Influence of electrical parameters on H2O2 generation in DBD non-thermal reactor with water mist

A dielectric barrier discharge (DBD) reactor is introduced to generate H2O2 by non-thermal plasma with a mixture of oxygen and water mist produced by an ultrasonic atomizer.The results of our experiment show that the energy yield and concentration of the generated H2O2 in the pulsed discharge are much higher than that in AC discharge,due to its high energy efficiency and low heating effect.Micron-sized liquid droplets produced by an ultrasonic atomizer in water mist have large specific surface area,which greatly reduces mass transfer resistance between hydroxyl radicals and water liquids,leading to higher energy yield and H2O2 concentration than in our previous research.The influence of applied voltage,discharge frequency,and environmental temperature on the generated H2O2 is discussed in detail from the viewpoint of the DBD mechanism.The H2O2 concentration of 30 mg 1-1,with the energy yield of 2 g kW-1h 1 is obtained by pulsed discharge in our research.     

Enhanced CO2 decomposition via metallic foamed electrode packed in self-cooling DBD plasma device

A self-cooling dielectric barrier discharge reactor, packed with foamed Cu and Ni mesh and operated at ambient conditions, was used for the composition of CO₂ into CO and O₂. The influences of power, frequency, and other discharge characteristics were investigated in order to have a better understanding of the effect of the packing materials on CO₂ decomposition. It is found that porous foamed Cu and Ni not only played a role as the carrier of energy transformation and electrode distributed in discharge gaps but also promoted the equilibrium shifting toward the product side to yield more CO by consuming some part of O₂ and O radicals generated from the decomposition of CO₂. The maximum CO₂ decomposition rates of 48.6% and 49.2% and the maximum energy efficiency of 9.71% and 10.18% were obtained in the foamed Ni and Cu mesh, respectively.     

Decomposition of a gas mixture of four n-alkanes using a DBD reactor

This study investigates the decomposition of a gas mixture of four n-alkanes (n-heptane, n-octane, n-nonane, and n-decane) using a dielectric barrier discharge reactor. We show that the conversion of n-alkanes increased from 7.2% (C₇H₁₆), 9.7% (C₈H₁₈), 8.4% (C₉H₂₀), and 10.5% (C₁₀H₂₂) to 23.8% (C₇H₁₆), 25.0% (C₈H₁₈), 27.9% (C₉H₂₀), and 32.1% (C₁₀H₂₂) when the energy density increased from 84 J l⁻¹ to 324 J l⁻¹. The conversion of n-alkanes when using the gas mixture is close to that found when using a single n-alkane. The influences of reaction temperature and O₂ concentration are also investigated, and the activation energies for the decomposition of each alkane are given.     

Strengthening decomposition of oxytetracycline in DBD plasma coupling with Fe-Mn oxide-loaded granular activated carbon

A catalytic approach using a synthesized iron and manganese oxide-supported granular activated carbon (Fe-Mn GAC) under a dielectric barrier discharge (DBD) plasma was investigated to enhance the degradation of oxytetracycline (OTC) in water. The prepared Fe-Mn GAC was characterized by x-ray diffraction and scanning electron microscopy, and the results showed that the bimetallic oxides had been successfully spread on the GAC surface. The experimental results showed that the DBD + Fe-Mn GAC exhibited better OTC removal efficiency than the sole DBD and DBD + virgin GAC systems. Increasing the fabricated catalyst and discharge voltage was favorable to the antibiotic elimination and energy yield in the hybrid process. The coupling process could be elucidated by the ozone decomposition after Fe-Mn GAC addition, and highly hydroxyl and superoxide radicals both play significant roles in the decontamination. The main intermediate products were identified by HPLC-MS to study the mechanism in the collaborative system.     

Study of selective hydrogenation of biodiesel in a DBD plasma reactor

In order to achieve the selective hydrogenation of biodiesel at room temperature and under normal pressure,we researched the upgrading of soybean biodiesel using a dielectric-barrier discharge (DBD) reaction system.Using Raney-Ni as the hydrogenation catalyst,the effects of the operating parameters on the hydrogenation depth and the selectivity of biodiesel were systematically analyzed.The results show that the polyunsaturated components in soybean methyl ester were reduced by 57.04％,and that the polyunsaturated components were hydrogenated to monounsaturated components with a selectivity of 77.75％.Based on the gas chromatography and mass spectrometry (GC-MS) test results,we established a kinetic model for biodiesel hydrogenation.A comparison of the calculated and experimental results shows that the hydrogenation of the biodiesel can be described by a quasi first-order reaction model.The calculated reaction rate constants indicate that under DBD plasma reaction conditions,the hydrogenation of biodiesel has high selectivity for the formation of rnonounsaturated components.     

Characteristics of DBD micro-discharge at different pressure and its effect on the performance of oxygen plasma reactor

The oxygen plasma reactor based on dielectric barrier discharge principle can produce a high concentration of reactive oxygen species, which can cooperate with hydraulic cavitation gas–liquid mixer to realize the application of advanced oxidation technology in water treatment. In this technology, the work pressure of the oxygen plasma reactor is decreased by the vacuum suction effect generated in the snap-back section of the gas–liquid mixed container. In this paper, the characteristics of single micro-discharge at different pressures were investigated with the methods of discharge image, electrical characteristics and spectral diagnosis, in order to analyze the electrical characteristics and reactive oxygen species generation efficiency of oxygen plasma reactor at the pressure range from 60 kPa to 100 kPa. The study indicated that, when the pressure decreases, the duty ratio of ionization in the discharge gap and number of electrons with high energy increases, leading to a rise in reactive oxygen species production. When the oxygen reaches the maximum ionization, the concentration of reactive oxygen species is the highest. Then, the discharge intensity continues to increase, producing more heat, which will decompose the ozone and lower the production of reactive oxygen species. The oxygen plasma reactor has an optimum working pressure at different input powers, which makes the oxygen plasma reactor the most efficient in generating reactive oxygen species.     

Experimental and simulated investigation of microdischarge characteristics in a pin-to-pin dielectric barrier discharge (DBD) reactor

Both experimental and simulated studies of microdischarge (MD) are carried out in a dielectric barrier discharge with a pin-to-pin gap of 3.5 mm, ignited by a sinusoidal voltage with a peak voltage of 10 kV and a driving frequency of 5 kHz. Statistical results have shown that the probability of the single current pulse in the positive half-period (HP) reaches 73.6% under these conditions. Experimental results show that great luminous intensity is concentrated on the dielectric surface and the tip of the metal electrode. A 1D plasma fluid model is implemented by coupling the species continuity equations, electron energy density equations, Poisson equation, and Helmholtz equations to analyze the MD dynamics on the microscale. The simulated results are in good qualitative agreement with the experimental results. The simulated results show that the MD dynamics can be divided into three phases: the Townsend phase, the streamer propagation phase, and the discharge decay phase. During the streamer propagation phase, the electric field and electron density increase with the streamer propagation from the anode to the cathode, and their maximal values reach 625.48 Td and 2.31 × 1019 m−3, as well as 790.13 Td and 3.58 × 1019 m−3 in the positive and negative HP, respectively. Furthermore, a transient glow-like discharge is detected around the anode during the same period of streamer propagation. The formation of transient glow-like discharge is attributed to electrons drifting back to the anode, which is driven by the residual voltage in the air gap.     

Decomposition of dioxin-like components in a DBD reactor combined with Hg/Ar electrodeless ultraviolet

A new combined reactor with Hg/Ar electrodeless ultraviolet(EDUV)activated by DBD for 3,4-dichlorodiphenyl ether abatement is presented.The effect of specific input energy and feeding gas component on 3,4-dichlorodiphenyl ether removal efficiency has been explored.Compared with a single DBD system,this new combined process performed a significant promotion on 3,4-dichlorodiphenyl ether abatement.Experiment results verified that active oxygen clearly contributed to the synergistic activity of DBD-EDUV system.Results of emission spectra showed that UV radiation of 253.7 nm could be detected in the DBD-EDUV system.Further,the products of DBD-EDUV process were analyzed via gas chromatographymass spectrometer(GC-MS)to reveal involved decomposition mechanism.     

Effects of O2 addition on the plasma uniformity and reactivity of Ar DBD excited by ns pulsed and AC power supplies

Dielectric barrier discharges (DBDs) have been widely used in ozone synthesis, materials surface treatment, and plasma medicine for their advantages of uniform discharge and high plasma-chemical reactivity. To improve the reactivity of DBDs, in this work, the O₂ is added into Ar nanosecond (ns) pulsed and AC DBDs. The uniformity and discharge characteristics of Ar ns pulsed and AC DBDs with different O₂ contents are investigated with optical and electrical diagnosis methods. The DBD uniformity is quantitatively analyzed by gray value standard deviation method. The electrical parameters are extracted from voltage and current waveforms separation to characterize the discharge processes and calculate electron density n_e. The optical emission spectroscopy is measured to show the plasma reactivity and calculate the trend of electron temperature T_e with the ratio of two emission lines. It is found that the ns pulsed DBD has a much better uniformity than AC DBD for the fast rising and falling time. With the addition of O₂, the uniformity of ns pulsed DBD gets worse for the space electric field distortion by O₂⁻, which promotes the filamentary formation. While, in AC DBD, the added O₂ can reduce the intensity of filaments, which enhances the discharge uniformity. The ns pulsed DBD has a much higher instantaneous power and energy efficiency than AC DBD. The ratio of Ar emission intensities indicates that the T_e drops quickly with the addition of O₂ both ns pulsed and AC DBDs and the ns pulsed DBD has an obvious higher T_e and n_e than AC DBD. The results are helpful for the realization of the reactive and uniform low temperature plasma sources.     

Hysteresis characteristics of the initiating and extinguishing boundaries in a nanosecond pulsed DBD

The dielectric barrier discharge (DBD) is presently used in many fields, including plasma medicine, surface modification, and ozone synthesis; the influence of airflow on the DBD is a widely investigated topic. In this work, a hysteresis characteristic on the initiating and extinguishing boundaries is observed in a nanosecond pulsed DBD, which is sensitive to the variation in the airflow velocities and pulse repetition frequencies (PRFs). It is found that, at a certain airflow velocity, the initiating PRF is higher than the extinguishing PRF. This difference between the initiating PRF and the extinguishing PRF leads to a hysteresis phenomenon on the initiating and extinguishing boundaries. When the airflow velocity is increased, both the initiating and extinguishing PRFs are increased and the difference between the initiating PRF and the extinguishing PRF also increased. The hysteresis width between the initiating and extinguishing boundaries is enhanced. To explain these results, the physical processes involved with the seed particles and the mechanisms of forming discharge channels are discussed.     

In-situ reduction of silver by surface DBD plasma: a novel method for preparing highly effective electromagnetic interference shielding Ag/PET

Electromagnetic interference(EMI) shielding composites with good flexibility and weatherability properties have attracted increased attention. In this study, we combined the surface modification method of sub-atmospheric pressure glow discharge plasma with in situ atmospheric pressure surface dielectric barrier discharge plasma(APSDBD) reduction to prepare polyethylene terephthalate supported silver(Ag/PET). Due to the prominent surface modification of PET film, mild plasma reduction, and effective control of the silver morphology by polyvinylpyrrolidone(PVP), a 3.32 μm thick silver film with ultralow sliver loading(0.022 wt%) exhibited an EMI shielding efficiency(SE) of 39.45 d B at 0.01 GHz and 31.56 d B at 1.0 GHz(30 d B in the range of 0.01–1.0 GHz). The SEM results and EMI shielding analysis indicated that the high performance originated from the synergistic effect of the formation of silver nanoparticles(Ag NPs) with preferentially oriented cell-like surface morphologies and layer-by-layer-like superimposed microstructures inside, which demonstrated strong microwave reflection properties. Fourier transform infrared spectrometer and x-ray diffractometer showed that the surface structures of the heat-sensitive substrate materials were not destroyed by plasma.Additionally, APSDBD technology for preparing Ag/PET had no special requirements on the thickness, dielectric constant, and conductivity of the substrate, which provides an effective strategy for manufacturing metal or alloy films on surfaces of heat-sensitive materials at a relatively low cost.     

Investigation on discharge characteristics of a coaxial dielectric barrier discharge reactor driven by AC and ns power sources

A coaxial dielectric barrier discharge(DBD) reactor with double layer dielectric barriers has been developed for exhaust gas treatment and excited either by AC power or nanosecond(ns)pulse to generate atmospheric pressure plasma. The comparative study on the discharge characteristics of the discharge uniformity, power deposition, energy efficiency, and operation temperature between AC and ns pulsed coaxial DBD is carried out in terms of optical and electrical characteristics and operation temperature for optimizing the coaxial DBD reactor performance. The voltages across the air gap and dielectric layer and the conduction and displacement currents are extracted from the applied voltages and measured currents of AC and ns pulsed coaxial DBDs for the calculation of the power depositions and energy efficiencies through an equivalent electrical model. The discharge uniformity and operating temperature of the coaxial DBD reactor are monitored and analyzed by optical images and infrared camera. A heat conduction model is used to calculate the temperature of the internal quartz tube. It is found that the ns pulsed coaxial DBD has a much higher instantaneous power deposition in plasma, a lower total power consumption, and a higher energy efficiency compared with that excited by AC power and is more homogeneous and stable. The temperature of the outside wall of the AC and ns pulse excited coaxial DBD reaches 158 ℃ and 64.3 ℃ after 900 s operation, respectively.The experimental results on the comparison of the discharge characteristics of coaxial DBDs excited by different powers are significant for understanding of the mechanism of DBDs,reducing energy loss, and optimizing the performance of coaxial DBD in industrial applications.     

Plasma-assisted ammonia synthesis in a packed-bed dielectric barrier discharge reactor: roles of dielectric constant and thermal conductivity of packing materials

In this article, plasma-assisted NH₃ synthesis directly from N₂ and H₂ over packing materials with different dielectric constants (BaTiO₃, TiO₂ and SiO₂) and thermal conductivities (BeO, AlN and Al₂O₃) at room temperature and atmospheric pressure is reported. The higher dielectric constant and thermal conductivity of packing material are found to be the key parameters in enhancing the NH₃ synthesis performance. The NH₃ concentration of 1344 ppm is achieved in the presence of BaTiO₃, which is 106% higher than that of SiO₂, at the specific input energy (SIE) of 5.4 kJ·l⁻¹. The presence of materials with higher dielectric constant, i.e. BaTiO3 and TiO₂ in this work, would contribute to the increase of electron energy and energy injected to plasma, which is conductive to the generation of chemically active species by electron-impact reactions. Therefore, the employment of packing materials with higher dielectric constant has proved to be beneficial for NH₃ synthesis. Compared to that of Al₂O₃, the presence of BeO and AlN yields 31.0% and 16.9% improvement in NH₃ concentration, respectively, at the SIE of 5.4 kJ·l⁻¹. The results of IR imaging show that the addition of BeO decreases the surface temperature of the packed region by 20.5% to 70.3°C and results in an extension of entropy increment compared to that of Al₂O₃, at the SIE of 5.4 kJ·l⁻¹. The results indicate that the presence of materials with higher thermal conductivity is beneficial for NH₃ synthesis, which has been confirmed by the lower surface temperature and higher entropy increment of the packed region. In addition, when SIE is higher than the optimal value, further increasing SIE would lead to the decrease of energy efficiency, which would be related to the exacerbation in reverse reaction of NH₃ formation reactions.     

Degradation of phenol using a combination of granular activated carbon adsorption and bipolar pulse dielectric barrier discharge plasma regeneration

A combined method of granular activated carbon (GAC) adsorption and bipolar pulse dielectric barrier discharge (DBD) plasma regeneration was employed to degrade phenol in water. After being saturated with phenol, the GAC was filled into the DBD reactor driven by bipolar pulse power for regeneration under various operating parameters. The results showed that different peak voltages, air flow rates, and GAC content can affect phenol decomposition and its major degradation intermediates, such as catechol, hydroquinone, and benzoquinone. The higher voltage and air support were conducive to the removal of phenol, and the proper water moisture of the GAC was 20％. The amount of H2O2 on the GAC was quantitatively determined, and its laws of production were similar to phenol elimination. Under the optimized conditions, the elimination of phenol on the GAC was confirmed by Fourier transform infrared spectroscopy,and the total removal of organic carbons achieved 50.4％. Also, a possible degradation mechanism was proposed based on the HPLC analysis. Meanwhile, the regeneration efficiency of the GAC was improved with the discharge treatment time, which attained 88.5％ after 100 min of DBD processing.     

Experimental study on the parameter optimization and application of a packed-bed dielectric barrier discharge reactor in diesel particulate filter regeneration

To compensate for the shortcomings of the thermal and catalytic regeneration of the diesel particulate filter(DPF),a self-designed packed-bed dielectric barrier discharge(DBD)reactor for DPF regeneration was developed.The DBD reactor with the main active substance of nonthermal plasma(NTP)as the target parameter was optimized by adjusting the feed gas,packing particles(material or size),and cooling water temperature.Moreover,a set of optimal working parameters(gas source,O2;packing particles,1.2-1.4 mm ZrO2;and cooling water temperature,20℃)was selected to evaluate the effect of different O3 concentrations on DPF regeneration.The research results showed that selecting packing particles with high dielectric constant and large particles,as well as reducing the cooling water temperature,with oxygen as the feed gas,contributed to an increase in O3 concentration.During DPF regeneration,the following changes were observed:the power of the NTP reactor decreased to lower than 100 W,the O3 concentration increased from 15 g m-3 to 45 g m-3,the CO and CO2 volume fractions of the particulate matter decomposition products increased,and the peak regeneration temperature increased to 173.4℃.The peak temperature arrival time was 60 min earlier,indicating that the regeneration rate of DPF increased with the increase in O3 concentration.However,the O3 utilization rate(the amount of carbon deposit removed per unit volume O3)initially increased and then decreased;when the O3 concentration was set to 25 g m-3,the highest O3 utilization rate was reached.The packed-bed DBD technology contributed to the increase in the concentration of NTP active substances and the regeneration efficiency of DPF.It provides a theoretical and experimental basis for high-efficiency regeneration of DPF at low temperatures(＜200℃).     

Improving the surface flashover performance of epoxy resin by plasma treatment:a comparison of fluorination and silicon deposition under different modes

This work treats the Al2O3-ER sample surface using dielectric barrier discharge fluorination(DBD-F),DBD silicon deposition(DBD-Si),atmospheric-pressure plasma jet fluorination(APPJ-F)and APPJ silicon deposition(APPJ-Si).By comparing the surface morphology,chemical components and electrical parameters,the diverse mechanisms of different plasma modification methods used to improve flashover performance are revealed.The results show that the flashover voltage of the DBD-F samples is the largest(increased by 21.2％at most),while the APPJ-F method has the worst promotion effect.The flashover voltage of the APPJ-Si samples decreases sharply when treatment time exceeds 180 s,but the promotion effect outperforms the DBD-Si method during a short modified time.For the mechanism explanation,firstly,plasma fluorination improves the surface roughness and introduces shallow traps by etching the surface and grafting fluorine-containing groups,while plasma silicon deposition reduces the surface roughness and introduces a large number of shallow traps by coating SiOx film.Furthermore,the reaction of the DBD method is more violent,while the homogeneity of the APPJ modification is better.These characteristics influence the effects of fluorination and silicon deposition.Finally,increasing the surface roughness and introducing shallow traps accelerates surface charge dissipation and inhibits flashover,but too many shallow traps greatly increase the dissipated rate and facilitate surface flashover instead.