Discharge Plasma System Research Articles

Pulse discharge plasma coupled with magnetic mesoporous silica for synergistic degradation of pharmaceutical wastewater and mechanism

In this study, pulse discharge technology was adopted for plasma generation. And it can be applied for the degradation of pharmaceutical wastewater. Several typical pharmaceutical, such as sulphadiazine, sulphamethoxazole, sulphadimidine, sulphamilone, norfloxacin, roxithromycin, gentamicin, chloramphenicol and penicillin, were selected to simulate pharmaceutical wastewater. Study on their degradation performance. Magnetic mesoporous silica (MMS) coupled with plasma can considerably increase thepenicillin removal efficiency more 45% than plasma alone. The pulse discharge can generate plasma to collide water molecules to produce the solvent electron, initiate excited species, such as hydroxyl radicals (•OH), superoxide anion radical (O2-•), hydrogen peroxide, ozone (O3) and so on, which contributed to decompose pharmaceutical efficiently. Furthermore, pharmaceutical removal efficiency can reach basically above 99%. The energy consumption in this system was relatively lower than that in other system. Penicillin is selected as the typical representative of organic pollutants in pharmaceutical wastewater. Density Functional Theory (DFT) and Δƒ(r) for nucleophilicity and electrophilicity were used to insight into the penicillin degradation mechanism. The calculation results indicated that the 20 C, 8 N, 9 C, 10 N, 12 C, 14 N, 17 S, 19 C and 7 C atoms were susceptible to be collided to excite by the solvent electron or excited species, resulting in the cleavage of the chemical bonds of penicillin, therefore, decomposing penicillin molecules to remove from wastewater in the catalytic pulse discharge plasma system. Further on, the experimental detection intermediates by UPLC-MS was in good agreement with the theoretical Δƒ(r) results. Thus, the degradation pathways and mechanism of penicillin could be clearly inferred. This study offers some theoretical guidance to purify all kinds of pharmaceutical wastewater, but many factors need to be involved in practical application.

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.

Analysis of underwater plasma discharge based on equivalent circuit parameters

The control of discharge mode and the optimization of energy efficiency are of particular concern as the significant impact on the application of the underwater plasma discharge system. In this paper, the RLC parameters of each part of the underwater discharge system are investigated, and the equivalent circuit is obtained. Typical waveforms of current and voltage for different underwater discharge modes are displayed. The correlation between the equivalent RLC parameters of the discharge system and the discharge modes and energy is illustrated. The equivalent circuit of the underwater plasma discharge system is utilized to analyze the effects of the power source, electrode, and liquid dielectric parameters. The influences of these parameters can be identical to the impacts on the RLC parameters of the underwater discharge system equivalent circuit simultaneously, and then, the effects on the discharge modes and energy can be better understood. It can be concluded that the relative relationship of system equivalent RLC parameters determines the discharge mode, and the impedance matching between the discharge channel and the external circuit determines the discharge energy.

An insightful analysis of dimethyl phthalate degradation by the collaborative process of DBD plasma and Graphene-WO3 nanocomposites

In this paper, the prepared graphene-WO3 nanocomposites (rGO-WO3) were added into a dielectric barrier discharge (DBD) plasma system with spiral discharge electrode to set up a collaborative process to treat the dimethyl phthalate (DMP) in water. Degradation of the DMP under different experimental conditions were studied to illustrate the catalysis of the rGO-WO3 in the DBD plasma system. The obtained results proved that there was the catalysis of the rGO-WO3 for the DMP degradation within the studied DMP concentration, solution initial pH values and conductivities. From the results of the energy utilization efficiency (G50) analysis, the catalysis was more apparent in the case of the oxygen bubbling system than that in the nitrogen or the air bubbling system, which was due to the higher oxygen constitution in the oxygen bubbling system. The reduction of the measured liquid phase ozone concentrations in the DBD/rGO-WO3 system bubbled with air as well as oxygen than those measured in the sole DBD system, which verified the consumption of the ozone by the catalysis of the rGO-WO3. Furthermore, the UV–Vis and the three-dimensional fluorescence spectra analysis were also carried out to state the catalytic effect of the rGO-WO3 for the DMP degradation. Toxicity analysis for the degradation byproducts confirmed the collaborative process could reduce the negative effect of the original DMP on the environment.

The effects of glazing with plasma-activated water generated by a piezoelectric direct discharge plasma system on whiteleg shrimp (Litopenaeus vannamei)

Multiple hard-to-reach spots on foods with rough surfaces (such as shrimp) limit the maximal exposure to antibacterial agents. In this study, we successfully generated plasma-activated water (PAW) using a low energy-consuming source of a non-thermal atmospheric piezoelectric direct discharge plasma (PDDP) system and evaluated its effectiveness as a glazing agent on shrimp, facilitating a whole surface treatment. During generation, a feeding gas mixture of N2 (80%): O2 (20%) and N2 (85%): O2 (15%) was revealed to optimally produce reactive oxygen species (ROS) such as H2O2 (60.7 ± 0.2 mg/L) and O3 (0.45 ± 0.02 mg/L) as well as reactive nitrogen species (RNS) such as NO2‾ (48.5 ± 0.5 mg/L). Furthermore, the application of PAW-glazing on shrimps was demonstrated to be capable of maintaining microbial growth below 6 log CFU/g throughout the storage period (9 days). This approach also possessed the capacity to retard the loss of both physical (color and firmness) and chemical characteristics (pH, total volatile basic nitrogen [TVBN], and thiobarbituric acid reactive substance [TBARS]) of PAW-glazed shrimps. Finally, this study demonstrated the effectiveness of glazing with PAW generated from the PDDP system as a potential prevention agent for shrimps.

Application of Non-thermal Plasmas in Medicine and Energy-Food-Water

Non-thermal plasma (NTP) due to their versatile nature have been successfully used in many applications ranging from hydrocarbon destruction to cancer treatment. The NTPs, can deliver high electron temperatures and high densities of radicals at near ambient conditions making it a unique source for applications ranging from treatment of extremely heat sensitive surfaces to complex chemical reactions which are feasible only at low temperatures. This work presents some of the recent understandings on how various NTP reactors can be designed and characterized for various applications. The results obtained from a pin-to-water plasma discharge system, in generating plasma activated water for agricultural applications are discussed. The application of NTPs in hydrocarbon reforming to obtain a tar-free gas from a waste to energy thermo-chemical process is discussed. The results of selective killing of cancer cells using a DBD is presented. Also, application of NTPs in wastewater treatment systems to treat household chemical products are presented.

Theoretical and experimental insights into the mechanisms of C6/C6 PFPiA degradation by dielectric barrier discharge plasma

As an emerging alternative legacy perfluoroalkyl substance, C6/C6 PFPiA (perfluoroalkyl phosphinic acids) has been detected in aquatic environments and causes potential risks to human health. The degradation mechanisms of C6/C6 PFPiA in a dielectric barrier discharge (DBD) plasma system were explored using validated experimental data and density functional theory (DFT) calculations. Approximately 94.5% of C6/C6 PFPiA was degraded by plasma treatment within 15 min at 18 kV. A relatively higher discharge voltage and alkaline conditions favored its degradation. C6/C6 PFPiA degradation was attributed to attacks of •OH, •O2−, and 1O2. Besides PFHxPA and C2 −C6 shorter-chain perfluorocarboxylic acids, several other major intermediates including C4/C6 PFPiA, C4/C4 PFPiA, and C3/C3 PFPiA were identified. According to DFT calculations, the potential energy surface was proposed for possible reactions during C6/C6 PFPiA degradation in the discharge plasma system. Integrating the identified intermediates and DFT results, C6/C6 PFPiA degradation was deduced to occur by stepwise losing CF2, free radical polymerization, and C-C bond cleavage. Furthermore, the DBD plasma treatment process decreased the toxicity of C6/C6 PFPiA to some extent. This study provides a comprehensive understanding of C6/C6 PFPiA degradation by plasma advanced oxidation.

Removal of metal ions from water using oxygen plasma

Zinc ion dissolved in water is attempted to be removed by generating the oxides of zinc using the oxygen gas in dielectric barrier discharge (DBD) plasma system. The removal rate of zinc oxides’ production (ZnO and Zn(OH)2) are measured at different treatment periods by the oxygen plasma penetration in water. The removal rate of the deposit increases initially and then decreases with the treatment period. The maximum removal rate (29%) of zinc ion from water is achieved at the treatment period of 10 min, where pH is lower (7.4). From FTIR the generation properties of zinc oxide can be recognized. Initially the amount of the deposit increases with the ozone treatment period due to production of both ZnO and Zn(OH)2. After that, the production of Zn(OH)42- increases even when the total removal rate of the deposit decreases. Therefore, to remove zinc ion from water forming metal oxide deposit, the penetration amount of the active oxygens to the water must be controlled to keep the pH lower than around 7.5. Because with increasing pH amount of removal rate of zinc oxides’ deposit decreases. The pH of the zinc dissolved water treated by ozone depends on both zinc ion and ozone concentration in water.

Potential application of non-thermal atmospheric plasma in reducing the activity of Pseudomonas-secreted proteases in milk

Application of non-thermal atmospheric plasma was examined against the activity of Pseudomonas-secreted proteases in milk. UHT milk samples were inoculated with crude extract of Pseudomonas-secreted proteases and treated in atmospheric plasma discharge system. Evaluation of the progress in protein hydrolysis of plasma-treated and non-treated milk samples revealed that the degree of hydrolysis was lower in plasma-treated milk samples. The longer the plasma treatment time, the lower the degree of hydrolysis during storage. Furthermore, plasma-induced changes in milk proteins and volatile compounds were also evaluated. Caseins, whey proteins, aldehydes, ketones, free fatty acids and hydrocarbons were all affected by plasma discharge. The amount of increase or decrease in these components was dependent on the duration of plasma treatment. Overall, this method is a promising approach that could be used to inactivate bacterial hydrolytic enzymes in milk.

Implicit and coupled fluid plasma solver with adaptive Cartesian mesh and its applications to non-equilibrium gas discharges

We present a new fluid plasma solver with adaptive Cartesian mesh (ACM) based on a full-Newton (nonlinear, implicit) scheme for non-equilibrium gas discharge plasma. The electrons and ions are described using drift–diffusion approximation coupled to Poisson equation for the electric field. The electron-energy transport equation is solved to account for electron thermal conductivity, Joule heating, and energy loss of electrons in collisions with neutral species. The rate of electron-induced ionization is a function of electron temperature and could also depend on electron density (important for plasma stratification). The ion and gas temperature are kept constant. The transport equations are discretized using a non-isothermal Scharfetter–Gummel scheme to resolve possible large temperature gradients in the sheaths. We demonstrate the new solver for simulations of direct current (DC) and radiofrequency (RF) discharges. The implicit treatment of the coupled equations allows using large time steps. The full-Newton method (FNM) enables fast nonlinear convergence at each time step, offering significantly improved simulation efficiency. We discuss the selection of time steps for solving different plasma problems. The new solver enables solving several problems we could not solve before with existing software: two- and three-dimensional structures of the entire DC discharges including cathode and anode regions, electric field reversals and double-layer formation, the normal cathode spot and an anode ring, moving striations in diffuse and constricted DC discharges, and standing striations in RF discharges. The developed FNM-ACM technique offers many benefits for tackling the disparity of gas discharge plasma systems' time scales and nonlinearity.

Volatile organic compounds sensing based on Bennet doubler-inspired triboelectric nanogenerator and machine learning-assisted ion mobility analysis

Ion mobility analysis is a well-known analytical technique for identifying gas-phase compounds in fast-response gas-monitoring systems. However, the conventional plasma discharge system is bulky, operates at a high temperature, and inappropriate for volatile organic compounds (VOCs) concentration detection. Therefore, we report a machine learning (ML)-enhanced ion mobility analyzer with a triboelectric-based ionizer, which offers good ion mobility selectivity and VOC recognition ability with a small-sized device and non-strict operating environment. Based on the charge accumulation mechanism, a multi-switched manipulation triboelectric nanogenerator (SM-TENG) can provide a direct current (DC) bias at the order of a few hundred, which can be further leveraged as the power source to obtain a unique and repeatable discharge characteristic of different VOCs, and their mixtures, with a special tip-plate electrode configuration. Aiming to tackle the grand challenge in the detection of multiple VOCs, the ML-enhanced ion mobility analysis method was successfully demonstrated by extracting specific features automatically from ion mobility spectrometry data with ML algorithms, which significantly enhance the detection ability of the SM-TENG based VOC analyzer, showing a portable real-time VOC monitoring solution with rapid response and low power consumption for future internet of things based environmental monitoring applications.

CO2 conversion promoted by potassium intercalated g-C3N4 catalyst in DBD plasma system

The direct conversion of CO2 to CO and O2 has attracted extensive attention as CO is a key C1 feedstock for chemical synthesis. The CO2 conversion promoted by γ-Al2O3 supported potassium intercalated g-C3N4 (KuCN/AO) catalyst in a packed-bed dielectric barrier discharge (DBD) plasma system was investigated. A coaxial cylinder DBD plasma reactor was used with Cu powder as the high voltage electrode. Reactor temperature showed converse effect on CO2 conversion. As the reactor temperature decreased from 120 ℃ to 50 ℃, CO2 conversion rate and energy efficiency both increased by ca. 50%. After the catalyst was filled into the discharge area, the discharge mode changed from filamentary discharge to the combination of filamentary-surface discharge. The morphology and structure of KuCN was characterized by SEM, XRD, FTIR and XPS. KuCN kept a porous structure and K element distributed uniformly between CN interlayer spacing. In KuCN/AO assisted DBD plasma system, the highest CO2 conversion rate, CO yield and energy efficiency were increased from 11.1%, 10.0% and 9.41% to 19.3%, 18.1% and 20.6% compared with pure DBD/γ-Al2O3 system, respectively. The main mechanism of KuCN assisted enhancing CO2 conversion in packed-bed DBD reactor was analyzed. The larger specific surface area, layers bridging and charge redistribution enabled KuCN/AO to obtain good plasma-catalytic CO2 conversion performance.

Generating Nitrate and Nitrite on Green Oak Lettuce in Hydroponic Farming by Plasma System

HighlightsAbstract. In this study, we developed an effective methodology to determine the suitable plasma-based generating system of reactive nitrogen species (RNS) targeting hydroponic farming systems using a full factorial design with center points and blocking. A 2k with 2 blockings plus 2 center points design was employed in the experiment to develop an efficient analytical model for nitrogen solution concentration and hydroponic vegetable growth incorporating the plasma discharge system process parameters, including water flow rate, plasma discharge duration, and air flow rate. This study designed and constructed an air plasma discharge system with DC power supply. Thereafter, nitrogen solution was generated under a parameter conditions setting by the design of experiments (DOE) method. RNS solution, which contained nitrate (NO3-) and nitrite (NO2-) ions with P and K added, was passed through the hydroponic system for growing green oak lettuce. The most promising plasma-generated nitrogen solution parameters were obtained for this set up at a water flow rate of 6 L/min, discharge duration of 60 min, and activated air flow rate of 60 mL/min. Keywords: Nitrate, Nitrite, Plasma discharge, Reactive nitrogen species.

Determination of bismuth by optical emission spectrometry with liquid anode/cathode atmospheric pressure glow discharge

Novel atmospheric pressure glow discharge (APGD) plasma systems, sustained between a miniaturized flowing liquid anode (FLA) or cathode (FLC) and a He nozzle jet, were investigated for the determination of Bi by optical emission spectrometry (OES).

Accelerated Fenton reaction for antibiotic ofloxacin degradation in discharge plasma system based on graphene-Fe3O4 nanocomposites

Abstract The reduced graphene oxide (rGO)-Fe3O4 nanocomposites were proposed to promote Fenton reaction for ofloxacin (OFX) degradation in discharge plasma system. The morphology, structure and optical absorption properties of the prepared rGO-Fe3O4 were characterized by SEM, TEM, XPS and UV-VIS spectrophotometer. The effect of various parameters on degradation efficiency of OFX was investigated. Besides, the effect of catalyst on the amount of ·OH in the discharge plasma system was analyzed. Finally, the degradation process of OFX was analyzed. The results showed that Fe3O4 can be successfully loaded on graphene, and has strong optical absorption properties. Compared with Fe3O4 alone, rGO-Fe3O4 further improved the degradation efficiency and kinetic constant of OFX in discharge plasma system. The highest degradation efficiency and kinetic constant reached 99.9% and 0.108 min−1 respectively after 60 min treatment. Increasing applied voltage and decreasing the initial solution concentration were beneficial to OFX degradation. The rGO-Fe3O4 enhanced ·OH formation in discharge plasma system. With the discharge going on, pH value of solution declined while the conductivity of solution increased. Compared with deionized water solution, the decrease of pH and the increase of conductivity in OFX solution were more obvious. The conjugated heterocyclic structure was destroyed gradually in the degradation process.

Understanding of TiO2 catalysis mechanism in underwater pulsed discharge system: Charge carrier generation and interfacial charge-transfer processes

Compared with traditional photocatalysis system, TiO2 charge carrier generation and interfacial charge-transfer process may be influenced by various chemical and physical effects in underwater pulsed discharge plasma system. Here, the role of high-energy electron, ozone in TiO2 charge carrier generation and transfer process has been investigated using phenol as the probe molecule. The introduction of electron-trapping agent (KH2PO4) have an inhibiting effect on TiO2 catalytic activity, indicating high-energy electrons played a significant role in TiO2 catalytic process. EPR analysis showed that TiO2 could be activated to initiate pairs of electron-hole by high-energy electrons from plasma, and the electrons on the conduction band (CB) could be trapped on the oxygen vacancies. XPS analysis showed that the Ti3+OH species formed during discharge process due to the capture of CB electrons by Ti4+OH groups located at the TiO2 surface. The CB electrons transfer processes on TiO2 surface was strongly dependent on the redox potential of electron acceptors, which adsorbed on the TiO2 surface. The CB electrons can be transferred to dissolved O3, resulting in more OH production. Meanwhile, the CB electron also transferred to benzoquinone adsorbed on TiO2, resulting in accumulation of hydroquinone.

Benchmark of the KGMf with a coupled Boltzmann equation solver

The Kinetic Global Model framework (KGMf) is an open-source general-purpose global model (spatially averaged) simulation code developed to explore the reaction kinetics and pathways in plasma discharge systems. It contains species continuity and electron energy balance equations, with a time-dependent evaluated electron energy distribution function (EEDF) for electron impact reactions. The EEDF is utilized to determine the rate coefficients for electron impact reactions, which can have profound impact on the temporal evolutions of plasma parameters. Previously, the EEDF was commonly assumed as Maxwellian or an analytical function of the effective electron temperature. In this work, the KGMf is coupled with a Boltzmann equation (BE) solver to self-consistently compute the EEDF. The EEDF evolution frequency is determined based on relative changes of the reduced electric field. The KGMf is benchmarked with the ZDPlasKin code based on high-pressure low-temperature argon plasma discharge cases. The temporal evolutions of reduced electric field, electron temperature, EEDF, reaction rates, and species densities, are obtained and compared under different discharge conditions, showing good agreement between the KGMf and the ZDPlasKin simulations. The application of the KGMf for predicting breakdown times in high power microwave discharges is also presented, which shows qualitative agreement with particle-in-cell simulations. The KGMf can be further applied for more complicated plasma discharge systems, where the reaction kinetics are more intricate (e.g., plasma-assisted combustion systems).

Gas Discharge Atmospheric Pressure Systems for the Biomedical Use

The analysis of world literature is carried out, which indicates the intensive development of the scientific and technical field “Plasma in Medicine” based on the use of different gas-discharges for biomedical purposes. The atmospheric pressure plasma discharge systems have the favorite features and are very suitable for medical physiotherapy, bactericide treating and even for sterilization. The systems with non-thermal plasma are in the most use and one of their applications is generation of gas ozone. The given paper is devoted to looking for atmospheric pressure discharge modes, which are more suitable for ozone therapy equipment taking into account the peculiarities of such type of electronic apparatus. As practice shows, for the generation of ozone, discharges with a secondary-emission cathode and non-thermal plasma are most preferable, and of these two types of discharges are discharges with a dielectric barrier and corona discharges with uncoated metal electrodes. The article focuses on the appropriateness of the use of a corona discharge for ozone therapy equipment. This is justified by the fact that the corona discharge ozonizers have certain design advantages over the ozonizers on the discharge with dielectric barriers, namely that the advantages of the ozonizers on the corona discharge are the absence of a expensive barrier and low resistance to the gas flow, so there is no need to significantly increase the pressure at the ozonizer oxygen inlet, and possibility of power supplying the ozonizer with DC voltage. Also, ozonizers on the corona discharge have a lower cost. From the literature and the authors' own practice, there is a wide variety of configurations of electrode systems for creating the corona discharge, but they always have electrodes with a small radius of curvature of the surface: threads, wires, nets, various pointed needles, serrated electrodes. The article considers the physical mechanism of maintaining the corona discharge of a unipolar or bipolar type and notes the role of secondary electron emission of the cathode. All types of corona discharge are capable of generating ozone because discharge electrons have the energy required to dissociate oxygen molecules in a non-thermal gas environment. Then a free oxygen atom attaches to an oxygen molecule to form a metastable ozone molecule. It is noted that the corona discharge and ozone generation were studied in detail mainly in unipolar point-of-plane or wire-in-pipe systems. The data on ozone generation in bipolar discharge is not enough to develop an ozone therapy apparatus, although this form of discharge is interesting because it requires relatively small values of the supply voltage and operates at a direct current. Based on the review of the prospects for the use of bipolar corona discharge in biomedical apparatus and practical considerations of the realistic and expanded future usage of bipolar corona equipment in the ozone therapy, the tasks have been formulated to be solved. It is necessary to thoroughly study the characteristics of the developed equipment and the influence of various external operational factors and physico-chemical processes in the ozonizer electrode system on them. It is necessary to ensure that the parameters of the equipment are maintained during operation, which means that during the eight-hour working day and with the total time between failures of at least 1000 hours. Also, it is necessary to take into account the effect of the decomposition of ozone molecules at elevated temperatures and not to allow excessive heating of the ozonizer. These requirements must be met by choice of the configuration and materials of the electrode system and must be experimentally verified. It is proposed to ensure the linearity of the calibration characteristics of the ozonizer and to formalize it mathematically to simplify the setting and maintenance of stable operating modes of ozone equipment. It is necessary to prove its therapeutic efficacy, including for sterilization treatment, with the participation of medical specialists.

Catalysis of rGO-WO3 nanocomposite for aqueous bisphenol A degradation in dielectric barrier discharge plasma oxidation process

Due to the multi-catalysis of the WO3 and excellent properties of the graphene (GO), a series of rGO-WO3 nanocomposites were prepared through the hydrothermal synthesis procedure by changing the material ratio, the reaction temperature and the reaction time in this paper, and then added it into a dielectric barrier discharge plasma (DBDP) system for investigating the bisphenol A (BPA)’s degradation and corresponding catalytic mechanism of the rGO-WO3 in the DBDP system. The obtained results show that there was an optimum dosage of the rGO-WO3 (40 mg/L) as well as the preparation conditions (5:1000 mass ratio of the GO and the WO3, 18 h reaction time and 120 °C reaction temperature) for achieving the highest catalytic effect, and the highest degradation rate constant of the BPA was 0.03129 min−1. The determined higher TOC removal, higher COD removal as well as UV–Vis analysis also demonstrated the catalysis of the rGO-WO3. The measurement of the change of the O3 and the H2O2 concentrations in the reaction system with or without the rGO-WO3 and with or without the BPA proved the catalysis of the rGO-WO3 on the ·OH formation, while the combination of the GO had the positive effect for enhancing the catalytic effect. A figure on the catalysis and degradation procedure of the BPA in the DBDP/rGO-WO3 system was provided in the paper.

Analysis of the critical active species for methylene blue decoloration in a dielectric barrier discharge plasma system

In the paper, a hybrid gas–liquid dielectric barrier discharge (DBD) plasma system was set up to treat a methylene blue (MB) solution. The effects of the change of the carrier gas, the gas bubbling rate and different kinds of scavenger addition, including sodium carbonate (Na2CO3), para benzoquinone (p-BQ), triethylenediamine and sodium dihydrogen phosphate (NaH2PO4), on the MB decoloration were reviewed to clarify the critical active species for the dye decoloration in the DBD plasma system. The obtained results show that higher decoloration of the MB solution could be achieved when O2 was used as the carrier gas, which could be 100% after 20 min discharge treatment, and the result confirmed the crucial effect of O3 in the MB decoloration. Based on the experiments of the scavenger addition, it could be concluded that O2·− and 1O2 were two other important reactive oxygen species (ROS) for the MB decoloration. The results of the higher chemical oxygen demand removal and faster disappearance of the characteristic peak of the MB from the UV–vis analysis under O2 bubbling conditions also proved the critical effect of the ROS formed by O2 on the MB decoloration.