Plasma catalysis is gaining increasing interest for various gas conversion applications, such as CO2 conversion into value-added chemicals and fuels, N2 fixation for the synthesis of NH3 or NOx, ...methane conversion into higher hydrocarbons or oxygenates. It is also widely used for air pollution control (e.g., VOC remediation). Plasma catalysis allows thermodynamically difficult reactions to proceed at ambient pressure and temperature, due to activation of the gas molecules by energetic electrons created in the plasma. However, plasma is very reactive but not selective, and thus a catalyst is needed to improve the selectivity.
In spite of the growing interest in plasma catalysis, the underlying mechanisms of the (possible) synergy between plasma and catalyst are not yet fully understood. Indeed, plasma catalysis is quite complicated, as the plasma will affect the catalyst and vice versa. Moreover, due to the reactive plasma environment, the most suitable catalysts will probably be different from thermal catalysts. More research is needed to better understand the plasma–catalyst interactions, in order to further improve the applications.
Cold plasma has emerged as a potential bio-decontamination technology for microbial and chemical risks associated with food products such as fruits and vegetables. This study investigated the ...efficacy of cold plasma treatment for the degradation of pesticides (boscalid and Imidacloprid) on blueberries in tandem with the need to retain critical quality attributes of a fresh high value berry product post treatment. An in-package high voltage dielectric barrier discharge plasma reactor was employed for this study. The degradation efficacy of pesticides after 80kV and 5min of cold plasma treatment were found to be 80.18% for boscalid and 75.62% for Imidacloprid. Total phenol and flavonoid contents of blueberries increased significantly for 1min treated samples for all applied voltages. However, plasma treatment significantly decreased the ascorbic acid at longer plasma doses. There was no significant effect on physical parameters such as color while acceptable changes were observed in blueberry firmness. This study demonstrates effective chemical decontamination of blueberries whilst maintaining critical nutritional and physical quality parameters, offering an alternative process for quality retention of processing sensitive high value berry products.
•Cold plasma efficiently degraded pesticides on blueberries.•The degradation achieved was 80% for boscalid and 76% for Imidacloprid.•Polyphenolic and flavonoid contents increased after 1 min of cold plasma treatment.•Cold plasma treatments of up to 5 min had minimal impact on blueberry quality.•Cold plasma presents a unique processing tool for agrochemical and biocontrol that retains nutritional quality parameters.
Dielectric barrier discharges (DBDs) are plasmas generated in configurations with an insulating (dielectric) material between the electrodes which is responsible for a self-pulsing operation. DBDs ...are a typical example of nonthermal atmospheric or normal pressure gas discharges. Initially used for the generation of ozone, they have opened up many other fields of application. Therefore DBDs are a relevant tool in current plasma technology as well as an object for fundamental studies. Another motivation for further research is the fact that so-called partial discharges in insulated high voltage systems are special types of DBDs. The breakdown processes, the formation of structures, and the role of surface processes are currently under investigation. This review is intended to give an update to the already existing literature on DBDs considering the research and development within the last two decades. The main principles and different modes of discharge generation are summarized. A collection of known as well as special electrode configurations and reactor designs will be presented. This shall demonstrate the different and broad possibilities, but also the similarities and common aspects of devices for different fields of applications explored within the last years. The main part is devoted to the progress on the investigation of different aspects of breakdown and plasma formation with the focus on single filaments or microdischarges. This includes a summary of the current knowledge on the electrical characterization of filamentary DBDs. In particular, the recent new insights on the elementary volume and surface memory mechanisms in these discharges will be discussed. An outlook for the forthcoming challenges on research and development will be given.
In this paper, an atmospheric-pressure dielectric barrier discharge is used to modify the surface of the epoxy material and enhance the dissipation of surface charge to reduce the accumulation of ...surface charge. In the experiments, atmospheric-pressure air dielectric barrier discharge is driven by a microsecond pulse generator. Surface properties of epoxy before and after the plasma treatment are characterized by water contact angle, surface potential, and surface/volume conductivity measurements. Atomic force microscope and X-ray photoelectron spectroscopy are used to investigate the changes of the morphology and the chemical composition of the epoxy surface. Experimental results indicate that the surface of epoxy is etched by the plasma and the increase of the surface roughness enhances the surface insulation ability. The O radicals in plasma and the carbonyl groups formed on the surface make the surface charge trap shallower, change the epoxy surface composition then increase the surface conductivity and accelerate surface charge dissipation. When the epoxy is treated for an appropriate time, the epoxy surface insulation performance will be enhanced obviously and the surface charge dissipation will be accelerated.
Nitrogen oxide‐generating dielectric barrier discharge plasma is shown to effectively inhibit microorganisms and maintain fruit freshness. Physical and biological mechanisms of the plasma‐electrified ...fungicidal effects suggest that plasma‐generated NO and ONOO− species and other factors are crucial to regulating physiological senescence in citrus fruit while controlling pathogens on their surface. The revealed Physico‐chemical effects explain the observed phenotypic changes and the suppression of surface pathogens, thus providing mechanistic insights into postharvest fruit processing with plasmas.
Nitrogen oxide‐generating dielectric barrier discharge plasma is shown to effectively inhibit microorganisms and maintain fruit freshness. Physical and biological mechanisms of the plasma‐electrified fungicidal effects suggest that plasma‐generated NO and ONOO− species and other factors are crucial to regulating physiological senescence in citrus fruits while controlling pathogens on their surface.
Effect of in-bag dielectric barrier discharge cold plasma (IB-DBD-CP) on the keeping quality of Asian sea bass slices (ASBS) packaged under different gases during refrigerated storage at 4 °C was ...studied. ASBS without and with IB-DBD-CP treatment packaged under the gas combination of argon and oxygen (10:90) (gas A) or the mixtures of carbon dioxide, argon and oxygen (60:30:10) (gas B) and the control (kept in air) were monitored for quality changes up to 18 days. ASBS treated with IB-DBD-CP, regardless of gas composition, had lower microbial loads than those without treatment and the control (p < 0.05). The shelf-life of ASBS was prolonged to 9 and 12 days after being packaged under gas A and B, respectively without IB-DBD-CP treatment, while 6 days were recorded for the control. However, ASBS treated with IB-DBD-CP, packaged under gas A and B had the shelf-life of 12 and 15 days, respectively. Throughout the storage, trimethylamine content and total volatile nitrogen base content were lower in ASBS treated with IB-DBD-CP, particularly those packaged under gas B than that without treatment and the control (p < 0.05). Nevertheless, lipid oxidation as well as protein oxidation were higher in samples treated with IB-DBD-CP, regardless of gas composition used, in comparison with untreated counterpart. Therefore, IB-DBD-CP of ASBS packaged under high ratio of CO2 (60%) along with argon and oxygen was the potential method for augmenting the shelf-life of ASBS for >15 days at 4 °C.
•Qualities of slices during storage was influenced by gas composition in packaging.•Microbial load in slices was reduced when treated with cold plasma.•Plasma with combination with high CO2 content in packaging increased shelf-life.•Protein and lipid oxidation was pronounced in slices treated with cold plasma.
Lindane is a broad-spectrum organochlorine insecticide which has been included in the persistent organic pollutants (POPs) list together with its two hexachlorocyclohexane (HCH) isomers. Due to its ...continuous use in the past decades, the environmental impacts of HCHs are still severe now. Therefore, in the present study, dielectric barrier discharge (DBD) plasma was used as an advanced oxidation process for the destruction of HCHs in water. The result indicated that in air-DBD system, over 95.4% of the initial 5 mg L−1 lindane was degraded within 60 min. Moreover, DBD plasma displayed high degradation efficiencies of other HCH isomers including α, β, and δ-HCH. Electron spin resonance spectra, scavenging experiments and theoretical calculations revealed that the synergistic effects of various reactive species were the main reason for the high efficiency of DBD plasma. For instance, both hydroxyl radicals (•OH) and electrons (e−) could initiate the degradation of HCHs, while other reactive species such as 1O2 and ONOOH played important roles in the decomposition of intermediates. Therefore, the present study not only provided an effective approach for the treatment of HCHs, but also revealed the underlying mechanism based on in-depth experimental investigation and theoretical calculation.
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•DBD can effectively degrade lindane and its isomers.•Various active species have different reactivities towards different isomers.•Synergistic effects of various active species are key to lindane degradation.•The anti-interference capability of DBD is superior to other AOPs.
Tetracycline (TC) and Oxytetracycline (OTC) are common antibiotics increasingly detected in the environment, posing a potential risk to human and aquatic lives. Although conventional methods such as ...adsorption and photocatalysis are used for the degradation of TC and OTC, they are inefficient in removal efficiency, energy yield, and toxic byproduct generation. Herein, a falling-film dielectric barrier discharge (DBD) reactor coupled with environmentally friendly oxidants (hydrogen peroxide (HPO), sodium percarbonate (SPC), and HPO + SPC) was applied, and the treatment efficiency of TC and OTC was investigated. Experimental results showed that moderate addition of the HPO and SPC exhibited a synergistic effect (SF > 2), significantly improving the antibiotic removal ratio, total organic removal ratio (TOC), and energy yield by more than 50%, 52%, and 180%, respectively. After 10 min of DBD treatment, the introduction of 0.2 mM SPC led to a 100% antibiotic removal ratio and a TOC removal of 53.4% and 61.2% for 200 mg/L TC and 200 mg/L OTC, respectively. Also, 1 mM HPO dosage led to 100% antibiotic removal ratios after 10 min of DBD treatment and a TOC removal of 62.4% and 71.9% for 200 mg/L TC and 200 mg/L OTC, respectively. However, the DBD + HPO + SPC treatment method had a detrimental effect on the performance of the DBD reactor. After 10 min of DBD plasma discharge, the removal ratios for TC and OTC were 80.8% and 84.1%, respectively, when 0.5 mM HPO + 0.5 mM SPC was added. Moreover, principal component and hierarchical cluster analysis confirmed the differences between the treatment methods. Furthermore, the concentration of oxidant-induced in-situ generated ozone and hydrogen peroxide were quantitatively determined, and their indispensable roles during the degradation process were established via radical scavenger tests. Finally, the synergetic antibiotic degradation mechanisms and pathways were proposed, and the toxicities of the intermediate byproducts were evaluated.
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•Complete degradation of TC and OTC by the falling-film DBD reactor.•Synergistic effect of SPC and HPO reduced the degradation time of TC and OTC.•Bio-toxicity of TC and OTC were alleviated after oxidant-induced DBD treatment.
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•A novel approach of air DBD plasma combined with PMS was investigated.•Under optimal operational settings >96% of BTA was removed in 20 min.•The addition of PMS significantly ...improved the energy yield of air-DBD.•Mechanisms and possible BTA degradation pathways in DBD-PMS system were proposed.•Toxicity of BTA was reduced during the air DBD-PMS oxidation process.
Benzotriazole (BTA) is a widely used chemical in domestic and industrial products. BTA is bio-refractory and has become an emerging contaminant in the aquatic environment. In this study, a new approach for degradation of BTA is developed by coupling falling water film dielectric barrier discharge (DBD) plasma with peroxymonosulfate (PMS) or persulfate (PS). The degradation of BTA is significantly improved (by 47%) by the introduction of PMS into the DBD plasma system. In addition, the energy yield is increased by 84%. The enhanced degradation efficiency may be attributed to the activation of PMS enriches the active species and increases the oxidation potential of the DBD plasma system. Radical scavenger experiments show that both sulfate radical and hydroxyl radical contribute to the degradation of BTA, but the latter has greater direct impact on BTA degradation. In addition, superoxide radicals, singlet oxygen and electrons have also played an important role in the DBD-PMS system. Degradation intermediates of BTA are identified and reaction pathways, including hydroxylation, cleavage and coupling reactions, are proposed. Further toxicity analysis of intermediates demonstrates that the toxicity of oral rat LD50 and the developmental toxicity of BTA are alleviated. Overall, the combination of DBD and PMS may be a promising technology for efficient, economical and environmentally friendly removal of refractory pollutants in water.
Plasma-enhanced catalytic ammonia synthesis has been proposed as an alternative pathway for green nitrogen fixation in the case of medium- and small-scale operation. Recently, Mehta et al. Nat. ...Catal. 2018, 1 (4), 269−275 postulated that plasma-induced vibrational excitations of N2 decrease the dissociation barrier, without influencing the subsequent hydrogenation reactions and ammonia desorption at atmospheric conditions. In this paper, this postulation is substantiated with experimental data of unpromoted and promoted, alumina-supported ruthenium ammonia synthesis catalysts. Within the temperature regime for plasma-enhanced catalytic ammonia synthesis over ruthenium-based catalysts (>200 °C), synergy is experimentally observed between the catalyst and the plasma by a lowered apparent activation energy. While the apparent activation energy for thermal-catalytic ammonia synthesis typically ranges from ∼60 to ∼115 kJ mol–1 depending on the promoters, the apparent activation energy for plasma-enhanced catalytic ammonia synthesis ranges from ∼20 to ∼40 kJ mol–1, consistent with the hypothesis that ammonia synthesis is enhanced via plasma-induced vibrational excitations of N2. Further support follows from the observation that the effects of promoters and supports on activity are similar for thermal catalysis and plasma-enhanced catalysis. As promoter and support influence activity via enhancing dissociation of N2, it follows that breaking the N–N bond is still relevant in plasma-enhanced catalytic ammonia synthesis.
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