Effects of Oxygen Concentration on Pulsed Dielectric Barrier Discharge in Helium-Oxygen Mixture at Atmospheric Pressure

In this work the effects of O_2 concentration on the pulsed dielectric barrier discharge in helium-oxygen mixture at atmospheric pressure have been numerically researched by using a one-dimensional fluid model in conjunction with the chosen key species and chemical reactions.The reliability of the used model has been examined by comparing the calculated discharge current with the reported experiments. The present work presents the following significant results. The dominative positive and negative particles are He_2~+ and O_2~-, respectively, the densities of the reactive oxygen species(ROS) get their maxima nearly at the central position of the gap, and the density of the ground state O is highest in the ROS. The increase of O_2 concentration results in increasingly weak discharge and the time lag of the ignition. For O_2 concentrations below 1.1%,the density of O is much higher than other species, the averaged dissipated power density presents an evident increase for small O_2 concentration and then the increase becomes weak. In particular,the total density of the reactive oxygen species reaches its maximums at the O_2 concentration of about 0.5%. This characteristic further convinces the experimental observation that the O_2 concentration of 0.5% is an optimal O_2/He ratio in the inactivation of bacteria and biomolecules when radiated by using the plasmas produced in a helium oxygen mixture.     

Conversion of NO with a catalytic packed-bed dielectric barrier discharge reactor

This paper discusses the conversion of nitric oxide (NO) with a low-temperature plasma induced by a catalytic packed-bed dielectric barrier discharge (DBD) reactor.Alumina oxide (Al2O3),glass (SiO2) and zirconium oxide (ZrO2),three different spherical packed materials of the same size,were each present in the DBD reactor.The NO conversion under varying input voltage and specific energy density,and the effects of catalysts (titanium dioxide (TiO2) and manganese oxide (MnOx) coated on Al2O3) on NO conversion were investigated.The experimental results showed that NO conversion was greatly enhanced in the presence of packed materials in the reactor,and the catalytic packed bed of MnOx/Al2O3 showed better performance than that of TiO2/Al2O3.The surface and crystal structures of the materials and catalysts were characterized through scanning electron microscopy analysis.The final products were clearly observed by a Fourier transform infrared spectrometer and provided a better understanding of NO conversion.     

Atmospheric Pressure Plasma Jet in Ar and O2/Ar Mixtures： Properties and High Performance for Surface Cleaning＊

An atmospheric pressure plasma jet generated in Ar and O2/Ar mixtures has been investigated by specially designed equipment with double power electrodes at 20~32 kHz, and their effects on the cleaning of surfaces have been studied. Properties of the jet discharge are studied by electrical diagnostics, including the waveform of discharge voltage, discharge current and the Q-V Lissajous figures. The optical emission spectroscopy is used to measure the plasma parameters, such as the excitation temperature and the gas temperature. It is found that the consumed power and the excitation temperature increase with increase of the discharge frequency. On the other hand, at the same discharge frequency, these parameters in O2/Ar mixture plasma are found to be much larger. The effect on surface cleaning is studied from the changes in the contact angle. For Ar plasma jet, the contact angle decreases with increase of the discharge frequency. For O2/Ar mixture plasma jet, the contact angle decreases with increase of discharge frequency up to 26 kHz, however, further increase of discharge frequency does not show further decrease in the contact angle. At the same discharge frequency, the contact angle after O2/Ar mixture plasma cleaning is found to be much lower compared to the case of pure Ar. From the results of quadrupole mass-spectrum analysis, we can identify more fragment molecules of CO and H2O in the emitted gases after O2/Ar plasma jet treatment compared with Ar plasma jet treatment, which are produced by the decomposition of surface organic contaminants during the cleaning process.     

Studies on Nitrogen Oxides Removal Using Plasma Assisted Catalytic Reactor

An electric discharge plasma reactor combined with a catalytic reactor was studied for removing nitrogen oxides. To understand the combined process thoroughly, discharge plasma and catalytic process were separately studied first, and then the two processes were combined for the study. The plasma reactor was able to oxidize NO to NO2 well although the oxidation rate decreased with temperature. The plasma reactor alone did not reduce the NOx (NO NO2) level effectively, but the increase in the ratio of NO2 to NO as a result of plasma discharge led to the enhancement of NOx removal efficiency even at lower temperatures over the catalyst surface (V2O5-WO3/TiO2). At a gas temperature of 100℃, the NOx removal efficiency obtained using the combined plasma catalytic process was 88% for an energy input of 36 eV/molecule or 30 J/L     

Fischer-Tropsch Performance of an SiO2-Supported Co-Based Catalyst Prepared by Hydrogen Dielectric-Barrier Discharge Plasma

A silica-supported cobalt catalyst was prepared by hydrogen dielectric-barrier dis- charge （H2-DBD） plasma. Compared to thermal hydrogen reduction, H2-DBD plasma treatment can not only fully decompose the cobalt precursor but also partially reduce the cobalt oxides at lower temperature and with less time. The effect of the discharge atmosphere on the property of the plasma-prepared catalyst and the Fischer-Tropsch synthesis activity was studied. The re- sults indicate that H2-DBD plasma treatment is a promising alternative for preparing Co/SiO2 catalysts from the viewpoint of energy savings and efficiency.     

快速灰化炉用NO_2气体的制备

本文报道了两种用于快速灰化炉的 NO_2气体的实验室制备方法及其发生装置。用 N_2O_4加热分解或用 NaNO_2和 H_2SO_4反应生成 NO 继与 O_2反应产生 NO_2气体。用上述方法制备的 NO_2气体,对多种生物样品进行了快灰化,结果表明,实验室制备的 NO_2气体可满足快速灰化炉灰化生物样品的要求。     

NO_x storage and reduction assisted by non-thermal plasma over Co/Pt/Ba/γ-Al_2O_3 catalyst using CH_4 as reductant

N_Ox storage and reduction(NSR) technology has been regarded as one of the most promising strategies for the removal of nitric oxides(NO_x) from lean-burn engines, and the potential of the plasma catalysis method for NO_x reduction has been confirmed in the past few decades. This work reports the NSR of nitric oxide(NO) by combining non-thermal plasma(NTP) and Co/Pt/Ba/γ-Al_2O_3(Co/PBA) catalyst using methane as a reductant. The experimental results reveal that the NO_x conversion of NSR assisted by NTP is notably enhanced compared to the catalytic efficiency obtained from NSR in the range of 150 °C–350 °C, and NO_x conversion of the 8% Co/PBA catalyst reaches 96.8% at 350°C. Oxygen(O_2) has a significant effect on the removal of NO_x, and the NO_x conversion increases firstly and then decreases when the O_2 concentration ranges from 2% to 10%. Water vapor reduces the NO_x storage capacity of Co/PBA catalysts on account of the competition for adsorption sites on the surface of Co/PBA catalysts. There is a negative correlation between sulfur dioxide(SO_2) and NO_x conversion in the NTP system, and the 8% Co/PBA catalyst exhibits higher NO_x conversion compared to other catalysts, which shows that Co has a certain SO_2 resistance.     

Degradation of Microcystin-LR by Gas-Liquid Interfacial Discharge Plasma

In this study, we report on the degradation of microcystin-LR （MC-LR） by gas- liquid interracial discharge plasma. The influences of operation parameters such as average input voltage, electrode distance and gas flow rate are investigated. Experimental results indicate that the input voltage and gas flow rate have positive influences on MC-LR degradation, while the electrode distance has a negative one. After 6 min discharge with 25 kV average input voltage and 60 L/h air aerati by discharge both in on, the degradation rate of MC-LR achieves 75.3%. distilled water and MC-LR solution are measured H202 and 03 generated Moreover, an emission spectroscopy is used as an indicator of the processes that take place on the gas-liquid boundary and inside plasma. Varied types of radicals （O, .OH, CO, 03, etc.） are proved to be present in the gas phase during gas-liquid interfacial discharge.     

Generation of reactive species in atmospheric pressure dielectric barrier discharge with liquid water

Atmospheric pressure helium/water dielectric barrier discharge(DBD) plasma is used to investigate the generation of reactive species in a gas–liquid interface and in a liquid. The emission intensity of the reactive species is measured by optical emission spectroscopy(OES)with different discharge powers at the gas–liquid interface. Spectrophotometry is used to analyze the reactive species induced by the plasma in the liquid. The concentration of OH radicals reaches 2.2 μm after 3 min of discharge treatment. In addition, the concentration of primary longlived reactive species such as H_2O_2, NO_3~- and O_3 are measured based on plasma treatment time.After 5 min of discharge treatment, the concentration of H_2O_2, NO_3~-, and O_3 increased from 0 mg?·?L~(-1) to 96 mg?·?L~(-1), 19.5 mg?·?L~(-1), and 3.5 mg?·?L~(-1), respectively. The water treated by plasma still contained a considerable concentration of reactive species after 6 h of storage. The results will contribute to optimizing the DBD plasma system for biological decontamination.     

Hybrid electric discharge plasma technologies for water decontamination: a short review

Electric discharge plasma (EDP) can efficiently degrade aqueous pollutants by its in situ generated strong oxidative species (·OH, ·O, H₂O₂, O₃, etc) and other physiochemical effects (UV irradiation, shockwaves, local high temperature, etc), but a high energy consumptions limit the application of EDP in water treatment. Some adsorbents, catalysts, and oxidants have been employed for enhancing the degradation of pollutants by discharge plasma. These hybrid plasma technologies offer improved water treatment performance compared to discharge plasma alone. This paper reviews the water decontamination performance and mechanisms of these hybrid plasma technologies, and some suggestions on future water treatment technologies based on discharge plasma are also proposed.     

Discharge characteristics and reactive species production of unipolar and bipolar nanosecond pulsed gas-liquid discharge generated in atmospheric

In this paper,unipolar pulse (including positive pulse and negative pulse) and bipolar pulse voltage are employed to generate diffuse gas-liquid discharge in atmospheric N2 with a trumpet-shaped quartz tube.The current-voltage waveforms,optical emission spectra of excited state active species,FTIR spectra of exhaust gas components,plasma gas temperature,and aqueous H2O2,NO2-,and NO3-production are compared in three pulse modes,meanwhile,the effects of pulse peak voltage and gas flow rate on the production of reactive species are studied.The results show that two obvious discharges occur in each voltage pulse in unipolar pulse driven discharge,differently,in bipolar pulse driven discharge,only one main discharge appears in a single voltage pulse time.The intensities of active species (OH(A),and O(3p)) in all three pulsed discharge increase with the rise of pulse peak voltage and have the highest value at 200 ml min-1 of gas flow rate.The absorbance intensities of NO2 and N2O increase with the increase of pulse peak voltage and decrease with the increase of gas flow rate.Under the same discharge conditions,the bipolar pulse driven discharge shows lower breakdown voltage,and higher intensities of excited species (N2(C),OH(A),and O(3p)),nitrogen oxides (NO2,NO,and N2O),and higher production of aqueous H2O2,NO2-,and NO3-compared with both unipolar positive and negative discharges.     

DeNOx Study in Diesel Engine Exhaust Using Barrier DischargeCorona Assisted by V2O5／TiO2 Catalyst

A plasma-assisted catalytic reactor was used to remove nitrogen oxides (NOx) from diesel engine exhaust operated under different load conditions. Initial studies were focused on plasma reactor (a dielectric barrier discharge reactor) treatment of diesel exhaust at various temperatures. The nitric oxide (NO) removal efficiency was lowered when high temperature exhaustwas treated using plasma reactor. Also, NO removal efficiency decreased when 45% load exhaust was treated. Studies were then made with plasma reactor combined with a catalytic reactor consisting of a selective catalytic reduction (SCR) catalyst, V2O5/TiO2. Ammonia was used as a reducing agent for SCR process in a ratio of 1:1 to NOx. The studies were focused on temperatures of the SCR catalytic reactor below 200℃. The plasma-assisted catalytic reactor was operated well to remove NOx under no-load and load conditions. For an energy input of 96 J/1, the NOx removal efficiencies obtained under no-load and load conditions were 90% and 72% respectively at an exhaust temperature of 100℃.     

Synthesis of Nano-Size AlN Powders by Carbothermal Reduction from Plasma-Assisted Ball Milling Precursor

Nano-size aluminum nitride(AlN) powders have been successfully synthesized with a high efficiency method through annealing from milling assisted by discharge plasma(p-milling)alumina(Al_2O_3) precursors. The characterization of the p-milling Al_2O_3 powders and the synthesized AlN are investigated. Compared to conventional ball milling(c-milling), it can be found that the precursors by p-milling have a finer grain size with a higher specific surface area,which lead to a faster reaction efficiency and higher conversion to Al N at lower temperatures. The activation energy of p-milling Al_2O_3 is found to be 371.5 kJ/mol, a value that is much less than the reported value of the unmilled and the conventional milled Al_2O_3. Meanwhile, the synthesized Al N powders have unique features, such as an irregular lamp-like morphology with uniform particle distribution and fine average particle size. The results are attributed to the unique synergistic effect of p-milling, which is the effect of deformation, fracture, and cold welding of Al_2O_3 powders resulting from ball milling, that will be enhanced due to the introduction of discharge plasma.     

Bromate removal by gamma irradiation in aqueous solutions

Bromate(BrO_3) is a disinfection by-product in drinking water, and its removal is very difficult especially at low levels.60 Co gamma rays were used to remove BrO_3in aqueous solution in this study. The effects of absorbed doses, BrO_3initial concentration, gas saturation, p H value and coexisting anions(Cl, NO 3, SO2 4and HCO 3=CO_3~(2 -))on BrO_3reduction were evaluated. After 4.0-k Gy irradiation of air-equilibrated solution of 30.7 lg/L BrO_3, the residual BrO_3was 8.3 lg/L, which is below the maximum contaminant level of drinking water. The BrO_3reduction rate increased with the dose, in the order of N2[ air [ O_2[ N_2O atmosphere under similar conditions. The results also show that high p H favored the BrO_3removal. According to the experimental results, it can be concluded that the efficiency of decomposing BrO_3by reactive species followed the order of e aq[ H [ HO_2 [ O_2. Coexisting Cl, HCO 3=CO_3~(2 -)and SO2 4ions have little effect on BrO_3removal, whereas NO_3can inhibit its removal as a result of competition with BrO_3for e aq.     

Evaluation and Optimization of Electrode Configuration of Multi-Channel Corona Discharge Plasma for Dye-Containing Wastewater Treatment

A discharge plasma reactor with a point-to-plane structure was widely studied experimentally in wastewater treatment.In order to improve the utilization efficiency of active species and the energy efficiency of this kind of discharge plasma reactor during wastewater treatment,the electrode configuration of the point-to-plane corona discharge reactor was studied by evaluating the effects of discharge spacing and adjacent point distance on discharge power and discharge energy density,and then dye-containing wastewater decoloration experiments were conducted on the basis of the optimum electrode configuration.The experimental results of the discharge characteristics showed that high discharge power and discharge energy density were achieved when the ratio of discharge spacing to adjacent point distance(d/s) was 0.5.Reactive Brilliant Blue(RBB) wastewater treatment experiments presented that the highest RBB decoloration efficiency was observed at d/s of 0.5,which was consistent with the result obtained in the discharge characteristics experiments.In addition,the biodegradability of RBB wastewater was enhanced greatly after discharge plasma treatment under the optimum electrode configuration.RBB degradation processes were analyzed by GC-MS and IC,and the possible mechanism for RBB decoloration was also discussed.     

A comparative study on the activity of TiO2 in pulsed plasma under different discharge conditions

In the present study,a combination of pulsed discharge plasma and TiO_2(plasma/TiO_2)has been developed in order to study the activity of TiO_2by varying the discharge conditions of pulsed voltage,discharge mode,air flow rate and solution conductivity.Phenol was used as the chemical probe to characterize the activity of TiO_2in a pulsed discharge system.The experimental results showed that the phenol removal efficiency could be improved by about 10%by increasing the applied voltage.The phenol removal efficiency for three discharge modes in the plasma-discharge-alone system was found to be highest in the spark mode,followed by the spark–streamer mode and finally the streamer mode.In the plasma/TiO_2system,the highest catalytic effect of TiO_2was observed in the spark–streamer discharge mode,which may be attributed to the favorable chemical and physical effects from the spark–streamer discharge mode,such as ultraviolet light,O_3,H_2O_2,pyrolysis,shockwaves and high-energy electrons.Meanwhile,the optimal flow rate and conductivity were 0.05 m~3l~(-1)and 10μS cm~(-1),respectively.The main phenolic intermediates were hydroquinone,catechol,and p-benzoquinone during the discharge treatment process.A different phenol degradation pathway was observed in the plasma/TiO_2system as compared to plasma alone.Analysis of the reaction intermediates demonstrated that p-benzoquinone reduction was selectively catalyzed on the TiO_2surface.The effective decomposition of phenol constant(D_e)increased from 74.11%to 79.16%when TiO_2was added,indicating that higher phenol mineralization was achieved in the plasma/TiO_2system.     

High-efficiency removal of NO_x using dielectric barrier discharge nonthermal plasma with water as an outer electrode

With the rapid increase in the number of cars and the development of industry, nitrogen oxide(NO_x)emissions have become a serious and pressing problem. This work reports on the development of a water-cooled dielectric barrier discharge reactor for gaseous NOxremoval at low temperature. The characteristics of the reactor are evaluated with and without packing of the reaction tube with 2 mm diameter dielectric beads composed of glass, ZnO, MnO_2, ZrO_2, or Fe_2O_3. It is found that the use of a water-cooled tube reduces the temperature, which stabilizes the reaction, and provides a much greater NO conversion efficiency(28.8%) than that obtained using quartz tube(14.1%) at a frequency of 8 k Hz with an input voltage of 6.8 k V. Furthermore,under equivalent conditions, packing the reactor tube with glass beads greatly increases the NO conversion efficiency to 95.85%. This is because the dielectric beads alter the distribution of the electric field due to the influence of polarization at the glass bead surfaces, which ultimately enhances the plasma discharge intensity. The presence of the dielectric beads increases the gas residence time within the reactor. Experimental verification and a theoretical basis are provided for the industrial application of the proposed plasma NO removal process employing dielectric bead packing.     

Spectroscopic diagnosis of plasma in atmospheric pressure negative pulsed gasliquid discharge with nozzle-cylinder electrode

The plasma characteristics of a gas-liquid phase discharge reactor were investigated by optical and electrical methods.The nozzle-cylinder electrode in the discharge reactor was supplied witha negative nanosecond pulsed generator.The optical emission spectrum diagnosis revealed that OH(A~2∑~+?→?X~2Π,306–309 nm),N~3_2(CΠ→B~3Π_g,337 nm),O(3p~5p→3s~5s~0,777.2 nm)and O(3p~3p→3s~3s~0,844.6 nm)were produced in the discharge plasma channels.The electron temperature(T_e)was calculated from the emission relative intensity ratio between the atomic O 777.2 nm and 844.6 nm,and it increased with the applied voltage and the pulsed frequency and fell within the range of 0.5–0.8 e V.The gas temperature(T_g)that was measured by Lifbase was in a range from 400 K to 600 K.     

Investigation of optimum discharge characteristics and chemical activity of AC driven air plasma jet and its anticancer effect

In this study,we investigated the effects of the quartz tube diameter,air flow rate,and applied voltage on the characteristics of an air plasma jet to obtain the optimized discharge characteristics.The physicochemical properties and concentration of reactive oxygen and nitrogen species(RONS)in plasma-activated medium(PAM)were characterized to explore their chemical activity.Furthermore,we investigated the inactivation effect of air plasma jet on tumour cells and their corresponding inactivation mechanism.The results show that the tube diameter plays an important role in sustaining the voltage of the air plasma jet,and the gas flow rate affects the jet length and discharge intensity.Additionally,the air plasma jet discharge displays two modes,namely,ozone and nitrogen oxide modes at high and low gas flow rates,respectively.Increasing the voltage increases the concentration of reactive species and the length of discharge.By evaluating the viability of A549 cells under different parameters,the optimal treatment conditions were determined to be a quartz tube diameter of 4 mm,gas flow rate of 0.5 SLM,and voltage of 18 kV.Furthermore,an air plasma jet under the optimized conditions effectively enhanced the chemical activity in PAM and produced more aqueous RONS.The air plasma jet induced significant cytotoxicity in A549 cancer cells after plasma treatment.H2O2 and NO2 are regarded as key factors in promoting cell inactivation.The present study demonstrates the potential use of tumour cell therapy by atmospheric air PAM,which aids a better understanding of plasma liquid chemistry.     

Water Content Effect on Oxides Yield in Gas and Liquid Phase Using DBD Arrays in Mist Spray

Electric discharge in and in contact with water can accompany ultraviolet (UV) radiation and electron impact,which can generate a large number of active species such as hydroxyl radicals (OH),oxygen radical (O),ozone (O3) and hydrogen peroxide (H2O2).In this paper,a non thermal plasma processing system was established by means of dielectric barrier discharge (DBD) arrays in water mist spray.The relationship between droplet size and water content was examined,and the effects of the concentrations of oxides in both treated water and gas were investigated under different water content and discharge time.The relative intensity of UV spectra from DBD in water mist was a function of water content.The concentrations of both O3 and nitrogen dioxide (NO2) in DBD room decreased with increasing water content.Moreover,the concentrations of H2O2,O3 and nitrogen oxides (NOx) in treated water decreased with increasing water content,and all the ones enhanced after discharge.The experimental results were further analyzed by chemical reaction equations and commented by physical principles as much as possible.At last,the water containing phenol was tested in this system for the concentration from 100 mg/L to 9.8 mg/L in a period of 35 min.