Non-equilibrium Atmospheric Pressure Plasma Jet Research Articles

Plasma catalysis: separating plasma and surface contributions for an Ar/N2/O2 atmospheric discharge interacting with a Pt catalyst

Atmospheric pressure non-equilibrium plasmas can form nitrogen oxide (NO x ) compounds directly from nitrogen and oxygen without a catalyst, and at lower catalyst temperatures than would be possible without plasma. In this work, the oxidation of plasma-produced NO from an Ar/N2/O2 non-equilibrium atmospheric-pressure plasma-jet (APPJ) over a platinum-on-alumina powder catalyst was investigated with in-situ infrared spectroscopy. Products downstream of the catalyst bed were analyzed along with catalyst surface species. The catalyst was exposed to plasma at both constant temperature and a cyclic temperature ramp in order to study long-lasting and transient surface changes. Primary incident reactive species to the catalyst were assessed to be NO and O3. Pt-Al2O3 at 350 °C increased oxidation of NO relative to Al2O3 or an empty chamber. The surface state of Pt-Al2O3 evolves during plasma-effluent exposure and requires upwards of 20 min exposure for stabilization compared to Al2O3. Once stable surface conditions are achieved, thermal cycling reveals a repeatable hysteresis pattern in downstream products. At low temperature, oxygen and NO x accumulate on the catalyst surface and react at elevated temperatures to form NO2. Increasing plasma power and O2:N2 ratio increases the hysteresis of the heating relative to the cooling curves in the pattern of NO2 formation. The limitation on NO oxidation at high temperatures was assessed to be Pt-O which is depleted as the catalyst is heated. Once stored species have been depleted, NO oxidation rates are determined by incoming reactants. Two overlapping NO oxidation patterns are identified, one determined by surface reactants formed at low temperature, and the other by reactants arriving at the surface at high temperature. The plasma is responsible for providing the reactants to the catalyst surface, while the catalyst enables reaction at high temperature or storage at low temperature for subsequent reaction.

Atmospheric Cold Plasma: A Brief Journey and Therapeutic Applications from Wound Healing to Cancer Biology

Cold Atmospheric Plasma (CAP) has now become a well-known new edge technology in the field of biomedical science to agriculture and food technology. Ionized gas known as cold atmospheric plasma has recently been the subject of intense inquiry by scientists for its potential application for treatment in oncology and dentistry. Air, Helium, Argon, Nitrogen, and other gases can all be used to create Cold Atmospheric Plasma. Cold plasma can effectively and safely inactivate spores, bacteria, fungi, viruses, and small molecules and thereby improving wound healing, combating microbial infections, and treating skin conditions with great efficiency. Interestingly the in vitro and in vivo demonstration of CAP has shown promising applications in cancer healing and treatment. The most widely employed technique for producing and sustaining a low-temperature plasma for use in technological and scientific applications involves applying an electric field to a neutral gas. The non-equilibrium atmospheric pressure plasma jet (NAPPJ) and the dielectric barrier discharge (DBD) have both been widely used in biomedical applications. This review aims to evaluate the emerging plasma technology - the basic science, technical aspects and provide insights of biomedical application in diverse area.

Influence of structural parameters of needle-ring electrode on the length of argon plasma jet under atmospheric pressure

In this paper, a multi-structure needle-ring electrode argon plasma jet device was designed to investigate the influence of reactor structure parameters and discharge parameters on the length of atmospheric pressure non-equilibrium plasma jet. Specifically, the effects of the discharge voltage, the electrode gap, the distance between the end of the high-voltage electrode and the ground electrode, and the volume flow of argon on the jet length were explored. The results demonstrate that the maximum length of the plasma jet in the external environment can reach 80 mm when the inner diameter of the tube is 15 mm; the jet length first increases and then tends to be stable with the increase in the discharge voltage; the jet length presents two peaks with the increasing voltage; the end of jet appears the unstable phenomenon of ‘beating’ when the discharge voltage is high. Besides, the longer the distance between the end of the high-voltage electrode and the ground electrode, the longer the jet length. Nevertheless, the relationship between the distance and the jet length is non-linear. The jet length first increases and then decreases with the increase in the electrode gap. The phenomenon of ‘particle countercurrent’ is observed when the electrode gap and discharge voltage are relatively large. With the increase in the argon volume flow, the plasma jet length also exhibits a trend of first increasing and then decreasing. To sum up, the main factors affecting the length of the plasma jet is transport mode during the plasma transport process.

Foundations of plasmas for medical applications

Plasma medicine refers to the application of nonequilibrium plasmas at approximately body temperature, for therapeutic purposes. Nonequilibrium plasmas are weakly ionized gases which contain charged and neutral species and electric fields, and emit radiation, particularly in the visible and ultraviolet range. Medically-relevant cold atmospheric pressure plasma (CAP) sources and devices are usually dielectric barrier discharges and nonequilibrium atmospheric pressure plasma jets. Plasma diagnostic methods and modelling approaches are used to characterize the densities and fluxes of active plasma species and their interaction with surrounding matter. In addition to the direct application of plasma onto living tissue, the treatment of liquids like water or physiological saline by a CAP source is performed in order to study specific biological activities. A basic understanding of the interaction between plasma and liquids and bio-interfaces is essential to follow biological plasma effects. Charged species, metastable species, and other atomic and molecular reactive species first produced in the main plasma ignition are transported to the discharge afterglow to finally be exposed to the biological targets. Contact with these liquid-dominated bio-interfaces generates other secondary reactive oxygen and nitrogen species (ROS, RNS). Both ROS and RNS possess strong oxidative properties and can trigger redox-related signalling pathways in cells and tissue, leading to various impacts of therapeutic relevance. Dependent on the intensity of plasma exposure, redox balance in cells can be influenced in a way that oxidative eustress leads to stimulation of cellular processes or oxidative distress leads to cell death. Currently, clinical CAP application is realized mainly in wound healing. The use of plasma in cancer treatment (i.e. plasma oncology) is a currently emerging field of research. Future perspectives and challenges in plasma medicine are mainly directed towards the control and optimization of CAP devices, to broaden and establish its medical applications, and to open up new plasma-based therapies in medicine.

Optimal Power of Atmospheric Pressure Plasma Jet with a Simple DBD Configuration for Biological Application

The new strategy, non-thermal atmospheric pressure plasma (N-APP), as a ’physical’ method, could offer a simple, fast, effective, and economic way of disinfection of equipment, surfaces, a method that is unlikely to cause micro-organisms resistance, or allergic, and toxic reactions. Recently, cold physical plasma had been extensively studied by researchers as a possible therapy in dentistry and oncology, as well as the application of non-thermal plasma in biomedical researches such as wound healing. In clinical dermatology, cold plasmas are mainly used for the treatment of chronic wounds and pathogen-based skin diseases, in which stimulation of tissue repair and decontamination. In this research, the characterization of home-made Helium Non-Equilibrium atmospheric pressure plasma jet (He -NAPPJ), that had been generated using a dielectric barrier discharge (DBD) configuration for exceptional standardization protocol of this plasma source that meets medical requirements. The device equipped with two powered electrodes as well as a grounded electrode, driven by an (8 kVp-p) voltage, the frequency (12 kHz), and the distance between the nozzle of the plasma jet and the target were used as constant data. As a working gas, the Helium gas (He) was used in different flow rates (2, 4, 6, and 8) slm. The optical emission spectroscopy was used to measure the plasma parameters, of which the electronic excitation temperature and density of electrons were determined by the Boltzmann’s plot method and Stark broadening effect equation respectively. The result of the emission line spectrum showed the presence of nitrogen and oxygen between lines 300 nm until 700 nm. Nitrogen and oxygen are involved in the oxidation process which is known as Reactive Nitrogen species and reactive oxygen species. These species are the main key in bacteria inactivation and the wound healing process. Furthermore, the results had revealed, the optimal condition using the flow rate (6 slm) with 32 °C He gas temperature that had been stabilized for 20 min, plume length 40 mm, The distance is 15 mm from the distal end of the Pyrex tube (DBD) and the wound surface, the power density 44 mWatt/cm2, and plasma radiation energy dose: 76 J/cm2. These results were considered in this study as a safe operating condition for biomedical applications.

Studying of Plasma- Polymerized Pyrrole at Variable Gas Flow Rates Via Plasma Jet

In this manuscript has investigated the synthesis of plasma-polymerized pyrrole (C4H5N) nano-particles prepared by the proposed atmospheric pressure nonequilibrium plasma jet through the parametric studies, particularly gas flow rate (0.5, 1 and 1.5 L/min). The plasma jet which used operates with alternating voltage 7.5kv and frequency 28kHz. The plasma-flow characteristics were investigated based on optical emission spectroscopy (OES). UV-Vis spectroscopy was used to characterize the oxidization state for polypyrrole. The major absorption appears around 464.1, 449.7 and 435.3 nm at the three flow rate of argon gas. The chemical composition and structural properties of the contained samples which synthesized at 0.5 L/min as a argon flow rate were analyzed by scanning electron microscopy (SEM), Fourier transformation infrared spectroscopy (FTIR), Raman spectroscopy and X-ray diffraction (XRD). SEM point to a uniform distribution of polypyrrole (PPY) nanoparticles matrix. XRD technique showed a semicrystalline pattern for PPY)thin film. It is expected, that the high-quality plasma polymer grown by atmospheric pressure plasma jet method contributes to serving as conducting materials.

Formation and behaviour of plasma spots on the surface of titanium film

Numerous studies have shown that dielectric barrier discharge (DBD) and DBD-like plasma jets interact with a treated surface in a complex manner. Eroded traces after treatment cannot be explained by conventional plasma-surface interaction theory. The mechanisms of a controlled formation of these plasma objects is still unclear. In this work, the authors show that the formation rate and characteristics of eroded traces, treating a titanium surface, can be controlled by process design and the combination of materials used. A thin (0.45 µm) layer of titanium film is deposited onto a glass substrate and is then treated in the effluent of a non-equilibrium atmospheric pressure plasma jet (N-APPJ) operated with argon or krypton flow. Plasma spots with diameters ranging from 100–700 µm are observed using an intensified digital camera on the titanium film surface. These plasma objects are strongly inhomogeneous, forming a core with a very high current density and leave erosion holes with diameters of about 1 µm. By using krypton as a working gas, effective erosion of the titanium substrate can be shown, whereas by using argon no traces are detected. For the latter case, traces can be provoked by deposition of a thin aluminum layer on top of the titanium substrate, by creation of artificial scratches or by an additional swirling flow around the discharge. Based on the experimental results presented in this and previous papers, it is assumed that plasma spots with dense cores are produced by an interaction of micro-vortices within the plasma channel and by the formation of an extremely high axial magnetic field. This assumption is confirmed by destruction of the treated surface material, extraction of paramagnetic atoms and toroidal substrate heating, which is most likely caused by a helical current of the plasma spot.

Atmospheric plasma VUV photon emission

Owing to its distinctive photon energy range, vacuum ultraviolet (VUV) emission plays a key role in diverse photo-induced natural and technological processes. Atmospheric-pressure plasma produced VUV is central to resolve long-held issues in dynamics of natural (e.g., lightning) and laboratory (e.g., streamer) plasmas. Challenging the seemingly unavoidable vacuum systems used to prevent VUV emission quenching by ambient gases, here we report the first observation of vacuum-free generation of stable sub-110 nm VUV emission from atmospheric-pressure plasmas jetted into open air and atmospheric air plasma. Emission from atomic helium at 58.4 nm is observed from a nonequilibrium atmospheric pressure plasma jet (N-APPJ), jetted directly into ambient air. In a similar experiment, we also report VUV emission from excited nitrogen species in an atmospheric pressure discharge in ambient air. The photon emissions detected expand the window of photo-induced processes beyond ∼10 eV commonly achievable by existing non-excimer VUV plasma sources, and enables direct photo-excitation and ionization of molecular species such as CO2 and many others. The thus-enabled direct photoionization of O2, O, and N species further justifies the role of direct photoionization in the dynamics of natural and laboratory atmospheric-pressure plasmas and informs the development of the relevant plasma photoionization models, which currently largely sidestep the sub-110 nm domain. These findings can make contribution to the complement of photoionization model of lightning, streamer, and other plasmas, open new avenues to quantify the yet elusive role of photoionization in the plasma dynamics.

Spatially resolved density measurements of singlet delta oxygen in a non-equilibrium atmospheric pressure plasma jet by molecular beam mass spectrometry

Singlet delta oxygen (O2(a1Δg)), the first electronically excited state of O2, plays an important role in many applications. We report the first measurements of absolute densities of O2(a1Δg) in an atmospheric pressure plasma jet (APPJ) by molecular beam mass spectrometry (MBMS). The ability to measure axial and radial profiles of O2(a1Δg) impinging on a substrate in the effluent of the APPJ is a key advantage of the MBMS diagnostic method over previously reported optical methods. The measured large O2(a1Δg) densities in the APPJ effluent, up to one order of magnitude higher than the O density, underline the potential importance of O2(a1Δg) in many applications using APPJs.

Effects of air-based nonequilibrium atmospheric pressure plasma jet treatment on characteristics of polypropylene film surfaces

Polypropylene (PP) film surfaces were treated using air-based nonequilibrium atmospheric pressure plasma jets generated with a twisted wires-cylindrical electrode configuration. For comparison, PP samples were also processed with Ar plasma jets. The flux of charged particles imparted to the polymer surface by the air plasma jet greatly increased with decreases in both the gas flow rate and nozzle-to-sample distance, which was not the case for the Ar plasma jet. Reducing the gas flow rate and the nozzle-to-sample distance greatly enhanced the extent to which the surface was rendered hydrophilic by the air plasma within a short treatment time of 1 min. This enhanced effect is believed to originate from a high concentration of oxygen-based functional polar groups (FPGs) containing CO/COH and CO/COOH bonds grafted onto the surface. The hydrophilic surfaces resulting from this process also exhibited nanopore structures. The large number of oxygen-based FPGs produced by the air plasma can be attributed primarily to oxygen radical ions impinging from the air plasma on the surface. This can further be attributed secondarily to heat-induced oxidation rather than the sticking of oxygen radicals and UV-induced oxidation from the plasma. The nanoporous structure can also be ascribed to oxidation from UV photogenerated holes.

Adding Water Droplets Into Atmospheric Pressure Plasma Jet of Helium

In this article, water droplets were added into nonequilibrium atmospheric pressure plasma jet (APPJ) of Helium and the effects on spectroscopic properties of water content on plasma have been studied. The APPJ was generated using alternating current (ac) power supply, and water droplets were sent to the plasma with the help of a separating funnel. The emission intensities from reactive oxygen and reactive nitrogen oxide species (ROS and RNOS) such as OH, NO, O, and H were measured by optical emission spectroscopy for ambient air + H2O, He, and He + H2O plasma at atmospheric pressure. An increase in OH radicals was detected when water droplets were added to APPJ generated with He. The electron excitation temperature and electron density of ambient air + H2O, He, and He + H2O plasma generated in atmospheric pressure were determined using Boltzmann approximation. Furthermore, it was observed that the plasma of the He + H2O mixture causes a decrease in the pH value of water in a very short application time.

Performance enhancement of dye-sensitized solar cells by plasma treatment of BaSnO3 photoanode

We describe here the synthesis of BaSnO3 nanopowder via simple co-precipitation method and its application as a substitute photoanode material in dye-sensitized solar cells. Different values of pH and calcination temperature have been applied and optimized. The production has been characterized by X-ray diffraction technique to understand the effect of pH and calcination temperature on its crystallinity and phase purity. Crystalline BaSnO3 with an average size of about 18 nm presented an excellent dye-loading capability within a short duration of time. In this report, also, porosity and microstructure improvement in the BaSnO3 layer was achieved by using non-equilibrium atmospheric pressure plasma jet treatment for the first time, which modified dye-loading and charge transport properties in BaSnO3 photoanodes, resulted in a brilliant enhancement of the DSSC efficiency. The DSSCs were fabricated using untreated and plasma-treated BaSnO3 photoanodes. The highest photon conversion efficiency of about 2.6% was observed for the highly crystalline BaSnO3 nanoparticles synthesized within pH 12, calcined in temperature 900 °C and 3 h dye-loading with a significantly high JSC = 7.10 mA/cm2, VOC = 0.74 V and FF ≈ 0.50. This value of efficiency is considerable in comparison to the previous phase pure BaSnO3-based DSSCs. After enhancement of plasma treatment time and modification of dye-loading duration, an improvement of more than 50% was recognized in DSSC efficiency (about 4%), and a reduction in dye-loading time was observed by one third, compared to the bare one.

Deposition of thin films containing carboxylic acid groups on polyurethane foams by atmospheric pressure non-equilibrium plasma jet

Thin films containing carboxylic acid groups are deposited on open-cell polyurethane (PU) foams by using an atmospheric pressure non-equilibrium plasma jet, in dielectric barrier discharge configuration, fed with helium, acrylic acid and ethylene.The arrangement of the plasma jet, the sample holder, and the substrate is carefully optimized to enable the penetration of the plasma ejected from the remote source throughout the three-dimensional (3D) porous structure of the foam, and, therefore, to achieve the uniform coverage of the entire substrate.X-ray photoelectron spectroscopy analyses and scanning electron microscopy observations confirm that both the outer and the inner surfaces of the foam can be functionalized with the plasma-deposited coating, showing moderate changes in surface chemical composition and coating thickness moving from the exterior to the interior of the plasma-treated samples.The ability of the foams to adsorb heavy metals from water is tested through evaluation of cadmium ions (Cd2+) removal. The foams adsorption capacity can increase more than 10 times after plasma deposition and remains unchanged over 8 adsorption-release cycles.

Direct Treatment of Liquids Using Low-Current Arc in Ambient Air for Biomedical Applications

In this work, we developed a portable device with low production and operation costs for generating an ambient air low-current arc (AALCA) that is transferred to the surface of a treated liquid. It was possible to generate a stable discharge, irrespective of the conductivity of the treated liquid, as a sequence of corona, repeating spark, and low-current arc discharges. The estimated concentration of reactive oxygen and nitrogen species (RONS) in plasma-treated water (PTW) produced using AALCA treatment was two orders of magnitude higher than that of PTW produced using conventional He nonequilibrium atmospheric pressure plasma jets or dielectric barrier discharges. The strong bactericidal effect of the treatment using AALCA and the water treated using AALCA was confirmed by survival tests of Escherichia coli. Further, the possibility of treating a continuous flow of liquid using AALCA was demonstrated.

The influence of plasma treatment on the photovoltaic performance of DSSCs fabricated from hydrothermally prepared Zn2SnO4 nanoparticles

We synthesize high-quality Zn2SnO4 nanoparticles by means of hydrothermal method and then the influence of precursor concentration and precursor solution pH as well as hydrothermal reaction temperature on the structural properties of the resulting nanoparticles is investigated. Having synthesized the Zn2SnO4 nanoparticles with high-quality structural properties, the prepared nanoparticles are employed to construct the photoanodes. In the next step, the prepared photoanodes are treated with non-equilibrium atmospheric pressure plasma jet and the effect of plasma treatment duration on the photovoltaic properties of the fabricated Zn2SnO4-based dye-sensitized solar cells is studied. In comparison with untreated photoanode, the photoanode, treated for 12 min, exhibits maximum short-circuit current density and power conversion efficiency growth of about 27% and 32%, respectively. The increase in these values is ascribed to the improvement of dye-loading on the surface of photoanode. Furthermore, electrochemical impedance spectroscopy reveals that the charge transfer process at the interface of photoanode and electrolyte efficiently takes place which can be attributed to the interfacial properties improvement.

Structure and optical properties of PANI/MWCNTs nanocomposites thin films prepared by plasma jet polymerization

Polyaniline Multi walled Carbon nanotubes (PANI/MWCNTs) nanocomposite thin films have been prepared by non-equilibrium atmospheric pressure plasma jet on glass substrate with different weight percentage of MWCNTs 1, 2, 3, 4%. The diameter of the MWCNTs was in the range of 8-55 nm and length - - 55 55 μm. the nanocomposite thin films were characterized by UV-VIS, XRD, FTIR, and SEM. The optical studies show that the energy band gap of PANI/MWCNTs nanocomposites thin films will be different according to the MWCNTs polyaniline concentration. The XRD pattern indicates that the synthesized PANI/MWCNTs nanocomposite is amorphous. FTIR reveals the presence of MWCNTs nanoparticle embedded into polyaniline. SEM surface images show that the MWCNTs homogenously inside the polyaniline house. It can be concluded that the nanocomposite can be prepared PANI/MWCNTs thin films by plasma jet polymerization and control the optical energy band gap irregulars by controlling the MWCNTs weight concentration.

Development of an Ambient Air Flow Rotating Arc Jet for Low-Temperature Treatment

For low-temperature atmospheric pressure plasma treatment applications, we developed a novel rotating arc jet operated using various gases, including ambient air. We demonstrate the operation of plasma via the injection of various gas mixtures and tune operation parameters to achieve a low-temperature gas output from the arc jet. The rotating arc jet has an efficiency two orders of magnitude higher in the generation of reactive oxygen and nitrogen species than commercially available conventional nonequilibrium atmospheric pressure plasma jets operated with He or Ar gases. The high concentration of reactive species and use of ambient air as a process gas is promising for biomedical and agriculture applications. This work is a step toward the commercial use of plasma jets operated with ambient air.

Triboelectric microplasma powered by mechanical stimuli

Triboelectric nanogenerators (TENGs) naturally have the capability of high voltage output to breakdown gas easily. Here we present a concept of triboelectric microplasma by integrating TENGs with the plasma source so that atmospheric-pressure plasma can be powered only by mechanical stimuli. Four classical atmospheric-pressure microplasma sources are successfully demonstrated, including dielectric barrier discharge (DBD), atmospheric-pressure non-equilibrium plasma jets (APNP-J), corona discharge, and microspark discharge. For these types of microplasma, analysis of electric characteristics, optical emission spectra, COMSOL simulation and equivalent circuit model are carried out to explain transient process of different discharge. The triboelectric microplasma has been applied to patterned luminescence and surface treatment successfully as a first-step evaluation as well as to prove the system feasibility. This work offers a promising, facile, portable and safe supplement to traditional plasma sources, and will enrich the diversity of plasma applications based on the reach of existing technologies.

Comparison on the Absolute Concentrations of Hydroxyl and Atomic Oxygen Generated by Five Different Nonequilibrium Atmospheric-Pressure Plasma Jets

Nonequilibrium atmospheric pressure plasma jets (N-APPJs) generate near or at room temperature plasmas in open space, which is attractive for various applications such as plasma medicine. Because of this advantage, different types of N-APPJs have been reported. Reactive species, such as hydroxyl (OH) and atomic oxygen (O), generated by N-APPJs, are believed to play important roles for many applications. However, there is no report on the comparison of the reactive species concentrations generated by different types of N-APPJs. In this paper, the absolute concentrations of OH and O generated by five different configurations of widely used N-APPJs are compared. For this initial study, all five N-APPJS are driven by the same pulsed dc power supply. Besides, the effects of different operating parameters, including the amplitude of the applied voltage, frequency, the content of the working gas, and the gas flow rate, on their concentrations are investigated. It is found that the OH and O concentrations of the five N-APPJs could have up to one order and five-folder difference, respectively. On the other hand, for all five devices, their peak O concentrations are about two orders higher than their peak OH concentrations. Finally, from the energy point of view, the reactive species generation efficiency of these devices are discussed and future work is proposed.

Plasma-induced flow instabilities in atmospheric pressure plasma jets

Pulsed plasma excitation of rare gases flowing into air has been shown to impact the stability of the flow in non-equilibrium atmospheric pressure plasma jets (APPJs). In this paper, the results from a numerical modeling investigation of the stability of a round He APPJ with a powered electrode exposed to the gas flow are discussed. Localized gas heating at the powered electrode occurs on the time scale of the voltage pulse, tens to 100 ns, which is short compared to the fluid timescales. An acoustic wave propagates from this heated, expanding gas and exits the jet. The wave disturbs the shear layer between the He and surrounding humid air, exciting a shear instability which grows downstream with the flow and increases the mixing of the humid air into the He. The effects of the eddy-dominated flow on ionization wave (IW) propagation in an APPJ were investigated. The IW followed the regions of the highest helium concentration, resulting in an increased production of NO, HO2, and NO2.