Plasma Chemistry and Plasma Processing最新文献

The disruption of the volumetric balance of water and oxygen molecules in a low-pressure DC glow discharge in mixtures of helium with water vapor and oxygen in a quartz discharge tube was studied experimentally and theoretically. The concentrations of H₂O and O₂ molecules were measured synchronously by absorption in the spectral regions of about 760 and 1390 nm in a two-channel diode laser spectrometer. The dependences of concentrations on time were studied in a cycle with duration of about 200 s. The cycle included a stage of filling a tube treated according to a set procedure with a plasma-forming gas, a stage of burning a 35 mA DC discharge, and a stage after switching off the discharge. It was found that a significant increase in the H₂O concentration only occurs during the discharge and in the presence of oxygen additives. To describe the observed dynamics of molecule concentrations, a plasma-chemical 0D model was created, which included reactions both in the volume and on the wall of the discharge tube, the Boltzmann equation for electron energies, and the equation of an external electric circuit. The presence of the ballast volume of the vacuum system and the heating of the neutral gas were taken into account. The observed misbalance is proposed to be associated with the heterogeneous reaction of oxygen atoms O(³P), produced in the gas-discharge plasma, with water molecules adsorbed on the tube wall. The estimated probability of this reaction is 5 10⁻⁶.

Plasma-activated water (PAW) is an innovative, eco-friendly technology that offers significant potential as a disinfectant in the food processing. Plasma-activated water is produced by subjecting water to cold plasma containing reactive species. This renders numerous microbes, including bacteria, viruses, and fungi, inactive by breaking their cell membranes and DNA, thereby imparting antibacterial characteristics. PAW is highly effective in reducing microbial load on the surfaces of diverse food items, including vegetables, fruits, cereals, meat, fish, shellfish, and dairy products. In contrast to traditional thermal disinfection methods, PAW is a nonthermal approach that improves food safety while preserving product quality. The interaction of plasma with water endows it with exceptional chemical characteristics that confer microbicidal activity. The work elucidates the mechanisms of antibacterial action by PAW, primarily through the production of oxidative and physical stress in bacterial cells. Empirical research substantiates PAW’s efficacy in surface decontamination of food products across several categories and in promoting seed germination and plant growth. The purpose of the review is to examine the impact of PAW on food processing, food safety, and food quality. The review encompassed the impact of Plasma Activated Water on the disinfection of fruits and vegetables. It examines the antibacterial mechanisms of PAW and the chemical decontamination processes utilising PAW. The impact of PAW on biochemical properties, vitamins, antioxidants, proteins, enzymes, carbohydrates, lipids, and sensory attributes is analyzed.

The discharge characteristics of low-pressure dual-frequency capacitively coupled argon plasma are investigated through a self-consistent integration of a collisional-radiative model (CRM) and a nonlinear global model. The CRM incorporates 18 excited energy levels, and the electron temperature ((:{text{T}}_{text{e}})) and electron density ((:{text{n}}_{text{e}})) are determined across a pressure range of 20–70 mTorr by calibrating the emission intensities of the 750.4 nm and 696.5 nm spectral lines. To examine impedance-related effects, an L–π type matching network is experimentally designed and incorporated into the system. The computed values of (:{text{T}}_{text{e}}:)and (:{text{n}}_{text{e}}) are then used as input parameters for the global model to analyze plasma current characteristics, including low- and high-frequency electron current components, and the corresponding plasma resistance and inductance, under fixed RF powers of 60 W at 13.56 MHz and 40.68 MHz, respectively, with varying chamber pressures. Fast Fourier Transform (FFT) analysis of the plasma current reveals distinct harmonic features, with pronounced peaks observed not only at the fundamental harmonic, but also at the 2nd, 4th, and 5th harmonic orders. These features are primarily attributed to nonlinear interactions between the plasma sheath and bulk regions, as well as impedance modulation introduced by the matching network. Furthermore, the harmonic structure is closely linked to electron-impact excitation processes between the 1s and 2p levels of argon and their associated reaction rate coefficients. This study establishes a comprehensive coupled modeling framework that connects microscopic excitation dynamics with macroscopic electrical behavior in dual-frequency plasmas, providing theoretical insights into nonlinear discharge mechanisms and valuable guidance for optimizing matching network design.

The conventional Haber-Bosch process for ammonia (NH₃) production is energy-intensive and environmentally unsustainable, driving the search for green alternatives. This study presents a novel plasma-electrocatalytic synthesis ammonia (PESA) strategy that integrates magnetically stabilized glow discharge (MSGD) plasma for NO_x⁻ generation from air with electrochemical NO_x⁻ reduction reaction (eNO_xRR) using Co₃O₄ catalysts to produce NH₃ under ambient conditions. The MSGD system achieves efficient nitrogen fixation with an energy consumption of 2.44 MJ/mol NO_x⁻ by leveraging vibrational N₂ excitation and ozone-enhanced gas-liquid conversion (96% efficiency). The Co₃O₄ electrocatalyst exhibits high activity (ECSA: 281.7 cm²/mg) and stability, enabling NH₃ production at 11.99 mg/h·cm² with 78% Faradaic efficiency and 1.76 MJ/mol energy cost. The combined PESA system thus demonstrates an overall energy cost of just 4.2 MJ/mol for NH₃ synthesis from air and water, outperforming many existing plasma and electrochemical methods. This study offers a scalable and sustainable pathway for green ammonia production under ambient conditions.

Plasma catalysis is promising for greenhouse gas conversion into value-added chemicals, yet this technology is still poorly understood due to the complexity of the underlying mechanisms. Therefore, we study the chemical kinetic effects of the interaction between plasma species and glass or transition metal (Ag, Cu, Pd and Rh) surfaces placed in the afterglow of a low-pressure CO₂ plasma. We developed a coupled plasma-surface model to study how different catalyst surfaces and reaction conditions (i.e., temperature, pressure and flow rate) affect the spatial evolution of the O₂ and CO mole fractions for plasma-catalytic CO₂ splitting. Moreover, we used density functional theory (DFT) to determine the reaction barriers on the metal surfaces and used these as input for our kinetic model. Although our model could not yet be validated against experimental data, it can provide qualitative trends, insights and comparisons on the influence of the different catalysts and reactions conditions. Firstly, our results indicate that Eley-Rideal (E-R), or more correctly Langmuir-Rideal (L-R), reactions play an essential role in the recombination of O atoms into O₂. Secondly, we find that the optimal catalyst depends strongly on the reactions conditions. For example, Cu performs very well at low and intermediate temperatures (500–1000 K) for which Ag performs poorly, while Ag yields the highest maximum O₂ fractions at higher temperatures (> 1000 K), and thus the least recombination between O and CO back to CO₂. Pd was found to be detrimental to CO₂ splitting, as it catalyzes the oxidation of CO, while Rh is relatively inactive for both O₂ formation and thermal catalytic CO oxidation under most conditions. Thus, the optimal catalyst depends both on its activity for O atom recombination into O₂, as well as for thermal catalytic CO oxidation to form CO₂. Moreover, if the catalyst is active for thermal catalytic CO oxidation, this back-reaction should be avoided by optimizing the flow rate or the length of the catalytic bed. Hence, this study illustrates how trends between different catalysts for plasma catalysis can change depending on the reaction conditions, which is important to consider when comparing different catalysts experimentally.

The combustion of carbon-free fuels, such as hydrogen-ammonia blends - promising candidates for long-haul transportation, can result in elevated nitrogen oxides (NO_x) emissions. Dielectric barrier discharge (DBD) plasma reactors offer a compelling non-thermal and non-catalytic approach for dynamic NO_x abatement. In this study, we evaluated the performance of conventional DBD and membrane DBD (mDBD) reactor configurations for the direct decomposition of NO_x. Our results demonstrated that both systems can achieve over 90% NO_x reduction at high plasma power. Notably, under lower power conditions and high flow rates, the mDBD configuration achieves up to 15% higher NO_x reduction compared to the conventional DBD. Species-resolved analysis indicates preferential removal of NO₂ in both configurations, while NO abatement is limited by NO₂ back-reactions that regenerate NO. The improved performance of mDBD under low-power high flow rate conditions is attributed to enhanced micro-discharge activity, driven by radial gas flow that disrupts charge accumulation on the membrane surface, and extended gas residence time in the plasma zone, which increases the likelihood of reduction reactions. These findings highlight the advantages of integrating porous dielectrics into DBD reactors and underscore the need for future research to reduce energy consumption and evaluate membrane durability for practical, real-world plasma-assisted NO_x abatement.

Plasma technology has emerged as a promising approach for regulating grain seed germination, offering dual effects of promotion and inhibition depending on treatment parameters. This review synthesizes mechanisms by which cold plasma (CP) and plasma-activated water (PAW) influence seed physiology. Reactive oxygen and nitrogen species (RONS) generated during plasma treatment modify seed coat hydrophilicity through etching, enhance water uptake, and alter metabolic pathways. Moderate RONS levels stimulate antioxidant systems, hormone balance (e.g., GA/ABA ratio), and enzyme activities (e.g., amylase, superoxide dismutase), accelerating germination. Conversely, excessive RONS induce oxidative damage, inhibit enzyme function, and impair DNA/protein integrity. PAW, enriched with nitrate, nitrite, and H₂O₂, further enhances germination by improving nutrient absorption and microbial decontamination. Notably, plasma efficacy varies with seed type, treatment duration, voltage, and gas composition. Short-term, low-dose CP promotes germination in crops like maize, wheat, and rice, while prolonged exposure or high-intensity treatment suppresses it. CP also mitigates abiotic stresses (e.g., drought, salinity) by enhancing stress-responsive pathways. Despite advantages such as residue-free processing and scalability, challenges persist, including equipment costs, inconsistent treatment efficacy, and unresolved safety concerns regarding long-term environmental and health impacts. Future research should prioritize elucidating molecular interactions, optimizing protocols for diverse crops, and advancing scalable plasma systems. With further refinement, plasma technology holds significant potential to revolutionize sustainable agriculture by improving seed storage, stress resilience, and crop productivity.

Film cooling shows significant potential for mitigating the “blackout” effect caused by plasma sheaths. In this paper, the influence of cooling gas film on the key characteristic parameters (electron density and collision frequency) and electromagnetic transmission characteristics of the plasma sheath are studied by controlling the shoulder of the aircraft to spray cooling gas to simulate energy injection and absorption. The results show that under hypersonic flow conditions, the electron density increases due to the dissociation of the counterflow jet medium and diffuses downstream over the vehicle body. The cooling gas film can be formed on the target wall by spraying CO₂ and N₂ through the shoulder, the electron density and plasma frequency on the wall decreases. Notably, the plasma collision frequency increases to varying degrees due to the dissociation of the injected particles. Under N₂/CO₂ film cooling, the Maximum attenuation intensity of electromagnetic wave is reduced by 15dB, the resonant frequency of electromagnetic wave and plasma sheath is increased. This study provides valuable insights for designing physical and chemical interventions to regulate the spatial distribution of plasma and the research of anti-black barrier communication.

AlN plasma emission behavior in argon atmosphere has been investigated by infrared nanosecond laser using optical emission spectroscopy (OES) diagnostics. The effect of argon pressure on the time–space evolution of the plasma composition, as well as the dependence of electron number density, has been studied. To investigate the impact of the ambient gas nature on the temporal behavior of plasma species, we performed space and time resolved emission spectroscopy. Time of flight (TOF) measurements of neutral and ionized Al, N, and Ar species revealed the presence of double and triple structure, depending on the ambient gas nature. In an argon atmosphere, slower components of Al and N exhibited backward motion. The faster Al⁺ component unaffected by the surrounding gas and followed a propagation profile like that observed in vacuum. The kinetics of all plasma species were investigated.

This paper aims to advance the achievement of industrial-scale efficient thermal decomposition of pulverized coal into acetylene utilizing arc plasma. A comprehensive physical model, incorporating detailed reaction mechanisms, has been constructed to elucidate the multi-field coupled interaction mechanism between coal particles and hydrogen plasma jets, alongside the millisecond-scale pyrolysis process. The core functionality of this model lies in elucidating the regulatory mechanisms through which distinct high-temperature zones within the reactor govern the elementary reactions pertaining to acetylene and tar. Building upon this, it further proposes a flow mixing optimization strategy: enhancing the contact area and duration between the > 2500 K region and pulverized coal. Additionally, the model clarifies the synergistic effects of the spatiotemporal characteristics of particle devolatilization in the main flow and near-wall regions under the tangential circular mixing regime on energy efficiency. Furthermore, by optimizing reactor structural parameters such as diameter, energy efficiency can be elevated to approximately 16%. This model establishes a robust framework for numerical simulations of future industrial-scale thermal plasma coal pyrolysis systems and offers pragmatic guidance for the industrialization of this technology.