Xingquan Wang

Treatment of enterococcus faecalis bacteria by a helium atmospheric cold plasma brush with oxygen addition

An atmospheric cold plasma brush suitable for large area and low-temperature plasma-based sterilization is designed. Results demonstrate that the He/O2 plasma more effectively kills Enterococcus faecalis than the pure He plasma. In addition, the sterilization efficiency values of the He/O2 plasma depend on the oxygen fraction in Helium gas. The atmospheric cold plasma brush using a proper ratio of He/O2 (2.5%) reaches the optimum sterilization efficiency. After plasma treatment, the cell structure and morphology changes can be observed by the scanning electron microscopy. Optical emission measurements indicate that reactive species such as O and OH play a significant role in the sterilization process.

Deactivation of A549 cancer cells in vitro by a dielectric barrier discharge plasma needle

An inactivation mechanism study on A549 cancer cells by means of a dielectric barrier discharge plasma needle is presented. The neutral red uptake assay provides a quantitative estimation of cell viability after plasma treatment. Experimental results show that the efficiency of argon plasma for the inactivation process is very dependent on power and treatment time. A 27 W power and 120 s treatment time along with 900 standard cubic centimeter per minute Ar flow and a nozzle-to-sample separation of 3 mm are the best parameters of the process. According to the argon emission spectra of the plasma jet and the optical microscope images of the A549 cells after plasma treatment, it is concluded that the reactive species (for example, OH and O) in the argon plasma play a major role in the cell deactivation.

First-principles investigations of Co- and Fe-doped SnO2

We have investigated the electronic and magnetic properties of Co- and Fe-doped SnO2 by first-principles methods. The obtained results show that the ferromagnetic order is energetically much favored relative to the antiferromagnetic order in all the considered models of Co- and Fe-doped SnO2. The exchange interaction between Co ions is a long-range ferromagnetic interaction and gradually weakened as the distance between Co ions increases. For Fe-doped SnO2, the exchange interaction is also a long-range ferromagnetic one, but it oscillates with the variation of the distances between Fe ions. In addition, we further probe the concentration effect on the magnetic properties in the doped systems. The obtained results show that the exchange interaction between Co and Fe ions is reduced, implying that the enhancement of Curie temperature is not favored by increasing Co- and Fe-doping concentrations.

Synergistic Effect of Atmospheric-pressure Plasma and TiO2 Photocatalysis on Inactivation of Escherichia coli Cells in Aqueous Media.

Atmospheric-pressure plasma and TiO2 photocatalysis have been widely investigated separately for the management and reduction of microorganisms in aqueous solutions. In this paper, the two methods were combined in order to achieve a more profound understanding of their interactions in disinfection of water contaminated by Escherichia coli. Under water discharges carried out by microplasma jet arrays can result in a rapid inactivation of E. coli cells. The inactivation efficiency is largely dependent on the feed gases used, the plasma treatment time, and the discharge power. Compared to atmospheric-pressure N2, He and air microplasma arrays, O2 microplasma had the highest activity against E. coli cells in aqueous solution, and showed >99.9% bacterial inactivation efficiency within 4 min. Addition of TiO2 photocatalytic film to the plasma discharge reactor significantly enhanced the inactivation efficiency of the O2 microplasma system, decreasing the time required to achieve 99.9% killing of E. coli cells to 1 min. This may be attributed to the enhancement of ROS generation due to high catalytic activity and stability of the TiO2 photocatalyst in the combined plasma-TiO2 systems. Present work demonstrated the synergistic effect of the two agents, which can be correlated in order to maximize treatment efficiency.

Characteristics of NOx Removal Combining Dielectric Barrier Discharge Plasma with Selective Catalytic Reduction by C3H6

Characteristics of NOx removal combining dielectric barrier discharge (DBD) plasma with selective catalytic reduction (SCR) by C3H6 were investigated under the conditions of high NOx concentration and high space velocity at various temperatures. Experiment results show that there were no obvious removal of NOx and NO in the only C3H6-SCR system and only DBD system individually. But the high NOx removal rate was achieved in C3H6-SCR cooperating with DBD plasma system. Especially NOx removal rate can reach up to 88.5% at 150 °C simulating diesel engine exhaust temperature. It can be seen that when discharge comes into being, the catalystic activity was enhanced with discharge strengthened, so that the NOx was almost completely removed. In the course of NOx removal, DBD played an important role in oxidizing NO to NO2 and activating C3H6 and catalysts to reduce NOx.

Non-equilibrium plasma prevention of Schistosoma japonicum transmission

Schistosoma japonicum is a widespread human and animal parasite that causes intestinal and hepatosplenic schistosomiasis linked to colon, liver and bladder cancers, and anemia. Estimated 230 million people are currently infected with Schistosoma spp, with 779 million people at risk of contracting the parasite. Infection occurs when a host comes into contact with cercariae, a planktonic larval stage of the parasite, and can be prevented by inactivating the larvae, commonly by chemical treatment. We investigated the use of physical non-equilibrium plasma generated at atmospheric pressure using custom-made dielectric barrier discharge reactor to kill S. japonicum cercariae. Survival rate decreased with treatment time and applied power. Plasmas generated in O2 and air gas discharges were more effective in killing S. japonicum cercariae than that generated in He, which is directly related to the mechanism by which cercariae are inactivated. Reactive oxygen species, such as O atoms, abundant in O2 plasma and NO in air plasma play a major role in killing of S. japonicum cercariae via oxidation mechanisms. Similar level of efficacy is also shown for a gliding arc discharge plasma jet generated in ambient air, a system that may be more appropriate for scale-up and integration into existing water treatment processes.

Decolorization of methyl violet in simulated wastewater by dielectric barrier discharge plasma

In this study, the decolorization ratio of methyl violet and energy consumption were individually investigated in dielectric barrier discharges of O2, He, and He + O2 gases. The results showed that the highest decolorization ratio was achieved in the O2 gas discharge, followed by the He + O2 and He gas discharges, and the decolorization was almost the same in the He + O2 and O2 gas discharges. For the He gas discharge, the energy consumption was lowest but the decolorization ratio was also lower than 50%. For the O2 gas discharge, a decolorization ratio of 99.5% was achieved but a high energy density of 32.5 kJ/L was required. For the He + O2 discharge, a decolorization ratio of 96% was achieved and the required energy density was only 7.7 kJ/L. Therefore, from the experimental results, the discharge in a mixture of He + O2 gases is optimal for the decolorization of methyl violet. When He is mixed into O2, a high decolorization ratio can be achieved and a low energy density is required.

Spectral characteristics of cotton seeds treated by a dielectric barrier discharge plasma

Cold atmospheric plasma has recently emerged as a simple, low-cost and efficient physical method for inducing significant biological responses in seeds and plants without the use of traditional, potentially environmentally-hazardous chemicals, fungicides or hormones. While the beneficial effects of plasma treatment on seed germination, disease resistance and agricultural output have been reported, the mechanisms that underpin the observed biological responses are yet to be fully described. This study employs Fourier Transform Infrared (FTIR) spectroscopy and emission spectroscopy to capture chemical interactions between plasmas and seed surfaces with the aim to provide a more comprehensive account of plasma−seed interactions. FTIR spectroscopy of the seed surface confirms plasma-induced chemical etching of the surface. The etching facilitates permeation of water into the seed, which is confirmed by water uptake measurements. FTIR of exhaust and emission spectra of discharges show oxygen-containing species known for their ability to stimulate biochemical processes and deactivate pathogenic microorganisms. In addition, water gas, CO2, CO and molecules containing −C(CH3)3− moieties observed in FTIR spectra of the exhaust gas during plasma treatment may be partly responsible for the plasma chemical etching of seed surface through oxidizing the organic components of the seed coat.

Effect of pulsed bias on the properties of ZrN/TiZrN films deposited by a cathodic vacuum arc

ZrN/TiZrN multilayers are deposited by using the cathodic vacuum arc method with different substrate bias (from 0 to −800 V), using Ti and Zr plasma flows in residual N2 atmosphere, combined with ion bombardment of sample surfaces. The effect of pulsed bias on the structure and properties of films is investigated. Microstructure of the coating is analyzed by X-ray diffraction (XRD), and scanning electron microscopy (SEM). In addition, nanohardness, Youngs modulus, and scratch tests are performed. The experimental results show that the films exhibit a nanoscale multilayer structure consisting of TiZrN and ZrN phases. Solid solutions are formed for component TiZrN films. The dominant preferred orientation of TiZrN films is (111) and (220). At a pulsed bias of −200 V, the nanohardness and the adhesion strength of the ZrN/TiZrN multilayer reach a maximum of 38 GPa, and 78 N, respectively. The ZrN/TiZrN multilayer demonstrates an enhanced nanohardness compared with binary TiN and ZrN films deposited under equivalent conditions.

Deposition of Ti-Al-N Films by Using a Cathodic Vacuum Arc with Pulsed Bias

Ti-Al-N hard films have been prepared by cathodic arc deposition by using an unipolar pulsed bias. In the present study, Ti-Al-N films were deposited on stainless steel and silicon wafers. The deposition rate, micrograph, preferred orientation and composition were systematically investigated by usingx-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), and a scanning electron microscope (SEM). It is shown that substate bias duty cycle and frequency have a great effect on film structure. A simple explanation for the results is also presented.