Plasma Chemistry and Plasma Processing最新文献

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).

Vacuum arc is one of the most widespread sources of multicomponent ion/plasma flows. In the paper, we examine how the emissive properties of mixed cathode components affect the parameters of generated plasma. The scheme of vacuum arc with a heated cathode made of CeO₂ + Cr and TiO₂ + Cr powders was used. The arc discharges in the current range of 30–90 A and in the cathode temperature range of 1.8–2.0 kK were studied. It was found that CeO₂ provides an intensive thermal electron emission and the arc with CeO₂ + Cr cathode has a diffuse current attachment, plasma parameters are controllable and mainly Cr ions appear in plasma. Conversely, the current constricts in the arc with a non-emissive TiO₂ + Cr cathode, the plasma parameters are unchangeable and Ti and Cr ions are generated in comparable amounts. The results presented may be useful in multicomponent plasma sources design.

Plasma agriculture is an emerging sector with potential to improve agricultural yield and promote sustainable development. While several studies have demonstrated positive impacts on seed germination and post-treatment plant growth indices, the response of vegetative stage plants to plasma-derived components remains underexplored. In this study, the effects of gaseous products generated by dielectric barrier discharge (DBD) plasma on the vegetative growth of mustard greens (Brassica juncea L.) were investigated. Fourteen-day-old plants were exposed to plasma gas (indirect plasma) at varying frequencies, and growth parameters were monitored after 7 and 14 days of treatment. The results revealed that exposure to plasma gas for 30–45 min per day positively impacted root length, plant height, leaf area as well new leaf formation rate, with increases ranging from 16 to 30%. Additionally, plasma-exposed plants exhibited significantly higher chlorophyll content (33%), total protein content (15–20%), and dry/fresh weight ratio (17%) compared to the control sample. Interestingly, cold plasma treatment demonstrated a greater influence on root growth, while a negative effect was observed on aboveground parts at high exposure frequencies. These findings demonstrate that plasma treatment not only benefits seed germination but also has the potential to enhance crop yield through its stimulatory effects on vegetative growth.

Swellable plasma polymer films have been deposited on silicon wafers and hydrogels in a low-pressure PECVD system. Deposition characteristics and physico-chemical characterization data of swellable oxygen-rich plasma polymerised ethylene films were studied. These films were deposited using gas flows consisting of C₂H₄ (5 sccm) and CO₂ (10–40 sccm). Using profilometry, changes in thickness of films over multiple water immersion and drying cycles were recorded. Changes in the structure and morphology of films was also evaluated by using scanning electron microscopy, dye permeation studies and atomic force microscopy. Mechanical properties of the films were studied by using nanoindentation experiments, and intrinsic residual stresses were also calculated for the films. The behaviour of films was dependent on the flexibility and water content of the underlying hydrogel substrates. These findings pave way for creation of stable plasma polymer films on biomedical devices made from hydrogels.

Important representatives of mucilaginous seeds from different plant species, namely amaranth (Amaranthus hypochondriacus L.), garden cress (Lepidium sativum L.), common flax (Linum usitatissimum L.), psyllium (Plantago ovata Forssk.), and chia (Salvia hispanica L.) were subjected to non-thermal plasma (NTP) generated by diffuse coplanar surface barrier discharge with different exposure times (1, 3, 5, 10, 20, 30 s). Seed water uptake, kinematic viscosity, parameters of seed germination and initial seedling growth were monitored along with chemical and morphological changes on the seed surface. Water absorption increased with increasing plasma exposure time for garden cress, psyllium and chia seeds, but it was greatest for chia seeds. For all seed species, the kinematic viscosity decreased with increasing plasma exposure time. The highest values were found for chia seeds after a treatment for 30 s. Surface analyses did not reveal any chemical and morphological changes of the seed surface. According to a PCA comparison of basic characteristics of germination and initial growth, common flax seeds differ in their reaction to NTP from the other tested plants. On the contrary, chia seeds showed the best water uptake and kinematic viscosity. It was shown that NTP treatment improves the absorption of mucilaginous seeds and does not change the surface and structural properties of the seeds. These mucilaginous seeds can be used as raw seed, whereby NTP accelerates their preparation during soaking.

Meaningful deployment of plasma water-based nitrogen fixation in agricultural application is hindered primarily due to its poor synthesis rate in compact systems. The study reports a directly deployable thermal plasma based portable catalytic compact system, offering typical synthesis rate as high as 1035 mg/min for nitrate and 635 mg/min for nitrite directly from naturally abundant atmospheric air and water. Developed technology is clean, sustainable, easily decentralizable, and completely free from fossil fuels and harmful intermediates like ammonia. The system avoids safety hazards and costs related to the requirements of continuous energy resources, pressurized environment for synthesis, regulated storage, refrigeration need, transportation of raw materials and distribution of fertilizer, as may be required by other competing technologies. Described system, consisting of air plasma torch, reaction chamber, water injection manifold and catalytic bed creates a unique nascent reactive plasma environment at ambient pressure that auto activates the catalyst in the field of thermal plasma for highly efficient fixation of nitrogen. Presented results indicate that use of combination catalysts with mechanically enhanced surface area allows drastic enhancement in the nitrogen fixation. Possible reaction chemistries, results of trials with different catalysts, time evolution of concentration, auto-conversion from nitrite to nitrate in aqueous media, time stability of concentration of the synthesized nitrate and observed remarkable effectiveness in the actual field trials are presented. Achieved synthesis rates are compared with those reported in literature in the area of thermal and non-thermal plasma.

The influence of quartz tube size on the surface distributions of reactive oxygen species (ROS) in model tissue treated with a He + O₂ plasma jet was investigated. Gelatin gel was used to construct the model tissue, and a KI-starch color agent was mixed with the model tissue to visualize the distribution of ROS. With increasing quartz tube diameter, the uniformity of the ROS distribution on the model tissue decreased, and the change in the surface distribution area of the ROS on the model tissue over the irradiation distance was quite different for different quartz tube diameters. The surface distribution of ROS on the model tissue was affected mainly by the working gas flow; thus, the diffusion range of the working gas flow on the model tissue surface determined the surface distribution area of ROS on the model tissue. The working gas flow was accelerated, and the diffusion range of the working gas flow on the model tissue surface expanded when the plasma was ignited, resulting from the modification of the working gas flow by the electrohydrodynamic (EHD) effect. The EHD effect on the expansion of the diffusion range of working gas flow on the model tissue was different for different quartz tube diameters, and the effect was determined mainly by the discharge current density of the plasma jet and the plasma propagation length.

This work presents the experimental study of the transport of typical air plasma long-lived reactive nitrogen species (RNS: HNO₂, NO₂, and NO) into deionized water and compares them with the most typical reactive oxygen species (ROS: H₂O₂ and O₃). RONS are generated either by external sources or by a hybrid streamer-transient spark plasma discharge, in contact with bulk water or aerosol of charged electrospray (ES) or non-charged nebulized microdroplets with a large gas/plasma-water interface. It was found that NO’s contribution to NO₂¯ ion formation was negligible, NO₂ contributed to about 10%, while the dominant contributor to NO₂¯ ion formation in water was gaseous HNO₂. A higher transport efficiency of O₃, and a much higher formation efficiency of NO₂¯ from gaseous NO₂ or HNO₂ than predicted by Henry’s law was observed, compared to the transport efficiency of H₂O₂ that corresponds to the expected Henry’s law solvation. The improvement of the transport/formation efficiencies by nebulized and ES microdroplets, where the surface area is significantly enhanced compared to the bulk water, is most evident for the solvation enhancement of the weakly soluble O₃. NO₂¯ ion formation efficiency was strongly improved in ES microdroplets with respect to bulk water and even to nebulized microdroplets, which is likely due to the charge effect that enhanced the formation of aqueous nitrite NO₂¯ ions when NO₂ or HNO₂ are transported into water. Comparisons of the molar amounts of O₃, H₂O₂, and NO₂¯ formed in water by hybrid streamer-transient spark plasma discharge with those obtained with single RONS from the external sources enabled us to estimate approximate concentrations of gaseous concentrations of HNO₂, NO₂, O₃, and H₂O₂. The medium or highly soluble gaseous HNO₂ or H₂O₂, with a low concentration of < 10 ppm are sufficient to induce the measured aqueous NO₂¯ or H₂O₂ amounts in water. This study contributes to a deeper understanding of the transport mechanism of gaseous plasma RONS into water that can optimize the design of plasma–liquid interaction systems to produce efficient and selected aqueous RONS in water.