Atmospheric Dielectric Barrier Discharge Research Articles

E. Coli inactivation by humidified air barrier discharge plasmas and the chemical stability of amino acids

In this study, we use atmospheric air dielectric barrier discharge (DBD) plasma to inactivate E. coli (E. coli) by changing the air humidity levels. In order to analyze the inactivation process of E. coli during the humidified air DBD plasma treatment, we analyze the byproducts of 12 representational amino acids and compare their chemical stability. The experimental results show that the E. coli surface density (CFU cm−2) on a steel disc decreased significantly when the air humidity was increased from 20% to 60%, and humidified air DBD plasma at 60% humidity is very effective in inactivating E. coli. A consistently potent deactivation effect on E. coli can be seen in plasma afterglow treatment experiments over a storage time of two minutes, indicating that plasma-activated long-lived reactive oxygen and nitrogen species play a crucial role in controlling the E. coli inactivation. Compared to the low humidity (20%) condition, the concentration of reactive species produced by the plasma at high humidity (60%) increased 2-fold for 2-hydroxyterephthalic acid and 5-fold for hydrogen peroxide while ozone production was halved. Amino acid experiments showed that amino acids may be oxidized, hydroxylated and nitroxylated by reactive species. The reduction of amino acids by air DBD plasma was even more pronounced at high air humidity compared to low air humidity. Our analysis indicates that the significant inactivation of E. coli by humified air DBD plasma is related to the chemical instability of amino acids.

Fluid simulation of atmospheric argon RF dielectric barrier discharges: Role of neutral gas temperature

For atmospheric argon RF dielectric barrier discharges, a self-consistent one-dimensional fluid model based on the drift-diffusive approximations of the particles is established to investigate the role of the neutral gas temperature on the discharge process and the plasma characteristics. A finite difference method is used to solve numerically the model, and the numerical results are obtained for the cases that the neutral gas temperature varies from 300 to 600 K. It shows that an increase in the neutral gas temperature causes a decrease in the ionization rate peak and a decrease in the plasma density, but the electric field and the electron temperature do not change very much. Moreover, the discharge mode transition from α mode to α-γ mode occurs because the growing ion flux induces more secondary electron flux, even if the ions entering the sheaths decrease. In addition, the ground state ionization and the ground state excitation are the main collisions in the argon discharges. When metastable atoms are focused on, the three-body quenching is also an important collision progress.

Surface modification of polymers by 50 Hz dielectric barrier discharge (DBD) plasma produced in air at 40 Torr

This study deals with the surface modification of polymer films utilizing a custom designed cost- effective dielectric barrier discharge (DBD) plasma produced in air at reduced pressure. We comprehensively examine diverse aspects of surface modification, encompassing electrical discharge characterization, optical signal analysis, contact angle measurements, and surface morphology assessment. Our observations unveiled the presence of distinctive filamentary streamer-based micro-discharges during the DBD process, with a power consumption of approximately 5.64 watts and an electron density of 3.4 × 1011 cm−3. Optical emission spectroscopy identifies multiple emission peaks attributed to nitrogen emissions. Notably, plasma treatment substantially reduced the water contact angle and augmented surface energy on polypropylene (PP) and polyethylene terephthalate (PET) films. Surface morphology analysis illustrated an increase in surface roughness following plasma treatment. Intriguingly, the initial rapid alterations in wettability and surface morphology attained equilibrium after approximately 30 seconds of treatment. This study highlights atmospheric DBD plasma's effectiveness in customizing polymer surfaces, improving wettability and roughness, offering promising applications for enhanced adhesion and wetting.

The effect of cold plasma treatment on quality attributes and shelf life of apples

The effectiveness of atmospheric air dielectric barrier discharge (DBD) cold plasma was compared with existing decontamination methods for improving the quality and shelf life of apples. The samples were stored in two different storage conditions (ambient, 27 ± 3 °C; and cold, 10 ± 1 °C) to check the effect of storage temperature on their shelf life. The microbial load on the apples was reduced after all the treatments, and samples stored at 10 ℃ showed a higher reduction in microbial load with increased shelf life. The polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL) enzyme activities showed a significant reduction after cold plasma treatment; however, peroxidase (POD) activity showed a lower reduction than PPO and PAL enzymes. Color changes evaluated using L*, a*, and b* values showed higher retention for the red color in the treated samples compared to control samples, and the firmness of all treated samples was maintained throughout the storage period. The total phenolic content (TPC) increased after cold plasma treatment and carotenoid content was retained in the treated samples. In addition, the present study demonstrated that the novel cold plasma decontamination method was more effective in reducing the pesticides (Malathion, Fenthion, and Chlorpyrifos) from the apple surfaces than the conventional methods. Cold plasma can be a better alternative for decontaminating apples; however, other hurdles may be required to increase their shelf life further.

Atmospheric pressure uniform dielectric barrier discharge (DBD) in a wide air gap initiated from a narrow starting point

Generating a uniform non-equilibrium plasma in atmospheric pressure air has always been a challenge. It is believed that the maximum spacing for generating a uniform non-equilibrium plasma in atmospheric pressure air, whether using AC or nanosecond pulse drive, is 4 mm. Discharges are always non-uniform when the spacing is greater than 4 mm. In this paper, we propose a new type of dielectric barrier discharge structure to address this challenge. The left end of the structure rapidly increases the discharge spacing from 0.5 mm to 6 mm, while the right side of the main discharge gap maintains a uniform spacing of 6 mm. Nanosecond pulse voltage is used to drive the plasma, an ICCD camera is used to capture the image of the plasma during a discharge pulse cycle, which indicates that a uniform plasma within the 6 mm spacing of the main discharge gap is generated. Upon further reducing the ICCD camera’s exposure time to 20 ns, it is revealed that the uniform plasma is formed due to the rapid propagation of the plasma from left to right at a speed of order of 105 m s−1. Due to the small transverse component of the external electric field, this rapid propagation behavior cannot be due to the external electric field. Therefore, this paper further proposes the hypothesis of electric dipole formation leading to this fast propagation. The hypothesis suggests that the charge separation on the surface of the anode forms an electric dipole, which generates a local discharge at its right end. This local discharge further triggers the discharge in the main gap, and the main gap discharge, in turn, forms a dipole due to charge separation again, by repeating this cycle, the plasma propagates rapidly to the right. Further analysis demonstrates that this dipole can indeed produce a strong electric field of up to 41 kV cm−1 at its right end, which is sufficient to induce a local discharge. Moreover, under such a strong electric field, the electron migration rate can indeed reach 105 m s−1. These findings support the plausibility of this hypothesis.

Integrated in-package treatment of hydrogen peroxide and cold plasma for microbial inactivation of cabbage slices.

The efficacy of an in-package microbial inactivation method, combining H2O2 and atmospheric dielectric barrier discharge cold plasma (ADCP) treatments (H2O2-ADCP), in reducing contamination of Brassica oleracea (cabbage) slices was investigated. Cabbage slices were placed in a polyethylene terephthalate container with a H2O2-soaked polypropylene pad attached to the inside of the lid, followed by subjecting the closed container to ADCP treatment. The H2O2-ADCP treatment inactivated Escherichia coli O157:H7 and Listeria monocytogenes, resulting in reductions of 1.8 and 2.0 log CFU/g, respectively, which were greater than the sum of the inactivation effects observed with each individual treatment. The combined treatment decreased the count of Bacillus cereus spores and indigenous bacteria by 1.0 log spores/g and 1.3 log CFU/g, respectively. Moreover, the in-package method did not alter the moisture content or texture of cabbage slices. These results demonstrate the potential of H2O2-ADCP as a microbial decontamination method for packaged cabbage slices.

Hydrophilic surface modification of polypropylene by AC-DBD and NS-DBD

Dielectric barrier discharge (DBD) is a method to modify material surfaces by creating low-temperature plasma at atmospheric pressure. However, in comparison to low-pressure discharge, atmospheric DBD has the drawback of uneven surface treatment due to the ease of forming filamentary channels. This limitation hinders the widespread application of DBD technology in material surface modification. In this study, the surface of polypropylene (PP) was treated using high frequency alternating current (AC) and nanosecond (NS) pulsed argon DBDs to improve surface hydrophilicity. The changes of the PP surface hydrophilicity and the treatment uniformity were characterized by water contact angle (WCA) measurement. The relationships between the DBD characteristics, the treatment effect and the treatment uniformity of the PP surface were investigated using electrical and optical diagnostic techniques. The PP material surfaces before and after plasma treatments were evaluated by the physical morphology and chemical composition measurements to examine the influence of DBD on the treatment effect and uniformity on the PP material surface. The findings show that the modification by AC-DBD reduces the WCA of PP material surface by 40°∼50° and exhibits a variance of 1.77, indicating an improvement in hydrophilicity to some extent. Furthermore, the modification by NS-DBD further decreases the WCA of PP material surface, reducing the variance to 1.14. Compared with AC-DBD, NS-DBD has a better uniformity, a higher concentration of active particles in plasma, a greater surface roughness of PP material after treatment, a better hydrophilicity and a more uniform effect with less energy consumption. The results are meaningful to improve the application of DBD in material surface modification and optimize the power source election and operation parameters.

Pesticide uptake and translocation in plants monitored in situ via laser ablation dielectric barrier discharge ionization mass spectrometry imaging

For reducing pesticide usage and enhancing the effectiveness of pest control, it is necessary to elucidate the mechanisms of pesticide uptake and translocation in plants. Here, atmospheric pressure laser ablation dielectric barrier discharge ionization mass spectrometry imaging (LA-DBDI-MSI) was used to for in-situ monitoring of pesticide uptake and translocation in plants with a spatial resolution of 25 μm, and only requiring minimal or no sample preparation. Roots and leaves of tomato plants that had been exposed to a systemic pesticide, difenoconazole, were studied. From MSI data of tomato leaves, we found that difenoconazole was mainly distributed in the leaf veins after 6 days of pesticide exposure, but distributed throughout the leaf after 10 days of pesticide exposure. Endogenous substances are mainly distributed in the mesophyll, but are not present in the veins. This study clarifies the uptake and translocation mechanism of pesticides in plants, which is of great significance for reducing the dosage of pesticides and improving the effect of plant disease control.

Effect of atmospheric dielectric barrier discharge treatment on the triboelectric charging properties of brominated Polyethylene granules

This paper aims to investigate the effect of dielectric barrier discharge (DBD) plasma treatment on the triboelectric charging properties of granular materials containing brominated flame retardants (BFRs). This work focuses on the impact of treatment time and the applied voltage frequency. Experiments were carried out on Polyethylene (PE) particles containing 40000 ppm of bromine (PE 4.6 % of Hexabromobenzene) and BFR-free PE. The DBD treated particles were then charged by triboelectric effect in a multi-cylinder device. The triboelectric charge acquired by each sample was quantified using a Faraday cage connected to an electrometer. The humidity of the ambient air ranged between 51 % and 60 % and the temperature varied from 16.5 °C to 19 °C during the experiments. Results show the significant influence of DBD treatment time on the triboelectric charging of brominated and non-brominated PE granules. In case of brominated PE, the particles acquire less charge than the non-brominated ones. Furthermore, it was found that the charge of DBD-treated particles is influenced by the applied voltage frequency. The observed variation in triboelectric behavior may be attributed to the changes in the roughness and wettability of the polymer surface caused by DBD.

Germination, Physicochemical Properties, and Antioxidant Enzyme Activities in Kangkong (Ipomoea aquatica Forssk.) Seeds as Affected by Dielectric Barrier Discharge Plasma

Dielectric barrier discharge (DBD) plasma has been utilized as a sustainable technology to enhance seed germination in various plant species. The objective of this research was to identify the mechanism of physicochemical properties and antioxidant enzyme activities to promote kangkong (Ipomoea aquatica Forssk.) seed germination using different durations of DBD plasma treatments. Seeds were exposed to atmospheric DBD plasma from 5 to 20 min, compared to non-treated seeds as the control. According to SEM images, the seed surface had cracks and grew wider as a result of the prolonged DBD plasma treatments. A longer DBD plasma treatment exhibited a lower water contact angle and increased water absorption. DBD plasma treatments strongly improved germination percentages and hydrogen peroxide (H2O2) contents. Seeds treated with DBD plasma for 20 min showed the highest malondialdehyde (MDA) content and the lowest field emergence. Catalase (CAT) activity increased under DBD plasma treatments for 5 and 10 min. Ascorbate peroxidase (APX) and superoxide dismutase (SOD) activities were not statistically different among the treatments. This finding suggested that DBD plasma treatments stimulated the germination of kangkong seeds by modifying the seed surface, and upregulating H2O2 content and CAT activity. Five minutes was an appropriate time to treat DBD plasma.

The effect of plasma treatment on the mode II interlaminar fracture toughness of Glass/Epoxy laminates

Despite the key advantages of fiber-reinforced polymer composites, such as high specific strength and stiffness, these materials are characterized by low interlaminar fracture toughness. This study aims to investigate the effect of dielectric-barrier discharge (DBD) plasma treatment of glass fibers on the mode II interlaminar fracture toughness (GIIC) of glass/epoxy composite laminates. To this aim, first, end-notched bending (ENF) specimens were fabricated using the vacuum infusion process. During the laminating process of the specimens, the two adjacent glass layers at the top and bottom faces of the pre-delamination were exposed to an atmospheric DBD plasma for different exposure times (R: reference specimens without plasma treatment, PT2: specimens with two rounds of treatment, and PT5: specimens with five rounds of treatment). Afterward, the ENF specimens were subjected to three-point bending loading according to ASTM D7905 standard. The results showed an increase of ∼ 51% and ∼ 56% in GIIC for PT2 and PT5 specimens compared to the reference specimens (R), respectively. The Fourier-transform infrared spectroscopy (FTIR) analysis indicated that the plasma treatment did not generate new functional groups at the surface of glass fibers; therefore, there was no increase in the chemical bonding strength of the fibers to the resin. However, scanning electron microscopy (SEM) revealed that the plasma treatment increased the adhesion of the glass fibers to epoxy by removing sizing of the glass fibers and increasing the surface roughness of the fibers. The results of the present study showed that the plasma treatment can be considered as a cheap, easy-to-use, cost effective and scalable method for toughening laminated composites instead of the costly and difficult methods such as electrospun nanofibers and z-pinning.

Inhibitory effects of non-thermal atmospheric plasma on Yersinia enterocolitica and Staphylococcus aureus in the Korean traditional non-fermented kimchi “Geotjeori”

Food-borne bacteria have frequently been detected in kimchi, a representative and traditional fermented ethnic food of Korea. This study investigated the effect of atmospheric dielectric barrier discharge (DBD) plasma treatment (1.1 kV, 43 kHz, N2: 1.5 m/s, 5–60 min) on reduction of Yersinia enterocolitica and Staphylococcus aureus and on quality parameters in Geotjeroi, a non-fermented kimchi. A decrease of 0.12/0.09, 0.19/0.19, 0.34/0.45, 0.64/0.72, and 1.13/1.12 log10 CFU/g was observed by 5, 10, 20, 30, and 60 min of DBD plasma, respectively. D-value of 52.83 and 51.95 min was determined for Y. enterocolitica (R2 = 0.99) and S. aureus (R2 = 0.98) using the first order kinetics model. The quality parameters (pH, Brix, and hardness) were not significantly different (P > 0.05) between treated and untreated Geotjeori. Moreover, a decrease of >1 log10 CFU/g, for both bacteria was observed without any change in the quality of Geotjeori. These findings imply that DBD plasma treatment enhances Geotjeori safety and protects product from microbial risk.

Effect of rotating a dielectric barrier on discharge energy and uniformity in an atmospheric pressure air DBD

The application performance of the dielectric barrier discharge (DBD) depends on plasma characteristics, especially discharge energy and uniformity. In this study, the plasma characteristics are investigated in a DBD device with a rotating dielectric barrier. The statistical results indicate that rotating a dielectric barrier can effectively improve discharge power and the number of current pulses. Compared to a stationary DBD, the grayscale standard deviation of the discharge images can be significantly reduced, and the microdischarges present a rather diffuse distribution in the rotational DBD. This rotation also leads to an increase in the number of microdischarges and their movement in the direction of rotation. Additionally, a computational fluid dynamics numerical simulation together with the solution of the diffusion and recombination equations for space charges is implemented to study the diffusion, recombination, and transfer with airflow of space residual charges. The results reveal that the space charges move farther than their diffusion limit in most regions when the rotating speed reaches 30 rps (revolution per second). The mechanism of enhancing the discharge energy and uniformity by rotating a dielectric barrier is analyzed based on the local electric field enhancement induced by surface charges and electron detachment from space negative charges.

Testing of Sr-Doped ZnO/CNT Photocatalysts for Hydrogen Evolution from Water Splitting under Atmospheric Dielectric Barrier Plasma Exposure.

Nonthermal plasma is a well-recognized environmentally advantageous method for producing green fuels. This work used different photocatalysts, including PZO, SxZO, and SxZCx for hydrogen production using an atmospheric argon coaxial dielectric barrier discharge (DBD)-based light source. The photocatalysts were produced using a sol-gel route. The DBD discharge column was filled with water, methanol, and the catalyst to run the reaction under argon plasma. The DBD reactor was operated with a 10 kV AC source to sustain plasma for water splitting. The light absorption study of the tested catalysts revealed a decrease in the band gap with an increase in the concentration of Sr and carbon nanotubes (CNTs) in the Sr/ZnO/CNTs series. The photocatalyst S25ZC2 demonstrated the lowest photoluminescence (PL) intensity, implying the most quenched recombination of charge carriers. The highest H2 evolution rate of 2760 μmol h-1 g-1 was possible with the S25ZC2 catalyst, and the lowest evolution rate of 56 μmol h-1 g-1 was observed with the PZO catalyst. The photocatalytic activity of S25ZC2 was initially high, which decreased slightly over time due to the deactivation of the photocatalyst. The photocatalytic activity decreased from 2760 to 1670 μmol h-1 g-1 at the end of the process.

Sterilization characteristics of narrow tubing by nitrogen oxides generated in atmospheric pressure air plasma

The sterilization characteristics of active species generated by an atmospheric dielectric barrier discharge plasma using air and oxygen at the inner surface of silicone tubing were investigated. A dielectric barrier discharge torch plasma device was installed at one end of the tube and generated long-lived active species that flowed into the tube. A strip-type biological indicator with a 105-cell bacterial spore was placed at the opposite end of the 60 cm tube. Sterilization was completed within 30 min by active particles generated from the air plasma. The main factors contributing to the sterilization by air plasma were HNO3 and N2O5. When organic materials (keratin, aspartic acid, and dipicolinic acid) reflecting components of the bacterial spore, were treated by the sterilization procedure there was little effect on dipicolinic acid. Keratin was oxidized by ozone and NOx generated from the oxygen and air plasmas, respectively. Aspartic acid underwent little change in composition from ozone generated from the oxygen plasma, whereas nitro (NO2), nitroso (NO), and aldehyde (CHO) groups were formed from ozone and NOx generated from the air plasma.

Plasma catalytic non-oxidative methane conversion to hydrogen and value-added hydrocarbons on zeolite 13X

Non-thermal plasma has unfolded highly efficient, safe to operate novel routes for methane conversion to hydrogen. In this work, methane conversion is performed under atmospheric dielectric barrier discharge (DBD) plasma with and without 13X zeolite-based catalysts i.e., 13X, Ga/13X, Pd/13X, and Pd-Ga/13X. Experimental results indicate that the plasma catalytic process delivered almost twofold higher product yield than the plasma only route. The binary Pd-Ga catalyst possesses highest catalytic performance with about 40 % CH4 conversion at an input flowrate of 5 cm3min−1 and 2 W due to the formation of the Pd-Ga alloy, which acts as catalytic active centre for activating C–H bonds. Product yield can be tailored by the catalyst design where the bimetallic Pd-Ga/13X preferably favours the hydrocarbon formation while H2 is the dominant product obtained over the Pd/13X. The cleavage of C–H bonds of methane molecule over the plasma only route is mainly governed by energetic electrons in the gaseous phase the catalyst activity, and plasma-catalyst synergism play a significant role in the plasma catalysis process. The findings from this work provide significant insights into the methane activation for subsequent optimization of the methane conversion processes operated on floating production, storage, and offloading vessels (FPSOVs). Exploiting untapped offshore natural gas reserves, where conventional pipeline systems are less economical.

Electron dynamics and metastable species generation in atmospheric pressure non-equilibrium plasmas controlled by dual LF–RF frequency discharges

In this work, we report an approach to control electron dynamics and metastable species generation and enhance the density of atmospheric pressure non-equilibrium plasmas by using dual-frequency excitation sources. The atmospheric dielectric barrier discharge (DBD) of an α-mode radio frequency (RF = 5 MHz) discharge controlled by a low-frequency (LF = 50 kHz) bias is studied based on a one-dimensional (1D) fluid model. Results show that the variation in amplitude ratio of RF and LF modulates the electron dynamic process, resulting in different spatial distributions of electron and metastable particle densities. Moreover, it is further shown that the electron density is substantially increased when the LF component voltage amplitude is larger than 300 V for the initial setting. The discharge process is characterized by fast Fourier transform of the spatio-temporal evolution of the electron power absorption and discharge current. As the LF is applied, three-wave interactions induced by LF and RF coupling are clearly observed, where the sum and beat frequencies between LF and RF are increased, which results in a substantial increase in the electron density. On the other hand, the high RF harmonics, especially for the fundamental and the third harmonic components, are suppressed when increasing the LF component. This work demonstrates that dual-frequency excitation is efficacious to modulate the electron dynamic behaviors and metastable species generation of atmospheric pressure plasma, which can provide a possible approach of optimizing plasma parameters.

Dissociation of CO2 in non-thermal atmospheric pressure planer dielectric barrier discharge

Increasing concentration of carbon dioxide [Formula: see text] in Earth’s atmosphere due to burning of fossil fuels is a major cause of global warming. To avoid catastrophic consequences of increasing global temperature, the conversion of [Formula: see text] is vital. Incidentally, synergistic effect of [Formula: see text] photocatalyst on [Formula: see text] dissociation in atmospheric pressure planer dielectric barrier discharge is investigated. Maximum dissociation fraction of 37% is achieved in undiluted [Formula: see text], 49% in [Formula: see text] and 44% in [Formula: see text] at 10[Formula: see text]kV applied voltage with 10[Formula: see text]kHz fixed frequency and 200[Formula: see text]SCCM total flow rate. Transitions from the Angstrom band of CO at 483.5[Formula: see text]nm and the 2nd positive system of [Formula: see text] at 380.4[Formula: see text]nm are used for molecular actinometry measurements. Rotational temperature is calculated, by employing the Boltzmann plot technique, using rotational spectra of Q-branch of CO (0-1) Angstrom band. To avoid inconsistency in rotational temperature measurement, rotational spectra of 1st negative system of [Formula: see text] (0-0) band are also used. For this, synthetic spectra have been fitted over experimentally recorded spectra of 1st negative system of [Formula: see text] (0-0) band using LIFEBASE software. Electrical characterization of the discharge suggests that power added to the plasma increased from 1.92 to 6.13[Formula: see text]W in undiluted [Formula: see text], from 1.81 to 6.4[Formula: see text]W in [Formula: see text] and from 1.71 to 7[Formula: see text]W in case of [Formula: see text] mixture plasma. A higher dissociation fraction is found in the case of [Formula: see text] mixture.

Effects of in-package atmospheric dielectric barrier discharge cold plasma treatment on the antimicrobial efficacy of whey protein isolate-based edible films that incorporate malic acid against Salmonella in chicken breast processed meat

Effects of in-package atmospheric dielectric barrier discharge cold plasma (CP) treatment on the antimicrobial efficacy of malic acid-incorporated whey protein isolate (MA–WPI) coating and MA diffusion in MA–WPI-coated skinless chicken breast processed meat (CBPM) were evaluated. MA–WPI coating followed by CP treatment (MA–WPI + CP) inactivated Salmonella (5.6 log CFU/g) in CBPM by 1.8 log CFU/g. CP treatment increased Salmonella reduction rates in MA–WPI-coated samples during storage at 4 and 10 °C and the diffusion coefficients of MA in the coating, which was confirmed by comparing results of MA–WPI + CP-treated and MA–WPI-coated samples. CP treatment facilitates MA diffusion in the coating, thereby increasing the Salmonella inhibition efficacy of the coating. MA–WPI + CP treatment did not influence the color and lipid oxidation of CBPM during storage at 4 °C and the water vapor permeability, elongation, and elastic modulus of MA–WPI films. Industrial relevanceThrough the technological development of in-package cold plasma treatment for decontamination of food in the industrial production line, the microbiological safety of ready-to-eat foods coated with antimicrobials can be effectively increased by exposing the coated foods to cold plasma to accelerate the diffusion of the antimicrobials in the coating to the site of microbial contamination at the surface. The effect of cold plasma treatment on the antimicrobial efficacy of the antimicrobial coating is useful, especially during the initial stages when the coating is expected to exhibit highly efficacious antimicrobial function.

Reaction mechanism explorations on non-thermal plasma reforming of CO2-CH4 by combining kinetics modeling and emission spectroscopy measurements

Plasma-based dry reforming in an atmospheric dielectric barrier discharge (DBD) reactor has been thoroughly studied by combination of experiments and detailed kinetics simulation. With the assistances of in-situ optical emission spectroscopy (OES) measurements and reaction pathway analysis based on plasma kinetic simulation considering non-constant electric field and thermal effects, this study provided deep insights into the reaction mechanism of plasma-based dry reforming under varied feeding gas composition, gas residence time and operation temperature. A CH4 conversion as high as 44.76 % could be achieved without catalyst at 300 °C, with an SEI of 78 J/cm3 and feeding CH4 ratio of 50 %. Increase of feeding CH4 proportions were found to enhance the generation of C2 and C3 hydrocarbons. Consistently, the OES analysis showed that the relative intensities of spectra bands induced by deexcitation of CH, CO, and C2 also increased monotonically. With the same increment in SEI, increasing gas residence time led to larger promotions in CH4 and CO2 conversion, as being compared to increase of input power. The reason could be explained as that CH4 and CO2 molecules experienced more successive micro-discharges with a longer gas residence time, so more energy would be devoted into CH4/CO2 conversion, whereas more energy was dissipated into heat as rudely increased the discharge power due to the limit of reaction time. CO2 conversion continuously decreased with increasing gas temperature, owing to the recombination of CO and O enhanced at higher gas temperatures. Reaction pathway analysis showed that CH4 conversion was mainly induced by electronic dissociation and ionization at the discharge stage, while CO2 was mainly converted by recombination reaction CO2 + CH2 → CH2O + CO and also electron collision vibrational reaction e + CO2 → e + CO2(vn). The formation of C2 hydrocarbon products was supposed to follow the path of CH4 ↔ CH3/CH → C2H6 ↔ C2H5 ↔ C2H4 → C2H2.