Double Dielectric Barrier Discharge Research Articles

Degradation of n-hexane by the high-throughput double dielectric barrier discharge: Influencing factors, degradation mechanism and pathways

The emission of volatile organic compounds (VOCs) is known to be a source of various environmental problems. N-hexane is a saturated aliphatic hydrocarbon that is a major precursor of ozone. For the decomposition of n-hexane, a novel double dielectric barrier discharge (DDBD) reactor design is developed and tested on a pilot scale. The factors influencing the plasma degradation of n-hexane have been thoroughly investigated. The degradation efficiency, carbon balance and nitrogen oxide concentration were measured and analysed. Through experiments, it was found that the maximum removal of n-hexane at an initial concentration of 2000 ppm and a flow rate of 5 L/min was 1544 ppm. The associated energy efficiency reached 67.71 ppm/J. The excited states of oxygen and nitrogen (O2+, O(3 s5S-3p5P), N2(C3Πu-B3Πg), N2+(B2Σu+-X2Σg+)) during n-hexane degradation were observed. Possible degradation pathways of n-hexane are proposed, and it is revealed that the active species play an important role in the formation of oxygen and nitrogen-containing volatile organic by-products. The results show that the pilot-scale design of the DDBD system provides a feasible way for the industrial treatment of n-hexane, and provides fundamental insights into the mechanism of plasma catalytic system operation.

Surface modification of carbon-based materials using a double dielectric barrier discharge for efficient removal of OPFRs with different polarity

This article utilizes a double dielectric barrier discharge (DBD) technology to enhance the removal of five commonly found highly toxic organophosphorus flame retardants (OPFRs) by modifying carbon-based materials. This study investigated the adsorption performance of carbon-based materials modified under various discharge times, frequencies, and voltage conditions on five different OPFRs. Before the modification, the adsorption amount of TPP was only 0.56 mg/g, but the modification significantly improved the adsorption effect of TPP to 14.8 mg/g. Furthermore, the overall adsorption amount of the flame retardants with five different polarities increased by 70.51 mg/g. The study also examined the adsorption kinetics and isotherms, the dosage effect, and the adsorption mechanism and reusability of the modified carbon materials for OPFRs. In the end, the study found that the optimal adsorption capacity for 5 types of OPFRs was achieved at a voltage frequency of 8 kHz, a voltage of 12 kV, and 15 min. The fitting kinetic and isotherm model determines that chemical adsorption is the main mechanism supplemented by physical adsorption, and Langmuir and Freundlich provide better fitting for the adsorption isotherms. The material exhibits a favorable pore structure, high adsorption capacity, and stable regenerative adsorption performance. The adsorption mechanism for OPFRs involves pore filling, hydrogen bonding, π - π conjugation, and strong electrostatic interaction. The optimal adsorption capacity is 109.81 mg/g. This study provides a new strategy for synthesizing activated carbon materials with broad polarity. The relative standard deviation of all experiments did not exceed 2.88 %.

Deep-dewatering of sewage sludge using double dielectric barrier discharge (DDBD) plasma technology

Deep dewatering of sewage sludge is essential for optimizing disposal and resource recovery. This study explores the potential of Double Dielectric Barrier Discharge (DDBD) plasma for enhancing waste activated sludge (WAS) dewatering. Key operational parameters (applied voltage, treatment duration, and air feeding rate) were systematically investigated using a two-step approach: Single Factor-at-a-Time (SFAT) and central composite design (CCD) within the response surface methodology (RSM) framework. The aim was to identify influential factors and their optimal settings for maximizing dewatering efficiency while minimizing energy usage. Higher applied voltages (30 kV) and longer treatment durations (40 min) notably improved % moisture reduction (%MR) (92.92 % and 94.35 %, respectively). ANOVA analysis emphasized the equal and substantial impact of applied voltage and treatment duration on %MR and energy efficiency (EE), whereas the air feeding rate exhibited no significant effect. However, it's worth noting that %MR and EE did not display a strictly linear relationship, suggesting complex interactions. Furthermore, two soft sensing models were developed: a quadratic model for %MR and a linear model for energy efficiency (EE). Results showed minimal reductions in TOC content, maintaining values between 13.68 % and 14.28 % compared to untreated sludge 14.37 %. The study also revealed that ROS generated by DDBD plasma played a key role in sludge disintegration, as observed through SEM and FTIR, enhancing dewatering efficiency by the destruction of sludge flocs and the transformation of organic substances. In conclusion, DDBD plasma technology offers a sustainable solution for effective sludge dewatering in WWTPs, preserving organic content.

Innovative carbon-nitrogen-TiO2 catalyst immobilised on stainless steel mesh for effective removal of orange II organic dye in the DCDBD plasma actuator

A double cylindrical dielectric barrier discharge (DCDBD) was optimised and coupled with SS/C-N-TiO2 photocatalysts produced by sol gel technique for the treatment of orange II (O.II) dye. The results show that degradation of 60 mg/L O.II with both systems followed first-order reaction. Higher removal of O.II was achieved with DCDBD-SS/C-N-TiO2 technology. The decomposition of O.II resulted in six and four degradation metabolites with DCDBD alone, and DCDBD-SS/C-N-TiO2, respectively. The COD and TOC removals reached 61.43% and 15.38%, respectively after 60 min of DCDBD run. This study demonstrates that DCDBD is a promising advanced technology for the treatment of dye wastewater.

Dielectric Barrier Discharge Plasma Coupled with Cobalt Oxyhydroxide for Methylene Blue Degradation.

In this study, the coupled use of a double dielectric barrier discharge (DDBD) and CoOOH catalyst was investigated for the degradation of methylene blue (MB). The results indicated that the addition of CoOOH significantly promoted MB degradation performance compared to the DDBD system alone. In addition, both the removal rate and energy efficiency increased with an increase in CoOOH dosage and discharge voltage. After 30 min of discharge treatment in the coupled system (with CoOOH of 150 mg), the removal rate reached 97.10% when the discharge voltage was 12 kV, which was 1.92 times that in the single DDBD system. And when the discharge time was 10 min, the energy efficiency could reach 0.10 g (k·Wh)-1, which was 3.19 times better than the one in the single DDBD system. Furthermore, the addition of CoOOH could also significantly enhance the TOC and COD removal rates of MB. In the DDBD-coupled-with-CoOOH system, TOC and COD were 1.97 times and 1.99 times those of the single DDBD system after 20 min of discharge treatment with a discharge voltage of 12 kV and 100 mg of CoOOH. The main active substances detected in the coupled system indicated the conversion of the active species H2O2 and O3 into a more oxidizing ·OH was enhanced through the addition of a CoOOH catalyst, resulting in the more effective decomposition of MB and intermediate molecules.

Degradation of methylene blue using a novel gas-liquid hybrid DDBD reactor: Performance and pathways

A novel gas-liquid hybrid double dielectric barrier discharge (DDBD) reactor with coaxial cylinder configuration was developed for the degradation of methylene blue (MB) in this study. In this DDBD reactor, the reactive species generation occurred in the gas-phase discharge, directly in the liquid, and in the mixture of the working gas bubbles and the liquid, which could effectively increase the contact area between the active substance and MB molecules/intermediates, resulting in an excellent MB degradation efficiency and mineralization (COD and TOC). The electrostatic field simulation analysis by Comsol was carried out to determine the appropriate structural parameters of the DDBD reactor. The effect of discharge voltage, air flow rate, pH, and initial concentration on MB degradation was evaluated. Besides, major oxide species, ·OH, the dissolved O3 and H2O2 generated in this DDBD reactor were determined. Moreover, major MB degradation intermediates were identified by LC-MS, based on which, possible degradation pathways of MB were proposed.

Degradation of trichloroethylene by double dielectric barrier discharge (DDBD) plasma technology: Performance, product analysis and acute biotoxicity assessment

Trichloroethylene is carcinogenic and poorly degraded by microorganisms in the environment. Advanced Oxidation Technology is considered to be an effective treatment technology for TCE degradation. In this study, a double dielectric barrier discharge (DDBD) reactor was established to decompose TCE. The influence of different condition parameters on DDBD treatment of TCE was investigated to determine the appropriate working conditions. The chemical composition and biotoxicity of TCE degradation products were also investigated. Results showed that when SIE was 300 J L−1, the removal efficiency could reach more than 90%. The energy yield could reach 72.99 g kWh−1 at low SIE and gradually decreased with the increase of SIE. The k of the Non-thermal plasma (NTP) treatment of TCE was about 0.01 L J−1. DDBD degradation products were mainly polychlorinated organic compounds and produced more than 373 mg m−3 ozone. Moreover, a plausible TCE degradation mechanism in the DDBD reactors was proposed. Lastly, the ecological safety and biotoxicity were evaluated, indicating that the generation of chlorinated organic products was the main cause of elevated acute biotoxicity.

Harmless process of organic matter in organosilicon waste residue by fluidization-like DDBD reactor: Temperature action and mechanism

Herein, the non-hazardous application of low-temperature plasma technology in solid waste from the silicone industry was investigated by using a fluidization-like double dielectric barrier discharge plasma (DDBD) reactor. The results show ∼92.9% TOC in the organosilicon waste residue could be removed at the conditions (Discharge power: 7.0 W, S/G: 12.5 gminL−1, SIE: 158.0 JL-1), i.e. TOC content decreases from 166.0 g/kg to 11.8 g/kg. At the same time, the energy efficiency of the TOC removal rate reach ∼732.1 gkWh−1, and the temperature of the discharge zone is below 280 °C. According to the TG-MS analysis and infrared thermal imager, it is considered that the heat energy generated in the plasma treatment process can affect the decomposition of organic matter. On the other hand, the samples were characterized before and after treatment by BET, SEM, XRD, FTIR, and GC-MS. It was proposed the organic matter was firstly gasified under the action of plasma and thermal. Then, the active group will generate and react with the C–H, C–C, or C–Si by the bombardment of sufficient energy of charged particles, leading the organic matter further to decompose into small molecules, such as CH4, H2, CO, and CO2.

Degradation of deoxynivalenol in wheat by double dielectric barrier discharge cold plasma: identification and pathway of degradation products.

Deoxynivalenol (DON) produced during the onset of fusarium head blight not only affects the quality and safety of wheat but also causes serious harm to human and livestock health. However, due to the high stability of DON, it is difficult to eliminate it or reduce it naturally after it has been produced. Cold plasma technology is a non-thermophysical processing technology that has been widely used for microbial inactivation and mycotoxin degradation. In this study, the degradation efficiency of double dielectric barrier discharge (DDBD) cold plasma on DON in aqueous solution and wheat was studied; the structures of degradation products of DON and its pathway were clarified, and the effect of DDBD plasma on wheat quality was evaluated. Double dielectric barrier discharge cold plasma was used for efficient degradation of DON (0.5 ~ 5μgmL^-1) solution and achieved a degradation rate of 98.94% within 25 min under the optimal conditions (voltage 100 V, frequency 200 Hz, duty cycle 80%). Furthermore, 10 degradation products (C15 H24 O5 , C15 H22 O6 , C15 H22 O9 , C16 H22 O7 , C15 H20 O7 , C15 H20 O9 , C15 H18 O8 , C15 H22 O5 , C16 H24 O5 , and C15 H18 O9 ) were identified by ultra-performance liquid chromatography-time of flight-mass spectrometry (UPLC-TOF-MS/MS) combined with Metabolitepilot and Peakview software. The degradation pathway of DON was obtained based on the chemical structures and accurate mass of these products. The DON degradation rate of 61% in wheat was achieved after treatment for 15 min, which slightly affects the moisture content, proteins, and wheat starch. Applying DDBD to wheat could effectively reduce the level of DON contamination, which provides a theoretical basis for applying cold plasma to the degradation of DON in wheat. © 2022 Society of Chemical Industry.

The effect of dual dielectric barrier discharge non-thermal plasma on the emission characteristics of diesel engine

Diesel engine have been applied to transportation due to its high efficiency, high output power, and high reliability. However, the emissions of diesel engines have become a serious problem and various technologies have been applied to reduce such emissions. Non-thermal plasma (NTP) is a notable potential measure for diesel engine emission control. The research investigated the effect of double dielectric barrier discharge (DDBD) NTP on diesel engine emission with different discharge voltages and duty ratios. The results shown that CO emission increases as the discharge voltage and duty ratio increases, with a maximum increasing rate of 8.59%. However, NOX, formaldehyde, acetaldehyde, VOCs, and PM2.5 emissions reduced, with a maximum reduction rate of 65.97%, 34.65%, 30.73%, 35.94%, and 85.21%, respectively. The research found that NTP can be used to control diesel engine emission, more importantly, it can achieve the reduction of NOX and PM emission simultaneously.

Synergy of dielectric barrier discharge plasma and magnetically separable MOF-derived Co@C composite for the improved degradation of norfloxacin antibiotic in water

Norfloxacin (NOR) is a highly toxic fluoroquinolone antibiotic, which is continuously discharged into aquatic environment. Due to its poor biodegradability, NOR is difficult to be removed and has exerted a serious impact on environmental risk. In this paper, a coaxial double dielectric barrier discharge (DBD) device was designed and built, then was synergic with cobalt-carbon (Co@C) composites for the improved degradation of NOR in wastewater with high degradation efficiency. The Co@C composite, a porous carbon material, was synthesized by calcination of Co-metal organic frameworks (Co-MOFs), and was further characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Brunauer-Emmett-Teller surface analyzer, Fourier transform infrared spectrometry and vibrating sample magnetometer. The combination of DBD with Co@C system has an obvious synergistic effect for the removal of NOR. The degradation rate could reach to 84.7% and the treatment time was in 15 min, which were 14.1% higher and 10 min shorter than those of solo DBD system. The synergistic factor was estimated to be 1.12, and the energy yield of process could reach to the maximum of 7.6 mg/kWh. The effects of discharge voltage, pH, NOR initial concentration and Co@C dosage on the degradation rate of NOR have been explored in detail. The experimental results indicated that the system of DBD coupled with Co@C for NOR degradation was appropriate in a wide initial pH from 3.0 to 11.0. Moreover, Co@C could be reused several times and convenient to be magnetically recycled. Furthermore, it was proved that O3, •OH and H2O2 were the main reactive oxygen species during the catalytic decomposition reactions of NOR, and the generated O3 in DBD system could be converted into •OH under the synergic catalysis of Co@C, further promoting degradation efficiencies for NOR. Finally, main intermediate products of NOR degradation were analyzed by liquid chromatography-mass spectrometry, and possible degradation mechanism and pathways were speculated.

Application of non-thermal plasma (NTP) for volatile compounds (VCs) removal at sewage sludge composting facility

Double dielectric barrier discharge (DDBD) reactors were used to evaluate the removal efficiency of volatile compounds (VCs) from the exhaust gas of sewage sludge (SS) composting facility at optimal conditions, i.e., input power 65.8W, gas feeding rate 4 L/min, plasma discharge gap 6 mm. Abatement of VCs from different processing periods of SS composting was determined. 100% removal of major species of VCs (methyl isobutyl ketone, carbon disulfide, chlorobenzene and methylene chloride, etc.) were determined during the ‘before turning (B.T)’ and ‘5 h after turning (A.T)’ process. In addition, the synergistic effect of plasma-catalyst (Pt–Sn/Al2O3, BaTiO3 and HZSM-5) on VCs abatement showed enhanced removal performance as the formation of reactive species (H and OH radicals) was increased, especially on the surface of the catalyst. Nevertheless, plasma alone and plasma-catalyst combine systems showed the most effective reduction in odor concentration at the ‘B.T’ process due to low initial concentration. The study could facilitate NTP-DDBD technology application and process optimization in exhaust gases treatment of composting plants.

Plasma-assisted chemical-looping combustion: Mechanistic insights into low temperature methane oxidation with CuO

The low-temperature oxidation of CH4 by CuO in a coaxial, fixed bed, double dielectric barrier discharge (DBD) reactor was investigated with time-dependent species measurements by an electron-ionization molecular beam mass spectrometer (EI-MBMS). In the experiment, 10% methane carried by noble gasses was flown at 50 sccm through 1 g CuO dispersed in quartz wool both under plasma and non-plasma conditions, while time-dependent gas-phase species profiles were collected. Plasma conditions were explored from 300 to 600 °C while the non-plasma conditions were set from 300 to 900 °C. Mechanistic insights into the oxidation of CH4 by CuO with plasma discharge at lower temperatures (≤ 600 °C) were obtained by quantifying the fuel oxidation, intermediate species, and CO2 production in comparison to the non-plasma conditions. We observed significant enhancement of fuel oxidation from the plasma discharge between 400 and 500 °C. The CO2 production at 500 °C with plasma was greater than that at 700 °C without plasma, reducing fuel oxidation temperature by 200+ °C. During tests, three distinct reaction stages were observed: a gas-phase transport limited stage, a surface reaction limited kinetic stage, and an oxygen ion diffusion limited stage. It was observed that plasma greatly improved the reactivity of the second stage at low temperature. In addition, no carbon deposits were observed on the resultant particles, even under the presence of plasma. M. species such as C4H2 and C6H6 not previously observed or predicted in CuO/CH4 chemical looping were observed, with some species such as CH3OH only becoming detectable as total flowrate was increased from 50 to 1500sccm. A non-plasma reaction pathway for CH4 based the observed species from the MBMS spectrum and previous predictions from reactive molecular dynamics simulations was created, providing a framework from which future, more complex plasma CuO mechanisms can be crafted from.

Experimental analysis of gas- and particle-phase organic byproducts formed by plasma-induced toluene destruction processes

• Organic byproducts were evaluated by NTP degradation of toluene at ambient temperature and atmospheric pressure. • PTR-TOFMS measurement showed that toluene degradation resulted in dozens of organic by-products. • Size distribution and number concentration of particles formed during toluene degradation were measured by SMPS. • NTP-induced polymerization and oxidation contribute to particle formation with diameters in the range of 10 and 100 nm. Non-thermal plasma (NTP) technology has great potential to treat volatile organic compounds (VOCs) at low concentrations and large volumes. In this work, toluene, one of the most stable VOCs, was employed as a model pollutant to study its degradation by double dielectric barrier discharge (DDBD) at ambient temperature and atmospheric pressure. The performance of the DDBD reactor was evaluated in terms of discharge power, removal efficiency, CO x selectivity, and byproduct formation. Online and continuous measurements by PTR-TOFMS showed that toluene degradation resulted in the formation of 12 major volatile organic byproducts as well as 7 minor ones with concentrations ranging from ppbv to ppmv. Moreover, the particle size distribution and number concentration of particles formed during toluene degradation were measured using a scanning mobility particle sizer, and the effects of discharge power, initial toluene concentration, gas flow rate and O 2 content on particle formation were systematically investigated. The results show that both NTP-induced polymerization and oxidation contribute to aerosol formation, and the total concentration of organic byproducts in the aerosol phase is about 10 7 cm −3 with diameters in the range of 10 and 100 nm. This pioneered investigation on gas- and particle-phase organic byproducts from toluene degradation by NTP would deepen the understanding of plasma degradation of VOCs and accelerate the practical application of NTP for VOCs treatment.

Advanced remediation of pyrene contaminated soil by double dielectric barrier discharge (DDBD) plasma and subsequent composting process

Due to increasing industrialization, soils are increasingly contaminated by polycyclic aromatics such as pyrene and need gentle treatment to keep the soil functioning. This study applied a double dielectric barrier discharge (DDBD) plasma reactor and composting reactor to remediate pyrene-contaminated soil. The effect of peak-to-peak applied voltages on the remediation efficiency of pyrene was investigated. The experimental results illustrate that pyrene remediation efficiency increased from 43% to 85% when the peak-to-peak applied voltage was increased from 28.0 to 35.8kV. When using the combined method of DDBD and composting, 90-99% of pyrene could be removed, while a reduction of 76.5% was achieved using only composting, indicating the superiority of the combined system. Moreover, the authors could demonstrate that DDBD plasma treatment improves humification in the post-composting process as humic acid (HA) concentrations increased to 7.7mg/g with an applied voltage of 35.8kV; when composting was used as the sole treatment method, only 3.4mg/g HA were produced. The microbial activity in the DDBD plasma-treated soil peaked on the 5th day and had a 2nd rise afterwards. The authors demonstrate that the combined technology of DDBD plasma and composting is a promising method for soil remediation with persistent organic pollutants. This treatment approach improves pollutant degradation efficiency and facilitates further humification, potentially restoring the function of contaminated soil. This approach could be considered a cost-effective and green strategy for soil remediation with persistent organic pollutants.

Modified Mn/ZSM-5 for Non-Thermal Plasma Mineralization of VOCs and DFT Simulation Using a Novel Y-Type ZSM-5 Model

Using a catalyst to mineralize volatile organic compounds (VOCs) in a Non-thermal Plasma (NTP) reactor is an effective method. In many kinds of catalysts for VOCs degradation, oxygen defect is a crucial factor affecting the catalytic activity. Three different methods (steaming, doping, plasma) were used to introduce possible oxygen defects into the Mn/ZSM-5 to prepare modified catalysts, which were evaluated in VOCs degradation activity using a Double Dielectric Barrier Discharge (DDBD) plasma device. Additionally, a novel Y-type ZSM-5 model was employed in the DFT simulation. The new Y-type ZSM-5 model used in this paper is a more realistic aperiodic model. It showed that introducing possible oxygen defects can substantially enhance degradation efficiency. Taking the catalyst with oxygen defects introduced by plasma as an example, the conversion (CO2 selectivity) of the methanol, acetone, and toluene could reach 100% (100%), 97.7% (99.1%), 91.2% (93.9%), respectively, at an initial concentration of 2000 ppm and specific input energy of 9 kJ/L. The results demonstrated that modification could significantly enhance the activity of the catalyst in decomposing VOCs at room temperature using non-thermal plasma catalysis. Theoretical simulation of density functional theory (DFT) revealed that the adsorption of adsorbate on the catalyst becomes easier after possible oxygen defects are introduced.

A novel double dielectric barrier discharge reactor for toluene abatement: Role of different discharge zones and reactive species

A coaxial cylindrical double dielectric barrier discharge (DDBD) reactor with two separate discharge zone was designed and the role of its different discharge zones and reactive species were explored in toluene degradation. The inner tube (the space between the high voltage electrode and the inner barrier) had a higher gas temperature and reactive species concentration due to its stronger discharge intensity compared with the outer tube (the space between the inner and outer barriers). The two discharge zones exhibited similar toluene removal efficiency, whereas the mineralization rate of the inner tube exceeded that of the outer tube under 18–22 kV, and the result was opposite under 24–28 kV. The gas-flow direction had no significant effect on the toluene removal efficiency, but the mineralization rate of the down-flow reactor (23.7%–54.4%) exceeded that of the reverse-flow reactor (20.7%–45.5%). The inner and outer tubes mainly responsible for the initial degradation and further oxidation of toluene, respectively. The role of long-lived (N2(A3∑u+) and metastable O2 (a1Δg and b1Σg+)) and short-lived (N2(C3∏u), N2(B3∏g), and atomic O (1D and 3P)) reactive species on toluene degradation and oxidation was analyzed. The plausible toluene degradation mechanism in the DDBD reactor was proposed based on the role of different discharge zones and reactive species. The finding herein is significant in the design, optimization and application of DBD reactors.

Ammonia decomposition over iron-based catalyst: Exploring the hidden active phase

The possible phase transformation of catalysts under reaction conditions brings lots of difficulties in establishing the active phase. Herein, we report a hidden active phase over iron catalyst uniquely for the dehydrogenation of ammonia (NH3). The highest dehydrogenation rate corresponds to an evanescent Fe/Fe4N mixing phase while the nitrogen (N) kept on accumulating and gradually deactivated the catalyst. Density functional theory (DFT) calculations demonstrated that deposition of an N on Fe(100) surface modifies the electronic structure of its surrounding iron atoms, causing a significant reduction of the initial dehydrogenation barrier of NH3. To recover the hidden active phase, ambient-pressure double dielectric barrier discharge (DDBD) plasma was applied to the reaction system in situ to remove the excessive surface N, which yields a pronounced improvement of the catalytic performance. The work demonstrates that hidden active phase in thermal catalysis can be unfolded when the rate-determining step is subdued by applied plasma.

Catalytic conversion and DFT analysis of post DDBD-catalysis system for degradation of toluene, ethyl acetate and acetone with different metal-oxides catalysts

A series of multiphase metal-oxide catalysts (MnOx/γ-Al2O3, CuOx/γ-Al2O3, FeOx/γ-Al2O3, CeOx/γ-Al2O3 and LaOx/γ-Al2O3) were prepared for plasma-catalyst degradation of multicomponent volatile organic compounds (VOCs, such as toluene, acetone and ethyl acetate). The results reveal that the degradation efficiency (DE) of acetone, toluene and ethyl acetate in the DDBD system can be arranged as follows: Mn2O3/γ-Al2O3> Fe2O3/γ-Al2O3> CuO/γ-Al2O3> CeO2/γ-Al2O3> La2O3/γ-Al2O3> γ-Al2O3, and the highest DE (49.5% for acetone, 93.3% for toluene and 79.8% for ethyl acetate) is obtained in Mn2O3/γ-Al2O3+double dielectric barrier discharge (DDBD) system at specific input energy (SIE) of 700 J/L. Compared with the other catalysts, Mn2O3/γ-Al2O3 also exhibits the most significant inhibitory effect on the production of ozone (O3). On the other hand, CeO2/γ-Al2O3 and La2O3/γ-Al2O3 catalysts display different catalytic selectivity. Both catalysts can slightly raise the DE of VOCs and remarkably facilitate VOCs' mineralization. The carbon balance (CB) is increased by 30.2% and 38.8%, and the CO2 selectivity (SCO2) is raised by 70.5% and 11.9% in the CeO2/γ-Al2O3+DDBD system and La2O3/γ-Al2O3+DDBD system at SIE of 700 J/L, respectively. To further understand the catalytic effect of the catalysts, the adsorption of O3 on different catalysts was simulated by a DFT model. According to the results of the DFT model, it is found that the adsorption energy of other metal oxides seems to be used as a reference for catalytic effect to a certain extent except CeO2. The higher the absolute values of adsorption energy, the higher the improvement of VOCs degradation efficiency by catalyst.

Preparation of graphene-based catalysts and combined DBD reactor for VOC degradation.

The objective of this study was to compare the transformation of by-products between single dielectric barrier discharge (SDBD) and double dielectric barrier discharge (DDBD), to optimize the preparation of graphene-based catalysts and apply them in combination with DBD for volatile organic compound degradation. We compared the degradation performance of SDBD and DDBD, prepared, and characterized graphene-based catalysts. SEM, BET, XRD, and FTIR analyses showed that the morphologies and internal structures of the three catalysts were the best when 0.25mL of [BMIM]PF6 was added. When MnOx/rGO, FeOx/rGO, and TiOx/rGO were used in combination with DDBD, the degradation rates of benzene were found to be 83.5%, 77.2%, and 63.8%, respectively, whereas the O3 transformation rates were 60%, 79%, and 40%, respectively. Moreover, the NO2 transformation rates were 70%, 55%, and 42.5%, respectively, whereas the NO transformation rates were 69%, 39%, and 33.5%, respectively. The CO2 selectivity was 62%, 51%, and 49%, respectively. MnOx/rGO exhibited superior performance in the degradation of benzene series, NO transformation, NO2 transformation, CO2 selectivity, and energy efficiency. On the other hand, FeOx/rGO exhibited superior performance for O3 transformation. Based upon the XPS analysis, it was found that Mn3O4 and Fe3O4 played a leading role in promoting the degradation of benzene series and the transformation of by-products.