Film Dielectric Barrier Discharge Research Articles

Nitrogen Fixation via Catalyst-Free Water-Falling Film Dielectric Barrier Discharge Plasma: A Novel and Simple Strategy to Enhance Ammonia Selectivity

Plasma–liquid reactions represent an emerging green chemical process for nitrogen fixation; however, these processes generally exhibit low selectivity for ammonium (NH4+). This limitation highlights the need to explore simple methods to increase NH4+; selectivity. In this study, a catalyst-free falling film dielectric barrier discharge plasma system was employed for the selective synthesis of NH4+. By manipulating the flow state of the discharge gas, NH4+ selectivity was found to increase by 138.4% in the sealed gas flow state compared to the flowing gas state. Furthermore, an increase in the discharge voltage positively influenced the NH4+ selectivity. This phenomenon can be attributed to higher energy input and longer reaction times, which facilitate the formation of nitrogen molecular ions, a critical intermediate in ammonia synthesis. The reaction products were analyzed by UV spectrophotometry and emission spectroscopy to investigate the underlying mechanisms of ammonia synthesis. This study reveals the highest reaction rate reported to date for ammonia synthesis via single-system plasma gas–liquid reactions and offers a novel way to improve both the yield and selectivity of ammonium synthesis via non-thermal plasma gas–liquid interactions.

Degradation of sulfamethoxazole in a falling film dielectric barrier discharge system: Performance, mechanism and toxicity evaluation

The ubiquitous presence of sulfonamides (SAs) in wastewater poses serious risks to human health and ecosystem safety. This study evaluated the performance of a falling film dielectric barrier discharge (DBD) system on the removal of five SAs, namely sulfamethoxazole (SMX), sulfisoxazole (SIZ), sulfathiazole (STZ), sulfadiazine (SDZ) and sulfamerazine (SMR). Removal efficiencies >99 % were observed for all target SAs within 30 min of treatment, with pseudo-first order rate constants varying between 0.17 and 0.27 min−1. Superior removal efficiencies were achieved under acidic conditions compared to neutral and alkaline conditions. Using SMX as a model compound, mechanistic investigations revealed that the synergy of reactive oxygen species (ROS) and reactive nitrogen species (RNS) led to its efficient degradation, with peroxynitrites (ONOO−/ONOOH) and hydroxyl radical (OH) playing pivotal roles. SMX degradation pathways encompassing nitration/nitrosation, hydroxylation, deamination, CS and SN bond cleavage were proposed. The toxicity evaluation results demonstrated that the solution toxicity diminished following the plasma treatment under specific conditions. In particular, the solution treated with air or oxygen discharge enhanced the growth of wheat seedlings, suggesting the potential for reusing plasma-treated wastewater in agriculture. This study enhances our understanding of the underlying mechanisms involved in the plasma degradation of SAs and reveals the significant potential of plasma technology as a sustainable approach for treating wastewater.

Mechanical and statistical pathway for the experimental investigation of the dairy industry effluent using non-thermal plasma

Globally, there is still a demand for effective removal of industrial pollutants using modern treatment technologies. Therefore, to achieve industrial implementation, treatment efficiency and energy demand, at present the new Non-Thermal Plasma (NTP) technology is adopted to treat the dairy industry pollutants. Falling Film Dielectric Barrier Discharge reactor (FF-DBD) is developed whereas the reactor is further characterized by the various operating parameters including electric field, gas source, flow rate and pH for the removal of COD and lactose content for different experimental conditions. In this present study, experimental works are carried out in ‘lab-scale experimental hardware to analyze the degradation efficiency of dairy effluent based on COD and lactose. For the maximum of 68 % and 75.56 % of COD and lactose removal is achieved at the maximum voltage of 30 k,Vp-p. Moreover, the interaction between COD and lactose is analyzed by using ANOVA and the p-value is < 0.001. Comparing to the air, oxygen as a discharge gas in a DBD reactor gives more treatment efficiency because it produces more oxygen-based oxidative species. Further the 2D - simulation model is employed to find the velocity profile of effluent inside the FF-DBD reactor.

Removal of per- and polyfluoroalkyl substances from water by plasma treatment: Insights into structural effects and underlying mechanisms

Non-thermal plasma emerges as a promising technology for per- and polyfluoroalkyl substances (PFAS) decomposition due to its notable efficacy and environmentally friendly characteristics. In this study, we demonstrated the efficacy of a falling film dielectric barrier discharge (DBD) system for the removal of 10 PFAS, including perfluoroalkyl carboxylic acids (PFCAs), perfluoroalkyl sulfonic acids (PFSAs) and hexafluoropropylene oxide (HFPO) oligomer acids. Results showed that compounds with fluoroalkyl chain length>4 were effectively decomposed within 100 min, with long-chain PFAS demonstrating more pronounced removal performance than their short-chain analogues. The superior removal but low defluorination observed in HFPO oligomer acids could be ascribed to their ether-based structural features. The integration of experimental results with density functional theory (DFT) calculations revealed that the synergistic effects of various reactive species are pivotal to their efficient decomposition, with electrons, OH•, and NO2• playing essential roles. In contrast, the degradation of PFSAs was more dependent on electron attack than that of PFCAs and HFPO oligomer acids. Significantly, the most crucial degradation pathway for HFPO oligomer acids was the cleavage of ether CO, whether through radical or electron attack. Furthermore, the demonstrated effective removal in various water matrices showed the potential of the plasma system for removing PFAS in complex aquatic environments. This study provided mechanistic insights into PFAS degradation behavior in plasma processes, and it underscored the vital influence of molecular structures on degradability, thereby contributing to the further development and regulation of plasma-based technologies for treating PFAS in water.

Sulfite activation by water film dielectric barrier discharge plasma for ibuprofen degradation: efficiency, comparison of persulfate, mechanism, active substances dominant to pathway, and toxicity evaluation

Herein, we proposed sulfite [S(IV)] activation by water film dielectric barrier discharge plasma (WFDBD) to produce ·SO4- to improve the removal efficiency of ibuprofen (IBP). The results show that the WFDBD/S(IV) system can significantly improve the removal rate of IBP by 22.3% compared with the WFDBD plasma system alone. Compared with persulfate (PS), a small amount of S(IV) can present a high degradation promotion, and S(IV) instead of PS can indeed reduce cost consumption. The active substances including ·OH, ·SO4-, 1O2, and ·O2–, were detected by electron paramagnetic resonance (ESR), and the quenching agents were added to verify the important role and contribution of the above active substances in the degradation of IBP. The degradation of IBP consumes H2O2, O3, ·OH, and ·SO4- in WFDBD/S(IV) system. Through liquid chromatography-mass spectrometry (LC-MS) and density functional theory (DFT) simulation, the degradation pathway of IBP and the role of active substances in the degradation process were inferred. Subsequently, by ECOSAR calculation and seed detection toxicity, it was found that the toxicity was significantly reduced after treatment with WFDBD/S(IV) system. The increase in input power, duty cycle, and solution flow rate all has a positive impact on the degradation of IBP, and IBP degrades better under acidic conditions. Finally, by treating different organic compounds and actual wastewater, it was found that inorganic ions have an impact on the WFDBD/S(IV) system, but the selectivity of the system is low and it has good effects on the treatment of domestic wastewater.

An in-depth insight into the simultaneous oxidation of sulfamethoxazole and reduction of Cr (VI) by one system of water film DBD plasma: The interaction effect, role of active species, and their dominant to pathways

This study aims to deeply investigate the simultaneous elimination of sulfamethoxazole (SMZ) and Cr (VI) through one system of water film dielectric barrier discharge (WFDBD) plasma. The interaction effect of SMZ degradation and Cr (VI) reduction and dominant effect of active species were highlighted. Results showed that the oxidation of SMZ and the reduction of Cr (VI) directly promote each other. When the concentration of Cr (VI) raised from 0 to 2 mg L−1, the degradation rate of SMZ enhanced from 75.6% to 88.6%, respectively. Similarly, when the concentration of SMZ improved from 0 to 15 mg L−1, the removal efficiency of Cr (VI) improved from 70.8% to 84.3%, respectively. ·OH, 1O2 and ·O2− play crical roles for SMZ degradation, and e−, ·O2−, ·H and H2O2 dominated to the Cr (VI) reduction. The variations of pH, conductivity and TOC during the removal process were also explored. The removal process was studied by UV–vis spectroscopy and a three-dimensional excitation-emission matrix. Based on DFT calculation and LC-MS analysis, free radicals dominated SMZ degradation pathways in the WFDBD plasma system were clarified. Besides, the influence of Cr (VI) on SMZ degradation pathway was clarified. The ecotoxicity of SMZ and the toxicity of Cr (VI) into Cr (III) were greatly reduced. This study provides a significant reference value for the application and mechanism of plasma simultaneous removal of organic pollutants and heavy metals in wastewater.

Oxidation of ciprofloxacin by the synergistic effect of DBD plasma and persulfate: reactive species and influencing factors analysis

A synergistic system of water falling film dielectric barrier discharge (DBD) plasma and persulfate (PS) was set up and used for oxidizing ciprofloxacin (CIP) in water. Results of reactive species formation in the DBD-only system as well as the DBD–PS system verified the PS activation in the DBD system. Influencing factors on CIP degradation and the degradation process were also been studied. The obtained results showed that the presence of PS could greatly improve the degradation and mineralization of CIP and that the degradation efficiency could reach 97.73% after only 40 min treatment with 4 mM PS addition. The increase of PS concentration, the lower CIP concentration, the acidic solution pH and the addition of metal ions (Fe2+ and Cu2+) enhanced the CIP degradation, while the existence of Cl− and HC had a negative effect. The experiments related to scavenger addition confirmed the contribution of the main reactive species to the CIP oxidation. Three probable degradation pathways were proposed by analyzing the inorganic ions and organic byproducts formed during the CIP degradation. The toxicity evaluation results of the CIP and its intermediates confirmed the effectiveness of the DBD–PS synergistic system.

Power dependence of reactive species generation in a water falling film dielectric barrier discharge system

The short-lived and long-lived reactive species generated in plasma-liquid interactions determine their potential applications in wastewater purification and plant growth stimulation. In this work, plasma-generated reactive species including hydroxyl radicals (∙OH), hydrogen peroxide (H2O2), ozone (O3), hydronium (H3O+), and nitrate (NO3-) were quantified in a water falling film dielectric barrier discharge system. The reaction kinetics of short-lived ∙OH were analyzed based on the quantification of ∙OH and degradation of salicylic acid, focusing on the contribution and utilization of ∙OH. The interconversion of ∙OH with H2O2 and O3 was also calculated. The accumulation rates of H3O+ and NO3- indicated the potential of this dielectric barrier discharge system in sustainable fertilizer production. In addition, the toxicity prediction of salicylic acid degradation intermediates and the cultivation of soybean seeds verified the feasibility of plasma-liquid interactions in organic wastewater recycling.

Application of liquid film dielectric barrier discharge plasma reactor in the degradation of rhodamine B: Performance optimization, mechanism and pathways

In the present work, the degradation pathways and mechanism of rhodamine B (RhB) using a novel liquid film dielectric barrier discharge (DBD) plasma reactor were examined. Moreover, the optimization of the performance of DBD was discussed. The results showed that the atmosphere of the discharge area and the input power had a significant effect on the removal of RhB. After 21 min of treatment using DBD plasma system, about 90.2 % of RhB was degraded under the following experimental conditions: initial RhB concentration of 40 mg/L; input power of 125 W and initial pH of 6.78. The use of free radical scavengers proved that hydroxyl radicals played a key role in the degradation of RhB. In addition, the degradation intermediates of RhB were identified using liquid chromatography mass spectrometry, and possible degradation pathways were proposed. During the degradation of RhB, with the extension of treatment time, the values of COD, BOD5 and TOC decreased. After the treatment using DBD plasma, the BOD5/COD of RhB solution increased from 0.0326 to 0.3867, and the biodegradability was also observed to have greatly improved. The potential toxicity was predicted by US-EPA-TEST software.

Activation of persulfate by a water falling film DBD process for the enhancement of enrofloxacin degradation

A synergetic system of water falling film dielectric barrier discharge (DBD) plasma and persulfate (PS) was established and applied to enhance the enrofloxacin (EFA) degradation in this study. The simultaneous existence of electrons, reactive species, heat and UV–visible light in the DBD plasma system were utilized together to activate the PS to form SO4−· and other reactive oxygen species (ROS), and then worked in synergy with the DBD plasma to oxidize the EFA. The obtained results verified that there was a significant increase in the degradation percentages of EFA (20 mg L−1) in the DBD/PS system, and the trend was more obvious under the condition of larger discharge power input. When 0.8 mM PS was added into the DBD system with 0.8 kW discharge power, the degradation percentage of EFA could reach 99.35% after 60 min treatment, the corresponding synergetic factor (SF) was 7.94. Analysis of the O3 and the H2O2 concentrations in the DBD plasma system before and after the PS addition explained the activation of the PS by the HO·. The quenching experiments on reactive species suggested that SO4-·, HO·, and 1O2 were all important reactive species for EFA degradation. The intermediates formed by the EFA degradation were detected and the degradation pathways were speculated. Results of toxicity analysis illustrated that the toxicity of the initial EFA solution decreased after degradation in the synergetic system of DBD/PS.

High-yield sample introduction using nebulized film dielectric barrier discharge assisted chelate vapor generation for trace rare earth elements determination by inductively coupled plasma mass spectrometry

A new sample introduction method of nebulized film dielectric barrier discharge (NFDBD) assisted chelate vapor generation coupled with inductively coupled plasma mass spectrometry (ICP-MS) for trace rare earth elements (REEs) determination in environmental water was developed in this work. Using 2,2,6,6-tetramethyl-3,5-heptanedione (DPM) as chelating reagent, the volatile and stable chelates of REE-DPM were effectively vaporized in NFDBD sampling system, leading to 8–9 folds enhancement of REEs sensitivity compared with solution nebulization sampling system, with the sample introduction efficiencies between 51.9% and 66.0%. The enhancement mechanism and the experimental parameters for REEs determination including the DPM concentration, the carrier solution concentration, the input discharge voltage and the argon flow rate were evaluated in detail. The interferences from sample matrix at 10 mg L−1 level and the degradation product of DPM at 0.5 mmol L−1 were also found negligible for trace REEs determination in NFDBD sampling system. Under optimized conditions, the relative standard deviations for 15 REEs were between 0.3% and 2.5% at the concentration of 0.5 μg L−1 and the detection limits for 15 REEs were between 0.0009 and 0.11 ng L−1, which were 1–2 orders of magnitude lower than other sampling systems such as solution nebulization, membrane desolvation, ultrasonic nebulization and electrothermal vaporization and 2–4 folds lower than NFDBD vapor generation system without chelate. This proposed method not only can be used for trace REEs determination directly in freshwater samples, but also is promising for seawater determination without column separation.

Catalytic degradation of chloramphenicol by water falling film dielectric barrier discharge and FeO catalyst

Herein, chloramphenicol (CAP) antibiotic was degraded by water falling film dielectric barrier discharge (WFFDBD) and FeO catalyst. The treatment performance and catalytic mechanisms were studied by experiments and density functional theory (DFT) simulations. The results show that 69.5% of CAP was degraded by WFFDBD at 8 min, and the degradation efficiency increased to 97.7% by WFFDBD/FeO at the same treatment time. The formation of OH caused by the catalytic reactions was mainly responsible for the catalytic effect. The electron transfer from FeO to the antibonding orbits of O3, H2O2 and dissolved oxygen was the key for the catalytic reactions, which promoted their decomposition and transformation. Dissolved oxygen was converted to O2.- that adsorbed on FeO by the electron transfer, which played an important role for the catalytic process. Oxygen vacancies raised the charge density of Fe and accelerated the electron transfer. Fe near the oxygen vacancies achieved the dissociated adsorption of H2O2 and O3, and transformed dissolved oxygen to O22- due to the enhancement of the electron transfer.

Sensitive determination of chromium by inductively coupled plasma mass spectrometry using chelate-enhanced nebulized film dielectric barrier discharge vapor generation

A sensitive procedure was developed for trace Cr determination by ICP MS with a DDTC enhanced nebulized film dielectric barrier discharge (NFDBD) vapor generation sampling system.

Application of a New Type of Liquid Film Dielectric Barrier Discharge Plasma Reactor in Rhodamine B Degradation: Performance Optimization, Degradation Mechanism and Pathways

Application of a New Type of Liquid Film Dielectric Barrier Discharge Plasma Reactor in Rhodamine B Degradation: Performance Optimization, Degradation Mechanism and Pathways

Degradation of sulfamethoxazole (SMX) by water falling film DBD Plasma/Persulfate: Reactive species identification and their role in SMX degradation

The performance and mechanism of persulfate on improving the degradation of sulfamethoxazole (SMX) in a water falling film dielectric barrier discharge (DBD) plasma reactor have been studied. Both peroxymonosulfate (PMS) and peroxydisulfate (PDS) improved the degradation and mineralization of SMX, but PMS presented higher SMX degradation than PDS. Moreover, increases in applied voltage, solution pH and PMS/PDS concentration promoted SMX degradation. The reactive species were qualitatively and quantitatively detected by electron paramagnetic resonance (EPR) spectra and chemical probes. The results show that the activation process of PMS/PDS by discharge plasma produced reactive radicals including ·OH and SO4·-, and PMS led to higher aqueous O3 and ·OH concentrations than PDS; scavengers of ·OH, SO4·-, O2·- and 1O2 in SMX solution decreased SMX degradation, but scavengers of hydrated electrons and H· in SMX solution had little effect on SMX degradation. The detected degradation products of SMX included 5-amino-3-methylisoxazole, 4-aminobenzenesulfonic acid, nitrosobenzene and 4-nitro sulfamethoxazole, etc., and the calculation results show that most of these products had lower toxicities than SMX. Our study indicates that the combination of DBD plasma and PMS/PDS is an efficient pretreatment method for bio-treatment of refractory SMX.

Insights into water film DBD plasma driven by pulse power for ibuprofen elimination in water: performance, mechanism and degradation route

• IBP elimination using water film DBD plasma by pulse power was investigated. • The impact of various parameters on IBP elimination was inspected. • OH, electron, 1 O 2 and · O 2 – participation in IBP decomposition. • The degradation route was proposed based on DFT calculation and LC-MS. • The toxicity of actual wastewater alleviated after water film DBD treatment. Development of efficient abatement technology for drugs and personal care products (PPCPs) has important scientific and practical significance to restrain its discharge to the natural water environment. This research aims to investigate ibuprofen (IBP) elimination in water film dielectric barrier discharge (DBD) plasma system driven by pulse power. With raising input power, the removal rate was improved. When input was 95 W, the removal rate and kinetic constant were up to 96.1% and 0.090 min −1 , respectively. Besides, heightening frequency, duty ratio and solution flowrate would promote the degradation of IBP. IBP were more favorably degraded at lower IBP concentration and neutral pH condition. Active species including ·OH, electron, 1 O 2 and · O 2 – dominated decomposition of IBP. The generation of O 3 , · OH and H 2 O 2 in deionized water and IBP solution was compared. UV–Vis spectrum and three dimensional fluorescence spectroscopy illustrated that IBP molecules could be decomposed effectively after DBD plasma treatment. During IBP degradation, COD and TOC was also relieved with extension of treatment time. The possible degradation routes of IBP in water film DBD plasma system were proposed based on LC-MS and Discrete Fourier transform (DFT) simulation. Based on the identified intermediates, their potential toxicity was evaluated with the help of US-EPA-TEST software. Water film DBD plasma technology was also suitable for actual wastewater treatment. The comparison of other technologies for IBP degradation was carried out finally. This work can provide exploratory platforms for comprehensively understanding and enhancing IBP degradation in DBD plasma technology.

Removal of chloramphenicol in water by an improved water falling film dielectric barrier discharge reactor: Performance, mechanism, degradation pathway and toxicity evaluation

Chloramphenicol (CAP) is a common antibiotic, which is difficult to be removed in water environment and has caused huge environmental risks. Herein, an improved water falling film dielectric barrier discharge (WFFDBD) reactor was built to treat 20 L of CAP wastewater. The effects of operating parameters of the reactor on CAP degradation were investigated, the main reactive species for CAP degradation were identified, the intermediates and degradation pathway of CAP were analyzed, and the toxicity of degradation products of CAP was evaluated by quantitative structure activity relationship (QSAR) models. The results show that CAP degradation efficiency was significantly increased by covering medical gauze. At 370 W of discharge power, CAP degradation efficiency was 88.7% and 59.9% after 140 min treatment with and without the gauze, and the energy efficiency of WFFDBD reactor with medical gauze was 2.53 times higher than that without medical gauze. The medical gauze significantly increased the yield of the reactive species of WFFDBD. Correlation matrix analysis showed that the contribution of H2O2, O3 and ·OH for CAP removal followed the order of ·OH > H2O2> O3. Moreover, O2⋅− and ·H were also the key species for CAP degradation. A possible degradation pathway was given based on the measured degradation products. The developmental toxicity of CAP and its degradation products were quantified, and the results indicate the toxicity of CAP wastewater was weakened after WFFDBD treatment.

Cover Feature: Direct Oxidative Nitrogen Fixation from Air and H2O by a Water Falling Film Dielectric Barrier Discharge Reactor at Ambient Pressure and Temperature (ChemSusChem 6/2021)

Cover Feature: Direct Oxidative Nitrogen Fixation from Air and H₂O by a Water Falling Film Dielectric Barrier Discharge Reactor at Ambient Pressure and Temperature (ChemSusChem 6/2021)

Direct Oxidative Nitrogen Fixation from Air and H2 O by a Water Falling Film Dielectric Barrier Discharge Reactor at Ambient Pressure and Temperature.

Current industrial production of HNO3 relies on the Ostwald process via catalytic oxidation of NH3 , which is responsible for the vast bulk of CO2 emission. An attractive alternative route to HNO3 is direct N2 oxidation to aqueous HNO3 , which avoids the NH3 intermediate. Herein, we for the first time report a non-thermal plasma-assisted nitrogen fixation process characteristic of a large gas-liquid contact based on the water falling film dielectric barrier discharge, wherein HNO3 is produced directly from ambient air and H2 O at atmospheric pressure and room temperature without the presence of any catalytic material. By optimizing the plasma reaction conditions, a relatively high synthesis rate and low energy consumption was achieved at the same time with good product selectivity.

Generation Characteristics of Long-Lived Active Species in a Water Falling Film DBD Reactor

Water falling film dielectric barrier discharge (WFFDBD) has been widely studied for water treatment, due to its good performance on production of active species, mass transfer of active species from gas phase into liquid phase, and therefore the degradation of pollutants. However, few studies have focused on the production characteristics of active species of WFFDBD. In this paper, the formation characteristics of hydrogen peroxide, ozone and nitrate ions in a WFFDBD reactor powered by bipolar pulsed generator were studied under different electric discharge time, peak pulse voltage, power–frequency, air flow rate, water circulation flow rate, pH value and conductivity. The results show that the concentrations of hydrogen peroxide, ozone and nitrate ions increased with the peak pulse voltage, power supply frequency and water circulation flow rate, but the inputted air flow rate presented different effect on the production of active species. Moreover, the increase in pH value and conductivity led to a decrease in the concentration of hydrogen peroxide, while nitrate ion increased with the water pH value and conductivity. The p-nitrophenol degradation result indicates that both ozone and hydrogen peroxide contribute to its degradation possibly via their reaction into hydroxyl radical.