Plasma Chemistry and Plasma Processing最新文献

The rise of water effluents containing emerging contaminants that resist conventional chemical and physical treatments makes the treatment of wastewater more complex. Plasma-based treatment methods have great potential to degrade many of the emerging contaminants, including dyes. In this study, using pulsed nanosecond discharges, we investigate the degradation of methylene blue (MB) dye in water by generating plasma in Ar-O₂ gas bubbles in water. The scalability of the setup is studied by producing discharges in a one electrode setup (a needle-to-plate configuration) and in a four electrodes setup (four needles-to-wire configuration). The discharge was characterized by electrical measurements (current and voltage waveforms) and optical emission spectroscopy. We find that the discharge properties are stable during the 30 min of processing, with and without the presence of MB in solution at low electrical conductivity. The production rate of H₂O₂ in the one electrode setup was measured in 0% and 70% O₂, and it was found to be ∼2.3 and 2.9 mg/Lmin, respectively. In the four electrodes setup, H₂O₂ production rate was lower: ∼1.2 and 1.9 mg/Lmin in 0% and 100% O₂. Degradation of MB was assessed in both setups for (i) different % of O₂ in the gas mixture, (ii) different MB initial concentration, and (iii) different initial water conductivity. In the one electrode setup, a high MB degradation (> 85%) was generally achieved in all conditions, but a better performance is noted in high O₂ percentage (> 50%) at low initial water conductivity. At low MB concentration and low electrical conductivity, the performance of the four electrodes setup was better than the one electrode setup.

Time-resolved optical emission and absorption spectroscopy was used to analyze a 50 kHz Ar-NH₃ dielectric barrier discharge operated in a homogeneous glow discharge regime at atmospheric pressure. In addition to the typical NH(A-X), N₂(C-B), and Ar(2p-1s) transitions, a continuum emission linked to de-excitation of ({{text{H}}}_{2}left({{text{a}}}^{3}{Sigma }_{{text{g}}}^{+}right)) states was detected between 180 and 250 nm and lasted for a long time after discharge extinction. Over the range of experimental conditions investigated, the emitting ({{text{H}}}_{2}left({{text{a}}}^{3}{Sigma }_{{text{g}}}^{+}right)) states are proposed to be populated by collisions of ({{text{H}}}_{2}left({{text{X}}}^{1}{Sigma }_{{text{g}}}^{+}right)) with Ar(1s) states during discharge, and by dissociative recombination of the vibrationally-excited ammonia ion (NH₃⁺(v)) after the discharge. NH₃⁺(v) is produced by charge transfer from Ar₂⁺ to NH₃, and it breaks into ({{text{H}}}_{2}left({{text{a}}}^{3}{Sigma }_{{text{g}}}^{+}right)) (or ({{text{H}}}_{2}left({{text{c}}}^{3}{Pi }_{u}right)) or ({{text{H}}}_{2}left({{text{d}}}^{3}{Pi }_{u}right))) and NH upon gas phase recombination with a low-energy electron. Based on this proposed mechanism, a 1D fluid model was refined to include these reactions and used to simulate the emission intensity from ({{text{H}}}_{2}left({{text{a}}}^{3}{Sigma }_{{text{g}}}^{+}right)) and revealed good agreement with experimental data.

In this work, the process of decomposition of 2,4-dichlorophenol (2,4-DCP) vapor under the influence of atmospheric pressure DBD in oxygen was studied. The studies were carried out in two modes: with a catalyst (natural vermiculite doped with zirconium) and without it. A number of basic characteristics of the catalyst were assessed. The rates and effective rate constants of sorption processes, as well as decomposition processes in plasma and plasma-catalytic systems, were determined. Based on these data, the energy efficiency of the decomposition process was calculated. The data obtained suggested that the initial stage of decomposition is the reaction of interaction of electrons with pollutant molecules. The catalyst has been shown to speed up the decomposition process, increase energy efficiency and the conversion of 2,4-DCP to CO₂ molecules, and prevent the formation of condensed products on the reactor walls. The work estimates the carbon and chlorine balances before and after treatment, which reach a maximum of 99 and 60%, respectively. It was also shown that the catalyst retains its activity for at least 7 h of continuous operation.

Abstract

Plasma-enhanced chemical vapor deposition is a well-developed technique that is commonly applied in the preparation of thin films. However, this technique is limited to thermodynamically stable and chemically inert precursor gases or vapors. Recently, pulsed aerosol-assisted plasma processes have emerged as an advantageous alternative that allows for the injection of various liquid solutions in the plasma, regardless of their properties. This study examines the production of thin films by pulsed injection of pentane aerosols into a low-pressure RF capacitively coupled plasma. This technique produces thin films with high material balance and a high degree of control by adjusting the pulsed injection parameters. At the pulse scale, pulsed injection induces a temporary increase in the working pressure, resulting in time-dependent mechanisms that can affect the dynamics of thin-film deposition at the process scale. Overall, the results show a key role of droplets and their kinetics (ballistic transport, vaporization kinetics, electrostatic confinement). Hence, to efficiently apply this method in the preparation of (multi-)functional coatings, the aerosol must be carefully characterized.

Abstract

In this work, we investigated the impacts of atmospheric pressure dielectric barrier discharge (DBD), i.e., plasma treatment, on pearl millet seeds germination and plant growth. The effect of plasma discharge on water activation, by introducing the reactive species, was explored. We evidenced that about 30 min plasma treated pearl millet seeds exhibited 20% higher germination rate than the control seed watered with tap water. The HR-SEM study revealed that the plasma treatment increased the roughness and FTIR study showed that new oxygen functional groups were introduced on the seed surface. Moreover, it was observed that the water contact angle decreased for plasma treated seeds (50%) and the water uptake also increased considerably as compared to control seeds. These findings indicate that the seed surface has turned more hydrophilic after plasma treatment. A cylindrical double dielectric barrier discharge (D-DBD) reactor was employed for water activation, and 30 min of treatment under air has decreased the pH of deionized water from 7.4 to 4.5 and produced about 1.78 ppm of nitrate (NO₃⁻) and 4.2 ppm of hydrogen peroxide (H₂O₂). Interestingly, the plasma activated water (PAW) improved the pearl millet seed germination by 30% (after 24 h of sowing) and plant growth as compared to tap water and deionized water. Remarkably, when PAW and plasma-treated seeds were combined, a beneficial impact in seed germination (95 ± 2%) and seedling growth have been evidenced owing to synergistic effect. We evidenced that among the long-lived species in PAW, NO₃⁻ enhanced the seed germination and plant growth under similar conditions. These findings demonstrate that the proposed cold plasma reactors could be utilized to boost seed germination and plant growth.Please confirm if the author names are presented accurately and in the correct sequence (given name, middle name/initial, family name). Author 4 Given name: [Amine Aymen] Last name [Assadi]. Also, kindly confirm the details in the metadata are correct.Yes, all author names are correctly editted. 

Normally, atmospheric air plasma is usually utilized to hydrophilize the substrate surface. In this paper, a facile and fast method is reported to prepare hierarchical superhydrophobic surface via atmospheric air dielectric barrier discharge (DBD) with sealed discharge zone. Siloxane monomers along with silica nanoparticles were used to construct micro-scale hierarchical morphology in gas phase. It is verified that the water repellency of sample could be regulated through adjusting volume and air humidity of discharge zone. The generated reactive oxygen species induced polymerization of long-chain alkyl silane and also caused the grafting of polar groups on substrate surface. Within 5 min, the long-chain alkyl silane coating could rapidly wrap silica nanoparticles layer-by-layer to form microspheres and hence the micro-scale hierarchical morphology. The discharge zone with appropriate sealing volume could balance the grafting amount of polar and nonpolar groups to optimize surface hydrophobicity. After repeating the plasma treatment three times, the sample possessed superhydrophobicity and excellent performance in water-in-oil emulsion separation. The study may offer an environment-friendly method to prepare water-repellent materials for industrial applications.

Atmospheric-pressure plasma processing (APPP) is an important method for the fabrication of high-precision optics because it involves highly efficient and nondamaging material removal based on its pure chemical etching mechanism. However, owing to the heat accumulation phenomenon caused by the jet heat flux, the nonlinearity of the material removal rate in APPP is inevitable, making it difficult to achieve deterministic optical surfacing. To bridge this gap, this study focused on analyzing the nonlinear relationship between the material removal rate and heat accumulation. The simulation results indicated that when the sliding distance increased from 10 to 50 mm, the surface temperature of the workpiece increased from 387.3 to 419.5 K, an increase of more than 8%. When the dwell time increased from 0.33 to 2 s, the surface temperature of the workpiece increased from 348.1 to 419.5 K (including the effect of sliding distance), an increase of more than 21%. A novel algorithm that simultaneously considers dwell time and sliding distance was proposed based on the results. A threshold parameter t_q was introduced to determine whether to correct the deviation caused by the sliding distance. With the proposed algorithm, the matching residual surface root-mean-square (RMS) error decreased from 97.5 to 39.6 nm. The RMS deviation error of the matching residual surface error converged from 11.6 to 4.7% after surface-figuring experiments. The proposed algorithm is expected to provide a promising solution for future deterministic optical surfacing.

In light of the adopted green policies and strategies, thermal plasmas are gaining interest as a potential solution to electrify the industry, particularly for endothermic processes, for their tunable enthalpy and the absence of direct CO₂ emissions. However, the majority of industrial applications of thermal plasma technologies are at atmospheric or lower pressure, whether for material processing, waste treatment, gasification, assisted combustion or in electric arc furnaces. Very little information exists on thermal plasmas at pressures above 1 bar, with the majority of academic publications using either analytical or numerical methodologies. The main experimental high-pressure plasma studies conducted date back to the 1960s, the 1970s and 1980s mainly in the US and the EU for aerospace applications, in addition to gas blast circuit breaker and underwater welding applications. However, these systems operate only for a few milliseconds to a few minutes at most. The interest in operating plasma systems at high-pressure is on one hand to reduce the volume of the facilities, and therefore, global costs, and on the other hand, is of practical necessity such as the case of underwater welding and in aerospace application where plasma technology plays a role in duplicating the conditions to which a vehicle is exposed to in atmospheric entry/reentry. This paper reports a thorough literature review on all high-pressure plasma arc studies available to date, including journal articles, books, and declassified reports. The findings of the studies are classified into four categories: DC and AC technologies, electrical characteristics, thermodynamics and heat transfer, and electrode erosion. The gaps and limitations are identified, and the main hypotheses are formulated, (re)opening the way for future high-pressure thermal plasma studies. Operating thermal plasma systems at high pressure could have considerable economic benefits, and thus, leading to competitive pricing for electrified high temperature processes, but faces many challenges.

Abstract

The activation of water by the atmospheric pressure air plasma is involved in the diffusion of reactive oxygen and nitrogen species (RONS) in air and water, their gas-phase and liquid-phase reactions, and their dissolution and evaporation. In this study, by generating the air spark discharge over the surface of water, we have evaluated the chemical and biological reactivities of direct–plasma treatment (DPT) and remote–plasma treatment (RPT) plasma-activated water (PAW) at different water temperatures. We have found that DPT-PAW is much more effective in increasing both the chemical and biological reactivities of PAW than RPT-PAW, and decreasing the water temperature from 40 to 6 °C leads to the rapid activation of water. Our analysis shows that when the water temperature varies from 6 to 40 °C, the activation of water by the air discharge is RONS solubility controlled, and the gas-phase and liquid-phase RONS diffusion and chemical reactions are not the controlling steps during the activation of water. The direct plasma treatment of water at a relatively low temperature contributes to an obvious increase in the RONS solubility, thus a rapid activation of DPT-PAW.