Product analysis and mechanism of toluene degradation by low temperature plasma with single dielectric barrier discharge

A single dielectric barrier discharge (DBD) low-temperature plasma reactor was set up, and toluene was selected as the representative substance for volatile organic compounds (VOCs), to study the reaction products and degradation mechanism of VOCs degradation by low-temperature plasma. Different parameters effect on the concentration of O₃ and NO_x during the degradation of toluene were studied. The exhaust in the process of toluene degradation was continuously detected and analyzed, and the degradation mechanism of toluene was explored. The results showed that the concentration of O₃ increased with the increase of the power density and discharge voltage of the plasma device. However, as the initial concentration of toluene increased, the concentration of O₃ basically keep steady. The concentration of NO_x in the by-products increased with the discharge voltage, power density, and initial concentration of toluene in the plasma device, and the concentration of NO₂ was much higher than the concentration of NO. The degradation process of toluene was detected and analyzed. The results showed that the degradation mechanism of toluene by plasma includes high energy electron bombardment reaction, active radical reaction and ion molecule reaction. Among them, the effect of high-energy electrons on toluene degradation is the largest, followed by the effect of free radicals, in which oxygen radicals participated in the reaction mainly through the formation of C–O bond, CO bond, (CO)–O– bond and –OH radical, while nitrogen radicals participate in the reaction mainly through the formation of C–NH₂, (CNH)- bond, CN bond and C–NO₂ bond. The results can provide some data supports for the study of low-temperature plasma degradation of VOCs.     

介质阻挡放电等离子体法制备优异光催化合成过氧化氢性能的氮空穴掺杂石墨相氮化碳（英文）

过氧化氢(H_2O_2)是一种绿色氧化剂,广泛应用于纺织、印染、造纸和医药等行业.目前,工业上采用蒽醌法制备H_2O_2,它由于需要多步加氢和氧化处理,因此能耗非常大.研究发现,采用贵金属催化剂可以将氢气和氧气直接合成H2O2,但催化剂价格过高,且反应本身存在爆炸风险.近年来,半导体光催化合成H_2O_2受到广泛关注.研究发现,在水存在下,光电子可以将氧气还原得到H_2O_2.介质阻挡放电(DBD)等离子体广泛应用于材料合成、挥发性有机物处理、汽车尾气净化和材料表面处理等.石墨相氮化碳(g-C_3N_4)是新型非金属光催化剂,以其性质稳定、能带适中和制备方便等优点而广受青睐.然而g-C_3N_4的比表面积和电荷分离效率较低,大大限制了其应用.本文采用DBD等离子体法在氢气气氛下制备了N空穴掺杂的石墨相氮化碳,采用XRD,N_2吸附,UV-Vis,SEM,TEM,XPS,EIS,EPR,O_2-TPD及PL等方法对催化剂进行了表征,并考察了N空穴对催化剂结构性质、光学性质及光催化合成H_2O_2性能的影响.结果显示,当DBD等离子体处理时间小于30 min时,所制催化剂颗粒尺寸显著小于焙烧法得到的,因而其比表面积显著提高.N空穴的引入降低了催化剂的能带,提高了可见光区的吸收.此外,N空穴作为反应活性位,既能吸附反应物氧气分子,又能捕获光电子并促进光电子从催化剂向氧气分子转移,进而发生后续还原反应.等离子体处理30 min得到的催化剂光催化合成H_2O_2性能最佳,是纯g-C_3N_4的11倍.本文为g-C_3N_4基催化剂的制备提供了一个新方法.     

A cold plasma dielectric barrier discharge atomic emission detector for atmospheric mercury

An automated atmospheric elemental mercury analyzer based on the dielectric barrier discharge (DBD) atomic emission technique was developed. The instrument is based on a gold-on tungsten coiled filament preconcentrator fashioned from commercial quartz-halogen lamps, a DBD excitation source and a radiation detector. An in-house program provided system control and data collection. Several types of radiation detectors, e.g., charge coupled device (CCD) array spectrometers, photomultiplier tubes (PMTs) and phototube (PT) are investigated. An argon plasma provided better performance than a nitrogen plasma. With ∼0.88 standard liters per min sampling rate and preconcentration for 2 min, the estimated (S/N = 3) detection limit was 0.12 ng/L (Hg⁰), the linear range extended at least to 6.6 ng Hg/L. Typical RSD values for determination at the single digit ng/L level ranged from 2.8 to 4.9%. In 19 separate calibrations conducted over 7 days, the calibration slope had a standard error of 1%. The system was applied to the determination of atmospheric mercury in two different locations.     

介质阻挡放电等离子体甲烷/水蒸气重整制氢

采用自制的介质阻挡放电实验系统,进行了甲烷/水蒸气大气压下重整制氢实验研究。考察了水碳比（水蒸气/甲烷物质的量比）、气体总流量、放电电压和放电频率对甲烷转化率及氢气等主要产物产率的影响。结果表明,甲烷转化率和氢气产率随着水碳比和放电电压的增加而增大,随着气体总流量和放电频率的增加呈现先增大后减小的变化规律。在放电电压18.6 kV、放电频率9.8 kHz、水碳比3.4、反应气体总流量79 mL/min时,获最大氢气产率（14.38%）。此外,利用发射光谱对放电过程中的活性基团进行了原位诊断,得到了CH·、OH·、H₂及H_α活性粒子的光谱信号强度随实验参数的变化规律,并结合放电机理推测了氢气的生成路径。     

Computer simulations of a dielectric barrier discharge used for analytical spectrometry

A model developed for a dielectric barrier discharge (DBD) in helium, used as a new spectroscopic source in analytical chemistry, is presented in this paper. The model is based on the fluid approach and describes the behavior of electrons, He⁺ and ions, He metastable atoms, He atoms in higher excited levels, and He₂ dimers. The He ground-state atoms are regarded as background gas. The characteristic effect of charging/discharging of the dielectrics which cover both electrodes is also simulated. Typical results of the model include the distribution of potential inside the plasma (and the potential drop across the dielectrics), the electric current and gap voltage as a function of time for a given applied potential profile, the spatial and temporal number-density profiles of the different plasma species, and the relative contributions of the mechanisms of their production and loss. Figure Schematic diagram of the dielectric barrier discharge (left) and typical temporal profiles of voltage and current, as obtained from the simulations (right)     

Evaluation of a hydride generation-atomic fluorescence system for the determination of arsenic using a dielectric barrier discharge atomizer

A new atomizer based on atmospheric pressure dielectric barrier discharge (DBD) plasma was specially designed for atomic fluorescence spectrometry (AFS) in order to be applied to the measurement of arsenic. The characteristics of the DBD atomizer and the effects of different parameters (power, discharge gas, gas flow rate, and KBH₄ concentration) were discussed in the paper. The DBD atomizer shows the following features: (1) low operation temperature (between 44 and 70 °C, depending on the operation conditions); (2) low power consumption; (3) operation at atmospheric pressure. The detection limit of As(III) using hydride generation (HG) with the proposed DBD-AFS was 0.04 μg L⁻¹. The analytical results obtained by the present method for total arsenic in reference materials, orchard leaves (SRM 1571) and water samples GBW(E) 080390, agree well with the certified values. The present HG-DBD-AFS is more sensitive and reliable for the determination of arsenic. It is a very promising technique allowing for field arsenic analysis based on atomic spectrometry.     

The impact of a dielectric barrier discharge on the catalytic oxidation of methane over Ni-containing catalyst

Methane oxidation with air was studied over a Ni-containing catalyst in a dielectric barrier discharge (DBD) at temperatures above 625 K. The DBD increases the methane conversion and shifts the process towards partial oxidation. This effect is related to a catalyst heating by the discharge. This revised version was published online in August 2006 with corrections to the Cover Date.     

Determination of bismuth in solid samples by hydride generation atomic fluorescence spectrometry with a dielectric barrier discharge atomizer

An atmospheric pressure dielectric barrier discharge (DBD) atomizer was investigated for bismuth (Bi) determination with hydride generation (HG) atomic fluorescence spectrometry (AFS). The characteristics of the atomizer and the effects of experimental parameters, including observation height, discharge power, flow rate of discharge gas and AFS carrier gas were optimized. The linear range of present method for Bi determination is 0.5-300.0 μg L⁻¹ with a detection limit of 0.07 μg L⁻¹ (3σ). The method was validated by the analysis of reference materials (GBW08517 and GSB-14) and the results agreed well with the reference values. The established method was applied to the determination of Bi in ore, soil and ash samples.     

Hydrogen generation from steam reforming of ethanol in dielectric barrier discharge

Dielectric barrier discharge (DBD) was used for the generation of hydrogen from ethanol reforming. Effects of reaction conditions, such as vaporization temperature, ethanol flow rate, water/ethanol ratio, and addition of oxygen, on the ethanol conversion and hydrogen yield, were studied. The results showed that the increase of ethanol flow rate decreased ethanol conversion and hydrogen yield, and high water/ethanol ratio and addition of oxygen were advantageous. Ethanol conversion and hydrogen yield increased with the vaporization room temperature up to the maximum at first, and then decreased slightly. The maximum hydrogen yield of 31.8% was obtained at an ethanol conversion of 88.4% under the optimum operation conditions of vaporization room temperature of 120 ?C, ethanol flux of 0.18 mL/min, water/ethanol ratio of 7.7 and oxygen volume concentration of 13.3%.     

Polymer matrix of polyethylene porous films functionalized by electrical discharge plasma

The polyethylene porous films were treated by dielectric surface barrier discharge (DSBD) plasma at atmospheric pressure in oxygen (O₂) or nitrogen (N₂), and by radio-frequency discharge (RFD) plasma in air at reduced pressure 46 Pa. The surface energy of films was carried out by direct measurements of contact angles of six testing liquids. The strength of adhesive joints in the system modified polyethylene porous films - polyacrylate was measured by peeling of the joints under the angle of 90°. The significant increase of the surface energy and its polar component of polyethylene porous films modified by all types of plasma were observed. The higher strengths of adhesive joints were found for modification of polyethylene porous films by radio-frequency discharge plasma in comparison with modification of the films by barrier discharge plasma.     

介质阻挡放电甲醇脱氢偶联一步合成乙二醇反应中氢气的催化作用

利用原位发射光谱表征和在线色谱分析,研究了甲醇介质阻挡放电脱氢偶联一步合成乙二醇反应中氢气的催化作用,考察了放电频率、甲醇和氢气进料量以及反应压力的影响.结果表明,在介质阻挡放电产生的非平衡等离子体中,H2不但能显著提高甲醇转化率,而且能显著提高乙二醇的选择性.在300°C,0.1 MPa,反应器注入功率为11 W,放电频率为12.0 k Hz,甲醇气体进料量为11.1 m L/min,氢气进料量为80–180 m L/min的条件下,甲醇转化率接近30%,乙二醇选择性大于75%.乙二醇收率与激发态氢原子的Hα谱线强度之间存在同增同减关系.由此推测,氢原子是起催化作用的活性氢物种.活性氢物种的生成途径是:基态氢分子通过与电子碰撞变成激发态,激发态氢分子通过第一激发态氢自动解离为基态氢原子.放电反应条件通过影响氢分子解离来影响氢气的催化作用.氢气在非平衡等离子体中显示的催化作用有可能为开辟新的化学合成途径提供重要机遇.     

Development of ambient sampling chemi/chemical ion source with dielectric barrier discharge

The development of a new configuration of chemical ionization (CI)‐based ion source is presented. The ambient air containing the gaseous sample is sniffed into an enclosed ionization chamber which is of sub‐ambient pressure, and is subsequently mixed with metastable species in front of the ion inlet of the mass spectrometer. Metastable helium atoms (He*) are used in this study as the primary ionizing agents and are generated from a dielectric barrier discharge (DBD) source. The DBD is powered by an AC high‐voltage supply and the configuration of the electrodes is in such a way that the generated plasma is confined within the discharge tube and is not extended into the ionization chamber. The construction of the ion source is simple, and volatile compounds released from the bulky sample can also be analyzed directly by approaching the sample to the sampling nozzle. When combined with heated nitrogen or other desorption methods, its application can also be extended to non‐volatile compounds, and the consumption for helium can be kept minimum solely for maintaining the stable discharge and gas phase ionization. Applications to non‐proximate sample analysis, direct determination of active ingredients in drug tablets and the detection of trace explosive such as hexamethylene triperoxide diamine are demonstrated. Copyright © 2010 John Wiley & Sons, Ltd.     

Surface modification of acrylate intraocular lenses with dielectric barrier discharge plasma at atmospheric pressure

Surface modification with dielectric barrier discharge (DBD) plasma was carried out at atmospheric pressure (argon as the discharge gas) to improve the biocompatibility of hydrophobic acrylate intraocular lens (IOL). Changes of the plasma-treated IOL surface in chemical composition, morphology and hydrophilicity were comprehensively evaluated by X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and water contact angle (WCA) measurements. The surface biocompatibility of the untreated and plasma-treated IOLs was compared with the adhesion behavior of platelets, macrophages and lens epithelial cells (LECs) in vitro. After DBD plasma treatment, the hydrophilicity of the IOL surface was obviously improved. The changes in WCA with treatment extension may be attributed to both the introduction of oxygen or/and nitrogen-containing polar groups and the increase of surface roughness induced by plasma etching effect. The existence of low molecular weight oxidized material (LMWOM) was proved on the plasmatreated IOL which was caused by the chain scission effect of the plasma treatment. The plasma-treated IOLs resisted the adhesion of platelets and macrophages significantly. The LECs spreading and proliferation were postponed on the IOLs plasma-treated for more than 180 s, with a well maintained epithelial phenotype of LECs. The IOL biocompatibility was improved after the DBD plasma treatment. We speculate that slighter foreign-body reaction and later incidence of anterior capsule opacification (ACO) may be expected after implantation of the argon DBD plasma-treated IOL. Supported by the Zhejiang Natural Science Foundation of China (Grant No. 2004C23003)     

Comparison of dielectric barrier discharge, atmospheric pressure radiofrequency-driven glow discharge and direct analysis in real time sources for ambient mass spectrometry of acetaminophen

Three plasma-based ambient pressure ion sources were investigated; laboratory constructed dielectric barrier and rf glow discharges, as well as a commercial corona discharge (DART source). All were used to desorb and ionize a model analyte, providing sampling techniques for ambient mass spectrometry (MS). Experimental parameters were optimized to achive highest signal for acetaminophen as the analyte. Insight into the mechanisms of analyte desorption and ionization was obtained by means of emission spectrometry and ion current measurements. Desorption and ionization mechanisms for this analyte appear to be identical for all three plasma sources. Emission spectra differ only in the intensities of various lines and bands. Desorption of solid analyte requires transfer of thermal energy from the plasma source to sample surface, in the absence of which complete loss of MS response occurs. For acetaminophen, helium was the best plasma gas, providing 100- to 1000-fold higher analyte response than with argon or nitrogen. The same trend was also evident with background ions (protonated water clusters). MS analyte signal intensity correlates with the ion density (expressed as ion current) in the plasma plume and with emission intensity from excited state species in the plasma. These observations support an ionization process which occurs via proton transfer from protonated water clusters to analyte molecules.     

Determination of ultratrace nitrogen in pure argon gas by dielectric barrier discharge-molecular emission spectrometry

A dielectric barrier discharge (DBD) was used as a new atmospheric optical emission detector for the determination of trace nitrogen in pure argon gas in this work. The whole system was composed of an ac ozone generation device for power supply, a six-way valve, a laboratory-built DBD device and a USB2000 charge coupled device (CCD). Trace nitrogen in argon was detected at nitrogen molecular emission line of 337 nm. This method features with several advantages: atmospheric working condition, low power consumption (≤ 12 W), simple and cheap instrumentation, fast response and high sensitivity and accuracy. Under the optimized conditions, the limits of detection can be down to 34 ppb.     

Removal of SO2 and the simultaneous removal of SO2 and NO from simulated flue gas streams using dielectric barrier discharge plasmas

A gas-phase oxidation method using dielectric barrier discharges (DBDs) has been developed to remove SO₂ and to simultaneously remove SO₂ and NO from gas streams that are similar to gas streams generated by the combustion of fossil fuels. SO₂ and NO removal efficiencies are evaluated as a function of applied voltage, temperature, and concentrations of SO₂, NO, H₂O_(g), and NH3. With constant H₂O_(g) concentration, both SO₂ and NO removal efficiencies increase with increasing temperature from 100 to 160°C. At 160°C with 15% by volume H₂0_(g), more than 95% of the NO and 32% of the S0₂ are simultaneously removed from the gas stream. Injection of NH₃ into the gas stream caused an increase in S0₂ removal efficiency to essentially 100%. These results indicate that DBD plasmas have the potential to simultaneously remove SO₂ and NO from gas streams generated by large-scale fossil fuel combustors.     

Analysis of part-per-billion level of arsine and phosphine in light hydrocarbons by capillary flow technology and dielectric barrier discharge detector

A practical gas chromatographic procedure has been developed and implemented for the measurement of arsine and phosphine in hydrocarbons such as propylene at the part-per-billion level. The successful measurement of arsine and phosphine at the level mentioned was attained by incorporating a large volume injection technique to increase the mass of solutes delivered for sensitivity improvement, capillary flow technology to keep the matrix from entering the detector by either back-flushing through the inlet vent, or by heart-cutting if required, and dielectric barrier discharge detector operating in argon mode for sensitivity enhancement, as well as offering improved selectivity towards the solutes cited. Using the technique described a complete analysis can be conducted in less than 4 min. A relative standard precision of less than 1.7% was achieved with repeated injections at the concentration level of 25 and 125 ppb (v/v) each of arsine and phosphine in nitrogen with a practical detection limit at the 5 ppb (v/v) level. Correlation coefficients of greater than 0.9999 were obtained for arsine and phosphine over a range from 10 to 2500 ppb (v/v). The analytical methodology was proven to be reliable in continuous operation during the first 6 months of deployment.     

Bifunctional AgCl/Ag composites for SERS monitoring and low temperature visible light photocatalysis degradation of pollutant

With the assistance of Polyvinylpyrrolidone (PVP), AgCl/Ag composites were fabricated in N, N-Dimethylformamide (DMF) solvent via a photoactivated route. The size of AgCl particles was in the range of 500 nm to 1 μm and the Ag particle's diameter was about 10–20 nm. Different from those core–shell structures reported before, the Ag nanoparticles were dispersed uniformly both on the surface and in the body of AgCl particles. The generation of such kind of composites was resulted from the reducing ability of DMF and light irradiation during the formation of AgCl particles. The as-obtained AgCl/Ag composites presented great activity for both surface-enhanced Raman scattering (SERS) detection and visible light photocatalytic degradation of organic dyes. Additionally, the AgCl/Ag composites could maintain high photocatalytic activity even though the ambient temperature was as low as 15 °C and recycle photocatalysis experiments indicated that the photocatalyst exhibited higher stability. Such kind of AgCl/Ag composites holds great potential for environmental monitoring devices and pollutant treatments.     

Application of Dielectric Barrier Discharge Reactor Immersed in Wastewater to the Oxidative Degradation of Organic Contaminant

Dielectric barrier discharge (DBD) is an effective method available for the production of ozone and ultraviolet light. The wastewater treatment system of this study was designed to utilize both ozone and ultraviolet light produced in the DBD reactor for the degradation of organic contaminant. The DBD reactor consisted of a quartz cylinder and a coaxial ceramic tube inside of which a steel rod was placed. The DBD reactor was immersed in the wastewater that was grounded. In this case, the wastewater acted not only as an electrode but also as the cooling medium for the DBD reactor. An azo dye, Acid Red 27, was used as the organic contaminant. In this system, the organic contaminant was degraded by two oxidation pathways induced by ozone and ultraviolet light. The concentration of ozone, the ultraviolet radiation intensity and the degradation efficiency of the organic contaminant were measured by varying the discharge. The results showed that the present system was very effective for the degradation of the organic contaminant. The energy requirement for the degradation was found to be 0.654 kJ/mg, which is much smaller value than those obtained with an ultraviolet/photocatalytic process.     

Deposition of polyacrylic acid films on PDMS substrate in dielectric barrier corona discharge at atmospheric pressure

This paper reports on deposition of acrylic acid films polymerized by an efficient and cost‐effective technique of dielectric barrier corona discharge at atmospheric pressure. The liquid acrylic acid was vaporized and carried by argon gas into plasma to deposit polyacrylic acid films on polydimethylsiloxane substrate. A nonthermal corona discharge was generated in a pyrex flask using a steel tube‐to‐plate asymmetric electrode configuration. The plasma was excited using an in‐house developed power supply operating with continuous wave signals of 10‐kHz frequency. The emission spectra of plasma species were recorded to know their contribution during deposition process. The deposited surfaces were characterized using contact angle measurements, atomic force microscopy, Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy and film thickness measurements. A maximum film growth rate of 363 nm/min was achieved under optimal condition of discharge. The results suggest that this plasma technique is capable of depositing organic coatings with a high concentration of carboxylic functional groups that could be potentially used for biomedical and microfluidic applications.