Effect of DBD Plasma Treatment on Activity of Mo-Based Sulfur-Resistant Methanation Catalyst.

By combining the advantages of dielectric barrier discharge (DBD) low temperature plasma and fluidized bed, the effect of plasma on the performance of supported Mo-based catalyst was studied in this paper. The performance of the catalyst obtained by plasma treatment, calcined, plasma+calcined was compared, and the appropriate catalyst preparation scheme was explored. Comparing with the three catalysts, it was concluded that the catalyst average conversion after 30 W plasma treatment is 33.40 %, which was 8.94 % and 12.75 % higher than the other two, respectively. The structure and properties of the catalyst were characterized by N2-Physisorption, H2-chemisorption, XRD, TEM, XPS, Raman and NO-pulse adsorption. Then, by analyzing the characterization results, it can be seen that plasma can make the catalyst have a higher specific surface area and a more dispersed active metal with smaller grain size. Through the surface species identification characterization, it was found that plasma can produce more defective structures and expose more active sites, which is the main reason for the difference in conversion.

Advancing DBD Plasma Chemistry: Insights into Reactive Nitrogen Species such as NO2, N2O5, and N2O Optimization and Species Reactivity through Experiments and MD Simulations.

This study aims to fine-tune the plasma composition with a particular emphasis on reactive nitrogen species (RNS) including nitrogen dioxide (NO2), dinitrogen pentoxide (N2O5), and nitrous oxide (N2O), produced by a self-constructed cylindrical dielectric barrier discharge (CDBD). We demonstrated the effective manipulation of the plasma chemical profile by optimizing electrical properties, including the applied voltage and frequency, and by adjusting the nitrogen and oxygen ratios in the gas mixture. Additionally, quantification of these active species was achieved using Fourier transform infrared spectroscopy. The study further extends to exploring the aerosol polymerization of acrylamide (AM) into polyacrylamide (PAM), serving as a model reaction to evaluate the reactivity of different plasma-generated species, highlighting the significant role of NO2 in achieving high polymerization yields. Complementing our experimental data, molecular dynamics (MD) simulations, based on the ReaxFF reactive force field potential, explored the interactions between reactive oxygen species, specifically hydroxyl radicals (OH) and hydrogen peroxide (H2O2), with water molecules. Understanding these interactions, combined with the optimization of plasma chemistry, is crucial for enhancing the effectiveness of DBD plasma in environmental applications like air purification and water treatment.

Cascade N2 Reduction Process with DBD Plasma Oxidation and Electrocatalytic Reduction for Continuous Ammonia Synthesis.

Due to the extremely high bond energy of N≡N (∼941 kJ/mol), the traditional Haber-Bosch process of ammonia synthesis is known as an energy-intensive and high CO2-emission industry. In this paper, a cascade N2 reduction process with dielectric barrier discharge (DBD) plasma oxidation and electrocatalytic reduction as an alternative route is first proposed. N2 is oxidized to be reactive nitrogen species (RNS) by nonthermal plasma, which would then be absorbed by KOH solution and electroreduced to NH4+. It is found that the production of NOx is a function of discharge length, discharge power, and gas flow rate. Afterward, the cobalt catalyst is used in the process of electrocatalytic reduction of ammonia, which shows high selectivity (Faradic efficiency (FE) above 90%) and high yield of ammonia (45.45 mg/h). Finally, the cascade plasma oxidation and electrocatalytic reduction for ammonia synthesis is performed. Also, the performance of the reaction system is evaluated. It is worth mentioning that a stable and sustainable ammonia production efficiency of 16.21 mg/h is achieved, and 22.16% of NOx obtained by air activation is converted into NH4+. This work provides a demonstration for further industrial application of ammonia production with DBD plasma oxidation and electrocatalytic reduction techniques.

A Meaningful Attempt: Applying Dielectric Barrier Discharge Plasma to Induce Polarization of Macrophages.

Macrophage polarization plays an important role in many macrophage-related diseases. This study was designed to preliminarily explore the effects of dielectric barrier discharge (DBD) plasma on the polarization direction and cell activity of macrophages with different phenotypes (ie, M0, M1, and M2). The M1 macrophage marker inducible nitric oxide synthase (iNOS) and M2 macrophage marker cluster of differentiation 206 (CD206) were detected by western blot (WB). The effects of DBD plasma on macrophage viability were analyzed by using a cell counting kit-8 detection kit. M0, M1, and M2 macrophages exhibited a decrease in iNOS expression and an increase in CD206 expression after the DBD plasma intervention. Additionally, the decrease in macrophage viability remained non-significant after initiating the intervention. DBD plasma can promote the transformation of M0 and M1 macrophages to M2 macrophages, and can further enhance the expression of the M2 macrophage phenotype marker CD206. Our study not only demonstrates the potential therapeutic value of DBD plasma for macrophage-related diseases, but it also provides a new direction for research to improve the treatment of macrophage-related diseases. © 2023 Bioelectromagnetics Society.

Characterization of Molecular Interactions in the Bondline of Composites from Plasma-Treated Aluminum and Wood.

Wood and aluminum composites are becoming increasingly attractive due to their ability to combine the advantages of both materials: the lightweight nature of wood and the strength of aluminum. However, using conventional wood adhesives like polyvinyl acetate (PVAc) to bond these dissimilar materials is challenging and requires special surface treatments. Prior studies have demonstrated that applying a dielectric barrier discharge plasma treatment significantly enhances shear and bending strengths in beech wood/aluminum bonds. This study focuses on the molecular interactions between PVAc and aluminum or beech wood influenced by plasma surface modification. Surface-sensitive methods, including X-ray photoelectron spectroscopy, infrared reflection adsorption spectroscopy and atomic force microscopy, were employed to characterize the PVAc films on the corresponding surfaces and to identify possible interactions. The ultrathin PVAc films required for this purpose were deposited by spin coating on untreated and plasma-treated aluminum. The aluminum surface was cleaned and oxidized by plasma. Additionally, hydroxyl species could be detected on the surface. This can lead to the formation of hydrogen bonds between the aluminum and the carbonyl oxygen of PVAc after plasma treatment, presumably resulting in increased bond strength. Furthermore, the beech wood surface is activated with polar oxygen species.

Oxidative lesions and post-treatment viability attenuation of listeria monocytogenes triggered by atmospheric non-thermal plasma.

AIMS: The aim of the current study was to investigate the effect of plasma-mediated oxidative stress on the post-treatment viability of Listeria monocytogenes at the physiological and molecular levels. METHODS AND RESULTS: 107  CFU/ml L. monocytogenes in 10 ml phosphate-buffered saline (PBS) was treated with atmospheric non-thermal plasma for 0, 30, 60, 90 and 120 s respectively. Optical diagnostics using optical emission spectroscopy (OES) confirmed that dielectric barrier discharge (DBD) plasma was a significant source of ample exogenous reactive oxygen and nitrogen species (RONS). The development of extracellular main long-lived species was associated with plasma exposure time, accompanied by a massive accumulation of intracellular ROS in L. monocytogenes (p < 0.01). With the exception of virulence genes (hly), most oxidation resistance genes (e.g. sigB, perR, lmo2344, lmo2770 and trxA) and DNA repair gene (recA) were upregulated significantly (p < 0.05). A visible fragmentation in genomic DNA and a decline in the secretion of extracellular proteins and haemolytic activity (p < 0.01) were noticed. The quantitate oxygen consumption rates (OCRs) and extracellular acidification rates (ECARs) confirmed the viability attenuation from the aspect of energy metabolism. Survival assay in a real food system (raw milk) further suggested not only the viability attenuation, but also the resuscitation potential and safety risk of mild plasma-treated cells during post-treatment storage. CONCLUSION: DBD plasma had the potential to inactivate and attenuate the virulence of L. monocytogenes, and it was recommended that plasma exposure time longer than 120 s was more suitable for attenuating viability and avoiding the recovery possibility of L. monocytogenes in raw milk within 7 days. SIGNIFICANCE AND IMPACT OF THE STUDY: The current results presented a strategy to inactivate and attenuate the viability of L. monocytogenes, which could serve as a theoretical basis for better application of non-thermal plasma in food in an effort to effectively combat foodborne pathogens.

Characterization of DBD plasma actuator with ZnO nanowire arrays.

Researches in the plasma actuation are increasingly scrutinizing the methodology to enhance the thrust density for the application in the aerodynamic flow control. In this paper, a new method has been proposed and experimentally evaluated. This method is based on the deposition of nanoscaled structures on the electrode surface and the tuning of the applied voltages and frequency. It is found that the thrust enhancement rate resulted from the incorporation of the nanostructures could be approximately 78%, relative to the controlled group, under 14 kV and 7 kHz. However, a threshold effect has been founded across all of the tested samples, where lower applied voltage and frequency could lead to the decrease in the thrust generation. Capacitor charging effects are basically not sensitive to the introduction of the nanostructures in electrical characteristic. Other experimental features and electric field simulation results also indicate the effectiveness of introducing nanoscaled structures into DBD plasma actuators, thus providing a new way to improve mechanical performance.

Theoretical-Computational Study of Atmospheric DBD Plasma and Its Utility for Nanoscale Biocompatible Plasmonic Coating.

In this study, time-dependent, one-dimensional modeling of a surface dielectric barrier discharge (SDBD) device, driven by a sinusoidal voltage of amplitude 1-3 kV at 20 kHz, in argon is described. An SDBD device with two Cu-stripe electrodes, covered by the quartz dielectric and with the discharge gap of 20 × 10-3 m, was assumed, and the time-dependent, one-dimensional discharge parameters were simulated versus time across the plasma gap. The plasma device simulated in the given arrangement was constructed and used for biocompatible antibacterial/antimicrobial coating of plasmonic particle aerosol and compared with the coating strategy of the DBD plasma jet. Simulation results showed discharge consists of an electrical breakdown, occurring in each half-cycle of the AC voltage with an electron density of 1.4 × 1010 cm-3 and electric field strength of 4.5 × 105 Vm-1. With SDBD, the surface coating comprises spatially distributed particles of mean size 29 (11) nm, while with argon plasma jet, the nanoparticles are aggregated in clusters that are three times larger in size. Both coatings are crystalline and exhibit plasmonic features in the visible spectral region. It is expected that the particle aerosols are collected under the ionic wind, induced by the plasma electric fields, and it is assumed that this follows the dominant charging mechanisms of ions diffusion. The cold plasma strategy is appealing in a sense; it opens new venues at the nanoscale to deal with biomedical and surgical devices in a flexible processing environment.

Effects of DBD air plasma treatment on the enhancement of black gram (Vigna mungo l.) seed germination and growth.

Effects of black gram (vigna mungo L.cv. Barimash 3) seed treatments with 400 torr dielectric barrier discharge (DBD) air plasma on seed surface morphology, seed germination, seedling growth and antioxidant enzyme activities in the roots, shoots and leaves were investigated. The plasma discharge voltage, frequency, electrode spacing, gas temperature and power were 5kV, 4.5kHz, 60mm, 310K and 45W, respectively. The seeds were treated for the duration ranging from 20 to 180 s. Seed germination rate, seedling growth, total chlorophyll content, total soluble protein and sugar concentrations in the seedlings grown from the treated seeds were found to increase 13.67%, 37.13%, 37.26%,53.60% and 51.71%, respectively, with respect to control. This study reveals that the DBD air plasma was involved in the enhancement of nitrogen complex in the seed coat of black gram which upregulated the protein through nitrogen conversion that was ultimately responsible for the increased seed germination and seedling growth of black gram.

A facile method to decompose CO2 using a g-C3N4-assisted DBD plasma reactor.

The present study accomplishes the partial reduction of CO2 to carbon monoxide in a dielectric barrier discharge (DBD) reactor packed with g-C3N4 and TiO2 or ZnO mixed with g-C3N4. Typical results indicate that the ZnO + g-C3N4 packed reactor provides ~12% CO2 conversion at SIE of 4.8 J/mL, whereas DBD yields only ~7.5% conversion under the same experimental conditions. The best performance of the ZnO integrated system is due to the presence of more basic sites than those of the TiO2 packed system, which enables effective adsorption of acidic CO2 on its surface. The highest energy efficiency of 1.106 mmol/kJ is achieved with 5% ZnO + g-C3N4 at SIE of 4.8 J/mL, whereas DBD exhibits only 0.746 mmol/kJ under the same conditions. Notably, catalyst packing also enables the highest carbon balance of ~97%.

Sterilizing Processes and Mechanisms for Treatment of Escherichia coli with Dielectric-Barrier Discharge Plasma.

With increasing attention toward novel sterilization methods, plasma sterilization has gained more and more interest. However, the underlying mechanisms are still unknown. In this paper, we investigated the inactivation of Escherichia coli using dielectric-barrier discharge (DBD) plasma in saline water. There were three processes shown in the survival curve, namely, during the preparation period, the reaction period, and the saturation period. Observations under a transmission electron microscope (TEM) and detection by Fourier transform infrared spectroscopy (FT-IR) supplied adequate details regarding these processes. Based on these results, we infer that during the preparation period, the main process is the accumulation of chemical substances. During the reaction period, adequate amounts of chemicals decompose and denature cell membranes and macromolecules to kill bacteria in large quantities. During the saturation period, the killing effect decreases because of the protection by clustered cells and the saturation of pH. This study of sterilizing processes systematically reveals the mechanisms of plasma sterilization.IMPORTANCE Compared with traditional methods, plasma sterilization has advantages of high efficiency, easy operation, and environmental protection. This may be more suitable for air and sewage sterilization in specific spaces, such as hospitals, laboratories, and pharmaceutical factories. However, the mechanisms of sterilization are still relatively unknown, especially for bactericidal activities. Knowledge of sterilization processes provides guidance for practical applications. For example, the bactericidal action mainly occurs during the reaction period, and the treatment time can be set based on the reaction period, which could save a lot of energy. The results of this study will help to improve the efficiency of plasma sterilization devices.

Pre-grafted Group on PE Surface by DBD Plasma and Its Influence on the Oxygen Permeation with Coated SiOx.

In this paper, we report on polyethylene (PE) film modified by atmospheric dielectric barrier discharge (DBD) plasma prior to the deposition of SiOx coating to improve its barrier properties. Three kinds of monomers: allylamine, acrylic acid, and ethanol, are used to modify the PE surface. For comparison, Ar and O2 plasma pre-treatments are also performed. It is found that with the addition of a monomer in the Ar DBD plasma, the grafted active groups on PE surfaces lead to dense, pinhole-free growth of the SiOx film. The oxygen transmission rate (OTR) decreases from 700 cc/m²·day·atm. for the pristine to ca. 70 cc/m²·day·atm. for the pretreatment-coated PE, which is more than a 10-fold reduction. The relationship between the grafted monomer and the great decrease of OTR is then explored via chemical composition by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and via morphology observation by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The results show that the grafted functional groups of -NH2, -COOH and -OH increase the surface energy and promote the nucleation of Si⁻O radicals on polymeric surfaces, and the formation of network and cage structures in SiOx film contributes to the significant improvement of OTR.

Inactivation of Escherichia coli and Staphylococcus aureus on contaminated perilla leaves by Dielectric Barrier Discharge (DBD) plasma treatment.

This study focused on sterilization methods for the reduction of microorganisms on perilla leaves by cylinder type Dielectric Barrier Discharge (DBD) plasma with underwater bubbler treatment. S. aureus and E. coli in a suspension were reduced to less than 3.4 and 0.5 log CFU/ml after the plasma treatment for 3 min, respectively. On the perilla leaves, they were also reduced to 4.8 and 1.6 log CFU/ml after the plasma treatment, respectively. The S. aureus and E. coli bacterial cell wall was damaged by the plasma treatment evident by scanning electron microscopic analysis. The observed infrared bands of the FTIR spectra demonstrated changes in protein, lipid, polysaccharide, polyphosphate group and other carbohydrate functionalities of plasma treated bacteria and untreated bacterial cell membranes. The degradation of the constituent bonds of the bacterial cell membrane by RONS generated from plasma destroys the DNA, RNA, and proteins within the cell, and may eventually cause cell death. In this study, H2O2 (13.68 µM) and NO3 (138 µM), which are the main factors generated by plasma, proved to have a bactericidal effect by inducing lipid peroxidation of bacterial cell membranes. In conclusion, cylinder type DBD plasma with underwater bubbler can be used as an environmentally friendly food disinfection device in cleaning processes of the food industry.

Microbubble-enhanced dielectric barrier discharge pretreatment of microcrystalline cellulose.

Cellulose recalcitrance is one of the major barriers in converting renewable biomass to biofuels or useful chemicals. A pretreatment reactor that forms a dielectric barrier discharge plasma at the gas-liquid interface of the microbubbles has been developed and tested to pretreat α-cellulose. Modulation of the plasma discharge provided control over the mixture of species generated, and the reactive oxygen species (mainly ozone) were found to be more effective in breaking-up the cellulose structure compared to that of the reactive nitrogen species. The effectiveness of pretreatment under different conditions was determined by measuring both the solubility of treated samples in sodium hydroxide and conversion of cellulose to glucose via enzymatic hydrolysis. Solutions pretreated under pH 3 buffer solutions achieved the best result raising the solubility from 17% to 70% and improving the glucose conversion from 24% to 51%. Under the best conditions, plasma-microbubble treatment caused pronounced crevices on the cellulose surface enhancing access to the reactive species for further breakdown of the structure and to enzymes for saccharification.

Production of ammonia from plasma-catalytic decomposition of urea: Effects of carrier gas composition.

Effects of carrier gas composition (N2/air) on NH3 production, energy efficiency regarding NH3 production and byproducts formation from plasma-catalytic decomposition of urea were systematically investigated using an Al2O3-packed dielectric barrier discharge (DBD) reactor at room temperature. Results show that the presence of O2 in the carrier gas accelerates the conversion of urea but leads to less generation of NH3. The final yield of NH3 in the gas phase decreased from 70.5%, 78.7%, 66.6% and 67.2% to 54.1%, 51.7%, 49.6% and 53.4% for applied voltages of 17, 19, 21 and 23kV, respectively when air was used as the carrier gas instead of N2. From the viewpoint of energy savings, however, air carrier gas is better than N2 due to reduced energy consumption and increased energy efficiency for decomposition of a fixed amount of urea. Carrier gas composition has little influence on the major decomposition pathways of urea under the synergetic effects of plasma and Al2O3 catalyst to give NH3 and CO2 as the main products. Compared to a small amount of N2O formed with N2 as the carrier gas, however, more byproducts including N2O and NO2 in the gas phase and NH4NO3 in solid deposits were produced with air as the carrier gas, probably due to the unproductive consumption of NH3, the possible intermediate HNCO and even urea by the abundant active oxygen species and nitrogen oxides generated in air-DBD plasma.

Modification of Catalyst Surface from Interaction Between Catalysts and Dielectric Barrier Discharge Plasma.

This paper describes modification of catalyst surface from interaction between catalysts and dielectric barrier discharge (DBD) plasma. Ru/γ­Al2O3 catalyst was exposed to DBD plasma for CO2 methanation and CH4 direct conversion reactions. Parameters related to the modification of catalyst surface were investigated by SEM and EDS analysis.

Effects of high voltage nanosecond pulsed plasma and micro DBD plasma on seed germination, growth development and physiological activities in spinach.

In this study, we analyzed seed germination, seedling growth, and physiological aspects after treatment with high voltage nanosecond pulsed plasma and micro DBD plasma in spinach (Spinacia oleracea L.), a green leafy vegetable known to have low germination rate. Both germination and dry weight of seedlings increased after high voltage pulse shots were applied to spinach seeds. However seeds treated with many shots (10 shots) showed a decrease in germination rate and seedling growth. Seeds treated with air DBD plasma exhibited slightly higher germination and subsequent seedling growth than those treated with N2 plasma. Seed surface was degenerated after treated with high voltage pulsed plasma and micro DBD plasma but no significant difference in the degree of degeneration was observed among micro DBD plasma treatment time. Level of GA3 hormone and mRNA expression of an amylolytic enzyme-related gene in seeds were elevated 1 day after treatment with high voltage pulsed plasma. The relative amount of chlorophyll and total polyphenols in spinach seedlings grown from seeds treated with air DBD plasma was increased in 30 s, 1 min, and 3 min treatments. Taken together, our results suggest a possibility that plasma can enhance seed germination by triggering biochemical processes in seeds.

Development of wastewater treatment system based on cascade dielectric barrier discharge plasma atomizers.

A novel design for a cascade dielectric barrier discharge (DBD) atomizer was applied for treating samples of water containing biological and organic contaminants. Several experimental investigations were conducted on artificial samples and real sample (digested sludge collected from a wastewater treatment plant, WWTP). The artificial water samples were prepared by using different concentrations of E. coli for biological samples, whereas acetic acid was used to prepare the organic samples. The biological samples were subjected to the plasma effect for different treatment periods, and the growth curves of E. coli were generated for 24 h after treatment. Moreover, the viable cells were counted after each treatment period and the change in E. coli morphology was monitored. The results showed that a significant reduction in the viable cell number, by 3 orders of magnitude, occurred for an artificial biological sample after only 5-min treatment. The treatment of organic samples for 10 min showed a significant reduction in the concentration of acetic acid by 50%. In consequence, treatment of real wastewater sample for 10 min resulted in more than 70% reduction in BOD5 and 30% reduction in COD.

Synergistic Effects of Combined Flavourzyme and Floating Electrode-Dielectric Barrier Discharge Plasma on Reduction of Escherichia coli Biofilms in Squid (Todarodes pacificus).

This study investigated the synergistic effect of combining flavourzyme, a natural enzyme, and floating electrode-dielectric barrier discharge (FE-DBD) plasma (1.1 kV, 43 kHz, N2 1.5 m/s) treatment, a non-thermal decontamination technology, against Escherichia coli biofilms in squid. E. coli (ATCC 35150 and ATCC 14301) biofilms were formed on the surface of squid and treated with different minimum inhibitory concentrations (MICs) of flavourzyme (1/8; 31.25 µL/mL, 1/4; 62.5 µL/mL, 2/4; 125 µL/mL, and 3/4 MIC; 250 µL/mL) and FE-DBD plasma (5, 10, 30, and 60 min). Independently, flavourzyme and FE-DBD plasma treatment decreased by 0.26-1.71 and 0.19-1.03 log CFU/cm2, respectively. The most effective synergistic combination against E. coli biofilms was observed at 3/4 MIC flavourzyme + 60 min FE-DBD plasma exposure, resulting in a reduction of 1.55 log CFU/cm2. Furthermore, the combined treatment exhibited higher efficacy in E. coli biofilm inactivation in squid compared to individual treatments. The pH values of the synergistic combinations were not significantly different from those of the untreated samples. The outcomes indicate that the combined treatment with flavourzyme and FE-DBD plasma can effectively provide effective control of E. coli biofilms without causing pH changes in squid. Therefore, our study suggests a new microbial control method for microbial safety in the seafood industry.

Air disinfection by nanosecond pulsed DBD plasma.

Atmospheric pressure dielectric barrier discharge (DBD) plasma is an emerging and promising technique for air disinfection in public environments. Power supply is a crucial factor but it remains unclear about its impacts on the air disinfection performance of plasmas. In this work, a nanosecond (ns) pulsed power supply was applied to drive an in-duct grating-like DBD array to achieve fast single-pass air disinfection. The influence of pulse parameters and environmental factors on both the discharge characteristics and the single-pass bacterial inactivation efficiency were uncovered. At a close relative humidity (RH) level, the efficiency was dominated by the discharge power, namely, specific input energy could serve as the disinfection dose. A higher frequency, shorter pulse rising time, and suitable pulse width are preferred to obtain a higher Z value. The pulsed source was not notably superior to an alternating current source, or even worse at a low voltage frequency at the same discharge power. Airflow humidity was a predominant factor to improve the efficiency and a single-pass efficiency of ∼ 99% and a Z value of 2.2 L/J were achieved under an optimal RH of 50%-60%. This work provides fundamental knowledge of ns-pulsed DBD on discharge characteristics and air disinfection behaviors.