Plasma Chemistry and Plasma Processing最新文献

Cold atmospheric plasma (CAP) has been reported as a promising technique in dentistry. The biosafety and mechanisms on periodontal tissue are especially important in clinical practice. This study aims to evaluate the cytotoxicity, genotoxicity and mechanisms of human periodontal ligament fibroblasts (hPDLFs) induced by CAP. The antimicrobial effect on Porphyromonas gingivalis (P. gingivalis) was evaluated using the colony-forming unit methods (CFU). Human periodontal ligament fibroblasts were treated with CAP for variable times (1, 2, 4, 8, and 16 min). CCK-8 assays were performed to detect cell viability and flow cytometry was performed to measure the cell cycle and apoptosis. Cell migration ability was determined by scratch assays. The physicochemical properties of plasma activated medium were evaluated, including the pH values, H₂O₂ and NO levels. DCF-DA staining and analysis were performed to evaluate intracellular ROS levels inside cells using flow cytometry. Immunofluorescence of DNA double-strand breaks (DSBs) marker, phosphorylated γH2AX was used to establish the genotoxicity of plasma. The results showed that CAP has a significant inhibition effect of P. gingivalis after 6 min treatment. It has significantly dose-dependent effects that ranging from increasing cell proliferation to inducing apoptosis. A low doses (1, 2, 4, and 8 min) could enhance the cell proliferation. A high dose (16 min) resulted in the inhibition of cell proliferation (p < 0.01). It is also shown that these effects are primarily due to the formation of reactive oxygen and nitrogen species (RONS).

In this work, the successful synthesis of nanostructures based on MXenes by initiating a pulse discharge between titanium wires immersed in carbon tetrachloride is presented. By choosing carbon tetrachloride as the environment, the formation of oxide structures in the synthesized samples could be avoided. The characterization of the obtained structures was carried out using various techniques, including scanning electron microscopy, X-ray phase analysis, EDS, Raman and FTIR spectroscopy. The results confirmed the successful formation of MXenes with a Cl⁻ occupying the interlayer space. The properties of the discharge initiated in CCl₄ were also determined. The results suggest the potential of this plasma-liquid method for the synthesis of high-purity MXenes without impurities commonly found in conventionally prepared samples.

The stepped-nozzle arc plasma torch (SNAPT) is a promising arc source due to the advantages of high stability and high energy density, but the micro-time scale discharge characteristics have not yet been adequately investigated. In this study, a SNAPT was designed and studied, in order to investigate the effects of discharge current, gas flow rate, and nozzle morphology on the discharge characteristics. The results show that the volt-ampere characteristics of the SNAPT have an increasing curve when the gas flow rate is greater than 4 Nm³/h, and a decreasing curve when the gas flow rate is 3 Nm³/h. This result is related to the position of the arc root, and an arc constriction phenomenon occurs at high current and low gas flow rate. The thermal efficiency of the SNAPT decreases with the increasing current and decreasing gas flow rate, ranging from 69.6 to 82.3% within the experimental parameters. The optical emission spectroscopy results show that there are many active particles inside the plasma. The experimental parameters of the heavy particle temperature of 4851.5 to 9189.3 K and the electron temperature of 7846.9 to 10185.6 K both correspond to the Boltzmann distribution and are close to the local thermodynamic equilibrium state. Comparative experimental results show that the cylindrical-nozzle has the decreasing volt-ampere characteristics and higher voltages, but has large voltage fluctuations and poor stability compared with the stepped-nozzle. The results of the study are of guiding significance for design, selection of operating parameters, and application scenarios for this type of plasma torch.

In this work, we investigate the effect of an external transverse weak magnetic field on the creation of metastable helium atoms and excited helium molecules in a high-voltage pulsed discharge in helium at medium pressure. A two-dimensional fluid model is used to describe a high-voltage pulsed discharge in helium in the external transverse weak magnetic field. The dynamics of discharge development in the high-voltage pulsed discharge in helium at a pressure of 30 Torr in the presence and absence of the magnetic field is studied. The effect of the external magnetic field on the behavior of the density of charged particles, metastable helium atoms, and excited helium molecules in the high-voltage pulsed helium discharge has been investigated. It is shown that in the discharge region, the density of metastable atoms decreases when a transverse magnetic field is applied, which is a consequence of an increase in the frequency of stepwise ionization.

In this study, a coaxial dielectric barrier discharge (DBD) reactor was employed using various gases: compressed air (CA), helium (He), or argon (Ar) to produce plasma-activated water (PAW) from deionized water. The influence of these gases on the generation and quantification of reactive oxygen and nitrogen species (RONS) was examined. Their impact on PAW's physicochemical properties, including pH, oxygen reduction potential (ORP), and conductivity, was also assessed. In parallel, the efficacy of produced PAW against microbial species such as Staphylococcus aureus, Escherichia coli, and Candida albicans was evaluated, in addition to their cytotoxicity to mammalian cells. Notably, after a 10-min contact, a 99.99% reduction in S. aureus and E. coli was observed when CA and Ar were used, and reductions of 99.96% and 99.95% were seen when He was employed, respectively. For C. albicans, reductions of 12.05% with CA, 22.89% with Ar, and 39.76% with He was observed. After 30 min, a reduction of up to 53.41% was achieved with Ar. Additionally, PAW generated with all the gases were classified as non-cytotoxic. These findings underscore the potential of the coaxial DBD reactor system in PAW production, emphasizing its significant antimicrobial properties and low toxicity to mammalian cells.

Over the last decade, more and more attention has been paid to applications of non-thermal plasma in agriculture, where it is used to decontaminate various microorganisms and to improve the seed germination. In this study, we present the results of a newly developed point-to-ring NTP transient spark discharge apparatus (NTP), plasma activated water (PAW) and their combined treatment on Durum wheat and Common wheat grains under laboratory conditions. Transient spark discharge treatment was used as direct treatment while indirect treatment of wheat grains was performed by PAW produced in point-to-plane NTP transient spark apparatus. We found that the degree of grain surface decontamination was in order NTP > PAW > combined treatment. In the case of Durum wheat grain germination, all treatments increased germination with increasing exposure times, while in the case of Common wheat, PAW treatment and combined treatment did not significantly increase the grain germination. In conclusion, plasma treatment has enormous potential for use in agriculture and its possibilities need to be fully explored.

The increased usage of diesel in the past 20 years, particularly in developing countries like India, has resulted in serious concerns in abating gaseous pollutants such as oxides of nitrogen (NO_X) and hydrocarbons (HC). On the other hand, the growing metallurgical processing industries leave behind tons of solid waste, making waste management a bigger issue. In the current work several industry wastes have been tested under discharge plasma environment for their catalytic properties in the removal of HCs from diesel exhaust. To explore the benefit of metal oxide components, present in industry wastes, a new approach was proposed in this work wherein two industrial wastes were blended to form a composite waste which was then powdered and bound to form pellets. Four such composite waste-based pellets, namely red mud + iron tailing, iron tailing + lignite ash, lignite ash + copper slag and red mud + oyster shells, were tested for their catalytic properties under plasma environment. Exhaust emanating from a 6 HP engine is sampled and studied for HC removal in a pulsed plasma reactor embedded with composite wastes. The pellets being porous in nature, studies were also conducted for HC adsorption by cascading composite wastes with plasma alone while treating the exhaust. All the composite wastes exhibited good plasma catalysis in HC removal (58–73%) when compared to that with plasma alone (31%). Further, there is a marked difference between plasma adsorption and plasma catalysis by a factor of 1.75–2.2 indicating synergy between plasma and metal oxides present in composite wastes while catalysing HC removal.

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.