gasification mechanism in nonthermal plasma catalysis of DMR were discussed based on the catalyst effectiveness factor: low-temperature plasma catalysis is equivalent to the high-temperature thermal catalysis.

Formaldehyde is one of the most common volatile organic compounds and indoor contaminant, and one known to cause a variety of health problems. This paper proposes a streamer discharge reactor with negative or positive discharge for formaldehyde removal. The removal of HCHO and the simultaneous production of O3 in a DC streamer plasma were investigated. The performances of the positive and negative discharges were compared. The electrical characteristics such as U-I characteristics, discharge pattern, and power source efficiency were studied, and the reaction results were evaluated by O3 production, HCHO removal, and energy yield. Optical emission spectra were used to characterize the streamer and reactive species produced. A maximum HCHO removal rate of 78% was achieved at a specific energy density of 1700 J l−1. Results suggest that the positive streamer is better at producing O3 and oxidizing HCHO, compared to the negative counterpart. For the positive streamer plasma, the G-values of ozone production and formaldehyde decomposition are 0.59 molecules per 100 eV and 0.035 molecules per 100 eV, respectively. Interestingly, the production of O3 and degradation of HCHO were found to be simultaneous but quasi-individual processes. Both reactions were controlled by the generation of O atoms, however they consumed O atoms independently. The active species of OH, H and O radicals were observed, which had contribution to the degradation of formaldehyde. Finally, the reaction mechanism and most possible reaction pathways for the two processes were discussed.

There are several applications for non-thermal plasma at atmospheric pressure, such as the sterilization of infected tissues, wound healing, and delicate surgery. Non-thermal plasma generates reactive oxygen/nitrogen species (RONS). In this study, we examined human red blood cells (RBCs), platelet function, and blood coagulation, following treatments with different feeding gases (air, nitrogen (N2), and argon (Ar)) of the dielectric barrier discharge plasma (DBDP) at different exposure times. This is the first study to evaluate the effects of DBDP on hemolysis, deformability, aggregation, and morphology of RBCs, as well as platelet function and blood coagulation at three doses (5, 10 and 15 min exposure). In comparison to N2 and Ar DBDP, air DBDP at more than 10 min exposure to RBC in culture plate with 2 ml liquid solution caused hemolysis and alterations in RBC deformability and aggregation owing to the higher levels of hydrogen peroxide, hydroxyl oxidants and other RONS. Moreover, air DBDP affected platelet function at high doses (more than 10 min exposure). Consequently, the air DBDP at, or more, than 10 min exposure affects blood coagulation and blood cells. The proposed method is useful for assessing the performances and dose optimization of various non-thermal plasma types used with different type of gases in biological applications.

The oxidation behavior of Ni/Al2O3 catalyst in CO2 plasma was investigated compared with CO2 thermal oxidation, aiming for providing new insight into oxidation-reduction cycle of plasma catalysis of dry methane reforming (DMR). Temperature programmed reaction spectrometry was applied to enable a quantitative analysis of gas consumption which is related to the oxidation and reduction of Ni/Al2O3 catalysts. The nonthermal plasma oxidation mechanism was further analyzed by Raman spectroscopy, showing the cross-sectional distribution of NiO over the 3 mm spherical catalyst pellets. Nonthermal plasma-excited CO2 oxidizes Ni only near the external surface of spherical pellets with 20 μm depth: both dielectric barrier discharge generation and plasma-excited species diffusion into the internal pores are inhibited. The partially oxidized Ni catalyst in the external surface would promote plasma-enabled oxidation-reduction cycle, which was further correlated with coke formation behavior in plasma catalysis of DMR.

Nitrogen oxides (NOx) emitted from power plants and combustion sources cause air pollution problems. Selective catalytic reduction technology is remarkably useful for NOx removal. However, there are several drawbacks such as preparation of reducing agents, usage of harmful heavy metals, and higher cost. On the other hand, trace NO is a vasodilator agent and employed in inhalation therapies for treating pulmonary hypertension in humans. Considering these factors, in the present study, a wet-type nonthermal plasma reactor, which can control NOx and nanoparticle emissions and generate NO, is investigated. The fundamental characteristics of the reactor are investigated. First, the experiment of nanoparticle removal is carried out. Collection efficiencies of over 99% are achieved for nanoparticles at 50 and 100 ml min−1 of liquid flow rates. Second, experiments of NOx removal under air atmosphere and NOx generation under nitrogen atmosphere are carried out. NOx-removal efficiencies of over 95% under the air plasma are achieved in 50–200 ml min−1 liquid flow rates. Moreover, under nitrogen plasma, NOx is generated, of which the major portion is NO. For example, NO concentration is 25 ppm, while NOx concentration is 31 ppm at 50 ml min−1 liquid flow rate. Finally, experiments of NO generation under the nitrogen atmosphere with or without flowing water are carried out. When water flows on the inner surface of the reactor, approximately 14 ppm of NO is generated. Therefore, NO generation requires flowing water. It is considered that the reaction of N and OH, which is similar to the extended Zeldovich mechanism, could occur to induce NO formation. From these results, it is verified that the wet-type plasma reactor is useful for NOx removal and NO generation under nitrogen atmosphere with flowing water.

Non-thermal atmospheric pressure plasmas enable plasma treatment of surfaces without requiring a low-pressure environment. These plasmas are currently of interest for, among other things, their biomedical applications, many of which are enabled by production of reactive oxygen and nitrogen species (RONS). Plasma?liquid interactions are especially important due to the high amounts of water in biological materials. However, the chemistries of these plasmas are very complex and are not well-understood. One method to quantify plasma?liquid interactions is to dissolve a reactant into the liquid which, when exposed to plasma-created RONS, forms a measurable product. In particular, the oxidation of the spin trap TEMP to TEMPO has been used to track trends in reactive oxygen species. However, the effect of individual species on TEMP has not previously been determined. This paper differentiates the oxidation of TEMP due to various oxygen species produced by a He plasma jet operating in a controllable environment. Oxidation of TEMP is mainly to O atoms, with small or negligible contributions from other species. Thus, the TEMPO yield will also be used to illuminate trends in O atom production.

Results of the simulation of transient plasma discharges in a stoichiometric atmospheric-pressure methane–air mixture are presented. It is shown that current control allows one to produce non-thermal plasma with parameters (the gas temperature, the molar fractions of active species) varying over a wide range. The calculated plasma parameters are used in the modelling of ignition of the mixture. Estimated values of the ignition delay time and the minimum ignition energy are given.

Dissociation reactive thermal conductivity (DRTC) is the transfer of dissociation energy in plasma with temperature and, therefore, composition gradient. In the existing theories, calculation of the DRTC coefficient consists of the calculation of diffusion coefficients and plasma composition. The heat flux is then calculated by assigning to every molecule the dissociation energy and by the multiplication of the molecule flux density by this energy.This approach, correct for the LTE plasma, is not adequate for the non-equilibrium two-temperature plasma: it does not allow one to separate the total DRTC coefficient into two components responsible for the heat transfer by electrons and heavy particles (atoms, molecules, ions). Only at LTE, during atom reassociation, do the electrons recuperate the energy they spent during the molecule dissociation. Therefore, in order to separate these two components of DRTC, the kinetics of the dissociation?reassociation processes should be considered. This is done in this paper for nitrogen plasma at atmospheric pressure. Fe, the electron fraction of the total DRTC coefficient, was calculated for Te (electron temperature) in the range 0.4?1.0?eV and Th (heavy particles temperature) from 0.2?eV to Te. It is shown that Fe depends mostly on the electron temperature and increases with increasing electron temperature.

A self-consistent model of a non-equilibrium spherical microwave discharge is presented. We use a two-temperature plasma model. Numerical experiments are carried out for the discharge in argon at atmospheric pressure. Results are presented for the characteristics of the discharge plasma against the external parameters (the power and frequency of the applied electromagnetic field and the size of the discharge chamber).

Non-thermal plasmas under atmospheric pressure are of great interest in material surface processing because of their convenience, effectiveness and low cost. In this paper, the treatment of a glass surface for improving hydrophobicity using a non-thermal plasma generated by a dielectric barrier corona discharge (DBCD) with a needle array-to-plane electrode arrangement in atmospheric air is conducted, and the surface properties of the glass before and after the DBCD treatment are studied using contact angle measurement, surface resistance measurement and the wet flashover voltage test. The effects of the plasma dose (the product of average discharge power and treatment time) of DBCD on the surface modification are studied, and the mechanism of interaction between the plasma and glass surface is discussed. It is found that a layer of hydrophobic coating is formed on the glass surface through DBCD treatment, and the improvement of hydrophobicity depends on the plasma dose of the DBCD. It seems that there is an optimum plasma dose for the surface treatment. The test results of thermal ageing and chemical ageing show that the hydrophobic layer has quite stable characteristics.

A reaction mechanism has been developed that is appropriate for the plasma aftertreatment of diesel exhaust gas. It is based on a simulated gas mixture containing propene, nitric oxide, nitrogen dioxide, oxygen and nitrogen. The reaction mechanism has been used to determine the end-products from the plasma processing and their concentrations using a chemical kinetics modelling procedure. It has been validated by a range of experiments using the same gas mixture with a packed bed, a dielectric barrier plasma reactor and a wide range of end-product analysis techniques. Using a wide range of experimental conditions has enabled us to validate the model and its predictions and to critically evaluate several alternative reaction mechanisms for the oxidation of propene and the formation of end-products in a more systematic and reliable manner than before.

An AC-driven, non-thermal, atmospheric pressure air plasma is generated within the gap separating a disc-shaped metal electrode and a water electrode. The ignition phase and the steady-state are studied by a high-speed CCD camera. It is found that the plasma always initiates at the surface of the water electrode. The plasma exhibits different structures depending on the polarity of the water electrode: when the water electrode plays the role of cathode, a relatively wide but visibly dim plasma column is generated. At the maximum driving voltage, the gas temperature is between 800 and 900 K, and the peak current is 67 mA; when the water electrode is anode, the plasma column narrows but increases its light emission. The gas temperature in this case is measured to be in the 1400–1500 K range, and the peak current is 81 mA.

OH radicals play a very important role in non-thermal plasma chemical reactions for decomposition of gaseous pollutants or synthesis of methanol from methane, etc. In this paper, the CO oxidation monitoring method, which has been used in atmospheric chemistry, was examined to measure the concentration of OH radicals produced by a pulsed discharge plasma. The concentration of OH radicals in the discharge plasma of H2O/Ar mixture gas was estimated by measuring the amount of CO2 produced through oxidation of CO by OH radicals. The experimental results and the calculated results showed that it is possible to measure OH radicals using this simple method. In this experimental work, the maximum concentration of OH radicals produced by the pulsed discharge plasma of H2O/Ar was measured to be 9.4×1014 molecules cm−3 pulse−1. Within the temperature range investigated in this study (50–150°C), the formation of OH radicals increased with increase in the specific input energy (discharge energy dissipated in unit volume of the gas; SIE) value and the content of H2O; in contrast, it decreased with increase in the gas temperature.

Hydroxyl radicals generated by a pulsed corona discharge are measured by laser-induced fluorescence (LIF) with a tunable KrF excimer laser. The discharge with 35 kV voltage and 100 ns pulse current occurs between needle and plate electrodes in H2O/O2/N2 mixture at atmospheric pressure. The density and decay profile of OH radicals are studied. OH radicals decay with time after the discharge with a time constant of about 30-60 µs. The OH density is estimated to be about 7×1014 cm-3 in H2O(2.4%)/N2 mixture 10 µs after the discharge. The OH density is approximately proportional to the energy dissipated in the discharge. The O2 content influences the OH production. When the O2 content is varied in H2O(2.4%)/O2/N2 mixture, the OH density is maximum at an O2 content of 2%. The spatial distribution of OH density shows that OH radicals are produced in the streamers under positive discharge.

This paper presents a two-temperature model for compressible plasma flows. This study concentrates on the behaviour of the plasma jet in the expansion region. The conditions used correspond to the conditions of low-pressure plasma spraying, with slightly supersonic conditions with thermal and chemical non-equilibrium. The flow dynamics results are analysed with different turbulence models and appear to be consistent with results previously published by the authors [3] on the dynamics of low-temperature air jets and favour the Reynolds stress turbulence model. Chemical as well as thermal non-equilibrium are studied.

It is clearly seen that the application of non-thermal plasmas (NTP) to remove NOx from gas mixture containing a large amount of oxygen (O2) is dominated by NO to NO2 oxidation. Experiments have been conducted using a NTP generated by a nanosecond pulsed dielectric barrier discharge in synthetic exhaust gas, prepared from N2, O2, NO, H2O, and C3H6, over a large range of gas temperature (20-300\r{}C). Results show that the NOx removal rate significantly increased with increasing specific energy deposition. For example, at a temperature of 100\r{}C and an energy deposition of 27 J l-1, 92% of the NO molecules have been removed. The W values for NO is dramatically reduced to values scaling from ≈15 eV at 27 J l-1 down to ≈4 eV at 7 J l-1. NOx removal efficiency around 43% was obtained at a temperature of 260\r{}C and a space velocity of 60 000 h-1 for a specific input energy of 27 J l-1. W values for NOx were less than ≈30 eV. Such treatments in exhaust gas with and without the presence of water vapour induced reactions leading to the production of a large variety of by-products such as acetaldehyde, propylene oxide, formic acid, methyl nitrate, and nitromethane.

Elucidating the electron density of streamer discharges propagating in atmospheric-pressure air is critical for achieving a systematic understanding of the production mechanisms of reactive species. Using Shack–Hartmann-type laser wavefront sensors with a temporal resolution of 2 ns, we carried out single-shot two-dimensional electron density measurements for positive primary streamers generated in a 13 mm air gap between pin-to-plate electrodes. The electron density over the positive primary streamers decayed from 1015 to during the propagation. The decay time constant of the electron density in the primary streamer channels was estimated to be ~2 ns. The distribution widths of the electron density were in good agreement with those of the light emission, typically ranging from 0.8 to 1.5 mm.

Ethanol reforming in non-thermal plasma generated in atmospheric-pressure argon bubbles immersed in liquid ethanol/water solution is studied using a self-consistent multi-species fluid model. The influence of the dielectric constant of the liquid on the plasma dynamics and its effect on the generation of active species is analyzed. Several modes of discharge are obtained for large liquid dielectric constant. In these modes, we obtain either an axial streamer or a combination of two simultaneous streamers propagating along the bubble axis and near the liquid wall. The influence of these modes on the production of active species is also studied. The main reactions responsible for the generation of molecular hydrogen and light hydrocarbon species are analyzed. A possible mechanism of hydrogen generation in liquid phase is discussed.

In this paper, we will report NOx removal via reduction processes using two types of combined system of pulse corona discharge and catalysts: the single-stage plasma-driven catalyst (PDC) system, and the two-stage plasma-enhanced selective catalytic reduction (PE-SCR) system. Several catalysts, such as γ-alumina catalysts, mechanically mixed catalysts of γ-alumina with BaTiO3 or TiO2, and Co-ZSM-5 were tested. In the PDC system, which is directly activated by the discharge plasma, it was found that the use of additives was necessary to achieve NOx removal by reduction. Removal rates of NO and NOx were linearly increased as the molar ratio of additive to NOx increased. The dependence of NO and NOx removal on the gas hourly space velocity (GHSV) at a fixed specific input energy (SIE) indicates that plasma-induced surface reaction on the catalyst plays an important role in the PDC system. It was found that the optimal GHSV of the PDC system with the γ-alumina catalyst was smaller than 6000 h-1. Mechanical mixing of γ-alumina with BaTiO3 or TiO2 did not enhance NO and NOx removal and γ-alumina alone was found to be the most suitable catalyst. The dielectric constant of the catalyst only influenced the plasma intensity, not the NOx removal. In the PE-SCR system, plasma-treated NOx (mostly NO2) was reduced effectively with NH3 over the Co-ZSM-5 catalyst at a relatively low temperature of 150 °C. Under optimal conditions the energy cost and energy yield were 25 eV/molecule and 21 g-N (kWh)-1, respectively.

A comparative modelling of pulsed-corona and silent discharges for removal of NOx, NyOx, SO2, CO and CH2O using operating equipment is presented. The main purpose is to compare, by modelling, the energy efficiency on removal of toxic impurities between two types of discharges at similar gas composition and temperature. Three different gas compositions: diesel engine exhaust, methane combustion products and pollutant air are considered. The simulation is based on an approximate mathematical model for plasma cleaning of a waste gas. The influence of non-uniform species distributions arising from a great number of streamer or microdischarge channels in a discharge chamber is taken into account. The modelling is carried out for a pulse series, considering after each discharge pulse the chemical and diffusion processes inside and outside the streamer trace. The distinctions of the cleaning processes in the pulsed-corona and barrier discharges are presented. It is also recommended when each of the examined discharges should be used.

A new method for the removal of harmful organic molecules from water is described. A low power corona discharge is created over the aqueous solution. Chemically active species diffuse into the water and then oxidize the target compound, which in this case is the model compound phenol. The energy consumption per removed phenol molecule is one order of magnitude lower compared to the discharge techniques that create a plasma in the water. The reaction mechanism of the conversion is shown by measuring the ozone concentration over the water, the intermediate/final oxidation products and the release of CO2 from the water. Indications are found that the discharge is more than merely an ozone generator.

This study is devoted to an investigation of the energy consumption and byproduct generation of the nonthermal plasma-chemical NO-reduction process. Nitrogen gas with a 200 ppm NO impurity has been processed at a pressure of 1.3 atm in a silent discharge reactor with a gap spacing of 50 µm. Detailed measurements of NO, NO2 and N2O concentrations at the reactor outlet were carried out and analysed by means of the created model. On the basis of the proposed three-collision reaction mechanism of N2O generation the byproduct-suppression effect has been predicted and experimentally confirmed. An extremely low energy consumption (less than 150 eV per molecule) for NO reduction by the discharge nonthermal plasma has been attained.

The inactivation of Bacillus atrophaeus by OH radicals is measured. This study aims to evaluate the bactericidal effects of OH radicals produced by atmospheric-pressure nonthermal plasma widely used for plasma medicine; however, in this study, OH radicals are produced by vacuum ultraviolet (VUV) photolysis of water vapor instead of plasma to allow the production of OH radicals with almost no other reactive species. A 172 nm VUV light from a Xe2 excimer lamp irradiates a He–H2O mixture flowing in a quartz tube to photodissociate H2O to produce OH, H, O, HO2, H2O2, and O3. The produced reactive oxygen species (ROS) flow out of the quartz tube nozzle to the bacteria on an agar plate and cause inactivation. The inactivation by OH radicals among the six ROS is observed by properly setting the experimental conditions with the help of simulations calculating the ROS densities. A 30 s treatment with approximately 0.1 ppm OH radicals causes visible inactivation.

Improvements in ozone synthesis from air and oxygen by increasing the number density of plasma channels and lower voltage for the same specific input energy (SIE) were explored in a nonthermal plasma based on a sliding discharge. The number of plasma channels and energy per pulse increased in direct proportion to the increase in the effective length of the anode (the high voltage electrode). Decreasing the discharge gap increased the energy per pulse for the same length and allowed the installation of more electrode pairs in the same space. It allowed the increase of the number of plasma channels in the same space to achieve the same SIE at a lower peak voltage with less energy per plasma channel. The ozone concentration gradually increased to ~1500 ppmv (140 to 50 g kWh−1) from air and to ~6000 ppmv (400 to 200 g kWh−1) from oxygen with a gradual increase in the SIE to ~200 J L−1, irrespective of the variations in electrode geometry, applied voltage or flow rate of the feed gas. A gradual increase in SIE beyond 200 J L−1 gradually increased the ozone concentration to a certain maximum value followed by a decline, but the rate of increase and the maximum value was higher for the greater number of plasma channels and lower peak voltage combination. The maximum ozone concentration was ~5000 ppmv (~30 g kWh−1) from air and ~22 000 ppmv (~80 g kWh−1) from oxygen. The results are explained on the basis of characteristics of the plasma and ozone synthesis mechanism.