Plasma Chemistry and Plasma Processing最新文献

The behavior of mixed composition cold non-equilibrium plasmas was investigated in a low-pressure capacitively coupled reactor using optical emission spectroscopy (OES). By fitting experimental data to simulations of the Second Positive System ((:{C:}^{3}{{Pi:}}_{u}-{B:}^{3}{{Pi:}}_{g})) of N₂, rotational and vibrational temperatures were determined for various Ar/N₂ mixtures as a function of plasma input power (40–100 W) and pressure (300–700 mTorr). Simulations of the plasma were performed for comparison. For pure N₂, the observed trends revealed that both the rotational and vibrational temperatures increased with input power, ((:{T}_{rot}) of (:v=0) increased from 369 to 396 K and (:{T}_{vib:}) from 5938 to 6542 K, at 40–100 W, 100 SCCM and 293 mTorr) but both temperatures showed minimal response to the applied changes in pressure. The rotational and vibrational temperatures for the mixed composition Ar/N₂ plasmas were significantly higher compared to the pure N₂ plasmas (e.g. (:{T}_{rot}) of 1308 K and (:{T}_{vib}) of 7279 K for 1.8% of N₂ in Ar; at 50 W, 4 SCCM of N₂, 220 SCCM of Ar for a total pressure of 587 mTorr). Moreover, the addition of Ar caused a larger separation between the rotational and vibrational temperatures compared to the pure N₂ case. These phenomena illustrate the effects of Ar on the non-equilibrium energy distribution and more generally the influence that the gas mixture composition may have on the plasma reactivity.

Essential oils rich in limonene are widely used in various citrus-flavored products due to their distinctive aroma. However, achieving a specific citrus-like scent often requires a blend of essential oils from the Citrus genus. This study explored the impact of cold plasma treatment on limonene-rich essential oil, with a focus on the chemical reactions triggered by this process and the subsequent changes in aroma. The research involved treating a limonene-rich essential oil with dielectric barrier discharge (DBD) and glow discharge (GD) plasma processing. Different excitation frequencies were used for DBD, while varying air flow rates were applied for GD. The application of cold plasma technology was found to reduce the citrus notes of the oil while enhancing its secondary characteristics. The specific plasma system and operating conditions played a crucial role in determining the selectivity of the chemical and aroma modifications. This study demonstrated that cold plasma treatment could effectively alter the secondary notes of limonene-rich essential oil, resulting in the development of new oils with enhanced floral, woody, herbal, minty, and aldehydic notes. These findings suggest that cold plasma technology offers a promising method for modifying the aroma profile of essential oils, potentially leading to innovative applications in the flavor and fragrance industries. The ability to fine-tune the scent of essential oils through controlled plasma treatment could pave the way for the creation of customized aromatic products, meeting specific consumer preferences and expanding the versatility of essential oils in various commercial applications.

The elementary processes during the fixation of nitrogen by plasma catalysis are studied in a low-pressure plasma experiment with N(_2) and O(_2) as source gases. The formation of surface groups on an iron oxide foil is monitored with infrared reflection absorption spectroscopy. Surface nitrates (NO(_3^-)) are formed when the substrate is exposed to a 1:1 N(_2):O(_2) plasma, as well as N(_2)O(g), NO(g), NO(_2)(g), and O(_3)(g) in the gas phase. It is postulated that NO(_{1,2})(g) species created by the plasma, adsorb at the surface and create these nitrates. This constitutes an intermediate step for nitrogen oxidation by plasma catalysis.

In this study, air transient spark discharge (Air-TSD) plasma, helium atmospheric pressure plasma jet (He-APPJ), air surface dielectric barrier discharge (Air-SDBD) plasma, and nitrogen micro hollow cathode discharge (N₂-MHCD) plasma were used to inactivate Escherichia coli (E. coli). The results showed that Air-SDBD plasma achieved a 6-log reduction of E. coli in 30 s, whereas the other three sources failed to achieve complete inactivation even after the treatment of 120 s. The concentrations of aqueous H₂O₂, NO₂⁻ and NO₃⁻ produced by Air-SDBD are 2–3 times higher than those of Air-TSD and He-APPJ. The concentration of O₃ produced by Air-SDBD is more than 4 times that of N₂-MHCD. To further explore the relationship between RONS produced by the four sources and E. coli inactivation, we analyzed the effects of the four sources on 12 representative amino acids. Liquid chromatography-mass spectrometry (LC–MS) analysis showed that amino acids, including phenylalanine (Phe), methionine (Met), tryptophan (Trp), tyrosine (Tyr), glutamic (Glu), lysine (Lys), histidine (His), arginine (Arg), and cysteine (Cys), underwent significant oxidation after treatment of the four sources. And the reduction of Met, Trp and Cys after Air-SDBD treatment was more pronounced compared to the other three sources. Our results indicates that a strong correlation exists between the inactivation of E. coli and the modification of amino acids by RONS.

Plasma-activated water (PAW) produced by different methods has been intensively studied for its biomedical applications due to the antimicrobial effects of reactive oxygen and nitrogen species within. While many of these studies focus on the effects of PAW on bacterial death, other bacterial responses to PAW are seldom assessed. Herein, we report an evaluation of PAW produced by a falling-film plasma reactor (FFPR) on the growth of Lysobacter enzymogenes and its biosynthesis of the natural products - heat stable antifungal factor (HSAF) and its analogs. An FFPR setup was demonstrated to effectively create plasma-treated deionized water under atmospheric conditions for the generation of PAW. These PAW samples were shown to contain nitrite, nitrate, and hydrogen peroxide of concentrations that were dependent on the plasma activation time. Short periods of PAW activation caused L. enzymogenes to significantly increase the production of HSAF, its analogs, and total cell growth. The PAW produced with a longer plasma activation period had higher concentrations of nitrate and hydrogen peroxide, and was found to have decreased growth in L. enzymogenes. These results shed new light that PAW can also be used to stimulate the production of natural products. Furthermore, the activation period of PAW can be optimized to stimulate either an increase in the total HSAF yield or HSAF yield per optical density unit in a cell culture.

Non-thermal plasma-based technologies have emerged as versatile tools for various industrial processes due to their ability to induce chemical reactions efficiently under ambient conditions. In particular, dielectric barrier discharges (DBDs) are of interest because of their robust and reliable design and scalability. This study investigates the role of pressure in tuning conversion, plasma parameters, and flow patterns in a plasma-assisted chemical reaction using a surface DBD (SDBD) reactor. The removal of O₂ traces in H₂ was used as a model reaction, where an unexpected increased conversion at elevated pressure was observed at high powers. This effect was studied using high-speed photography to analyze streamer dynamics and optical emission spectroscopy to determine plasma parameters. With increasing pressure, both the plasma area and the number of individual streamers decreased, and the electron density decreased as well. Fluid simulations were conducted to examine the impact of increased pressure on mass transport pointing to an enhanced contact time as the origin of the increased conversion at high dissipated powers. The findings highlight the importance of optimizing pressure and power conditions to maximize the efficiency of plasma-based chemical processes.

Dust-forming low-temperature plasmas are versatile systems for the production of nanoparticles with tunable functionalities. While attractive from a materials processing point of view, these systems are inherently complex, with several plasma-induced phenomena determining the properties of the produced materials. Here, we characterize a carbon nanoparticle-forming plasma using coherent anti-Stokes Raman spectroscopy (CARS), with the primary goal of measuring gas temperature. While gas temperature is typically assumed to be at or slightly above room temperature in these reactors, we measure gas temperatures exceeding 1000 K under typical process conditions. We find a correlation between the gas temperature and the nanoparticle yield, suggesting that the particle nucleation and growth process releases energy within the reaction volume, leading to significant gas heating. In addition, we find that the relaxation of vibrationally excited species at the particle surfaces is a major contributor to their heating. These results underscore the complexity of these systems and the need for their more in-depth characterization using advanced techniques such as CARS.

Direct current (DC) plasma torches play a pivotal role in the field of material processing, with their performance largely determined by the characteristics of the plasma jet. However, the cascade DC plasma torch produces a plasma jet that has a small high-temperature region and a high velocity, which limits their powder processing rate. This paper designs a novel triple-anode plasma torch (TAPT) equipped with annular powder feeding to address these challenges. Comprehensive investigation into the plasma jet characteristics of the TAPT was carried out through a combination of experimental measurements and numerical simulations. Results show that the TAPT produces an optimal plasma jet for powder processing, marked by a large high-temperature region, low velocity, and high uniformity. The plasma jet’s peak temperature reaches over 20,000 K, with a 4,000 K region of 160 mm in length and 33 mm in diameter, and minimal regions exceeding a velocity of 80 m/s. The annular powder feeding of the TAPT guarantees a stable plasma jet for effective material processing, with the arc voltage exhibiting a small standard deviation of just 1.08 V. Furthermore, the TAPT’s effectiveness in powder processing was exemplified by spheroidization trials involving aluminum oxide powder, which yielded a practical specific energy requirement of approximately 4.35 kWh/kg. Overall, the TAPT shows considerable potential in the field of powder processing, specifically in raising the efficiency of powder spheroidization processes.

A coaxial dielectric barrier discharges based Kr/Cl₂ excilamp featuring a double dielectric barrier has been developed to generate 222 nm Far UV-C radiation. The excilamp is excited by a short unipolar pulse (rise time 800 ns, FWHM: ~2µs) of negative polarity and investigated at different operating conditions to efficiently generate 222 nm radiation. The investigation includes the electrical and optical characterisation of the excilamp under varying Cl₂ proportion (0.1-3%) and total gas pressures (100–300 mbar). The typical V-I characteristics and the corresponding Q-V curve have been analysed to understand the discharge characteristics and determine the electrical parameters, including the capacitance of the excilamp and input power. The optical characterization included emission spectroscopy and absolute radiance measurements, focusing on the 222 nm spectral band, a key emission wavelength of KrCl* excimers. The emission spectra reveal the emission of the 222 nm spectral band, along with relatively weak bands of 235 nm, 258 nm, and 325 nm, particularly at higher pressures. The absolute irradiance at 222 nm was found to increase with Cl₂ concentration up to 1%, reaching a peak value of 2.09 mW/cm² (at 300 mbar) before significantly decreasing at 3%, indicating an optimal Cl₂ content for KrCl^* excimer formation. Similarly, increasing the total gas pressure from 100 mbar to 400 mbar led to a substantial enhancement in 222 nm emission, with irradiance rising from 0.47 mW/cm² to 2.35 mW/cm². This comprehensive analysis provides crucial insights into the development and optimization of Kr/Cl₂ excimer lamps for efficient 222 nm far-ultraviolet (Far-UV) radiation generation.