Plasma Chemistry and Plasma Processing最新文献

The large natural metabolic diversity of microorganisms has allowed them to survive in very harsh conditions of high temperature, high ionizing radiation, and high concentrations of reactive chemical species. The environment of low temperature plasma generated with liquids is comparable to many natural conditions (high temperature, highly oxidative, presence of various types of radiation) and thus suggests microbes can evolve or be engineered to not only survive but thrive in such extreme conditions. The evidence from the literature and previous work suggests that the in-situ coupling of engineered and evolved strains of bacteria with low temperature plasma generated with liquid water may provide enhanced functionality with respect to organic chemical reactions.

High-energy chemistry is a method of accelerating chemical reactions by transferring copious amounts of energy to individual molecules. The synthesis of acetylene and benzene is a valuable chemical process used in many organic products. The article proposes an original scheme of experimental setup and technology for plasma-activated methane conversion into acetylene and benzene. The system enables the creation of two distinct active zones within the reactor: the “hot zone,” where plasma and active elements are generated, and the “relaxation zone,” where the synthesis of organic products occurs. The optimal temperature of the blowing gas, i.e., the gas that propels the plasma reactor walls, has been found to be a crucial factor in heat removal from reaction zones. This temperature has been observed to vary within an interval of 290–310°K, while the reactor gas pressure has been identified as a significant variable within a range of 10–40 mbar. These two factors have been identified as the primary determinants of the yield of products, with acetylene yields reaching approximately 70–80% and maximal benzene yields reaching 40%. Furthermore, the duration of plasma exposure is a critical variable in methane conversion. The optimal acetylene yield of 80% was achieved when the reactor was operated in stationary mode for 15 s. A variation of the input gas flow in flow mode within an interval of 5–15 m³/h resulted in a decrease in the yield of acetylene to 60 percent, while an increase in the benzene yield up to 50 percent was observed. This was accompanied by an overall increase in the total volume of products produced per time unit. A general qualitative model of methane reforming is proposed, combining methane dehydration in the plasma flame with direct synthesis of acetylene from carbon and hydrogen atoms in the relaxation zone. Benzene formation occurs through the trimerization of acetylene molecules under heat dissipation near the reactor walls.

For improving the jet stability of pure laminar plasma torch to ensure the consistency of the surface treatment, based on previous studies, a novel anode structure, named as internal step anode, has been proposed. Sequences, the effects of axial lengths of the internal step anode on the jet stability and heat flow characteristics have been explored by using a home-made simulation model. Finally, corresponding experiments have been conducted to verify the effectiveness of the anode optimization. Research results show that: (1) With increasing the axial lengths of the internal step anode, the temperature and velocity of the anode area increase slightly, on the contrary, the corresponding anode current density decreases slightly, which is conducive to extending the electrode life; (1) the internal step anode is beneficial for improving the jet stability of pure laminar plasma torch. With increasing the axial length of the internal step anode, the jet stability increases to certain level and then decreases smoothly. When the axial length is 5 mm, the plasma torch presents the highest jet stability.

The paper is focused on studying magnesium spinel-doped alumina tapes and their effect on plasma. Developed tapes were made from a mixture of (15,mathrm {vol.%}) of (mathrm {MgAl_2O_4}) by the gel tape casting method. Ceramic tapes were sintered at different temperatures from (1450,^circ {textrm{C}}) up to (1700,^circ {textrm{C}}). The sintering temperature significantly influenced the material’s grain sizes, but the material’s chemical and phase composition was the same for all sintering temperatures. We measured the surface potential decay and showed that it is not enough to have fast surface potential decay for Atmospheric Pressure Townsend Discharge, but the homogeneity of the surface itself crucially influences the stability of Atmospheric Pressure Townsend Discharge. On the other hand, the ignition voltage of coplanar dielectric discharge was not influenced by the gran size difference.

The objective of this study was to evaluate the efficacy of humified air dielectric barrier discharge cold plasma (CP) and ultraviolet (UV) at a wavelength of 254 nm in inactivating Escherichia coli (E. coli) and Bacillus subtilis spores (B. subtilis spores). The experimental results showed that simultaneous treatment with CP and UV had the highest antimicrobial activity, followed by sequential and individual treatments. Individual treatment of CP and UV for 10 s decreased E. coli by 2.4 Logs and 1.3 Logs, respectively. After 60 s of CP and UV treatment, B. subtilis spores were decreased by 2.6 Logs and 1.1 Logs, respectively. Simultaneous treatment of CP and UV for 10 s reduced E. coli by 4.6 Logs and B. subtilis spores by 4.4 Logs after 60 s, which was attributed to their synergistic effects. To elucidate the mechanism of protein oxidation in simultaneous treatments, we investigated the chemical stability of simultaneous treatments with CP and UV on 11 amino acids and 4 nucleobases in aqueous solution. Phenylalanine (Phe), methionine (Met), tyrosine (Tyr), tryptophan (Trp), and histidine (His) were oxidized by plasma-generated reactive oxygen and nitrogen species. In addition, guanine (G) and thymine (T) exhibited structural instability; both the five- membered and six-membered rings of guanine can be oxidized, and thymine undergoes oxidative cross-linking by UV-induced formation of thymine dimers. The analysis showed that the chemical instability of amino acids and nucleobases was closely related to the synergistic inactivation effect of CP and UV.

Plasma–liquid interaction remains a crucial phenomenon influencing numerous applications. Plasmas produced by electrical discharges exhibit properties that depend on the voltage polarity as well as on the liquid properties. In this study, we investigate the impact of liquid permittivity (({upvarepsilon }_{{text{r}}} = { }32,{ }56,{text{ and }},80)) and water electrical conductivity (σ = 2, 500, and 1000 μS/cm) on negative discharges initiated in air at atmospheric pressure. Using a negative pulsed nanosecond high-voltage setup with a pin-to-liquid configuration, experimental results demonstrate that increasing ({varepsilon }_{r}) leads to faster discharge ignition and higher discharge current. ICCD imaging reveals a decrease in the maximal radial extension of the discharge over the liquid surface with increasing ({varepsilon }_{r}). Also, rising σ lead to an increase of the discharge current, and the ICCD images show a decrease in the radial propagation of the discharge over the solution. To gain deeper insights into the discharge dynamics and properties, a 2D fluid model is employed to simulate the various conditions. The results indicate that increasing ({varepsilon }_{r}) decreases the radial E-field produced by the surface ionization wave and increases the electron density in the air gap. Regarding σ, high-conductivity conditions result in lower radial E-field in the front of the surface ionization wave, explaining the shorter radial propagation of the discharge. Comparing negative with positive discharge, we observe that the former travels a shorter distance over the liquid surface due to its more diffuse front. Moreover, we note the absence of filamentation in the negative surface discharge, unlike the positive counterpart. This disparity is attributed to a relatively lower space charge contained in the front, thereby prohibiting the formation of individual filaments.

The humid air gliding arc plasma (GP) has demonstrated its capability to synthesize catalysts (metal (hydr)oxides and supported catalysts) with intriguing properties and significant catalytic activity while employing interesting synthesis conditions compared to conventional catalyst synthesis. However, previous studies exposed various precursors to the plasma without prior knowledge of their reactivity through GP. The objective of this paper is to investigate the parameters influencing precursor reactivity and precipitation under humid air GP, by identifying commonalities between reactive and non-reactive precursors. Several factors were identified as predominant: the solubility of the precursor and precipitate, the acidification of the medium along exposure, the redox potential of reactions between the precursor and HNO₂/NO₂⁻ species plasma-generated, and the metal precursor nature. These identified factors have enabled us to create a dichotomous key that can be used for any type of precursors, allowing to anticipate their potential precipitation when exposed to the GP. By utilizing this key, we have identified two new precursors that react, forming new types of solids never synthesized before by GP: Au and Ru-based solids. This demonstrates that GP may be a promising method for developing new types of catalysts, such as metal-supported catalysts, but also indicates that a limited number of precursors may react, at least without changing the conventional synthesis parameters. Therefore, this article highlights both the possibilities and limitations of GP catalyst synthesis.

Nitric oxide (NO) generation-enhanced atmospheric-pressure plasma technology has been investigated as a nonthermal intervention technology for prolonging the ripening period of tomatoes. UV-irradiated dielectric barrier discharge plasma reaches the NO-enhanced mode earlier, and NO is rapidly involved in the inhibition of tomato respiration. With as little as 26 W of power in total, the NO-processing of tomatoes using plasma technology helps control the postripening of tomatoes. The NO-enrichment mechanism was analyzed through numerical calculations, which revealed that the photolysis of ozone (O₃) and nitrous acid (HONO) occurred during UV irradiation. The measured amount of CO₂ emitted from plasma-treated tomatoes was ~ 300 ppm lower than that emitted from nontreated tomatoes, indicating that metabolism and respiration were inhibited. In addition, the NO-enhanced plasma treatment of tomatoes is considered to be more effective because the so-treated tomatoes emitted 100 ppm less CO₂ than the plasma-treated tomatoes. The delay of respiration through plasma treatment can help prevent color changes or decreases in the firmness of tomatoes.

The study aims to synthesize and homogeneously functionalize iron oxide nanoparticles (IONPs) using a non-thermal atmospheric pressure (NTAP) plasma for biological applications. IONPs were synthesized using a new NTAP plasma assisted electrolysis technique. The utilization of a unique NTAP plasma rotating reactor allows for a uniform surface functionalization throughout the IONP surface. The precursor used for the functionalization process was acrylic acid (AAc), and it was carried out in response to the applied voltage and monomer flow rate. Optical emission spectroscopy (OES) was used to investigate the reactive species in-situ throughout the functionalization process. Vibrating-sample magnetometry (VSM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and X-ray photo electron spectroscopy (XPS) were used to analyse the changes in the chemical, structural, morphological, and magnetic properties of the untreated and functionalized IONPs. Subsequently, chemical dosimetry and the in vitro metabolic activity assay (MTT) were used to analyse the OH• radical production capacity and toxicity of IONPs. The findings showed that the experimental working conditions had a significant impact on retaining the distinctive COOH functional groups on the surface of functionalized IONPs. The coexistence of the hematite (Fe₂O₃) and magnetite (Fe₃O₄) phases is revealed by the untreated and functionalized IONPs, which also exhibit marked super paramagnetic performance and a spherical shape. In the end, the IONPs demonstrated clear nontoxicity when they were functionalized at greater flow rates and reduced applied voltage. The analysis results unequivocally demonstrated the functionalized IONPs’ non-toxicity, highlighting their prospective application in the field of biomedicine.

The ability of atmospheric pressure plasma jets to treat complex non-planar surfaces is often cited as their advantage over other atmospheric plasmas. However, the effect of complex surfaces on plasma parameters and treatment efficiency has seldom been studied. Herein, we investigate the interaction of the atmospheric pressure plasma slit jet (PSJ) with block polypropylene samples of different thicknesses (5 and 30 mm) moving at two different speeds. Even though the distance between the slit outlet and the sample surface was kept constant, the treatment efficiency of PSJ ignited in the Ar and (hbox {Ar/O}_2) gas feeds varied with the sample thickness due to the plasma parameters such as filament count and speed being affected by the different distances of the ground (the closer the ground is, the higher the discharge electric field). On the other hand, the (hbox {Ar/N}_2) PSJ diffuse plasma plumes were less affected by the changes in the electric field, and the treatment efficiency was the same for both sample thicknesses. Additionally, we observed a difference in the efficiency and uniformity of the PSJ treatment of the edges and the central areas in some working conditions. The treatment efficiency near the edges depended on the duration of the filament contact, i. e., how long the local electric field trapped the filaments. Conversely, the treatment uniformity near the edges and in the central areas was different if the number of filaments changed rapidly as the discharge moved on and off the sample (the 5 mm samples treated by easily sustained Ar PSJ).