Electrode Dielectric Barrier Discharge Research Articles

Inactivation of L. monocytogenes and S. typhimurium Biofilms by Means of an Air-Based Cold Atmospheric Plasma (CAP) System.

Previous (biofilm) inactivation studies using Cold Atmospheric Plasma (CAP) focused on helium (with or without the addition of oxygen) as feeding gas since this proved to result in a stable and uniform plasma. In industry, the use of helium gas is expensive and unsafe for employees. Ambient air is a possible substitute, provided that similar inactivation efficacies can be obtained. In this research, 1 and 7 day-old (single/dual-species) model biofilms containing L. monocytogenes and/or S. typhimurium cells were treated with an air-based Surface Barrier Discharge (SBD) plasma set-up for treatment times between 0 and 30 min. Afterwards, cell densities were quantified via viable plate counts, and predictive models were applied to determine the inactivation kinetics and the efficacy. Finally, the results were compared to previously obtained results using a helium-based SBD and DBD (Dielectric Barrier Discharge) system. This study has demonstrated that the efficacy of the air-based CAP treatment depended on the biofilm and population type, with log-reductions ranging between 1.5 and 2.5 log10(CFU/cm2). The inactivation efficacy was not significantly influenced by the working gas, although the values were generally higher for the air-based system. Finally, this study has demonstrated that the electrode configuration was more important than the working gas composition, with the DBD electrode being the most efficient.

Sanitary effect of FE-DBD cold plasma in ambient air on sewage biosolids

Sewage sludge is treated by means of cold plasma and stabilization in terms of biological load deactivation is achieved. The plasma is produced by floating electrode dielectric barrier discharge operating with air under atmospheric pressure conditions. The process is presented in detail and the discharge is characterized electrically. Additionally, simulation of the thermal flow inside the process chamber is implemented, using computational fluid dynamics. Deactivation of the serotypes S. Paratyphi B., S. Livingstone, S. Mbandaka and S. Typhimurium, and Escherichia coli and Coliforms, is hereby claimed. The process involves mean electrical power in the range of tens of watts, treatment time in the scale of minutes, and maximum instantaneous temperature <400 K. The present work is a preliminary contribution towards the promotion of advanced methods for the pro-ecological management of biosolids, according to European Regulations.

Plasma skincare device based on floating electrode dielectric barrier discharge

A portable skincare plasma-device with a rechargeable battery is presented here. The device comprises two pads made of thin polyimide film as the dielectric layer, namely, the dielectric barrier discharge pad (DBD-pad) for skin-touch and a capacitive ground-pad (G-pad) for hand holding. High AC voltage of approximately 1 kV with frequency of 40 kHz is induced in the DBD-pad that contacts the skin, which serves as the floating electrode, while low voltage is induced on the G-pad. Considering the requirement for impedance matching between the DBD-pad capacitance and the inverter along with the need for low skin current less than approximately 5 mA for electrical safety, the electrode area of the DBD-pad is minimized to be smaller than that of the G-pad.

(Invited) Challenges and Opportunities in Dye Sensitized Solar Cells Using DBD Plasma Treated Upconversion Nanoparticles

1. Introduction The dye-sensitized solar cells(DSSC) are widely receiving increasing attention as low-cost solar cells. The photoelectrode of the DSSC is composed of a nanoporous TiO2film which has a very large specific area, on which a sensitizing dye is adsorbed [1]. The specific chemical composition, surface area and surface profiles of the TiO2films determine the energy conversion efficiency of the DSSCs. Through surface treatment, these properties of TiO2can be enhanced [2]. DSSCs generally use visible light for photo-electric conversion. In a DSSC, light absorption is conducted by a light sensitive dye. The ability of the dye to capture light in a wide band range of the light spectrum determines the conversion efficiency of the DSSC. The currently employed dyes in DSSC with the highest conversion efficiencies (N-719) have a light spectrum absorption range of 300-750 nm [1]. Consequently, the inability of these dyes to absorb near infrared (NIR) light, which makes up to 48% of energy of the entire solar spectrum, forms the main energy loss mechanism of DSSC. To realize photo-current conversion from these light, rare-earth luminescent phosphors, which have large band gap, high refractive index, low phonon energy are promising to circumvent the photon transmission losses [2]. 2. Experimental details 2.1 Sample preparation A facile urea based homogeneous precipitation method was employed for the fabrication of Y2O3:Er3+/Yb3+nanoparticles. DSSC was fabricated via the conventional doctor blade method. For the preparation of the DSSC photoanode, transparent TiO2 colloids were deposited on the conductive glass substrate (FTO) to form a transparent photoelectrode and then sintered at 500℃ for 2 hours. In the case of the UC photoanode, transparent TiO2 colloids were screen printed on the FTO and sintered at 500 for 2hours. Reflective TiO2colloids mixed with 5 wt% Y2O3:Er3+/Yb3+nanoparticles were subsequently screen-printed on-top of the TiO2film and sintered at 500℃ for 2 hours. The photoanodes were placed on a dielectric barrier discharge (DBD) grounded plate electrode of DBD, then the TiO2film was treated using DBD under room air conditions for 10 minutes. The distance between the surface of the photoelectrode and the DBD electrodes was 5 mm. After the DBD treatment, the photoanodes were finally soaked in the dye (Solaronix N-719 0.2mM/L in ethanol) solution for 24 hours. Eventually the sandwich-type DSSC were fabricated with platinum-coated FTO glass and iodine electrolyte. 2.2 DBD plasma treatments Plasma treatments of upconverting nanoparticle films were carried out using a scalable dielectric barrier discharge device [3]. The device consisted of 20 electrodes of a stainless rod of 1 mm outer diameter and 60 mm length covered with a ceramic tube of 2 mm outer diameter. The electrodes were arranged parallel to each other at a gap of 0.2 mm. The discharge voltage and frequency were 7.96 kV and 9.2 kHz, respectively. The discharge power, which was obtained from Q-V Lissajous characteristics, was 2.17 W. 3. Results and Discussion The photoluminescence spectra of upconversion (UC) nanoparticles under IR laser diode excitation (λ= 980 nm) for three different laser power were measured. We also confirmed both green and red UC emissions, corresponding to the Yb (5F5/2-2Fj) and Er (4F7/2-4Ij) transitions. This indicates that the up converters we developed are capable of transforming NIR radiation into visible light thereby contributing to more photogeneration and have the potential for enhancement of photovoltaic performance of DSSCs. The device characteristics (short-circuit current density (Jsc), open-circuit voltage (Voc), fill factor (FF), of the corresponding DSSC devices are showed in Figure 1. The DSSC with the DBD treated TiO2/Y2O3:Er3+/Yb3+composite double layer had a Jscvalue of 10.08 mA. Also, the voltage of the DSSC increased from 0.70 to 0.72 V. The overall efficiency of the DSSC increased from 4.31 % for the untreated TiO2/Y2O3:Er3+/Yb3+composite double layer to 5.15 % for the treated composite double layer. The conceivable reasons for the improvement of the plasma DBD treated cells are as follows [4]; a)Plasma treatment causes surface modification on the TiO2/Y2O3:Er3+/Yb3+double composite film, which enhances the light absorption by the film particles (not by the adsorbed dye). b) Plasma treatment increases the specific surface area of the composite film by changing the surface morphology of the film particles. This increases the amount of the dye adsorbed by the composite film. 4.

Atmospheric-pressure floating electrode-dielectric barrier discharge with flexible electrodes: Effect of conductor shapes

The plasma characteristics of atmospheric-pressure floating electrode-dielectric barrier discharges (FE-DBDs), which comprised flexible electrodes and were able to generate a plasma along the curvature of skin, were investigated using Cu conductors with various shapes in the flexible powered electrode. These Cu conductors have similar areas but different contour lengths and the shapes of a square, a dumbbell, a star, and a zigzag pattern. The optical intensity and electron temperature of the atmospheric-pressure FE-DBDs increased with the contour length of the conductor used in the flexible powered electrode. This behavior is explained in terms of the changes in the strength of the electric field with the contour length of the conductor, implying that the plasma properties of atmospheric-pressure FE-DBDs with flexible electrodes can be controlled by modulating the contour length or the shape of the electrical conductor in the flexible powered electrode. These results are expected to contribute to the development of an atmospheric-pressure FE-DBD system for plasma medicine.

Artificially aged spruce and beech wood surfaces reactivated using FE-DBD atmospheric plasma

Abstract Although weathering is usually carried out in outdoor conditions, even ageing in indoor conditions can cause significant changes to wood surfaces. We found these to notably impact wetting and coatability of surfaces of common beech (Fagus sylvatica L.) and Norway spruce [Picea abies (L.) Karst.] wood. These effects were well overcome and the surfaces reactivated using a novel kind of a plasma device. On both kinds of wood, ageing caused significant changes in their colour, opening of pits and cell wall destruction. Infrared spectra indicated a significant decrease of aromatic lignin and production of non-conjugated carbonyl groups. Surface free energies and spreading kinetics varied much upon this kind of ageing. In beech, pull-off strengths for a commercial waterborne wood coating slightly decreased for longer exposure times. For the reactivation of wood surfaces, we employed a novel approach using a floating electrode dielectric barrier discharge (FE-DBD) plasma, which had not been done on wood before. Similar to other plasma techniques, the surface free energy (SFE) increased after treatment. On beech wood, the plasma treatment (PT) led to higher pull-off strengths of the waterborne coating. On spruce wood, the coating mostly showed cohesive failures after ageing, and thus the PTs showed less improvements.

In Plasma Catalytic Oxidation of Toluene Using Monolith CuO Foam as a Catalyst in a Wedged High Voltage Electrode Dielectric Barrier Discharge Reactor: Influence of Reaction Parameters and Byproduct Control.

Volatile organic compounds (VOCs) emission from anthropogenic sources has becoming increasingly serious in recent decades owing to the substantial contribution to haze formation and adverse health impact. To tackle this issue, various physical and chemical techniques are applied to eliminate VOC emissions so as to reduce atmospheric pollution. Among these methods, non-thermal plasma (NTP) is receiving increasing attention for the higher removal efficiency, non-selectivity, and moderate operation, whereas the unwanted producing of NO2 and O3 remains important drawback. In this study, a dielectric barrier discharge (DBD) reactor with wedged high voltage electrode coupled CuO foam in an in plasma catalytic (IPC) system was developed to remove toluene as the target VOC. The monolith CuO foam exhibits advantages of easy installation and controllable of IPC length. The influencing factors of IPC reaction were studied. Results showed stronger and more stable plasma discharge in the presence of CuO foam in DBD reactor. Enhanced performance was observed in IPC reaction for both of toluene conversion rate and CO2 selectivity compared to the sole NTP process at the same input energy. The longer the contributed IPC length, the higher the toluene removal efficiency. The toluene degradation mechanism under IPC condition was speculated. The producing of NO2 and O3 under IPC process were effectively removed using Na2SO3 bubble absorption.

Influence of plasma characteristics on the efficacy of Cold Atmospheric Plasma (CAP) for inactivation of Listeria monocytogenes and Salmonella Typhimurium biofilms

Abstract The biofilm mode of growth protects bacterial cells from applied disinfection methods for abiotic (food) contact surfaces. Therefore, new inactivation technologies such as Cold Atmospheric Plasma (CAP) should be considered. However, the influence of different plasma characteristics on the CAP efficacy for biofilm inactivation requires further study. In this research, the influence of (i) the applied plasma configuration (Dielectric Barrier Discharge (DBD) and Surface Barrier Discharge (SBD)), (ii) the oxygen level of the gas flow (He + 0.0/0.5/1.0 (v/v) % O2), and (iii) the plasma intensity (13.88, 17.88, and 21.88 V input voltage) on the CAP efficacy for inactivation of L. monocytogenes and S. Typhimurium biofilms was investigated. Depending on the applied plasma characteristics, log10-reductions up to approximately 3.5 log(CFU/cm2) were obtained. Nevertheless, it could be concluded that the highest log-reductions were in general obtained while using the DBD electrode, 0.0 (v/v) % O2, and an input voltage of 21.88 V. Industrial relevance This study demonstrated the potential application of CAP for inactivation of pathogenic biofilms developed on abiotic (food) contact surfaces. The effect of different plasma characteristics on the CAP inactivation efficacy was investigated and determined optimal conditions resulted in promising reductions of the biofilm-associated cells. By incorporating this novel technology in a complete cleaning and disinfection process, the risk of (cross) contamination of food products might extensively be reduced.

Evaluation of Photoelectric Characteristics of a Volume DBD Excited by Power Density Modulation

Photoelectric characteristics are an important reference for high-voltage discharges and are closely related to the excited mode of the high-voltage source. In this paper, we built a large-scale volume dielectric barrier discharge (DBD) system, which is composed of multilayer parallel-plate DBD electrodes and is excited by a high-voltage source in the power density modulation (PDM) mode. Subsequently, we analyzed the applied energy equation and evaluated the DBD systems photoelectric characteristics. The results show that the energy values of different applied voltage cycles during a PDM period exhibit significant differences. However, the average energy in a PDM period is approximately constant. Moreover, the equivalent capacitance of the DBD cell is a function of both the applied voltage and energy density. For the DBD cell, with the increase in both the applied voltage and energy loaded on the DBD cell, the total equivalent capacitance (C) is approximately constant, the dielectric capacitance (C d ) increases exponentially and decreases linearly, while the discharge gap capacitance (C g ) decreases and increases in the same cases. In addition, the relative intensities of the discharge emission increase and the energy efficiency ratios of the relative photoquantum yield of active species decline with the increase in both the applied voltage and energy density loaded on the DBD cell. The experimental results have been analyzed by evaluating the influence of the electrical parameters, and the underlying physical principles have been discussed. This paper clearly demonstrates that the photoelectric characteristics of the DBD reactor are significantly influenced by both the applied voltage and energy density, thus providing helpful insights into the energy evaluation and application of high-voltage discharges.

Two-dimensional simulation of dielectric barrier discharge with ring electrodes at atmospheric pressure

A two-dimensional fluid model was used to investigate the characteristics of helium dielectric barrier discharge (DBD) equipped with ring electrodes at atmospheric pressure. Simulation results show that the transition of discharge also exists as the traditional parallel-plate DBD. The discharge mode translates from the Townsend mode to the glow mode during the rising phase and returns to the Townsend mode in the falling phase of the discharge. Meanwhile, symmetric discharge current and current densities at different radial positions are observed in each cycle, and the current density peak at the radial center of the ring electrode is always higher than that at other positions. In addition, the charged particles follow a periphery-advantage spatial distribution, and the relative temporal variation of charged particles is faster in the periphery than in the central region because of the higher electric field existing there. Moreover, the density of surface charges assembled in the periphery changes faster than that in the central region of the upper dielectric barrier and exhibits an uneven periphery-advantage distribution, which is also ascribed to the higher electric field in the periphery resulted from the ring electrode configuration. Comparing the ring electrode DBD with the traditional one indicates that an inverse discharge structure is observed between the two electrode configurations.

Characteristics and applications of diffuse discharge of water electrode in air

Plasma water treatment technology, which aims to produce strong oxidizing reactive particles that act on the gas–liquid interface by way of discharging, is used to treat the organic pollutants that do not degrade easily in water. This paper presents a diffuse-discharge plasma water treatment method, which is realized by constructing a conical air gap through an uneven medium layer. The proposed method uses water as one electrode, and a dielectric barrier discharge electrode is constructed by using an uneven dielectric. The electric field distribution in the discharge space will be uneven, wherein the long gap electric field will have a smaller intensity, while the short one will have a larger intensity. A diffuse glow discharge is formed in the cavity. With this type of plasma water treatment equipment, a methyl orange solution with a concentration of 10 mg l−1 was treated, and the removal rate was found to reach 88.96%.

Mechanism of Ampicillin Degradation by Non-Thermal Plasma Treatment with FE-DBD

This research focused on determining the effectiveness of non-thermal atmospheric pressure plasma as an alternative to advanced oxidation processes (AOP) for antibiotic removal in solution. For this study, 20 mM (6.988 g/L) solutions of ampicillin were treated with a floating electrode dielectric barrier discharge (FE-DBD) plasma for varying treatment times. The treated solutions were analyzed primarily using mass spectrometry (MS) and nuclear magnetic resonance spectroscopy (NMR). The preliminary product formed was Ampicillin Sulfoxide, however, many more species are formed as plasma treatment time is increased. Ampicillin was completely eliminated after five minutes of air-plasma treatment. The primary mechanism of ampicillin degradation by plasma treatment is investigated in this study.

Enhancement of thin air jets produced by ring-shaped dielectric barrier discharges using an auxiliary electrode

A ring-shaped dielectric barrier discharge (DBD) was explored as a small form factor ionic wind device. Using a concentric ring electrode geometry, the DBD produced a converging ionic wind that leads to a vertical flow away from the DBD electrodes. The vertical flow was channeled through an outlet nozzle to produce a thin air jet, and a grounded auxiliary electrode was placed at the nozzle to enhance the exit velocity. The inner diameter of the ring-shaped DBD electrode and the auxiliary electrode ranged 3.18–9.54 mm and 1.0–4.0 mm, respectively. Results showed that the auxiliary electrode generated an ionic wind velocity up to 3.7 m/s and increased the conversion efficiency from discharge to flow power by a factor of 30 by strengthening the electric field where the ions are accelerated.

Neutralization of charged dielectric materials using a dielectric barrier discharge

Safety and efficiency are two characteristics that must be satisfied by an electric charge neutralizer. The dielectric barrier discharge (DBD), which has the advantage of preventing arc transition, is an interesting tool to safely neutralize unwanted charge. This paper is aimed at studying the efficiency of neutralizing charged polyethylene (PE) granules by using a dielectric barrier discharge. During this study, several factors were considered such as the amplitude and the frequency of the AC voltage, the polarity and the charging mode of the samples, as well as the electrode configuration. Two DBD electrode configurations were considered: simple DBD and a DBD with installed metallic grid. The obtained results show that using the DBD can lead to excellent neutralization results when the grid is installed. With the appropriate voltage amplitude and frequency and with grid installed, the elimination of nearly 99% of the initial surface charges can be achieved. The metallic grid placed between the DBD electrode and the target enhances significantly the neutralization efficiency.

Biomolecule Response to Nonthermal Plasma

This work demonstrated the decomposition products of several amino acids when exposed to nonthermal atmospheric pressure plasma. A floating electrode dielectric barrier discharge plasma was used to treat 20 mM solutions of cysteine, glutamine, alanine, and lysine for varying treatment times to investigate possible mechanisms in cell wall degradation and treatment of tissue. The treated solutions were analyzed primarily using gas chromatography-mass spectrometry (GC-MS) and nuclear magnetic resonance (NMR). The primary targets of the plasma treatment were found to be the sulfur or nitrogen species. Acetic acid and lactic acid were observed throughout all solutions as oxidative products from the plasma treatment. This work suggests that the primary targets for plasma treatment of cell wall components is the amino acids.

Plasma Treatment of Onychomycosis

We report on the use of three “cold” atmospheric plasma (CAP) devices in treating model nails that have been coated on the backside of the nail with either Escherichia coli (E. coli) bacteria or Trichophyton rubrum (T. rubrum) fungus. We tested a helium plasma jet; a surface microdischarge plasma device; and a floating electrode dielectric barrier discharge. All of the devices, acting through the model nail, showed significant log reductions of bacterial and fungal targets in several tens of minutes. CAP technology appears to offer promise as a safe, effective, and inexpensive therapy for fungal nail infection treatment.

Measurement of Electron Density and Ion Collision Frequency with Dual Assisted Grounded Electrode DBD in Atmospheric Pressure Helium Plasma Jet**supported by National Natural Science Foundation of China (No. 11105093), the Technological Project of Shenzhen, China (No. JC201005280485A), and the Planned S&T Program of Shenzhen, China (No. JC201105170703A)

The properties of a helium atmospheric-pressure plasma jet (APPJ) are diagnosed with a dual assisted grounded electrode dielectric barrier discharge device. In the glow discharge, we captured the current waveforms at the positions of the three grounded rings. From the current waveforms, the time delay between the adjacent positions of the rings is employed to calculate the plasma bullet velocity of the helium APPJ. Moreover, the electron density is deduced from a model combining with the time delay and current intensity, which is about 1011 cm−3. In addition, The ion-neutral particles collision frequency in the radial direction is calculated from the current phase difference between two rings, which is on the order of 107 Hz. The results are helpful for understanding the basic properties of APPJs.

Spectroscopic measurements of the electron number density, electron temperature and OH(A) rotational distribution in a liquid electrode dielectric barrier discharge

The electron temperature and number density as well as the OH(A) rotational distribution of a discharge with flowing liquid electrode and dielectric barrier coupling (a liquid electrode dielectric barrier discharge, LE-DBD) were investigated by means of optical emission spectroscopy. By using the Stark broadening of three Strontium lines, the electron number density Ne and the lower bound of the electron temperature Te can be simultaneously measured. The values obtained were Ne=(0.8−1.6)×1016cm−3 and Te>1.1eV, respectively. The OH(A) rotational distribution deviates from equilibrium and can be described by a superposition of two Boltzmann distributions with T1=(3230±90)K for K'≤15 and T2=(7300±300)K for K'≥16. Consideration of the formation mechanisms of OH(A) and reaction rates suggests that the dissociative recombination of H2O+ and H3O+ is responsible for the higher rotational state distribution, where these ions can only be produced in the LE-DBD through an electrospray-like process.

Three-electrode plasma reactor for the removal of toxic gases

Electrical and spectroscopic measurement for the characterization of a novel three- electrode plasma reactor for the treatment of toxic gases is presented. The three-electrode discharge consists in a dielectric barrier discharge (DBD) combined with a corona discharge (CD). The DBD is generated by applying an alternating high voltage signal between two circular aluminium plate electrodes attached to opposite sides of a disk made of dielectric material. The CD is generated applying a continuous negative high voltage to an external cylindrical mesh electrode, coaxial with the DBD electrode system. The gap between the edge of the DBD system and the mesh electrode is approximately 20 mm wide. Up to five DBD electrode systems can be connected in parallel inside the reactor, axially separated from each other by 30 mm. The electrical characterization consisted in the measurement of the current between the DBD system and the external mesh, and the voltages of the electrodes. In order to understand the dynamics of the streamers, a theoretical determination of the laplacian electric field generated by the biased electrodes was done. Optical emission spectroscopy was performed in the range of wavelengths 280-480 nm, containing the typical spectral bands 2nd positive and 1st negative systems of molecular nitrogen.

Investigations into modeling and further estimation of detection limits of the liquid electrode dielectric barrier discharge.

The liquid electrode dielectric barrier discharge (LE-DBD) is a miniaturized atmospheric pressure plasma as emission excitation source for elemental determination with pulsed behavior. Metals dissolved in liquids are detectable in flow systems with low flow rates of 20 μL min(-1) by means of optical emission spectrometry using a simple portable spectrometer. Time-resolved determination of the hydrogen excitation temperature Tαβ indicates that the LE-DBD does not reach a stable state during a burning phase, whereat the maximum and minimum Tαβ is independent of the flow rate. Adding dissolved metals to the liquid electrode does not influence the minimum Tαβ at the end of a burning phase. With the help of measured doubly charged lanthanum lines and spatially resolved measurements, the mechanism of the liquid transfer into the plasma will be clarified. Emissions from metal oxides indicate a thermal evaporation transfer mechanism, but only an additional electrospray-like transfer mechanism can explain the observed La III emissions and nonhomogeneous spatial distribution of exited species. The reaction pathways for electrosprayed hydrated metal ions are discussed for triply and doubly charged ions. The analytical performance is evaluated for 23 elements from the categories of alkali, alkaline earth, transition, and poor metals. The achieved detection limits are between 0.016 mg L(-1) for Li and 41 mg L(-1) for Bi.