Low Temperature Atmospheric Pressure Plasma Research Articles

Incremental effects of near-atmospheric-pressure low-temperature air plasma jet irradiation on polyphenol content in harvested onions

Abstract We present a new food processing method to increase the content of polyphenols, which are a type of health-promoting food component, in harvested onions using atmospheric-pressure low-temperature plasma technologies. Harvested onions were locally irradiated for different times with a low-temperature air plasma jet generated near atmospheric pressure and stored in the dark for various periods. The plasma-irradiated area was 7 mm2. The plasma irradiation was performed without removing the onion peel. After storage following plasma irradiation, the onion was peeled and cut into the outer, middle, and inner parts, analysing polyphenol content at each edible onion part, namely the bulb. The polyphenol content in the onions irradiated for 30 min and stored for 3 days increased over that of unirradiated onions stored for the same period. This increase occurred regardless of the bulb parts. Neither the plasma-irradiated onions without storage nor the air gas-irradiated onions without air plasma irradiation exhibited a higher polyphenol content. In particular, quercetin aglycone, quercetin 4’-O-glucoside, quercetin 3-O-glucoside, and quercetin 3,4’-O-glucoside were increased in the polyphenol content, contributing to an increase in the antioxidative activity. NO3− and NO2− were introduced into water under an onion peel by air plasma irradiation for 30 min and decreased after 3 days of storage but remained. However, no H2O2 was introduced. The plasma-introduced NO3− was distributed throughout the onion owing to the plasmodesmata serving as channels for cell-to-cell transports of molecules. These results suggest that the increased polyphenol content originates from the transcriptional factors acting in stress responses to the plasma-introduced NO3− and NO2−, not the electric field-induced electroporation, in onion cells. The present study provides valuable insights into interactions between low-temperature air plasma jets and onion cells.

The impact of atmospheric air plasma treatment on the polyfunctional end-use polyester fabric using new synthetic pyrazole dye

Before gluing, bonding, and painting, a variety of materials' surfaces can be modified using the widely used plasma treatment technique. These materials include plastics, glass, metals, and wood. Materials' physical and chemical properties are changed in an environmentally responsible way to enhance or confer particular qualities. The recently used technology known as low-temperature atmospheric pressure plasma (LTAPP) allows heat-sensitive materials to be surface modified in a simple, one-step process. Polymer-based materials are frequently surface modified using LTAPP treatment to improve adhesion, printability, and surface sterility. Polyester's superior mechanical and physical qualities have led to its widespread use as a technical textile and garment material in the form of fibers, films, and plastics. Its limited versatility in terms of end use has been caused by its poor surface properties as the hydrophobic nature of polyester surface, roughness, the crystallinity, and lack of dyeability which are the main drawback restricting its use in different textile applications especially during wet treatments unlike natural fibers. In order to increase the fabric's hydrophilicity and dyeability, the surface of a polyester fabric was altered in this study using atmospheric pressure plasma treatment with atmospheric plasma jet and dielectric barrier discharge (APJ-DBD) technology in air. The primary obstacles in making dielectric barrier discharge (DBD) plasma treatment suitable for industrial purposes are the extended duration of treatment and the utilization of elevated voltage levels. The combination between the atmospheric plasma jet and the dielectric barrier discharge reduces the optimal treatment time to 1 min and the applied voltage to 3.3 kV. After being exposed to oxygen plasma species for a brief period of time (between 30 and 300 s), and were analyzed using an X-ray diffraction machine, an X-ray photoelectron spectroscopy (XPS), static contact angle, and a scanning electron microscope (SEM) to investigate changes in the morphology and chemical nature of the surface, respectively. Fabric wettability increased as a result of plasma treatment, which also increased the fabric's surface roughness, as demonstrated by SEM and X-ray diffraction. The contact angle decreases by increasing the treatment time. The dyeability of untreated and plasma-treated samples was examined with respect to washing, rubbing, perspiration, sublimation, and light fastness. Additionally, color strength was examined. Adequately, compared to the untreated fabric, polyester treated with plasma showed improved dyeing performances. The technical reactivity of poly (ethylene-terephthalate) (PET) fabrics was found to be effectively increased by atmospheric air plasma treatment, creating new avenues for surface modification in light of the expanding environmental and energy-saving concerns.

Effects of the application of low-temperature atmospheric plasma on titanium implants on wound healing in peri-implant connective tissue in rats

PurposeThis study aimed to clarify the effects of surface modification of titanium (Ti) implants by low-temperature atmospheric pressure plasma treatment on wound healing and cell attachment for biological sealing in peri-implant soft tissue.MethodsHydrophilization to a Ti disk using a handheld low-temperature atmospheric pressure plasma device was evaluated by a contact angle test and compared with an untreated group. In in vivo experiments, plasma-treated pure Ti implants using a handheld plasma device (experimental group: PL) and untreated implants (control group: Cont) were placed into the rat upper molar socket, and samples were harvested at 3, 7 and 14 days after surgery. Histological evaluation was performed to assess biological sealing, collagen- and cell adhesion-related gene expression by reverse transcription quantitative polymerase chain reaction, collagen fiber detection by Picrosirius Red staining, and immunohistochemistry for integrins.ResultsIn in vivo experiments, increased width of the peri-implant connective tissue (PICT) and suppression of epithelial down growth was observed in PL compared with Cont. In addition, high gene expression of types I and XII collagen at 7 days and acceleration of collagen maturation was recognized in PL. Strong immunoreaction of integrin α2, α5, and β1 was observed at the implant contact area of PICT in PL.ConclusionsThe handheld low-temperature atmospheric pressure plasma device provided hydrophilicity on the Ti surface and maintained the width of the contact area of PICT to the implant surface as a result of accelerated collagen maturation and fibroblast adhesion, compared to no plasma application.

Low-Temperature Atmospheric Pressure Plasma Jets and their Applications in the Surface Activation of some Polymeric Substrates for Advanced Electronic Packaging

The present study applied low-temperature atmospheric plasma (LTAPP) jets to modify polymer substrates used in chip packaging. These substrates include bismaleimide triazine (BT), polyimide (PI) and PTFE materials. All these materials play important roles in modern semiconductor packaging. During the study, focuses were aimed the effects of reactive species (mainly OH and atomic oxygen) generated by atmospheric plasma jets on surface energy, water contact angle (WCA) and surface composition of these three substrates. In order to better understand and apply LTAPP jets, another focus will be on the understanding of the relationship among (1) the generation and distribution of various reactive species, (2) parameters for generating LTAPP jet, and (3) plasma characteristics. The plasma activation mechanism of these substrates was also discussed. In addition to plasma generation using AC high-voltage supplies, plasma characterization using optical emission spectroscopy (i.e., analysis of electron density, electron temperature, plasma temperature, and reactive species), XPS and water WCA analysis were used to understand surface activation mechanisms. In sum, Ar and Ar-O2 plasma jets can be used to modify the surfaces of these three substrates, although the latter relies on the generation of O radicals, while the former relies on OH radicals more. According to the results obtained by XPS analysis, the formation of C-O and C=O bond after plasma treatment is the main reason for surface activation in this study.

Effect of electron temperature and concentration on production of hydroxyl radical and nitric oxide in atmospheric pressure low-temperature helium plasma jet: Swarm analysis and global model investigation

Effect of electron temperature and concentration on production of hydroxyl radical and nitric oxide in atmospheric pressure low-temperature helium plasma jet: Swarm analysis and global model investigation

Silicon oxide anticorrosion coating deposition on alloy steel surface by low temperature plasma

In this work, honeycomb-like SiOx coating was successfully prepared on steel surface by atmospheric pressure low temperature plasma jet. The surface morphology, corrosion resistance and stability of the coating were systematically analyzed. In addition, the growth mechanism of the coating was discussed. The analysis revealed that the coatings were primarily composed of Si-O-Si and Si-OH groups, with a minor presence of Si-CH3 moieties. The coating obtained after two deposition cycles exhibits the highest level of uniformity and density, with minimal porosity and superior corrosion resistance. The increase in deposition cycles led to particle aggregation, augmented particle dimensions and porosity, which adversely affected the coating's performance. The dense SiOx coating resulted in a significant reduction in the corrosion current density of the alloy steel, and showed no significant corrosion defects when exposed to the crude oil simulant in 25 °C. The coating simultaneously enhanced the hydrophilicity and oil transfer of the steel surface. Finally, the coating exhibited self-cleaning properties, stability and high potential for safeguarding steel pipes against low-viscosity crude oil contamination. This study provides a general surface modification method for the preparation of corrosion-resistant coatings on metal surfaces under mild conditions.

Quantitative evaluation of the low-temperature pulsed plasma-wound interaction based on splint model

An atmospheric pressure low-temperature plasma jet has a promising application prospect in biomedical fields due to its low operating temperature and its ability to act in open space. In this paper, a mouse excisional wound splinting (MEWS) model is developed using a BALB/c strain of mice. A pulsed low-temperature plasma jet close to the human temperature is generated to treat the wound of the mouse skin. We have demonstrated that the pulsed low-temperature plasma jet can effectively promote wound healing. The large number of active particles contained in the plasma, such as reactive oxygen species, reactive nitrogen species, etc., may be responsible for its ability to increase the wound healing rate and promote skin tissue regeneration. The MEWS model adopted in this experiment reduces the interference in the evaluation of the wound healing effect caused by skin contraction and wound dressing, and thus is closer to the healing process of human wounds, and the method of wound area acquisition and calculation based on image processing reduces human interference and is more standardized, which can be used to evaluate the effect of the pulsed low-temperature plasma jet on promoting wound healing.

Microanalysis of Active Nitrogen Oxides (RONS) Generation Characteristics during DC Negative Corona Discharge at a Needle-Plate Electrode

The DC negative corona of needle-plate electrodes can generate atmospheric pressure low-temperature plasma active particles, which have important effects on biological mutagenesis. The DC negative corona discharge of an air needle-plate electrode with effective consideration of NOx particles was simulated and the Trichel pulse current was obtained, focusing on the development of particles and the distribution of active nitrogen oxides (RONS) at four moments in the pulse process. The simulation results indicate that the positive ions (N2+ and O2+) and negative ions (O− and O2−) were closely related to the current changes, and the negative ions (O− and O2−) presented a typical stratification phenomenon. RONS (H2O2, O3, and NO) were approximately uniformly distributed above the level of the plate electrode at the same instant, with H2O2 and O3 except for the area below the needle tip. They trended to a cumulative increase in concentration with time. This study provides a theoretical basis for corona discharge plasma seed treatment technology.

Distribution patterns of reactive species in the interaction between atmospheric pressure plasma jet and fiber membrane

Surface modification of polymer fiber membranes using atmospheric pressure low-temperature plasma has gained significant attention in recent years. The effectiveness of surface modification determined by the uniform distribution of reactive species when plasma touching the fibers. In this study, we investigated the distribution patterns of plasma reactive species on the fibers surface with different fiber spacings by both experiment and modeling. The results revealed that reduced fiber spacing produced an obstructive effect on the propagation of reactive species. This obstruction was primarily caused by the accumulation of a significant charge on the windward side of the fiber. Consequently, there was a substantial difference in the fluxes of reactive species between the windward and leeward sides of the fiber membrane, resulting in poor uniformity of the reactive species distribution. It was worth noting that the fluxes of reactive species exhibited a double-peak distribution on the circumferential surface of the fiber filaments. This phenomenon was attributed to the coupling effect between the fiber filaments, wherein the electric field strength was higher within the gap. High electric field strength facilitated the generation and propagation of reactive species. However, as the fiber spacing decreased, the propagation of high field strength became limited until it merged into the fiber gap.

Modeling of reactive species interphase transport in plasma jet impinging on water

The interaction between low-temperature atmospheric pressure plasma and water is of primary relevance to an increasing number of applications, from water treatment to medicine. The interaction between an argon plasma jet and water is investigated using a three-dimensional (3D) time-dependent computational model encompassing turbulent gas flow and induced liquid motion, gas–water interface dynamics, multiphase species transport, and gas- and liquid-phase chemical reactions. A single-field approach based on the volume-of-fluid (VoF) method together with conditional volume averaging (CVA), is used to consistently describe the dynamics of the interface together with interfacial reactive mass transfer. Three CVA-based interface species transport models, based on arithmetic, harmonic, and unified mixture species diffusivities, are evaluated. Simulations of a plasma jet impinging on water at different gas flow rates are presented. The resulting deformation of the interface and the production and accumulation of hydrogen peroxide, reactive oxygen, and nitrogen species corroborate prior findings in the research literature showing that higher jet velocities and associated increased interface deformation led to the enhanced transport of reactive species across the plasma-water interface. The VoF-CVA approach appears promising for the modeling of general plasma-liquid multiphase systems.

The Cell Adhesion and Proliferation Enhancement Impact of Low-Temperature Atmospheric Pressure Plasma-Polymerized Heptylamine on the Surface of Ti6Al4V Alloy.

To chemically functionalize the Ti6Al4V alloy surface, a custom-made low-temperature atmospheric pressure plasma reactor device was used to polymerize heptylamine on it. The effect of different deposition times, an important process parameter, was also investigated. For each deposition time group, the surface morphology was observed via scanning electron microscopy (SEM). The surface chemical content was analyzed via X-ray photoelectron spectroscopy, and surface hydrophilicity was measured via water contact angle. The adhesion of bone marrow stromal cells (BMSCs) on the modified Ti6Al4V alloy surfaces was also observed via SEM. A quantitative evaluation of cell proliferation was performed via the Cell Counting Kit-8 assay. The results revealed that amino groups were introduced on the Ti6Al4V alloy surface via plasma-polymerized heptylamine (PPHA). The percentages of NH2/C for various deposition times (0 s, 30 s, 45 s, 60 s, 90 s, and 120 s) were 3.39%, 5.14%, 6.71%, 6.72%, 7.31%, and 7.65%. A 30 s, 45 s, and 60 s deposition time could significantly increase surface hydrophilicity with a mean water contact angle of 62.1 ± 1.6°, 65.7 ± 1.1°, and 88.2 ± 1.4°, respectively. Meanwhile, a 60 s, 90 s, and 120 s deposition time promoted BMSCs cell adhesion and proliferation. However, this promotion effect differed non-significantly among the three groups. In conclusion, the introduction of amino groups on the Ti6Al4V alloy surface exhibited surface modification and enhancement of cell adhesion and proliferation, which was partially associated with deposition time.

Rapid Free Electron Reduction in Plasma Irradiated Microscale Water Droplets

Many reaction studies show that microdroplets can provide a new avenue for green chemistry by enabling the electrochemical activity of water molecules. The observation of enhanced chemical reaction rates in gas-phase microdroplets compared to bulk liquids, often by orders of magnitude, has sparked considerable research interest. A number of factors may be involved, including evaporation enhanced reactant concentration, partial solvation at the surface, high surface to bulk number ratio, enhanced surface rate constants, pH gradients, gas-phase reactions and mass transfer, electric field enhancement and surface charging. Plasma interactions with liquids involve the mass transfer and accommodation of reactive radicals and other plasma chemical species, often occurs in the presence of high electric field and temperature gradients, UV flux and electric currents.We have investigated the use of low temperature atmospheric pressure plasma irradiated liquid microdroplets. [1] Picolitre microdroplets are totally surrounded by plasma and their high surface area relative to volume receives chemical, photon and charge flux during flight leading to chemical reactions in the liquid at low temperature. With the inclusion of precursors, the small volume provides an excellent basis for gas phase chemical microreactors that can deliver products continuously and almost instantaneously downstream for applications such as plasma medicine and specialist chemical or nanomaterial printing.In particular, low temperature plasmas are a copious source of free electrons, up to 106 times greater than corona discharges, which can interact with the liquid surface to promote rapid reduction reactions and possibly on-water catalysis. We have observed the reduction of metal salts in flight to produce nanoparticles at rates many orders of magnitude greater than standard solution chemistry or via radiolysis. [2] We have measured the plasma gas temperature in the presence of microdroplet streams with droplet rates up to 5 x 104 s-1 and observed no significant increase in gas temperature, which is typically ~300 K, thus keeping the evaporation limited. [3] Recently, we carried out plasma simulations, coupled with downstream chemical flux measurements, to determine the evolution of gas-phase chemistry in the plasma and effluent. [4] We have also performed the first measurements of plasma charging of particles, at atmospheric pressure for diameters > 1 um. The determined average droplet charge per droplet was 2.5 x 106 electrons (400 fC). Using a number of plasma particle charging models we estimate the electron flux ranged from 5 x 1022 m-2 s-1 to 4 x 1025 m-2 s-1.In [2], at least 50% Au3+ to Au0 reduction of the droplet precursor (HAuCl4) was observed over a ~120 µs plasma flight time and the equivalent Au0 generation rate is ~1013 atoms s-1. The ratio of electron flux per droplet to metal generation rate provides a dimensionless figure of merit, e-/Au0, of ~100 - 1000. Using plasma chemistry simulations along with estimates of electron flux to the droplet surface, we then simulated the subsequent water reactions using a 1-D radial reaction – diffusion scheme. For 15 µm diameter droplets without precursor, surface H2O2 concentrations ranged from 0.1 M to 100 µM whereas surface OH· concentrations were almost constant (~1 mM), as electron flux density (m-2 s-1) increased. However the OH· concentration decayed rapidly with depth, reaching 1 nM within 1 µm. As the droplet size increased, surface concentration and penetration depth both decreased. For electron flux densities up to ~5 x 1022 m-2 s-1, the solvated electron surface concentration was ~0.1 mM and the penetration depth was ~250 nm but at higher fluxes, the penetration depth increases significantly likely due to the reduced concentration of sub-surface H2O2 and OH·, which scavenge electrons. When 1 mM HAuCl4 precursor is added, the surface electron concentration and penetration depth is significantly reduced (< 50 nm), even at very high flux densities. We also observe the loss of surface Au3+ and the increase in Au0 concentration. However, the maximum overall conversion rate is 15%, compared to the experimental observation of >50%. Enhanced conversion would likely require greater precursor transport from droplet centre to surface, either by internal fields or convection. We carried out preliminary simulations of (Au0)N (N: 2 → 20) cluster growth via simple collisions in this environment and observed almost complete conversion of Au0 to cluster (Au0)N with the concentration of (Au0)20 >> (Au0)2.[1] PD Maguire et al., Appl. Phys. Lett. 106, 224101 (2015); doi: 10.1063/1.4922034[2] PD Maguire et al., Nano Lett., 17, 1336–1343 (2017) doi: 10.1021/acs.nanolett.6b03440[3] N Hendawy et al 2020 Plasma Sources Sci. Technol. 29 085010 doi: 10.1088/1361-6595/aba2aa[4] H McQuaid et al 2022, in-press. See preprint - doi: 10.48550/arXiv.2207.04518

(Invited) In-Situ Optical Diagnostics of Plasma Electrochemical Reactors

Many methods for synthesizing nanomaterials are complex and can require high temperature, acids, bases, or reducing agents. The plasma electrochemical reactor (PEC), composed of an atmospheric-pressure low-temperature plasma in contact with an aqueous electrode, may provide unique physico-chemical conditions that sidestep these disadvantages because non-equilibrium electrochemistry and nucleation are initiated in solution without additional heating or strong/toxic reagents. Indeed, PECs have successfully synthesized graphene quantum dots (GQD) [1,2].The precise mechanism of GQD growth is likely to be complex, involving non-equilibrium plasma chemistry and interactions near the plasma-liquid interface. Up to now, investigations of the liquid-phase chemistry have relied principally on ex situ measurements with little or no spatially-resolved information. In addition, conventional experimental techniques can suffer from a lack of selectivity and/or degradation of dyes, chemical probes, or spin traps introduced into the liquid.To extend the scope of diagnostics, we employ an in situ approach using multiple diagnostic techniques to study a wide range of physical and chemical properties at the plasma-water interface. The centrepiece of this platform is in situ spontaneous Raman microspectroscopy, which is advantageous because of its non-intrusiveness, selectivity, versatility, and straightforward calibration. Shaping the laser beam into a light sheet enables probing of the interfacial region with micron-scale spatial resolution. To observe the effect of the plasma on the solvent, we tracked the Raman spectrum of water. Analysis of the –OH stretch band reveals that the plasma weakens the hydrogen bonding network of water. This effect becomes especially pronounced near the interface, at a depth of a few tens of microns. Likewise, at a similar depth, the concentrations of aqueous H2O2 and NO3 - both exceed those of the bulk liquid [3]. Similar interfacial layers have been modeled in past studies for radical species such as OH but not for long-lived species such as NO3 -.Concerning GQDs, we tracked their production via in situ photoluminescence (PL) and UV-VIS absorption spectroscopies. Both the PL and absorption intensities reached a maximum not at the interface but rather at a depth of a few millimeters. This observation corroborates with liquid flow field measurements by particle image velocimetry, which revealed a low-velocity zone at this depth. Under certain conditions, we could observe the consumption of the carbon precursor over the course of plasma treatment using in situ Raman spectroscopy. Finally, we characterized plasma properties near the interface, such as the electron number density, using optical emission spectroscopy. Together, these results provide the fullest description to date of the reaction environment during GQD synthesis. Acknowledgments Financial support: ANR grants ANR-15-CE06-0007-01 and ANR-11-LABX-0017-01, PHC Orchid 40938YL, CNRS-IEA “GRAFMET”, Fédération Plas@Par, EUR PLASMAScience, Poitou-Charentes region (CPER program) References [1] Orrière, T., Kurniawan, D., Chang, Y. C., Pai, D. Z., & Chiang, W. H. (2020). Nanotechnology 31 (485001).[2] Yang, J. S., Pai, D. Z., & Chiang, W. H. (2019). Carbon 153, 315-319.[3] Pai, D. Z. (2021) J. Phys. D. : Appl. Phys. 54, 355201

Diagnostics of Atmospheric Plasma Jets of Helium and Argon Barrier Discharge in a Cylindrical Microwave Cavity Resonator

Introduction. Technologies related to the use of low-temperature atmospheric plasmas are developing at a rapid pace. Creation of new low-temperature plasma sources for specific applications requires monitoring of dynamic processes in such discharges with a high time resolution. Electron concentration is one the most important plasma characteristics, which can be very low for a low-temperature atmospheric pressure plasma. However, the methods currently available for diagnostics of gas-discharge plasmas are either characterized by insufficient sensitivity or unable to monitor dynamic processes in non-stationary discharges. In this regard, the development of new diagnostic approaches to low-temperature atmospheric plasma seems to be a relevant research direction.Aim. To develop a diagnostic method for an atmospheric plasma with a low gas temperature and a low electron concentration in a cylindrical microwave resonator.Materials and methods. The proposed diagnostic method is based on the well-known principle of measuring the frequency shift and the Q-factor of the eigenmodes of the microwave resonator, inside which the plasma under study is located.Results. Measurements of the atmospheric barrier discharge plasma jets in a helium and argon stream in a cylindrical microwave resonator were performed. The proposed geometry made it possible to significantly increase the sensitivity of measurements. It became possible to exclude the effect of polarization degeneracy in a round cylindrical resonator. The developed system was also tested on test objects with a known value of permittivity.Conclusion. A method for microwave diagnostics of stationary and non-stationary cold atmospheric plasma jets in a cylindrical resonator, inside which transmitting and receiving antennas are installed, as well as an orthogonal thin conductor preventing the excitation of undesirable modes, was developed.

Low-Temperature Atmospheric Pressure Plasma Treatment in the Polymer and Textile Industry

Plasma treatment is a popular technique for modifying the surface properties of a wide range of materials (plastics, glass, metals, and wood) prior to gluing, bonding, and painting. Physical and chemical properties are altered to improve or confer specific characteristics of materials in an environmentally friendly manner. Low-temperature atmospheric pressure plasma (LTAPP) is an innovative technology offering surface modification of heat-sensitive materials using an easy one-step procedure. LTAPP treatment is routinely employed for the surface modification of polymer-based materials to enhance their adhesion, printability, and surface sterility. This article demonstrates that LTAPP plasma treatment also opens up new opportunities for the textile industry. It has a positive effect on fabric wettability, liquid repellency, dyeability, UV protection factor, shrink resistance, flame retardancy, and so on. This article describes selected applications of LTAPP in polymer science and the textile industry, highlighting current research trends in material science.

A green process for producing xylooligosaccharides via autohydrolysis of plasma-treated sugarcane bagasse

Due to alarming energy consumption and population growth, the transition to a circular economy is being pursued by searching for alternative resources to produce chemicals and energy. In this regard, lignocellulosic biomass, as the most abundantly accessible plant material, is a suitable alternative for satisfying this high demand. Sustainable lignocellulose biorefineries could convert cellulose, hemicellulose, and lignin into high-value products. Most available approaches prioritize cellulose and lignin over hemicellulose. In this work, autohydrolysis treatment of sugarcane bagasse is developed to produce xylooligosaccharides (XOS) with a variable degree of polymerization (2−6) using low-temperature atmospheric-pressure plasma and ball-mill treatment on raw bagasse. The reactive oxygen, ozone, hydronium ions (H3O+), and nitrogen species generated by plasma increase hemicellulose conversion. XOS hydrolysate obtained from plasma pre-treated samples (41.1%) was quantified for xylobiose (12.1%), xylotriose (10.1%), xylotetrose (6.9%), xylopentaose (7.1%), and xylohexaose (4.9%) (6 h of autohydrolysis at 135 °C). Xylan hydrolysate was also yielded 21.2% xylose, and 2.2% furfural, respectively. The entire process (plasma and autohydrolysis) was conducted in water without using any other chemicals. These results suggest the potential role of plasma pre-treatment prior to hydrothermal treatments to selectively produce XOS.

Understanding the Role of Plasma Bullet Currents in Heating Skin to Mitigate Risks of Thermal Damage Caused by Low-Temperature Atmospheric-Pressure Plasma Jets

Low-temperature atmospheric-pressure plasma jets are generally considered a safe medical technology with no significant long-term side effects in clinical studies reported to date. However, there are studies emerging that show plasma jets can cause significant side effects in the form of skin burns under certain conditions. Therefore, with a view of developing safer plasma treatment approaches, in this study we have set out to provide new insights into the cause of these skin burns and how to tailor plasma treatments to mitigate these effects. We discovered that joule heating by the plasma bullet currents is responsible for creating skin burns during helium plasma jet treatment of live mice. These burns can be mitigated by treating the mice at a further distance so that the visible plasma plume does not contact the skin. Under these treatment conditions we also show that the plasma jet treatment still retains its medically beneficial property of producing reactive oxygen species in vivo. Therefore, treatment distance is an important parameter for consideration when assessing the safety of medical plasma treatments.

Species, Pathways, and Timescales for NH3 Formation by Low-Temperature Atmospheric Pressure Plasma Catalysis

Species, Pathways, and Timescales for NH₃ Formation by Low-Temperature Atmospheric Pressure Plasma Catalysis

Real-Time Diagnosis of Plasma Molecular Temperature Based on OES and Elastic-Net Regression Analysis

The diagnosis of atmospheric pressure low-temperature plasma parameters is one of the research hot spots in plasma science. As important parameters, rotational temperature and vibrational temperature need to be measured in many application fields, such as plasma medicine, spraying, and combustion technology. Nowadays, as nonimmersion measurement technology, the plasma temperature diagnostic method based on optical emission spectroscopy (OES) shows greater advantages because it causes no pollution and interference to the plasma. However, the current measurement of molecular rotational and vibrational temperatures by OES is based on manual comparison and fitting, which has the disadvantages of cumbersome operation, heavy workload, and low efficiency. Therefore, an efficient method based on linear regression to process emission spectrum data has been proposed in relevant literature, but there is still room for improvement in accuracy and applicable range of temperature prediction. In this article, a theoretical spectral dataset with uniform and extensive temperature distribution is established, and some improvements and optimizations are made to the training variables and elastic-net regression model to obtain better fitting results. The fitting <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R^{2}$</tex-math> </inline-formula> of the experimental test dataset reaches 0.99427 and 0.96435 for these two temperatures, and the prediction time of a single spectrum data is less than 5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $</tex-math> </inline-formula> s, almost real time, which contributes new insights into the intelligent and efficient processing of plasma emission spectrum data.

Physico-chemical mechanism of surface dielectric barrier discharge product change based on spectral diagnosis

To gain an insight into the interaction mechanism among the gaseous products of atmospheric pressure air plasma, a surface dielectric barrier discharge is used as a study object. The dynamic processes of characteristic products (nitric oxide NO and ozone O&lt;sub&gt;3&lt;/sub&gt;) are measured by in-situ Fourier infrared spectroscopy and UV absorption spectroscopy. The real energy density of the plasma is calculated by Lissajous figure and ICCD optical image. The gas temperature is obtained by fitting the emission spectrum of the second positive band of the nitrogen molecule. The results show that the real energy density and gas temperature are highly positively correlated with the applied voltage and frequency. Higher applied voltages and frequencies can lead to lower peak absorbance of O&lt;sub&gt;3&lt;/sub&gt; and higher absorbance of NO, and accelerate the conversion of the products from O&lt;sub&gt;3&lt;/sub&gt;-containing state into O&lt;sub&gt;3&lt;/sub&gt;-free state. The microscopic mechanism of the product change is revealed by analyzing the effects of the real energy density and gas temperature on the major generation and quenching chemical reactions of the characteristic products. The analysis points out that there are two major reasons for the disappearance of O&lt;sub&gt;3&lt;/sub&gt;, i.e. the quenching effect of O and O/O&lt;sub&gt;2&lt;/sub&gt; excited state particles on O&lt;sub&gt;3&lt;/sub&gt; and the quenching effect of NO on O&lt;sub&gt;3&lt;/sub&gt;. And the mechanism that the disappearance of O&lt;sub&gt;3&lt;/sub&gt; accelerates with the increase of energy density and gas temperature, is as follows. The increase of real energy density means that the energy injected into the discharge region is enhanced, which intensifies the collision reaction, thereby producing more energetic electrons and reactive oxygen and nitrogen particles. Since the discharge cavity is gas-tight, the rapid generation of O leads to a rapid increase in the ratio of O to O&lt;sub&gt;2&lt;/sub&gt;, which accelerates the decomposition of O&lt;sub&gt;3&lt;/sub&gt;; besides, the gas temperature is raised due to the intensification of the collision reaction. Whereas the gas temperature can change the rate coefficients of the chemical reactions involving the excited state particles of nitrogen and oxygen to regulate the production and quenching of the products. The increase of gas temperature has a negative effect on O&lt;sub&gt;3&lt;/sub&gt;. The higher the gas temperature, the lower the rate of O&lt;sub&gt;3&lt;/sub&gt; generation reaction is but the higher the rate of dissociation, which is thought to be the endogenous cause of the rapid disappearance of O&lt;sub&gt;3&lt;/sub&gt;. In contrast, the gas temperature rising can significantly elevate the reaction rate of NO production and reduces its dissociation rate. This contributes to the faster production of massive NO, resulting in an accelerated quenching process of NO to O&lt;sub&gt;3&lt;/sub&gt;, which can be considered as the exogenous cause of the rapid disappearance of O&lt;sub&gt;3&lt;/sub&gt;. In a word, the present study contributes to a better understanding of the physico-chemical process in atmospheric pressure low-temperature plasma.