Plasma Chemistry and Plasma Processing最新文献

Plasma nitrogen fixation technology is of great significance in solving the problem of nitrogen fertilizer resource shortage, saving energy and reducing carbon emission, promoting sustainable development of agriculture and promoting resource recycling. To enhance the efficiency and treatment capacity of the two-dimensional, blade-type gliding arc nitrogen fixation reaction, a dielectric-boosted gliding arc discharge reactor with a 50-mm-diameter quartz dielectric (DBGAD_Φ50) was used to conduct N₂ fixation into NO_x. The impact of reactor parameters and gas parameters on the nitrogen fixation reaction was systematically investigated in this study. The findings revealed that the DBGAD_Φ50 significantly improved the nitrogen fixation effect. At a specific input energy of 2.7 kJ/L, the concentration of NO_x generated by the dielectric-boosted gliding arc air discharge was 1.12 times that of the conventional gliding arc discharge (GAD). By utilizing the DBGAD_Φ50 reactor, the energy efficiency of 6.83 g/kW h was achieved at a gas flow rate of 5.6 L/min. Appropriately increasing O₂ concentration favors the production of NO_x. In the DBGAD_Φ50, the NO_x concentration was 1.33 times higher than that in the air atmosphere when the added O₂ volume fraction reached 30%. Performance can be further enhanced by adding TiO₂ catalyst particles to the surface of the quartz dielectric to form a catalyst layer approximately 5 mm thick. At an O₂ concentration of 30%, the DBGAD_Φ50 reactor loaded with TiO₂ increased NO_x concentration by 26% and energy efficiency by 49%, respectively, resulting in an efficiency of 14.9 g/kW h compared to the case without catalyst.

The present study demonstrates the successful production of alkaline plasma-activated tap water (PATW), effectively addressing the challenge of acidity in traditional PATW for a range of applications. Through precise control of plasma-forming gases (oxygen, air, argon) and process parameters, particularly by producing PATW under sub-atmospheric pressure conditions, it becomes possible to shift the pH of acidic PATW towards the alkaline range. This transformation enhances its suitability for applications like agriculture, aquaculture, sterilization, wound healing, disinfection, and food preservation, etc.

The investigation encompassed the characterization of plasma and the identification of various plasma species/radicals. The impact of different plasma-forming gases on the pH of PATW and the concentration of reactive species in PATW was thoroughly analyzed. Plasma generated using oxygen and argon resulted in the production of reducing or alkaline PATW, while the use of air and air-argon mixtures led to an acidic or oxidizing nature.

The study also discussed the stability of nitrate ions, nitrite ions, and hydrogen peroxide in PATW, shedding light on their behavior over varying plasma treatment times and plasma-forming gas. Finally, the investigation explored the effects of gas flow rates, gas pressures, water volume, and plasma discharge powers on the concentration of H₂O₂ in PATW, providing valuable insights into optimizing the production process.

The great advantage of plasma technology in harnessing abundant clean energy for electrifying and decentralizing the chemical industry holds the promise of attaining carbon neutrality. Therefore, recent research efforts have been dedicated to reducing the energy costs of plasma processes to facilitate the commercialization of this technology. However, it has been noted an inconsistency in reporting energy costs across the literature resulted from inaccurate estimation of power consumption within the system, leading to the misevaluation of the process, its underlying mechanism, and the significance of critical factors. This study comprehensively addresses these challenges by discussing and refining methods for estimating power consumption in a plasma system. Insights are drawn from our ongoing research in plasma NO_x synthesis, specifically a thorough analysis of the discharge dynamics in a recently developed reactor “high-frequency spark discharge” using a high-speed camera, ICCD camera, and high-performance oscilloscope at various pulse widths of the applied voltage. The investigation revealed the importance of accounting for the post-spark period in the voltage cycle during power estimation, as it demonstrates an influence on NO_x synthesis. Furthermore, the study highlighted and addressed critical errors in power measurement and energy cost estimation in the literature. It is found that a significant error, exceeding ± 70%, arises from overlooking signals delay in the setup and improper adjustment of oscilloscope functions, particularly channel impedance, data averaging, bandwidth, and sampling rate. This paper serves as a valuable guide towards establishing standardized measurements toward the precise estimation of energy costs in plasma processes.

The process of texturing silicon surfaces is critical for enhancing the performance of complementary metal–oxide–semiconductor image sensors that utilize silicon-based photodetectors. Traditional wet etching methods using strong acids or alkaline solutions have been commonly used but present challenges in precision, particularly for microscopic devices. As a viable alternative, dry etching processes using patterned metals and plasma are being explored. However, extensive studies across various metals are necessary. This study introduces a silicon nanotexturing process using silver nanowires and Cl₂-based plasma. The etching mechanism involves accelerated etching through eddy currents and hole injection coupled with a diffusion phenomenon of silver. In this study, we examined variations in the etching profile with respect to etching time, upper and bottom radio-frequency powers, and process pressure. Additionally, we analyzed the effects of ion bombardment, enhanced by the introduction of Ar gas. The findings are expected to significantly contribute to the improvement of micro-optoelectronic devices.

Pulsed underwater direct current discharge is considered as a tool for a one-step process for ferrite synthesis and organic dye removal. The formation of cobalt, nickel and titanium ferrites during the discharge firing process was confirmed by methods of dynamic light scattering and X-ray phase analysis. The transformation of dye molecules (fluorescein, methylene green) during the combined action of plasma and ferrites was detected by UV absorption spectroscopy. The contributions of the separate action of plasma and ferrites to the process of dye removal from the solution were investigated. It was found that the synthesized structures have a high sorption capacity. It was found that fluorescein can be used as an indicator for the presence of nickel ferrites.

Plasma-based water treatment (PWT) is a promising technology that can degrade various emerging contaminants. However, PWT application on an industrially viable scale is hindered by the lack of an efficient reactor design that combines enhanced plasma-liquid contact with high liquid throughput. This work investigates the applicability of a bubble column gas–liquid contactor to PWT. A pulsed plasma bubble column reactor with a concentric rod-cylinder electrode configuration was used to correlate contaminant removal performance with the gas–liquid contact parameters of the bubble column. A surfactant, rhodamine B dye, and a nonsurfactant, caffeine, were used as model contaminants at µM concentration levels. The bubble column characteristics, i.e., gas holdup, bubble size distribution, and gas–liquid area, were measured as a function of superficial gas velocity using image-based methods. Degradation rates of both contaminants increased with gas flowrate. For caffeine, the increase was attributed to intensified bulk liquid mixing, while dye degradation increased due to the increased gas–liquid area. Ultimately, we show that bubble column contactors significantly improve the utilization of plasma-generated reactive species toward contaminant degradation by distributing them over a large contact area. As a result, a better match between the plasma species interfacial flux and the interfacial contaminant concentration leads to improved treatment energy efficiency. Typical degradation energy efficiencies were ~ 10 g/kWh for caffeine and ~ 60 g/kWh for rhodamine B.

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.