Plasma Chemistry and Plasma Processing最新文献

Dielectric barrier discharge is an important method in plasma-enabled energy conversion. By coupling different power sources, plasma parameters can be easily controlled by a variety of operating parameters to optimize plasma-enabled non-oxidative methane conversion and plasma-catalytic ammonia synthesis. Due to the complexity of the reactions in the plasma, the application of the trial-and-error experiment method to multi-parameter problems will consume a lot of resources and time. When the cause of the change in response can be known, multi-parameter regression and sure independence screening and sparsifying operator can reasonably predict the changing relationship between the influencing factors and the experimental results, and at the same time give the expression, which is applied to the prediction of plasma-enabled non-oxidative methane conversion under different rising times, pulse widths, frequencies, and voltages. However, catalysts are usually added in plasma energy conversion. The characteristics of catalysts are determined by multiple macro- and micro-characteristics. If fitting analysis is carried out for each feature, the problem of data explosion will be brought about, and this is not feasible in the experiment. Therefore, the artificial neural network is used to explain the influence of the N₂ ratio and gas temperature of different catalysts due to the lack of clear characteristic quantity to characterize the catalytic action in plasma-catalytic ammonia synthesis. Different machine learning methods applied to different problems will accelerate the parameter optimization in plasma-enabled energy conversion.

In the current study, a square assembly of four quad-atmospheric pressure plasma jets (q-APPJ) is used to treat large-sized chilli seeds simultaneously. Germination and growth characteristics improve significantly after a 10-sec treatment of q-APPJ employing argon as the working gas. Plasma-treated chilli seed is more etched and porous than those untreated seed surface, as shown in scanning electron microscopy. The chemical changes of the plasma-treated seeds showed that the Ar plasma-treatment oxidise the seed surface to enhance their wettability, stimulate the water uptake, increase the water electrical conductivity and result in improved seed germination. In addition, optical emission spectroscopy is used to detect the different plasma species present and evaluate their plasma parameters (electron temperature and density). These positive results suggested that Ar plasma-treatment, in APPJ setup, improve seed germination, and potentially improve crop yield, and food security issues.

Developing antibacterial materials is an efficient way to reduce the risk of harmful microorganism to human body. As a kind of popular textiles, cotton fabric (CF) is easy to breed microorganism and it is necessary to render it with biocidal effect. In this work, a water-soluble N-halamine precursor, (E)-1-(4-(allyloxy)phenyl)-N-(2-(piperazin-1-yl)ethyl)methanimine (APPEM), was synthesized and grafted onto cotton fabric through an argon plasma-induced grafting polymerization process. Afterward, the grafted cotton fabric was exposed to dilute sodium hypochlorite solution to change N–H bond into N–Cl bond and then the antibacterial cotton fabric (CF-APPEM-Cl) was obtained. The treated cotton fabric presented considerable biocidal efficacy and stability against UV light, washing, and storage. Escherichia coli (6.63 logs) and Staphylococcus aureus (6.44 logs) could be effectively inactivated within 60 min. Also, the oxidative chlorine on the fabric recovered over 76.9 and 81.5% after UV irradiation for 24 h and 50 washing cycles, respectively. And the oxidative chlorine remained 85% after 30 days of storage. Meanwhile, the mechanical properties of cotton fabric were hardly affected by this antibacterial treatment. This work provides a simple and efficient way to prepare antibacterial cotton fabric with high performance, which might be helpful to promote the development of antibacterial textiles.

A fundamental study of (hbox {CO}_2)/(hbox {CH}_4) plasma is performed in a glow discharge at a few Torr. Experimental and numerical results are compared to identify the main reaction pathways. OES-based techniques and FTIR (Fourier Transform Infrared) spectroscopy are used to determine molecules densities and gas temperature. Several conditions of pressure, initial mixture and residence time are measured. The main dissociation products are found to be CO and (hbox {H}_2). The LoKI simulation tool was used to build a simplified kinetic scheme to limit the uncertainties on rate coefficients, but sufficient to reproduce the experimental data. To this aim, only molecules containing at most one carbon atom are considered based on the experimental observations. Obtaining a good match between the experimental data and the simulation requires the inclusion of reactions involving the excited state (hbox {O}(^{1}hbox {D})). The key role of (hbox {CH}_3) radical is also emphasized. The good match obtained between the experiment and the simulation allows to draw the main reaction pathways of the low-pressure (hbox {CO}_2)-(hbox {CH}_4) plasmas, in particular to identify the main back reaction mechanisms for (hbox {CO}_2). The role of (hbox {CH}_2)O and (hbox {H}_2)O in the gas phase is also discussed in depth as they appear to play an important role on catalytic surface studied in the part II of this study.

The double-chamber arc plasma torch (DCAPT) is a promising arc source due to its high energy efficiency and low erosion rate. It has been widely used in various fields including coal powder ignition, boiler heavy oil-free ignition, and production of sheet-shaped carbon materials, among others, but research on its micro-discharge characteristics is still insufficient. In this work, a magnetically-stabilized DCAPT with a quartz window on the inner electrode is designed and studied, in order to investigate the effects of magnetic field position and intensity, discharge current, gas flow rate, electrode diameter, and electrode polarity on its discharge characteristics. Results show that both the volt-ampere characteristics and thermal efficiency of DCAPT exhibit a strictly decreasing trend, and both of them can be accurately predicted using similar theoretical approaches. The discharge characteristics of DCAPT differ significantly for different polarities. When in reverse polarity, the outer cathode arc root attaches to the outlet, resulting in an increased arc length and greater randomness in the arc-root fluctuations. As a result, the arc length, voltage, thermal efficiency, and voltage fluctuations are all greater than with normal polarity. Within the experimental range of the parameters, the thermal efficiency of DCAPT is between 40 and 74%. Due to the cathode's “easily mobility” characteristic, the rotation speed of the cathode arc root is always greater than that of the anode, resulting in higher thermal losses for the cathode than for the anode. This is the primary source of thermal loss and the main factor contributing to the rapid erosion of the cathode in the DCAPT. This study reveals the correlation between the volt-ampere characteristics, thermal characteristics, and dynamic evolution of the DCAPT. The research findings have significance for guiding the structural design, parameter selection, and choice of application of this type of plasma torch.

Ultraviolet B radiation (UVB) is widely used in agricultural plant growth and phototherapy. The traditional light sources have a low UVB radiation efficiency, poor uniformity radiation, high energy consumption, and short service lifetime. The multiband XeBr^* and XeCl^* planar excilamps as high-power UVB sources have not been researched in existing studies and the power density of XeBr^*/XeCl^* excilamps reported in the study are not high. This work presents a high-power density planar excilamp of homogeneous dielectric barrier discharge in a mixture of xenon and molecular bromine and chlorine (Xe/Br₂/Cl₂). The spectrum, electrical parameters, total gas pressure, and gas mixture composition, have been analyzed. For the multiband excilamp filled with Xe/Br₂/Cl₂, it has been demonstrated that the maximum UVB and total radiant efficiency is 7.9% and 9.7% with optimal chlorine ratio of 0.1% and the bromine ratio ranging from 0.1 to 0.2%, with the input power of 138 W at the total pressure of gas mixture of 200 mbar. This work has confirmed that the percentage of bromine molecules must be higher than the percentage of chlorine by a factor of about 2.6 to achieve the same intensities of the XeBr^* 282 nm and XeCl^* 308 nm bands. These results allow to find out the optimum radiation efficiency of multiband excilamps with a large planar geometry to meet the requirement of UVB industrial applications.

Gas–liquid discharge coupling with photocatalysts is an effective approach to enhance the chemical activity of plasma treated liquid. However, the incomplete understanding of the discharge characteristics with the addition of photocatalysts remain. The characteristics of pulsed gas–liquid discharge combining TiO₂ or WO₃ are studied in this work to address this issue. Results indicate that the addition of photocatalysts significantly promote the discharge, as evidenced by the diagnosis of discharge current, optical emission spectra, concentrations of aqueous species and solution properties. Specifically, the addition of catalysts enhances the discharge current and enrich the emission spectrum. The atomic emission lines O (3p–3s), N (3p–3s) and H_α were also observed with the addition of TiO₂, followed by higher content of reactive species in the solution. However, the addition of catalysts makes the discharge more unstable. This study contributes to an improved understanding of the mechanism of gas–liquid discharge coupled with photocatalysts for the improvement in applications.