Non-equilibrium Pressure Plasma Research Articles

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.

Application of Ultraviolet Light and Atmospheric Pressure Non-Equilibrium Plasma to Printing Process

Application of Ultraviolet Light and Atmospheric Pressure Non-Equilibrium Plasma to Printing Process

Non-equilibrium atmospheric pressure plasma assisted degradation of the pharmaceutical drug valsartan: influence of catalyst and degradation environment.

This paper investigated the degradation of the pharmaceutical drug Valsartan (VS) using non-equilibrium atmospheric pressure plasma (NEAPP) with various operating conditions. The heterogeneous photocatalyst ZnO nanoparticles (NP's) were synthesized using a hydrothermal process. The morphology, chemical composition and structure of as-synthesized ZnO NPs were examined by Field Emission Scanning Electron Microscopy (FE-SEM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD) analysis. Then, VS degradation was examined in three subsequent treatment conditions including plasma treatment alone, the combination of plasma with as-prepared ZnO NPs and various environments (air, oxygen and hydrogen peroxide) at fixed plasma operating potential and treatment time. The degradation efficiency of plasma-treated VS by various conditions was observed using UV-visible spectroscopy. Optical Emission Spectrometry (OES) was used to characterize the distribution and emission intensity of various reactive species (OH˙, N2-SPS and O) during the degradation processes which plays a vital role in the degradation of VS. The role of OH˙ and H2O2 during the degradation process was further examined by chemical dosimetry and spectroscopic techniques. Furthermore, pH, conductivity and TOC of the untreated and plasma-treated VS were also investigated. The results on the degradation of VS showed that plasma treatment combined with ZnO NP's has a significant effect on degradation of molecules of VS than degradation processes carried out by other experimental conditions due to the formation of higher concentrations of various reactive oxygen and nitrogen species during the degradation processes.

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.

The Effect of Phase Shift on the Plasma Driven by an AC Voltage and a Pulsed DC Voltage

One of the most important features of atmospheric-pressure nonequilibrium plasmas (APNPs) is its capability of generating high concentration of reactive species while keeping low gas temperature. To generate such plasma, alternative current (ac) voltage and pulsed dc voltage have been used separately. In this paper, the combination of ac voltage and pulsed dc voltage is used to generate APNPs for the first time. The plasma characteristics, including the power deposited to the plasma, the gas temperature, the emission spectra, and the O atom concentration of the plasma for different phase shifts of the two power supplies, are investigated. It is found that when the pulsed dc voltage is added on the negative ac half period at the phase shift of about 90°, the average power deposited to the plasma, the gas temperature, and the optical emission spectrum of O atom all reach their maxima. On the other hand, the ground state O atom concentration has two peaks; one of the peaks also appears when the phase shift is about 90°. When the pulsed dc voltage is applied on the positive half period at the phase shift of 270°, the O concentration reaches another peak and the peak value is higher than that when the ac or the pulsed dc power supply works alone. Furthermore, at the phase shift of 270°, the gas temperature of the plasma and the total power deposited to the plasma are all lower than the case when the ac or the pulsed dc power supply works independently. Thus, it is more energy efficient to adjust the phase shift to 270° for applications such as plasma medicine where the gas temperature of the plasma at or close to room temperature is strictly required.

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.

Measurement of electron temperature in a non-equilibrium discharge of atmospheric pressure supported by focused microwave radiation from a 24 GHz gyrotron

A microwave discharge of atmospheric pressure, maintained by focused CW radiation of a 24-GHz gyrotron in an argon flow in an external air atmosphere, was investigated. The electron temperature was determined by the current-voltage curve of a dual Langmuir probe placed in a plasma torch. The electron temperature was also estimated from plasma emission spectra within the framework of a coronal plasma model. The obtained values of the electron temperature coincide within the measurement accuracy. Also, the electron temperature is many times higher than the gas temperature. This fact allows us to stand of a significantly non-equilibrium atmospheric pressure plasma.

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.

The molecular chaperone Hsp33 is activated by atmospheric-pressure plasma protecting proteins from aggregation.

Non-equilibrium atmospheric-pressure plasmas are an alternative means to sterilize and disinfect. Plasma-mediated protein aggregation has been identified as one of the mechanisms responsible for the antibacterial features of plasma. Heat shock protein 33 (Hsp33) is a chaperone with holdase function that is activated when oxidative stress and unfolding conditions coincide. In its active form, it binds unfolded proteins and prevents their aggregation. Here we analyse the influence of plasma on the structure and function of Hsp33 of Escherichia coli using a dielectric barrier discharge plasma. While most other proteins studied so far were rapidly inactivated by atmospheric-pressure plasma, exposure to plasma activated Hsp33. Both, oxidation of cysteine residues and partial unfolding of Hsp33 were observed after plasma treatment. Plasma-mediated activation of Hsp33 was reversible by reducing agents, indicating that cysteine residues critical for regulation of Hsp33 activity were not irreversibly oxidized. However, the reduction yielded a protein that did not regain its original fold. Nevertheless, a second round of plasma treatment resulted again in a fully active protein that was unfolded to an even higher degree. These conformational states were not previously observed after chemical activation with HOCl. Thus, although we could detect the formation of HOCl in the liquid phase during plasma treatment, we conclude that other species must be involved in plasma activation of Hsp33. E. coli cells over-expressing the Hsp33-encoding gene hslO from a plasmid showed increased survival rates when treated with plasma while an hslO deletion mutant was hypersensitive emphasizing the importance of protein aggregation as an inactivation mechanism of plasma.

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.

Non-thermal plasma-activated medium modified metabolomic profiles in the glycolysis of U251SP glioblastoma

Non-equilibrium atmospheric pressure plasma (NEAPP) is a mixture of radicals, electrons, anions, cations and light at near body temperature. Plasma-activated medium (PAM) is realized using NEAPP provided by engineered devices and irradiated to a cell culture medium for a period of 600 s. Glioblastoma cells U251SP cultivated in PAM previously indicated that antitumor effects induced PAM-specific apoptotic cell-death. Metabolomic profiles of a hundred intracellular metabolites were analyzed using capillary electrophoresis mass spectrometry. The metabolomic profiles of the PAM-treated U251SP cells were changed significantly with inhibition of the glycolysis pathway and with enhancement of the pentose phosphate pathway.

Propeller arc: design and basic characteristics

A new atmospheric pressure non-equilibrium plasma source named the ‘Propeller Arc’ (PA) is developed using the concept of rotating electrodes. The PA device consists of a rotating cathode, driven by a motor, with one or more fixed anodes. Plasma is ignited at or near the narrowest gap as the rotating cathode passes by the anode and then it is extended up to a length of ∼66 mm or longer depending on the supplied power. This allows for efficient ignition, followed by a quick increase in plasma volume. The PA is similar to the widely used gliding arc (GA); however, unlike the GA, PA does not require imposed gas flow, and the PA discharge frequency can be easily controlled by the motor angular velocity. In this paper, the basic characteristics of PA are investigated using two different operation modes: pulse modulation and DC power. Discharge properties including electrical characteristics, time-resolved optical emission images, plasma electrical properties such as resistance and average electric field (discharge voltage divided by gap distance) and plasma power consumption are reported. Use of multiple anodes to increase the plasma volume is also demonstrated. As the PA has a compact design and is relatively easy to stabilize and control without the need for applied gas flow, it has potential to be adapted for many different applications such as nitrogen fixation, fuel and carbon dioxide conversion, waste, odor and hydrogen sulfide treatment, etc.

Atmospheric-pressure pulsed discharge plasma in capillary slug flow system for dye decomposition

In this study, the introduction of non-equilibrium atmospheric-pressure plasma in a slug flow reactor system is demonstrated as a chemical reaction medium. The water containing Coomassie Brilliant Blue R − 250 (CBB) and various gas species are used as the liquid and gas phases, respectively, which are flown at 1.5 and 0.5 mL/min. The optical emission spectra indicate that different reactive oxidation species are generated by each gas when the pulsed discharge plasma is applied to the slug flow reactor system. The oxygen-base reactive species are found in abundance. The decoloration of CBB seems to occur, which is indicated by a change in the color of the aqueous solution. The UV − vis spectra show that the order of the CBB decomposition rate is oxygen > air > nitrogen > argon > helium.

Synthesis of silver nanoparticles by atmospheric-pressure pulsed discharge plasma in a slug flow system

Application of nonequilibrium atmospheric-pressure plasma has been proven as a medium for silver particle formation in slug flow reactor systems. Argon gas was introduced in the slug flow reactor system in the gas phase. In the liquid phase, silver nitrate (AgNO3) with and without the addition of starch was dissolved in distilled water. The flow rates of the liquid and gas phases were 1.5 and 0.15 ml min−1, respectively. A yellow-colored solution product was obtained when the feed solution containing starch was fed. The optical emission spectrum showed that silver atoms were detected clearly at 328 nm. The ultraviolet–visible spectroscopy analysis showed that the solution products seemed to absorb light between 380 and 440 nm, corresponding to silver nanoparticle generation. Transmission electron microscopy revealed that the monodispersed silver nanoparticles were formed in a spherical morphology with diameter less than 10 nm on average.

Experimental study on inactivation of Escherichia coli by atmospheric pressure non-equilibrium plasma combined with photocatalysis

In order to improve the sterilization effect and energy efficiency of atmospheric pressure non-equilibrium plasma (APNP), a synergistic treatment system of APNP combined with photocatalysis was established to inactivate Escherichia coli. TiO2 is selected as the photocatalyst. The colony counting result indicates that APNP treatment combined with photocatalysis has an enhancement effect on sterilization. The enhancement factor η is up to 80.2%. The SEM images show that 30 s APNP treatment combined with photocatalysis causes greater structural damage than traditional APNP treatment. The discoloration photometric suggests that up to 120% more ROS are produced in APNP combined with photocatalysis. Optical emission spectra show that photocatalysis leads to weakening of the ionization process and thus weakens the plasma discharge. In accordance with the infrared thermal images, temperature rise in APNP combined with photocatalysis is 4 °C lower than that in traditional APNP treatment, which may enlarge the application area of biomedical field.

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.