Plasma Chemistry and Plasma Processing最新文献

A co-axial packed-bed DBD reactor was used to conduct plasma-assisted non-oxidative coupling of methane (NOCM) utilizing glass beads as packing material at a fixed plasma power of 30 W. The influence on NOCM of five different bead size distributions (2000–5000 µm, 900–1100 µm, 425–600 µm, 212–300 µm, 150–212 µm) and operating pressure (1.2 bar, 1.7 bar) was investigated. The observed products consist of a mixture of saturated and unsaturated C₂–C₅ hydrocarbons. The conversion of methane decreased from 8.5 to 3.7% with decreasing bead size, while the selectivity towards unsaturated C₂ compounds increased from 16 to 50% with decreasing bead size. These reactor performance variations are associated with the transitional plasma dynamics and degree of partial discharging, as determined by characterization of non-ideal charge–voltage plots for the five tested glass bead sizes.

Oral cancer presents significant challenges with available treatment options; therefore, innovative treatment strategies are urgently needed. Nonthermal atmospheric pressure plasma (NAPP) is well known to be effective against various cancers. However, the effect and underlying mechanism of NAPP on YD-10B oral cancer cells are widely unknown. We have selected the oral cancer YD-10B cell line because the effect of NAPP on this particular cell line has not been investigated before. This study explored the therapeutic potential of NAPP via both direct and indirect NAPP treatments and their underlying mechanism on YD-10B cells for the first time. The viability of the oral normal HGF cells remained unchanged while significantly decreased in YD-10B cells using direct and indirect NAPP treatments. Direct treatment significantly increased intracellular reactive oxygen and nitrogen species (ROS/RNS), while indirect treatment mainly elevated RNS levels, with a modest but significant ROS increase in the NO-PAW15. The DNA damage and apoptosis markers are significantly upregulated in both direct and indirect treatments in YD-10B cells, though the expression levels are different. The western blot analysis confirms that both NAPP treatments (direct/indirect) are effectively inducing apoptosis in YD-10B cells. Furthermore, the utilization of N-Acetyl Cysteine and cPTIO as inhibitors confirms that the ROS/RNS are mainly responsible for inducing DNA damage and promoting apoptosis. Interestingly, both NAPP treatments are effective and follow the same molecular pathways to induce apoptosis. This study presents a promising avenue for the development of novel and targeted oral cancer treatments, with molecular insights providing valuable guidance for future investigations in the field.

Using the Langmuir probe method, the spatial distributions of plasma parameters (plasma potential, electron number density and mean electron energy) in a discharge supported by a rectangular hollow cathode in helium at reduced pressure were studied. Measurements were carried out both inside the geometric aperture between the cathode and the anode, and outside it, including the region behind the anode. In the experiments, different anode designs were used: a rectangular metal grid and a grid with an adjacent solid metal or dielectric plate. It is shown that there is a noticeable number density of electrons in the region behind the anode, and the highest is observed in the case of a grid anode. Using the electric field component E_x(х), measured along the central axis X of the discharge gap for the case of grid anode, electron number density profile N_e(x) was calculated within the 1D Monte Carlo model. In the cathode-anode gap, the calculation results agree satisfactorily with the experimental data, but behind the anode, they are significantly lower than those measured. This difference is explained by the fact that under experimental conditions some of the electrons enter this region not by flying through the grid anode, but by flying around it.

Biomass gasification is a renewable technology for energy storage and hydrogen production. As a model example, in an earlier paper by Hirka et al. Plasma Chem. Plasma Process. (2017) 37:947–965, the gasification process of crushed wood was numerically modelled for three different mean diameters of the feed particles in a reactor using a water and argon generated DC-plasma torch at a current of 400 A and compared with experimental data of the composition at the reactor outlet. Good agreement with experiment was obtained, however, a more extensive parametric study is desirable for more general conclusions and optimization of operating conditions, which is the subject of this paper. Here, currents of 400, 500, and 600 A and multiple mean particle diameters ranging from 0.2 to 20 mm were studied. The resulting parameters were averaged over a sufficiently long iterative process. The resulting characteristics include temperature, velocity, current field distributions, molar fraction of synthesis gas, as well as discrete phase and particle trajectories. With increasing diameter from about 1 mm, the produced synthesis gas becomes concentrated in the center of the reactor chamber. The numerical model has been created using ANSYS Fluent software.

The plasma treatment of micro-droplets significantly enhances the reactivity transfer of gas phase species into the liquid phase and enables more efficient conversion of chemical compounds. While OH fluxes to the droplet have been obtained using gas phase density measurements, the determination of these fluxes involved assumptions. In this work, the H₂O₂ production and OH flux to the droplet have been quantified using a combined approach of liquid phase measurement and 1D reaction-diffusion modeling. It was found that H₂O₂ is majorly produced in the gas phase. To quantify the OH flux, four compounds (formate, ascorbic acid, ferrocyanide, caffeine) that readily react with OH were treated at varying initial concentrations. Two transport limited trends were observed: (1) solute diffusion limited conversion for lower initial concentrations, and (2) gas phase species flux limited conversion for higher initial concentrations. The latter limit allows for the OH flux determination. Furthermore, it was found that competing reactive chemistry in the liquid phase, as in the cases of ferrocyanide and caffeine, can result in reaction limited conversion and skew the OH flux quantification. The OH flux derived from the formate and ascorbic acid measurements showed excellent agreement with previous OH gas phase measurements and are recommended to be used for OH flux measurements in plasma-liquid setups for which the liquid phase chemistry is not dominated by other oxidizing species such as ozone.

This study investigates the electrical and chemical characteristics of a non-thermal atmospheric pressure DC plasma discharge in a needle-to-liquid configuration. A high-voltage (HV) needle is placed at 2 mm above the liquid surface, while the ground electrode is submerged in a potassium halide solution (potassium iodide (KI) or potassium chloride (KCl)). The reactive species in the liquid are estimated based on their reaction with KI, producing iodine (I₂), either through direct titration of the plasma-treated KI or back titration of the plasma-treated KCl. Different discharge regimes are identified for each polarity: Trichel corona, unstable glow, and stable glow for negative polarity, and onset streamer, Hermstein glow corona, unstable glow, and stable glow for positive polarity. The presence of a liquid surface allows for higher voltage and current ranges without sparking and facilitates the establishment of a stable glow discharge, which is challenging in the case of a needle-to-plate configuration. The concentration of reactive species in the liquid is significantly lower in corona regimes compared to glow regimes, due to their lower power consumption, and the absence of direct contact between the plasma and the liquid. Moreover, the positive unstable glow is three times more efficient than the negative stable glow. One explanation is that the flow induced within the liquid during the positive unstable glow discharge enhances mixing of reactive species, preventing their saturation at the gas-liquid interface and improving their penetration into the liquid phase.

Hydrocarbon chains produced as byproduct of natural gas extraction and petrochemical processing can be valorised into syngas/H₂ and oxygenated fuels in a modular fashion through electrified modular plasma reactors. A plethora of configurations is available for light hydrocarbons reforming, with cold plasma assemblies emerging as the favourite option for both gas-phase and biphasic gas/liquid set-ups. Accurate control of dehydrogenation or partial oxidation reactions is provided by the implementation of a catalyst or through microreactor technology. On the contrary, warm plasma reactors are more suitable for reforming of gasoline/diesel chains, promoting higher throughput of H₂ per energy input. This reaction route does not necessarily require the deployment of a catalyst, hence making these systems more suitable for modular, decentralized processes. Online diagnostic techniques shed light on the reaction mechanism, where solid carbon deposits embody a low-value byproduct.

The reactive oxygen and nitrogen species generated by plasma have demonstrated consequential effects on diverse commercial applications. Hence, studying the chemistry and spatial distribution of reactive species in plasma is imperative for understanding the influence of plasma in various applications. This study aims to systematically explore the plasma chemistry of a pin-to-plate negative direct current (DC) corona discharge in dry air, using simulations based on a two dimensional (2D) axisymmetric fluid model. The model encompasses a comprehensive set of chemical reactions involving 33 biomedically active species (ROS and RNS). This study entails a rigorous evaluation of the 2D spatial distribution of all chemical species, detailing their minimum and maximum values, at a needle voltage of −10 kV. To enhance visualization and enable comparisons, we integrate contour lines into the density distributions to indicate the average density of each species. ({text{N}}_{2}left({text{A}}^{3}sumright)) among nitrogen species, O₃ and ({text{O}}_{2}left({text{a}}^{1}Deltaright)) among oxygen species, and N₂O among NOx species exhibit the highest average density in the simulation domain. Furthermore, key reactions involved in the production and consumption of each species are thoroughly discussed. Additionally, the research examines the influence of needle voltage, ranging from −5 to −12.5 kV, on the peak and average densities of all species investigated. Lastly, to validate the simulation model, an experimental study of the pin-to-plate negative DC corona discharge is conducted, during which the voltage-current characteristics and optical emission spectrometry (OES) profiles are measured. The simulation results are in good agreement with the experimental data.

This study focuses on tuning the metal content in a polymer/metal composite produced by a low-pressure cold plasma process using an organometallic precursor. Firstly, the evolution of the metal content is studied according to the experimental parameters. Monomer fragmentation and the balance between ablation and polymerization influence the metal content in the composite. In addition, physical sputtering through argon plasma treatment of the composite can be used to significantly increase its metal content. Finally, the ageing of the composite is studied. Both the inorganic and organic parts of the material are affected by oxidation. A comparison of the composite ageing with a purely organic polymer highlights the effect of copper on oxidation.