Effects of electrode geometry on the performance of dielectric barrier/packed-bed discharge plasmas in benzene degradation

Butachlor (BTR) degradation by dielectric barrier discharge plasma in soil: Affecting factors, degradation route, and toxicity assessment

Over the past few decades, the frequent and excessive usage of pesticides has had detrimental effects on the soil and other habitats. In terms of removing organic contaminants from soil, non-thermal plasma has become one of the most competitive advanced oxidation methods. The study used dielectric barrier discharge (DBD) plasma to repair soil contaminated by butachlor (BTR). BTR degradation was investigated in actual soil under various experimental parameters. According to the results, DBD plasma treatment at 34.8 W destroyed 96.10% of BTR within 50 min, and this degradation was consistent with the model of first order kinetics. Boosting the discharge power, lowering the initial BTR concentration, using appropriate soil moisture content and air flow rate, and using oxygen as the working gas for discharge are all beneficial to the degradation of BTR. The changes in soil dissolved organic matter (DOM) before and after plasma treatment were assessed using a total organic carbon (TOC) analyzer. A Fourier transform infrared (FTIR) spectroscopy and an Ultra Performance Liquid Chromatography Tandem Mass Spectrometry (UPLC-MS) were employed to investigate the degradation of BTR. A wheat growth test showed that the best growth was achieved at 20 min of plasma soil remediation, but too long treatment would lower soil pH and thus affect wheat growth.

Volatile organic compounds degradation by nonthermal plasma: a review

Volatile organic compounds (VOCs) have posed a severe threat on both ecosystem and human health which thus have gained much attention in recent years. Nonthermal plasma (NTP) as an alternative to traditional methods has been employed to degrade VOC in the atmosphere and wastewater for its high removal efficiency (up to 100%), mild operating conditions, and environmental friendliness. This review outlined the principles of NTP production and the applications on VOC removal in different kinds of reactors, like single/double dielectric barrier discharge, surface discharge, and gliding arc discharge reactors. The combination of NTP with catalysts/oxidants was also applied for VOC degradation to further promote the energy efficiency. Further, detailed explanations were given of the effect of various important factors including input/reactor/external conditions on VOC degradation performance. The reactive species (e.g., high-energy electrons, HO·, O·, N₂⁺, Ar⁺, O₃, H₂O₂) generated in NTP discharge process have played crucial roles in decomposing VOC molecules; therefore, their variation under different parameter conditions along with the reaction mechanisms involved in these NTP technologies was emphatically explained. Finally, a conclusion of the NTP technologies was presented, and special attention was paid to future challenges for NTP technologies in VOC treatment to stimulate the advances in this topic.

Degradation of pyrene in contaminated soil by the dielectric barrier discharge combined with the MnFe2O4 catalyst

In this work, a spinel oxide of MnFe₂O₄ was used as the dielectric barrier discharge (DBD) catalyst for the remediation of pyrene-contaminated soil. The performances were investigated through tuning voltage, frequency, catalyst dosage, and soil moisture. Under the optimal conditions, such as the voltage of 10.0 kV, the discharge frequency of 1.0 kHz, MnFe₂O₄ dosage of 0.3 g, air flow rate of 2.0 L min^-1, soil humidity of 5.3%, and degradation efficiency of DBD/MnFe₂O₄ for pyrene could reach 79.26% after 10 min treatment, which was much higher than that of DBD for pyrene of 42.56%. The DBD/MnFe₂O₄ system also showed the high degradation efficiency of other pollutants including phenanthrene, p-nitrophenol, and p-nitrophenol in contaminated soil. The enhancing mechanism of the DBD/MnFe₂O₄ system was discussed.

Recent Advances of Emerging Organic Pollutants Degradation in Environment by Non-Thermal Plasma Technology: A Review

Emerging organic pollutants (EOPs), including endocrine disrupting compounds (EDCs), pharmaceuticals and personal care products (PPCPs), and persistent organic pollutants (POPs), constitute a problem in the environmental field as they are difficult to completely degrade by conventional treatment methods. Non-thermal plasma technology is a novel advanced oxidation process, which combines the effects of free radical oxidation, ozone oxidation, ultraviolet radiation, shockwave, etc. This paper summarized and discussed the research progress of non-thermal plasma remediation of EOPs-contaminated water and soil. In addition, the reactive species in the process of non-thermal plasma degradation of EOPs were summarized, and the degradation pathways and degradation mechanisms of EOPs were evaluated of selected EOPs for different study cases. At the same time, the effect of non-thermal plasma in synergy with other techniques on the degradation of EOPs in the environment was evaluated. Finally, the bottleneck problems of non-thermal plasma technology are summarized, and some suggestions for the future development of non-thermal plasma technology in the environmental remediation were presented. This review contributes to our better understanding of non-thermal plasma technology for remediation of EOPs-contaminated water and soil, hoping to provide reference for relevant practitioners.

The Bibliometric Analysis and Review of the Application of Plasma in the Field of VOCs

The application of plasma in the field of volatile organic compounds (VOCs) can be traced back to the 1990s and has gradually developed into an important research field. In this regard, this article primarily sorts and analyzes the literature on the “application of plasma in the field of VOCs” in the Web of Science core collection database from 1992 to 2021 and, subsequently, obtains important data and trends, including the annual number of articles published, country, institution analysis, and journal, as well as discipline analysis, etc. The results show that China is not only in a leading position in the field of research, but also has six top-ten research institutions. This field has more research results in engineering, chemistry, physics, and environmental disciplines. In addition, this article summarizes dielectric barrier discharge (DBD) and titanium-containing catalysts, which represent the discharge characteristics and type of catalyst highlighted through the hot keywords. This review will provide certain guidance for future, related research.

C-dot doping for enhanced catalytic performance of TiO2/5A for toluene degradation in non-thermal plasma-catalyst system

Non-thermal plasma (NTP) is gaining attention as a powerful tool to induce various reactions. The combination of NTP with catalysts has been successfully used to degrade volatile organic compounds (VOCs) for pollution control. In this study, a series of TiO₂-C/5A catalysts, synthesized by carbon dots (C-dots) that decorate TiO₂ by sol-gel and wetness impregnation methods, were incorporated with a dielectric barrier discharge (DBD) reactor in a single-stage structure to degrade toluene at atmospheric pressure and room temperature. A proton-transfer reaction mass spectrometer and a CO₂ analyzer were used to monitor the concentration variations of organic by-products and CO₂ online. The effects of input power, mass ratio of C-dots/TiO₂ (TiO₂/5A (0 wt%), TiO₂-C1/5A (2.5 wt%), TiO₂-C2/5A (5 wt%), TiO₂-C3/5A (10 wt%)), gas flow rate, initial concentration of toluene on the toluene degradation efficiency, and CO₂ selectivity were studied. The plasma-catalyst hybrid system could effectively improve the energy efficiency and reaction selectivity, attaining a maximum toluene degradation efficiency of 99.6% and CO₂ selectivity of 83.0% compared to 79.5% and 37.5%, respectively, using the conventional plasma alone. Moreover, the generation of organic by-products also declined dramatically, averaging only half as much in plasma alone. The results also indicated that the appropriate amount of C-dot doping could greatly improve the catalyst efficiency in the hybrid plasma system. This is because the interaction between C-dots and TiO₂ favors the formation of photoelectron holes and reduces the energy band gap and the recombination rate of photogenerated electron holes, which facilitates the generation of more active species on the catalyst surface, thereby leading to a more effective degradation reaction. These observations will provide guidance for the interaction studies between NTP and catalysts, not only for the exploration of new chemical mechanisms of aromatic compounds, but also for the screening of favorable materials for the desired reactions.

The chemistry of gaseous benzene degradation using non-thermal plasma

In this study, the abatement of benzene in a dielectric barrier discharge (DBD) reactor was studied. The efficiency was investigated in terms of benzene conversion and product formation. The composition of gas-liquid-solid three-phase product produced during degradation was observed by GC-MS. Under the optimal SED, the solid-phase product was analyzed by FT-IR, SEM, and EDS. The results suggested that the product were mainly benzonitriles, benzenedicarbonitrile, phenols, esters, and amides. The wt% of C in product decreased as SED increased, demonstrating that the high discharge voltage facilitated the conversion of VOCs to gaseous intermediate product and CO₂. Possible degradation mechanism and pathways of benzene destruction in the DBD reactor were proposed.

Niobium doping enhanced catalytic performance of Mn/MCM-41 for toluene degradation in the NTP-catalysis system

The destruction of toluene in a dielectric barrier discharge (DBD) reactor with Nb-Mn/MCM-41 had been investigated and compared with X (X = Cu, Ce, Co)-Mn/MCM-41 catalysts. The XRD and TEM result confirms that the metal species were highly dispersed on the MCM-41. The results of XPS, O₂-TPD and H₂-TPR clearly demonstrate that Nb doping facilitated formation of lattice oxygen (O_latt) and the acid sites, which are all beneficial to catalytic degradation of toluene. Compared to X (Cu, Ce, Co)-Mn/MCM-41, Nb-Mn/MCM-41 had the most contents of O_latt, the most amounts of acid sites and the strongest acidity. Consequently, the catalytic performance tests identify that Nb-Mn/MCM-41 had the best catalytic performance, the highest removal efficiency and CO₂ selectivity as well as carbon balance especially at low SIE. These results indicate that Nb was an important promoter improving the activity and CO₂ selectivity of Mn/MCM-41 for the decomposition of toluene in NTP-catalysis system.

Percarbonate promoted antibiotic decomposition in dielectric barrier discharge plasma

A coupling technique introducing sodium percarbonate (SPC) into a dielectric barrier discharge (DBD) plasma was investigated to enhance the degradation of antibiotic tetracycline (TC) in aqueous. The dominant effects of SPC addition amount and discharge voltage were evaluated firstly. The experiments indicated that the moderate SPC dosages in the DBD presented an obvious synergistic effect, improving the TC decomposition efficiency and kinetics. Elevating the voltage was conducive for the promotion of antibiotic abatement. After 5 min treatment, the removal reached 94.3% at the SPC of 52.0 μmol/L and voltage of 4.8 kV for 20 mg/L TC. Especially the defined synergy factors were greater than one since the SPC being added, and the energy yield was increased by 155%. Besides, the function mechanism was explained by the hydrogen peroxide and ozone quantitative determinations and radical scavenger test, and the results confirmed that the collaborative method could increase the generation of reactive species, and the produced hydroxyl and superoxide radicals both played the significant roles for the TC elimination. Furthermore, the decomposition and mineralization of the synergism were verified by UV-vis spectroscopy, TOC and COD analyses, and the degradation byproducts and transformation pathways were identified based on the analysis of HPLC-MS finally.

Application of proton transfer reaction mass spectrometry for the assessment of toluene removal in a nonthermal plasma reactor

Proton transfer reaction mass spectrometry (PTR-MS) is a mature technique for the real-time measurement and monitoring of volatile organic compounds in the atmosphere. In this paper, a modified quantification method for PTR-MS was used to assess the performance of nonthermal plasma (NTP) reactor for the removal of toluene which was widely used in industrial production processes. Toluene and 11 corresponding organic by-products were tentatively identified and quantified by a proton transfer reaction time-of-flight mass spectrometer. The degradation dynamics of toluene and the formation of organic by-products were monitored in real-time (resolution = 1 second) under "plasma off" and "plasma on" conditions. We conclude that initial concentration and gas flow rate were the key parameters in the health risk assessment of NTP for the removal of toluene. The toluene removal efficiency and CO₂ selectivity decreased with increasing upstream toluene concentration or gas flow rate, whereas the health risk influence index increased with increasing upstream toluene concentration or gas flow rate. The highest removal efficiency of toluene (100%), CO₂ selectivity (53.2%), and the best health risk influence index for organic by-products (0.11) were achieved when the toluene concentration was kept at 105 ppmv and flow rate at 0.4 L/minute. The results demonstrate that PTR-MS is a promising tool to improve the practical applications of volatile organic compound removal by NTP because it can be used to optimize the NTP working conditions by providing a precise, fast, and clear health risk assessment for organic by-products based on their real-time analysis.

Abatement of SF6 in the presence of NH3 by dielectric barrier discharge plasma

In this paper, the degradation rate, energy yield and the degradation by-products of SF₆ was studied when different concentrations of NH₃ were added. When NH₃ concentration increased from 0 to 2%, the degradation rate efficiency(DRE) of SF₆ increased from 60% to 97.23% under the flow rate of 50ml/min and 94W input power. The energy yield(EY) reached 4.16g/kWh. In addition, we found that increasing the flow rate to 250ml/min, the DRE decreased to 58.71%, but the EY increased to 12.55g/kWh. The main gas by-products are SOF₂, SO₂F₂, SO₂, OF₂, HF and NF₃. When the concentration of initial NH₃ increased, the SO₂ concentration increased while the concentrations of SOF₂, SO₂F₂, SOF₄ decreased. In addition, we found that a pale yellow film formed on the surface of the reactor wall. XPS analysis showed that the solid products were mainly S, NH₃HF and NH₄HF₂. The emission spectra show that NH₃ addition can effectively promote the formation of active particles and increase plasma density.The addition of NH₃ can convert some of the sulfur and fluorine into solid products and reduce the production of toxic gases.

Enhanced removal of humic acid from micro-polluted source water in a surface discharge plasma system coupled with activated carbon

Surface discharge plasma (SDP) combined with activated carbon (AC) was employed to eliminate dissolved organic matter from micro-polluted source water, with humic acid (HA) as the model pollutant. Synergistic effect on HA removal was observed in the SDP-AC system; HA removal efficiency reached 60.9% within 5-min treatment in the SDP-AC system with 5.0 g AC addition, whereas 16.7 and 17.4% of HA were removed in sole SDP system and AC adsorption, respectively. Scanning electron microscope and Boehm titration analysis showed that chemical reactions between active species and functional groups of AC occurred. The existence of isopropanol or benzoquinone exhibited inhibitive effects on HA removal in the SDP system, while these inhibitive effects were weakened in the SDP-AC system. The influences of AC on ozone equivalent concentration and H₂O₂ concentration were evaluated, and there were approximately 39 and 20% decline in ozone equivalent concentration and H₂O₂ concentration within 6-min treatment in the SDP-AC system, respectively, compared with those in the sole SDP system. Dissolved organic carbon, specific ultraviolet absorbance, and UV absorption ratios analysis demonstrated that the SDP treatment destroyed the chromophoric groups, double bonds, and aromatic structure of HA molecules, and these destructive actions were strengthened by AC.

Glyphosate contaminated soil remediation by atmospheric pressure dielectric barrier discharge plasma and its residual toxicity evaluation

Glyphosate was one of the most widely used herbicides in the world. Remediation of glyphosate-contaminated soil was conducted using atmospheric pressure dielectric barrier discharge (DBD) plasma. The feasibility of glyphosate degradation in soil was explored, and the soil leachate toxicity after remediation was assessed via a seed germination test. The experimental results showed that approximately 93.9% of glyphosate was degraded within 45min of DBD plasma treatment with an energy yield of 0.47gkWh-1, and the degradation process fitted the first-order kinetic model. Increasing the discharge voltage and decreasing the organic matter content of the soil were both found to facilitate glyphosate degradation. There existed appropriate soil moisture to realize high glyphosate degradation efficiency. Glyphosate mineralization was confirmed by changes of total organic carbon (TOC), chemical oxygen demand (COD), PO43- and NO3-. The degradation intermediates including glycine, aminomethylphosphonic acid, acetic acid, formic acid, PO43- and NO3-, CO2 and CO were observed. A possible pathway for glyphosate degradation in the soil using this system was proposed. Based on the soil leachate toxicity test using wheat seed germination, the soil did not exhibit any hazardous effects following high-efficiency glyphosate degradation.

Characteristics of back corona discharge in a honeycomb catalyst and its application for treatment of volatile organic compounds

The main technical challenges for the treatment of volatile organic compounds (VOCs) with plasma-assisted catalysis in industrial applications are large volume plasma generation under atmospheric pressure, byproduct control, and aerosol collection. To solve these problems, a back corona discharge (BCD) configuration has been designed to evenly generate nonthermal plasma in a honeycomb catalyst. Voltage-current curves, discharge images, and emission spectra have been used to characterize the plasma. Grade particle collection results and flow field visualization in the discharge zones show not only that the particles can be collected efficiently, but also that the pressure drop of the catalyst layer is relatively low. A three-stage plasma-assisted catalysis system, comprising a dielectric barrier discharge (DBD) stage, BCD stage, and catalyst stage, was built to evaluate toluene treatment performance by BCD. The ozone analysis results indicate that BCD enhances the ozone decomposition by collecting aerosols and protecting the Ag-Mn-O catalyst downstream from aerosol contamination. The GC and FTIR results show that BCD contributes to toluene removal, especially when the specific energy input is low, and the total removal efficiency reaches almost 100%. Furthermore, this removal results in the emission of fewer byproducts.

Acetamiprid removal in wastewater by the low-temperature plasma using dielectric barrier discharge

Degradation of acetamiprid in wastewater was studied in a dielectric barrier discharge (DBD) reactor. This reactor produces ultraviolet light and reactive species like ozone (O₃) can be used for the treatment of wastewater. We examined the factors that could affect the degradation process, including the discharge power, and the initial concentrations of acetamiprid, and O₃ which is generated by the DBD reactor. We also investigated the effect of adding Na₂B₄O₇ as a radical scavenger to probe the role of hydroxyl radical in the reaction. The results indicated that acetamiprid could be removed from aqueous solution effectively and hydroxyl radicals played an important role during the degradation by the low temperature plasma. The degradation process of acetamiprid fits the first-order kinetics. The degradation efficiency was 83.48 percent at 200 min when the discharge power was 170 W and the initial acetamiprid concentration was 50 mg/L. The removal efficiency of acetamiprid decreased with the increasing concentration of Na₂B₄O₇ because B₄O₇(2-) is an excellent radical scavenger that inhibited the generation of OH during the DBD process. The removal efficiency of acetamiprid improved in the presence of O₃. The main reason was that O₃ can oxidize certain organic compounds directly or indirectly by generating hydroxyl radicals. The degradation products of acetamiprid were characterized qualitatively and quantitatively using high performance liquid chromatography, mass spectrometry and UV-vis spectroscopy.