Plasma Chemistry and Plasma Processing最新文献

Electrified, small-scale, remote approaches are needed as an alternative to conventional centralized methods for nitrogen fixation in order to reduce our reliance on fossil fuels and ensure global food security. Plasma-based electrolytic processes offer a promising solution by directly reacting molecular nitrogen and water under mild conditions. However, the complex non-equilibrium chemistry results in a diverse range of gas-phase and liquid-phase reactions, which impacts selectivity toward desired products. In this study, we investigate the influence of feed gas composition, specifically the presence of molecular oxygen at minute quantities, on the liquid-phase nitrogen products. Specifically, oxygen gas concentrations as low as 0.1% in the gas feed are found to substantially affect the selectivity towards ammonium ions. We additionally show that the total gas flow rate has an indiscriminate effect on both ammonium and nitrate/nitrite ion yields because of the presence of water vapor. By carefully controlling these process parameters, a production rate for ammonium ions exceeding 1 mg/h with a molar selectivity of ~ 14 is achieved. Our results highlight the importance of gas-phase chemistry in plasma-based electrolytic nitrogen fixation.

A two-dimensional axisymmetric fluid model was employed to investigate the influence of varying argon volume fraction in the working gas on the propagation characteristics and reactive species generation of pulsed He + Ar + O₂ plasma jet. The results demonstrate that at an argon volume fraction of 10%, the Penning effect between He and Ar is most pronounced, and the electron temperature and electron density of the He + Ar + O₂ plasma jet reach their maxima. The electron temperature in the upstream region of the jet front dissipates more slowly due to Penning ionization between helium and argon. At the end of the pulse, higher—temperature electrons accumulate near the tube nozzle in a triangular distribution. During propagation from the tube into open air, the ionization wave of the He + Ar + O₂ plasma jet evolves from a hollow ring to a solid bullet shape, with the highest bullet velocity observed at an argon volume fraction of 10%. The densities of Ar⁺ and Ar^* reach their maxima at argon volume fractions of 10% and 30%, respectively, while the densities of He⁺ and He^* decrease monotonically as the argon volume fraction increases. Notably, the ozone generation efficiency is maximized at an argon volume fraction of 10%.

As a volatile organic pollutant, toluene is difficult to be activated and removed at low temperature by conventional thermal catalytic oxidation. Therefore, we reported an Ag-Co bimetallic catalyst which is supported on hydroxyapatite (HAP) and prepared by the equal-volume distribution impregnation method and investigated its performance in toluene oxidation. Enhanced toluene removal was achieved by synergizing plasma with 3Ag/15Co/HAP catalysts at low temperatures, which also improved CO₂ selectivity. Toluene conversion and CO₂ selectivity peaked at 100% and 88%, respectively, at the input power of 13 W, while the removal process demonstrated good stability during a 32 h test. The uniform dispersion of Ag NPs on the carrier facilitates the conversion of filamentary discharge into a more uniform and efficient discharge, promoting the activation of surface oxygen and thereby improving toluene removal efficiency. Additionally, the interaction between Ag and Co generated more surface-active oxygen and lattice defects on the catalyst surface, resulting in excellent low-temperature reducibility.

A reflection on the phenomenon of plasma-activated water (PAW), its brief history and properties. PAW arises from the accumulation of reactive plasma products (mainly H₂O₂, NO₂⁻, NO₃⁻, O₃ and sometimes HNO, ONOOH) in water and has many interesting and beneficial properties on both living and non-living biological objects. It has attracted considerable attention in the last 15 years and raises the question whether it might not be simpler to prepare it artificially (APAW) directly by mixing chemical compounds. There are several papers which have compared the effects of PAW with APAW and conclude that there is probably no significant difference. In this paper, we conclude that the preparation of PAW is several times more expensive than that of APAW. However, we also note that there may be specific situations in which the production of PAW could be advantageous, such as its efficient role in storing energy in the form of nitrate ions, which can serve as a nutritional source for plants.

The study investigates the potential of Plasma-Activated Water (PAW) as a nitrogen supplement in hydroponic cultivation (HS-N + PAW), specifically focusing on radish seed germination and subsequent plant growth. PAW, produced using a dielectric barrier discharge pencil plasma jet using air as plasma forming gas, is compared against conventional hydroponic solution (HS) and hydroponic solution without nitrogen (HS-N). PAW treatment completely eliminates microbial growth in seeds. Radish plants cultivated with HS-N + PAW display approximately 30% and 3% longer roots compared to those grown with HS-N and HS, respectively, with shoot length increasing by ~ 16.5% (HS-N) and < 1% (HS). Root weight sees a substantial increase of ~ 51% with HS-N + PAW compared to HS-N, while the increase with HS is not significant. Similarly, shoot fresh weight sees a notable increase of 50% (HS-N) and 10% (HS). In terms of biochemical composition, radish roots show a significant increase of approximately 15.3% in soluble sugar concentration with HS-N + PAW compared to HS-N. Protein concentration in radish leaves increases by ~ 5.1% and ~ 19.0% with HS-N + PAW compared to HS-N and HS, respectively. Heightened soluble sugar and protein concentrations in HS-N + PAW-grown plants, indicating enhanced metabolic activity and nutrient uptake. However, variations in chlorophyll and carotenoid concentrations in leaves among different growth media are statistically insignificant. The H₂O₂ concentration in both roots and shoots remains consistent across different growth media. However, variations in electrolytic leakage, phenolic leakage, and antioxidant enzyme activities reveal differential responses depending on growth conditions, highlighting how these conditions influence plant stress responses. Furthermore, sensory evaluation and physical attributes analysis underscore the negative effects of nitrogen deficiency in radish plants grown with HS-N. Conversely, HS-N + PAW cultivated plants exhibit improved visual appearance, surface texture, and overall acceptance, highlighting PAW’s potential as a nitrogen source for enhancing plant growth and quality in hydroponic systems.

Electrodes are core components in plasma discharge technology, and their material selection and structural design directly affect the performance and stability of the system. As plasma technology is widely applied in environmental treatment, materials preparation, and biomedicine, there is a growing demand for optimizing electrode materials. However, the diversity of discharge forms and application scenarios makes it difficult to draw unified conclusions about the applicability and performance of electrode materials across studies, particularly in liquid-phase discharges, where corrosion of metal electrodes becomes more prominent, posing challenges to the selection and design of electrodes. This review systematically summarizes the performance of various metal electrode materials in plasma discharge technology in different applications, particularly the generation of corrosion products in water treatment, disinfection, and sterilization, and their influence on the treatment efficacy.

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.