Plasma Chemistry and Plasma Processing最新文献

Stainless steel is one of the most essential materials in daily life due to its corrosion-resistant properties. One of the vital metal components in stainless steel is chromium, which forms a protective layer on the surface of stainless steel when exposed to air. The chromium used in stainless steel production typically comes from ferrochrome, produced through chromite ore's carbothermic reduction. This production process results in CO₂ emissions of 5.4 tCO₂-eq/t ferrochrome. Hydrogen plasma smelting reduction (HPSR) has emerged as a critical area of contemporary research and development to achieve more sustainable metal production. Here, we show that HPSR can produce ferrochrome containing 50% chromium from chromite ore within 6 min. The ferrochrome produced contains no carbon, which means that no AOD (argon oxygen decarburization) converter nor VOD (vacuum oxygen decarburization) is required for stainless steel manufacturing, which leads to a shorter process route and more sustainable stainless steelmaking.

In this study, we explore, for the first time, the use of a new pyridine-covalent triazine framework (py-CTF), containing both nitrogen and oxygen, as a metal-free catalyst in a post-plasma catalytic (PPC) system for abatement of toluene, a common volatile organic compound (VOC). The PPC system was evaluated under varying specific energy densities (SEDs) from 100 to 400 J/L and catalyst temperatures ranging from room temperature to 200 °C. Our findings reveal that combining py-CTF with non-thermal plasma significantly enhanced toluene removal efficiency compared to both plasma alone and catalyst alone systems. A remarkable toluene removal efficiency of 97.2% and CO_x (CO + CO₂) selectivity of 67.1% were achieved in the PPC system at an optimal catalyst temperature of 150 °C and an SED of 400 J/L, with minimized ozone production. In contrast, the plasma alone showed a removal efficiency of 54.8% and CO_x selectivity of 21.6% at the same SED, while the catalyst-alone reached 31.1% removal efficiency and 50.4% CO_x selectivity at the higher temperature of 400 °C. Notably, the energy yield (EY) improved from 4.1 g/kWh in plasma alone to 14.0 g/kWh in PPC at an SED of 100 J/L. Moreover, the py-CTF catalyst demonstrated excellent long-term stability, maintaining high efficiency and selectivity over extended operation times. Catalyst characterization before and after plasma treatment demonstrated minimal changes in physicochemical properties, confirming its durability. This study thus highlights the potential of py-CTF as a sustainable alternative to metal-based catalysts in plasma-catalytic VOC abatement.

Due to the increasing water pollution worldwide, wastewater treatment remains one of the most important issues. Cold atmospheric plasma (CAP) has emerged as a promising and versatile technology for wastewater treatment in recent years, offering potential advantages in terms of effectiveness and cost-efficiency. Although several studies have been conducted, the mechanisms by which CAP degrades antibiotics, one of the main pollutants in pharmaceutical wastewater, remain unclear. In this study, we investigate the degradation mechanisms of the antibiotic amoxicillin using reactive molecular dynamics simulations. Specifically, we explore the interaction mechanisms between reactive oxygen and nitrogen species (i.e., O, OH, HO₂, H₂O₂, O₃, NO, NO₂, NO₂¯ and NO₃¯) generated by CAP and the amoxicillin molecule. Our simulation results reveal that some of these species form weak attractive (HO₂, H₂O₂, NO₂¯ and NO₃¯) and weak repulsive (NO and NO₂) interactions, whereas O₃ exhibits both weak attractive and weak repulsive interactions with the amoxicillin molecule. OH radicals exhibit the same interaction mechanisms as O atoms; in other words, O atoms react with amoxicillin in a manner similar to two OH radicals. The simulation results for O atoms show that their reactions with amoxicillin lead to the formation of hydroxyl and hydroperoxide groups, the opening or breakage of the β-lactam ring, the shortening or widening of the benzene ring, and the fragmentation of the structure. Our findings are consistent with experimental outcomes on CAP treatment of amoxicillin. This study provides a deeper understanding of the mechanisms of antibiotic degradation by CAP in wastewater treatment.

The modeling and numerical simulation of plasma jet dynamics inside and outside the modified Ar-H₂ air plasma spray torches were carried out. The simulation was made for three different anode nozzle configurations geometrically modified with the internal powder injector to generate ultra-high temperature oxide-free molten metal droplets. The effects of various working conditions, including nozzle geometry, and hydrogen mass flow rates on the plasma jet temperatures, the corresponding flow fields, and plasma compositions were examined. It was found that adding a diverging section or a converging section inside the torch has a major effect on the plasma jet temperature, velocity, and overall mixing of atmospheric oxygen into the plasma jet. Thus, the shape change of the internal torch section can play a major role in regulating the plasma jet characteristics that consequently control particle oxidation. Furthermore, the compositions of plasma jets were also simulated to examine the evolution of the oxygen along the plasma jet axis. The experimental results were used for the model validations and to investigate the spray distance-dependent oxygen content in plasma jets. The reaction between O₂ and H₂ is modeled, and it was recognized that an increment in H₂ significantly increases the oxygen consumption in the formation of water vapor in the near spray distances, and higher H₂ contents would effectively control the oxidation of spraying particles along using divergent nozzle design.

We utilized a combination of experimental alongside data-driven and theoretical modelling techniques to study non-thermal plasma properties and observables including optical emission spectral intensities, electron temperature, species concentrations, degree of ionization, and reaction rates. As a case study we measured the plasma properties of Argon gas in the low-pressure regime using optical emission spectroscopy (OES) while varying plasma input power and gas flow rate. We used data-driven and drift-diffusion modeling techniques to obtain complementary information, including electron temperature, reduced electric field, and species densities. The calculated density number of excited argon has a linear correlation to measured emission intensity, and we found that the dominant effect on Ar I intensity is the applied power with the gas flow (or pressure) the secondary factor (77% and 20%, respectively). The electron temperature increases with power but decreases with flow (or pressure). Combining the measured and modelling results help to understand the cold plasma dynamics and chemistry towards more complex plasma chemistry applications.

In this study, atmospheric pressure air dielectric barrier discharge plasma was used to inactivate Bacillus subtilis (B. subtilis) spores by varying the concentration of plasma-activated hydrogen peroxide (({text{H}}_{2}{{text{O}}}_{2})). The results showed that the inactivation effect significantly increased as the ({text{H}}_{2}{{text{O}}}_{2}) solution concentration rose from 0 to 30%. The inactivation effect on B. subtilis spores was almost the same for 15% and 30% ({text{H}}_{2}{{text{O}}}_{2}), and it shows a 6 Logs decrease after 15 s of treatment. When the gas temperature of the chamber was fixed at 85 °C, the ({text{CFU/cm}}^{2}) decrease of B. subtilis spores at 15% and 30% ({text{H}}_{2}{{text{O}}}_{2}) is 1.4 and 1.7 Logs, respectively. Compared to the 0% ({text{H}}_{2}{{text{O}}}_{2}) condition, the concentration of reactive species produced by the plasma at 30% ({text{H}}_{2}{{text{O}}}_{2}) increased 57% for 2-hydroxyterephthalic acid, 8% for nitrate and sevenfold for ({text{H}}_{2}{{text{O}}}_{2}) while nitrite production was decreased 24%. To elucidate the inactivation process of B. subtilis spores treated with ({text{H}}_{2}{{text{O}}}_{2}) added to humidified air plasma, we analyzed and compared the chemical stability of 11 representative amino acids. Our LC–MS measurements showed that amino acids can be hydroxylated, nitrated and oxidized by the reactive species in the plasma. The addition of ({text{H}}_{2}{{text{O}}}_{2}) to the plasma promotes the oxidation of Glu, Lys and Arg, leading to an increase the relative abundance of by-products. Our analyses revealed that the addition of ({text{H}}_{2}{{text{O}}}_{2}) to humidified air plasma significantly inactivated B. subtilis spores, which was in close correlation with the chemical stability of amino acids.

The intensive operations of enterprises across various sectors, such as textiles, chemicals, and electronics, generate significant amounts of contaminated water discharges, commonly referred to as industrial wastewater. The application of Advanced Oxidative Technologies, including ozonation, UV irradiation, Fenton processes, and plasma chemistry, is becoming increasingly prevalent for purification purposes. Among these methods, plasma chemistry is regarded as the most promising due to its integration of physical and chemical effects. The combination of plasma with liquids activates the liquid and generates chemically reactive species (atoms, radicals, ions, etc.), whose interactions facilitate the degradation of organic compounds, the binding and precipitation of inorganic ions, and the synthesis of new structures. This study provides a concise review of the use of plasma in contact with liquids for the removal of organic and inorganic components from wastewater. The development of oxide structures during plasma combustion positively influences the removal of impurities.

We study a formation process of single-layer anti-reflection coatings using porous silicon oxide (SiO_x) films formed in atmospheric-pressure (AP), very high-frequency (VHF) plasma. A two-step process is proposed for forming porous SiO_x films: deposition of carbon and hydrogen-containing silicon oxide (SiOCH) layers on a substrate on which polystyrene nanospheres are pre-arranged in hexamethyldisiloxane and hydrogen-fed AP-VHF plasma and subsequent removal of the polystyrene nanospheres/transformation of the SiOCH layer into inorganic SiO_x one by post-oxidation in oxygen-fed AP-VHF plasma. Transmission electron microscopy and energy dispersive X-ray analyses have confirmed that the polystyrene nanospheres underlying the SiOCH layer are effectively removed by the post-oxidation and that air is introduced into the place where the polystyrene nanospheres are present, which are supported by the optical reflectance measurements. The reaction mechanism during the post-oxidation process is discussed, based on the Fourier transform infrared adsorption spectroscopy measurements.

The conversion of atmospheric nitrogen into nitrogen fertilizer has gained much attention owing to the increasing demand for food given the growth of the world’s population. The gliding arc plasma exhibited great potential in this area and constitutes a green alternative to the conventional Haber–Bosch process of nitrogen fixation by mitigating carbon footprints. The moist air gliding arc plasma treatment has been reported to be effective for the production of nitrogen species for agricultural applications. However, the amount of nitrogen species in the treated water rapidly reached a maximum value within a short time and then no longer increased. Thus, this work proposed an innovative approach to allow nitrate production to continually increase by incorporating a natural harmless dolomite mineral. Interestingly, the results demonstrated a significant effect of dolomite on increasing the nitrate concentration from 115.76 ± 3.15 to 263.19 ± 4.31 mg/L. The effects of operating parameters such as the nature of the feeding gas, the flow rate, the dolomite dosage, and the temperature were investigated. The optimal conditions were established as follows: flow rate, 800 L/h; dolomite dose, 2 g/L; temperature, 45 °C; and moist air gas. Under these conditions, the nitrite and nitrate concentrations reached 16.09 ± 0.50 mg/L and 294.73 ± 5.14 mg/L, respectively, within 60 min of aging. The mechanism of nitrate production was investigated, revealing that the plasma-generated acid species catalyzed dolomite dissolution, releasing Ca²⁺ and Mg²⁺ ions. In turn, these species react simultaneously with the produced nitrate ions to form double salts of Ca(NO₃)₂ and Mg(NO₃)₂, which serve as reservoirs to promote their accumulation. This study demonstrated substantial nitrate production improvement in distilled water via the use of moist air gliding arc plasma and offered a promising green alternative for nitrogen-based fertilizer production.

Numerical modeling of atmospheric pressure current-carrying argon plasma containing a single spherical metal particle was performed. The plasma is described in the hydrodynamic approach with account for its thermal and ionization non-equilibrium near the particle. Spatial distributions of electric current, electric potential, and electron flux around a single particle were calculated. The electric current flowing through the particle in the plasma was determined and compared with the model of the highly conducting particle in the uniform conducting media. The surface distribution and total heat flux density from plasma to the particle were studied. The range 10⁻⁵–10⁻⁴ m of particle radius and the range (0.5–2)×10⁷ A/m² of current density in unperturbed plasma, corresponding to the conditions of plasma transferred arc surfacing and plasma powder spheroidization, were considered. The electron temperature was assumed to be constant.