Pressure Glow Discharge Research Articles

Novel Signal Enhancement Strategy for Laser-Induced Breakdown Spectroscopy via Miniaturized Atmospheric Pressure Glow Discharge.

Herein, a sensitivity enhancement technique for laser-induced breakdown spectroscopy (LIBS) by atmospheric pressure glow discharge was proposed, while cylindrical confinement was used for further improvement. A comprehensive parameters evaluation of the proposed technique was carried out (at the laser energy of 30 mJ), with the emission intensities of Ti, Ni, Cu, Y, Ba, La, Eu, Yb, and Lu in soil samples enhanced by 17.8, 5.7, 5.2, 10.5, 7.4, 6.1, 8.7, 7.8, and 8.7 times, respectively. The limits of detection (LODs) of Ti, Ni, Cu, Y, Ba, La, Eu, Yb, and Lu were significantly decreased from 246, 356, 133, 158, 10, 175, 102, 105, and 262 mg kg-1 to 43, 67, 31, 20, 2, 35, 21, 18, and 49 mg kg-1, respectively. In addition, the possible signal enhancement mechanism was preliminarily explained by studying the plasma electron temperature and density with and without the proposed sensitization strategy.

Various concentric-ring patterns formed in a water-anode glow discharge operated at atmospheric pressure

Pattern formation is a very interesting phenomenon formed above a water anode in atmospheric pressure glow discharge. Up to now, concentric-ring patterns only less than four rings have been observed in experiments. In this work, atmospheric pressure glow discharge above a water anode is conducted to produce diversified concentric-ring patterns. Results indicate that as time elapses, the number of concentric rings increases continuously and up to five rings have been found in the concentric-ring patterns. Moreover, the ring number increases continuously with increasing discharge current. The electrical conductivity of the anode plays an important role in the transition of the concentric patterns due to its positive relation with ionic strength. Hence, the electrical conductivity of the water anode is investigated as a function of time and discharge current. From optical emission spectrum, gas temperature and intensity ratio related with density and temperature of electron have been calculated. The various concentric-ring patterns mentioned above have been simulated at last with an autocatalytic reaction model.

Coupling of chemical vapor generation with atmospheric pressure glow discharge optical emission spectrometry generated in contact with flowing liquid electrodes for determination of Br in water samples

Miniaturized atmospheric pressure glow discharge (APGD) microplasma devices, operated in contact with a flowing liquid anode (FLA) or a flowing liquid cathode (FLC) and a He jet, were studied for the determination of Br by optical emission spectrometry (OES), after oxidizing the Br- ions to volatile Br2 in the reaction with KMnO4. The concentrations of all reagents needed for the successful operation of the proposed systems were found to be the most crucial parameters and their impact on the intensity of the Br analytical line was studied. Under the optimal conditions, the analytical figures of merit were assessed. The endurance to the matrix effects of both developed methods was also investigated and both of them were found to be strongly insusceptible to the presence of foreign ions. The detection limits (DLs) of Br and was established to be 0.05 and 0.2 mg L-1 for CVG-FLA- and CVG-FLC-APGD, respectively. The developed methods were successfully applied for the determination of relatively low concentrations of Br in selected water samples, spiked with this element, with very good precision (0.9–6.1% as RSD) and trueness (94–110% as recovery). In addition, no significant differences between the results obtained using the external standard calibration and the standard addition method were noted.

Detection of solvated electrons below the interface between atmospheric-pressure plasma and water by laser-induced desolvation

We have developed a new method to detect solvated (hydrated) electrons at the plasma–water interface. The method is based on laser-induced desolvation followed by the release of free electrons into the plasma. We employed an atmospheric-pressure dc glow discharge, in which the water surface worked as the cathode, in the experiment. When the region just below the water cathode was irradiated with a pulsed laser beam, we observed the pulsed increase in the discharge current. The increase in the discharge current was caused by the release of free electrons, which were produced from hydrated electrons by the laser-induced desolvation. The pulsed increase in the discharge current was sensitive to the laser wavelength. We compared the relationship between the pulsed increase and the laser wavelength with the distribution of the solvation energy of hydrated electrons using Monte Carlo simulation on the transport of free electrons in water. As a result, it was concluded that hydrated electrons produced under the experimental conditions were located at a distance of 7–15 nm from the plasma–water interface.

A novel solution cathode glow discharge geometry for improved coupling to optical emission spectrometry

The Solution-Cathode Glow-Discharge (SCGD) is an atmospheric pressure glow discharge used for atomic emission spectrometry that is sustained between a metallic pin-anode and a liquid cathode, which is also the sample solution.

Ac-Driven Atmospheric Pressure Glow Discharge Co-Improves Conversion and Energy Efficiency of Co2 Splitting

Ac-Driven Atmospheric Pressure Glow Discharge Co-Improves Conversion and Energy Efficiency of Co2 Splitting

The sensitive determination of Ag, Pb and Tl as well as reduction of spectral interferences in a hanging drop cathode atmospheric pressure glow discharge excitation microsource equipped with a Dove prism system

A hanging drop cathode APGD-OES system coupled with Dove prism is reported. The reduction of spectral interferences and enhancement of the Ag, Pb and Tl atomic emission lines was the most spectacular and resulted in improved LODs of these elements.

Rapid detection and classification of hongmu by atmospheric pressure ionization mass spectrometry.

Hongmu, a Chinese customary noun representing 29 kinds of wood species such as some Pterocarpus species (abbreviated as spp. hereinafter), Dalbergia spp. and Diospyros spp., is popular among Chinese people due to the furniture made from it. The slow regeneration of hongmu resources led to a decline in production, making hongmu prices high and illegal businesses profit from it. Therefore, it is necessary to identify and distinguish different varieties of hongmu for commercial trade. Herein, a cost-effective and rapid methodology was first developed via atmospheric pressure glow discharge mass spectrometry (APGD-MS) to classify three Dalbergia spp. and three Pterocarpus spp. Meanwhile, principal component analysis (PCA) was further applied to distinguish wood species and six kinds of hongmu extracts were able to be approximately separated into six units. Besides, hongmu could be clearly distinguished from their counterfeits, such as Guibourtia spp., using the method provided here. This method may provide a timely and necessary way for the determination of ingredients and identification of the authenticity of hongmu.

Ac-Driven Atmospheric Pressure Glow Discharge Co-Improves Conversion and Energy Efficiency of Co2 Splitting

Ac-Driven Atmospheric Pressure Glow Discharge Co-Improves Conversion and Energy Efficiency of Co2 Splitting

Ultra-sensitive determination of mercury by atmospheric pressure glow discharge atomic emission spectrometry coupled with cold vapor generation

In this work, DC glow discharge atomic emission spectrometry coupled with cold vapor generation was used to achieve the ultra-sensitive analysis of mercury, with good anti-interference ability.

Dry reforming of methane in an atmospheric pressure glow discharge: Confining the plasma to expand the performance

We present a confined atmospheric pressure glow discharge plasma reactor, with very good performance towards dry reforming of methane, i.e., CO2 and CH4 conversion of 64 % and 94 %, respectively, at an energy cost of 3.5–4 eV/molecule (or 14–16 kJ/L). This excellent performance is among the best reported up to now for all types of plasma reactors in literature, and is due to the confinement of the plasma, which maximizes the fraction of gas passing through the active plasma region. The main product formed is syngas, with H2O and C2H2 as by-products. We developed a quasi-1D chemical kinetics model, showing good agreement with the experimental results, which provides a thorough insight in the reaction pathways underlying the conversion of CO2 and CH4 and the formation of the different products.

How does direct current atmospheric pressure glow discharge application influence on physicochemical, nutritional, microbiological, and cytotoxic properties of orange juice?

We proposed an innovative and economic method for rapid production of functionalized orange juice (OJ) with excellent nutritional properties, prolonged shelf life, and safe consumption. To reach this goal, we have employed direct current atmospheric pressure glow discharge, generated in contact with a flowing liquid cathode (FLC-dc-APGD) in a highly-throughput reaction-discharge system. It was found that controlled FLC-dc-APGD-treatment of OJ lead to increase the concentration of selected metals and phenolic compounds.The so-obtained OJ had the same qualitative composition of fragrance as the untreated one, however, its shelf life was prolonged up to 26 days. Furthermore, OJ exposed to FLC-dc-APGD-treatment did not exhibit any cytotoxic properties towards non-malignant human intestinal epithelial cell lines. On the other hand, the induction of cell cytotoxicity was observed in human colorectal adenocarcinoma cells line after FLC-dc-APGD-treated OJ application. We truly believe that produced by us functionalized OJ might be a tempting alternative to classic, non-treated by FLC-dc-APGD OJ.

Efficient production and transport of OH radicals in spatial afterglow of atmospheric-pressure DC glow discharge using intersecting helium flows

An efficient method for generating OH radicals in the spatial afterglow of atmospheric-pressure plasma was investigated. The method employed a DC glow discharge along two intersecting helium flows in air. Tiny helium flows were ejected from two metal nozzles with inner diameters of 0.5 mm, and they intersected at a distance of 3–5 mm from the nozzles. A stable glow discharge was formed along the intersecting helium flows by applying a DC high voltage between the two nozzles. It was shown by laser-induced fluorescence spectroscopy that an origin of OH radicals was water vapor admixed into the intersection point of the two helium flows from ambient air. OH radicals were transported from the intersection toward the spatial afterglow along the coalesced helium flow. This is a distinctive feature of the present plasma source, by which we can obtain the stream of OH radicals in the outside of the active plasma zone even though we employ the DC discharge. In addition, we observed the production of OH radicals in the spatial afterglow. We presume that the production process of OH radicals in the spatial afterglow is dissociative electron attachment to H2O2.

(Invited) Atmospheric Pressure Plasmas for Gas Processing : N2 Fixation and CO2 Conversion into Value-Added Compounds

Plasma-based N2 fixation into NH3 or NOx (for fertilizer applications) and plasma-based CO2 conversion into value-added compounds are gaining increasing interest [1-4]. However, for real implementation, these applications need to be further improved, in terms of conversion, energy efficiency and product formation. We perform experiments in different types of plasma reactors (i.e., gliding arc (GA) plasmas in various configurations, dielectric barrier discharges (DBDs), microwave (MW) plasmas and atmospheric pressure glow discharges (APGD)), as well as plasma-liquid interactions, to investigate their performance. This is supported by computer modelling, to obtain a better insight in the underlying mechanisms.We will first provide a brief overview of the state-of-the-art in plasma-based CO2 (and CH4) conversion and N2 fixation, with different types of plasma reactors, and explain the benefits and limitations compared to other technologies. Subsequently, we will present some recent results obtained in our group. This includes experiments in the various plasma reactors, as well as modeling. We use 2D or 3D computational fluid dynamics modelling for improving the plasma reactor design. This is complemented with 0D (or quasi-1D) chemical kinetics modeling, which solves continuity equations for the various plasma species, based on production and loss terms, as defined by the chemical reactions.We will show the role of vibrationally excited CO2 or N2 levels for energy-efficient CO2 or N2 conversion, as well as the role of thermal conversion in warm plasmas (such as GA and MW plasmas) and quenching after the plasma.[1] R. Snoeckx and A. Bogaerts, Plasma technology – a novel solution for CO2 conversion ? Chem. Soc. Rev. 46, 5805-5863 (2017).[2] A. Bogaerts and E. Neyts, Plasma technology: An emerging technology for energy storage, ACS Energy Lett. 3, 1013-1027 (2018).[3] K.H.R. Rouwenhorst, Y. Engelmann, K. van ‘t Veer, R.S. Postma, A. Bogaerts and L. Lefferts, Plasma-driven catalysis: green ammonia synthesis with intermittent electricity, Green Chemistry, 22, 6258-6287 (2020).[4] K. H. R. Rouwenhorst, F. Jardali, A. Bogaerts and L. Lefferts, Plasma-based NOX synthesis: From the Birkeland-Eyde process towards energy-efficient plasma technology, Energy Envir. Sci. (2021). (DOI: 10.1039/D0EE03763J)

Application of atmospheric pressure glow discharge generated in contact with liquids for determination of chloride and bromide in water and juice samples by optical emission spectrometry

Novel atmospheric pressure glow discharge (APGD) microplasma systems, sustained between a miniaturized flowing anode (FLA) or cathode (FLC) and a He jet, were investigated for the direct determination of Br and Cl, using optical emission spectrometry (OES). The impact of the most crucial operating parameters, i.e., the acid type and its concentration, the discharge current, the gas flow rate, and the sample flow rate, was studied for each of the proposed APGD-based systems. Under the optimized conditions, the analytical figures of merit were determined. The susceptibility to the matrix effects of both developed methods was verified as well. It was found that the mechanism of the analytes transport into the discharge likely relied on the cathode sputtering in the case of FLC-APGD and the formation of the volatile Br and Cl species for FLA-APGD. The DLs of Br and Cl were established to be relatively high, i.e., 0.15 and 1.5 mg L−1 for FLA-APGD and 2.1 and 18 mg L−1 for FLC-APGD. However, both studied methods turned out to be resistant to the presence of foreign ions in a sample, at relatively high concentrations. Hence, the proposed methods could be successfully applied for the determination of Br and Cl in water and juices samples and no major differences between the results obtained using the external standard calibration and the standard addition method were found.

Morphology evolution of an atmospheric pressure glow discharge initiated in the air gap between a liquid cathode and a needle anode

Self-deformation has been observed for an atmospheric pressure diffuse discharge initiated in the air gap between a needle anode and a water cathode, which undergoes a morphology scenario from a cone, an axially symmetric horn, to a rectangular horn as time elapses. During the self-deformation process, pH value and electric conductivity of the water cathode vary with time. Moreover, electrical measurements indicate that applied voltage and discharge current are time-invariant for the conical discharge, while periodically pulsed for the other two discharges. This may suggest different formation mechanisms of them. Hence, fast photography is implemented by a high-speed video camera and an intensified charge coupled device. Results indicate that the diffuse discharges with different morphologies belong to a glow discharge regime. Among them, the conical discharge is composed of stationary micro-discharge, and the horn-shaped discharges consist of moving micro-discharge. Moreover, the axially symmetric horn is a self-rotating version of the rectangular horn. Furthermore, the rectangular horn originates from the swing of a micro-discharge filament like a pendulum motion. Finally, qualitative explanations are given for the experimental phenomena mentioned above.

Effects of solvent composition on ionization and fragmentation within the solution-cathode glow discharge

Recently, solution-electrode glow discharges (SEGDs) have shown great utility as ionization sources for mass spectrometry (MS). The solution composition of SEGD electrodes is pivotal to their performance as it influences analyte-ion formation. The performance of electrospray ionization is heavily dictated by spray-solution composition, which can alter ionization efficiency and pathways. While SEGDs produce Taylor cones similar to electrospray ionization, the influence of solution-electrode composition on molecular-ion formation has not been studied. Here, we examine how additives to an atmospheric-pressure solution-cathode glow discharge (SCGD) influence molecular ionization and fragmentation. The impact of several additives to the acidic solution of an SCGD ionization source was evaluated based on mass-spectrometric performance. Addition of methanol increased molecular- and fragment-ion signals for peptide angiotensin II. This effect is likely due to improved desolvation and a greater interaction of analyte molecules with glow-discharge species. Several high-boiling-point reagents were tested to examine changes in the ion signal, the average charge state, and the degree of fragmentation. Overall, these additives inhibited fragmentation but significantly lowered intact molecular-ion signals. Interestingly, loss of fragment ions trended with the boiling point of the reagent used. We hypothesize that analyte molecules become trapped in droplets produced at the solution-cathode surface. These droplets do not fully desolvate before escaping the discharge region, sparing analyte molecules from fragmentation. For low volatility additives, droplets do not desolvate, even as they enter the heated MS, which yields a loss in molecular ions. The changing composition of the SCGD solution alters analytical performance, but also provides insight into analyte ionization and fragmentation processes.

Study of the characteristic differences of positive and negative half-cycles from atmospheric pressure glow discharge driven by resonant AC voltage

There are many advantages in obtaining low-temperature plasmas that are rich in active particles by atmospheric pressure glow discharge, so there has been a lot of research on the acquisition method and application of it. However, there is a lack of knowledge about the mechanism of atmospheric pressure glow discharge driven by an AC resonant power supply. In this paper, we describe our study of the characteristic differences between half-cycle positive and negative atmospheric pressure glow discharges driven in open air by an AC resonant power supply, and we describe our analysis of the associated physical mechanism. The comparison and analysis of experimental results indicate that both positive-cycle and negative-cycle discharges led to typical glow discharge and no streamer discharge appeared in the discharge process. There were still charged particles in the discharge channel when the discharge current was zero. With increasing amplitude of the output voltage of the power supply, the glow area near the electrode surface and the plasma distribution area in the discharge channel increased. When the output voltage of the power supply was low, the negative polarity discharge was more likely to form in the gap of the pin-to-plate electrode. In the AC discharge process, the α-mode discharge was dominant, and the developing speed of the positive-cycle discharge was faster than that of the negative-cycle discharge. The polarity effect became less obvious with the increase in the output voltage amplitude of the power supply.

Modulation of the solution-cathode glow-discharge and solution-anode glow discharge using a rotating magnetic field

The effects of an external magnetic field on the solution-cathode glow-discharge (SCGD) and solution-anode glow-discharge (SAGD) are investigated. The SCGD is atmospheric-pressure glow discharge sustained between a metal pin and a liquid cathode electrode in the ambient atmosphere, and it is often used for trace elemental analysis by atomic emission spectroscopy. Here, the SCGD is modified to allow an external permanent magnetic field to be applied, either in a static orientation or as a rotating field, as a means of stabilizing the SCGD plasma and modulating atomic emission from the discharge. The effect of the external magnetic field on the physical structure, electrical characteristics, and spectroscopic response of the SCGD and SAGD are investigated. A rotating external magnetic field was found to change both SAGD and SCGD structure and spatial emission pattern. Analytical figures of merit are examined, and a lock-in amplifier is used to discriminate analytical atomic emission from background emission, improving limits of detection.

Multivariate Optimization of the FLC-dc-APGD-Based Reaction-Discharge System for Continuous Production of a Plasma-Activated Liquid of Defined Physicochemical and Anti-Phytopathogenic Properties

To the present day, no efficient plant protection method against economically important bacterial phytopathogens from the Pectobacteriaceae family has been implemented into agricultural practice. In this view, we have performed a multivariate optimization of the operating parameters of the reaction-discharge system, employing direct current atmospheric pressure glow discharge, generated in contact with a flowing liquid cathode (FLC-dc-APGD), for the production of a plasma-activated liquid (PAL) of defined physicochemical and anti-phytopathogenic properties. As a result, the effect of the operating parameters on the conductivity of PAL acquired under these conditions was assessed. The revealed optimal operating conditions, under which the PAL of the highest conductivity was obtained, were as follows: flow rate of the solution equaled 2.0 mL min−1, the discharge current was 30 mA, and the inorganic salt concentration (ammonium nitrate, NH4NO3) in the solution turned out to be 0.50% (m/w). The developed PAL exhibited bacteriostatic and bactericidal properties toward Dickeya solani IFB0099 and Pectobacterium atrosepticum IFB5103 strains, with minimal inhibitory and minimal bactericidal concentrations equaling 25%. After 24 h exposure to 25% PAL, 100% (1−2 × 106) of D. solani and P. atrosepticum cells lost viability. We attributed the antibacterial properties of PAL to the presence of deeply penetrating, reactive oxygen and nitrogen species (RONS), which were, in this case, OH, O, O3, H2O2, HO2, NH, N2, N2+, NO2−, NO3−, and NH4+. Putatively, the generated low-cost, eco-friendly, easy-to-store, and transport PAL, exhibiting the required antibacterial and physicochemical properties, may find numerous applications in the plant protection sector.