Removal of four kinds of volatile organic compounds mixture in air using silent discharge reactor driven by bipolar pulsed power

A silent discharge reactor initiated by bipolar pulsed power substituting the traditional ac power was used to remove the volatile organic compounds (VOC_s) mixture of acetone, benzene, tetrachloroethylene and m-xylene. The results indicated that the silent discharge driven by bipolar pulsed power could effectively input pulsed energy, produce strong instant discharge and energetic particles, and thus enhance the removal efficiency of the mixed VOC_s. The order of the removal efficiency of mixed VOC_s followed as acetone < benzene < tetrachloroethylene < m-xylene no matter what power supply was used. Comparing with single-compound, the removal efficiency of m-xylene only fell a little but those of the other three components fell a lot in the process of the mixed VOC_s treatment. In addition, controlling the status of electrical discharge plasma by changing the discharge parameters (such as capacitance of the pulse capacitor and pulse repetitive rate) was found to be an efficient way to enhance the removal efficiency of the mixed VOC_s. In this system, the Cp = 2 nF was the optimal capacitance for the bipolar power supply combined with the silent discharge reactor that had the best energy conversion efficiency for removal of mixed VOC_s. A higher pulse repetitive rate and longer residence time could also increase the removal efficiency of mixed VOC_s.     

Decomposition of benzene using wire-tube AC/DC discharge reactors

Decomposition of benzene was investigated using single and two-stage stainless steel reactors with application of high-voltage AC and DC currents. Benzene removal, CO, and CO₂ were measured as a function of reactor diameter, applied voltage, and stage of reactor configuration. The results showed that, benzene removal and CO₂ selectivity improved in two-stage configuration and reached up to 59% and 97.8% respectively, where the gap size was 8.5 mm. Formation of OH, N-H and N=O function groups were seen in the exhaust gas. Subsequently, organic acids, phenols, and alcohols were identified as the main byproduct of benzene decomposition considering GC-MS analysis.     

Decomposition of chlorinated volatile organic compounds (CVOCs) using NTP coupled with TiO2/GAC,ZnO/GAC,and TiO2–ZnO/GAC in a plasma-assisted catalysis system

No study was found in the literature on the catalytic effect of TiO₂/GAC (Granular activated carbon), ZnO/GAC, and TiO₂–ZnO/GAC combined with non-thermal plasma (NTP) for the decomposition of chlorinated volatile organic compounds (CVOCs) in gas streams. In the present study, this catalytic NTP process was investigated to examine the effect of specific input energy (SIE), initial concentration, as well as residence time on the removal efficiency (RE) of CVOCs in a corona discharge reactor energized by a high frequency pulsed power supply. A dip-coating sol–gel impregnation technique was used to coat TiO₂, ZnO, and mixture of TiO₂–ZnO nanoparticles on GAC, which were then combined with NTP in a two-stage configuration. The results revealed that the efficacy of the catalysts was in the order TiO₂–ZnO/GAC ≅ TiO₂/GAC > ZnO/GAC with chloroform feeding, while when chlorobenzene introduced, the order changed to TiO₂–ZnO/GAC > ZnO/GAC > TiO₂/GAC. A significant enhancement was observed with RE as catalysts coupled with NTP in all cases and a RE of 100% was achieved in the presence of both TiO₂/GAC and TiO₂–ZnO/GAC at SIE of ca. 400 J L⁻¹. Considerable improvement was also noticed for coupling TiO₂ and ZnO in both efficiency and catalyst life time.     

Characteristics of DC discharge in a wire-cylinder configuration at high ambient temperatures

In the present work, the characteristics of direct-current (DC) discharge in a wire-cylinder configuration at an ambient temperature range of 350–850 °C were studied by analyzing photographs of the discharging process and the corresponding V–I characteristics, with the aim of facilitating the application of plasma technology in the fields of energy and the environment. The influences of the ambient temperature, the inter-electrode gap, the gas medium and the cathode material on the DC discharge were investigated. The corona-onset threshold voltage (COTV) and the spark-breakdown threshold voltage (SBTV) decrease as the ambient temperature increases, and the SBTV decreases more rapidly. Increasing the inter-electrode gap enlarges the difference between the SBTV and the COTV. After spark breakdown, in an air atmosphere, glow discharge is more likely to take place under conditions of high ambient temperatures or small inter-electrode gaps. The values of the SBTV in different atmospheres have the following relation: air ≈ O₂ > CO₂. At an ambient temperature range of 350–850 °C and in an atmosphere of N₂, glow discharge and arc discharge occur successively as the output voltage of the power supply is increased, while in an atmosphere of O₂ and CO₂, only corona and arc discharge are successively observed. In an air atmosphere, when the inter-electrode gap is 29 mm, corona, glow and arc discharge occur successively with increasing output voltage when the ambient temperature is 850 °C, while only corona and arc discharge appear when the temperature is 350–750 °C. When the inter-electrode gap is 5 mm in an air atmosphere, corona, glow and arc discharge occur successively in an ambient temperature range of 350–850 °C. The cathode material has a minor influence on the COTV and a more significant influence on the SBTV. In a device using a cathode with a low work function, the SBTV is low, and the power to maintain arc discharge is small.     

The effects of power ultrasound (24 kHz) on the electrochemical reduction of CO2 on polycrystalline copper electrodes

The electrochemical CO₂ reduction reaction (CO2RR) on polycrystalline copper (Cu) electrode was performed in a CO₂-saturated 0.10 M Na₂CO₃ aqueous solution at 278 K in the absence and presence of low-frequency high-power ultrasound (f = 24 kHz, P_T ~ 1.23 kW/dm³) in a specially and well-characterized sonoelectrochemical reactor. It was found that in the presence of ultrasound, the cathodic current (I_c) for CO₂ reduction increased significantly when compared to that in the absence of ultrasound (silent conditions). It was observed that ultrasound increased the faradaic efficiency of carbon monoxide (CO), methane (CH₄) and ethylene (C₂H₄) formation and decreased the faradaic efficiency of molecular hydrogen (H₂). Under ultrasonication, a ca. 40% increase in faradaic efficiency was obtained for methane formation through the CO2RR. In addition, and interestingly, water-soluble CO₂ reduction products such as formic acid and ethanol were found under ultrasonic conditions whereas under silent conditions, these expected electrochemical CO2RR products were absent. It was also found that power ultrasound increases the formation of smaller hydrocarbons through the CO2RR and may initiate new chemical reaction pathways through the sonolytic di-hydrogen splitting yielding other products, and simultaneously reducing the overall molecular hydrogen gas formation.     

Synergistic effect of sonication on photocatalytic oxidation of pharmaceutical drug carbamazepine

Photocatalytic, sono-photocatalytic oxidation of pharmaceutical drug of carbamazepine was successfully carried out using Ag/AgCl supported BiVO₄ catalyst. For this purpose, firstly, photocatalytic oxidation was optimized by central composite design methodology and then synergistic effect of sonication was investigated. Low frequency (20 kHz) probe type and high frequency (850 kHz) plate type sonication at pulse and continuous mode were studied to degrade the carbamazepine (CBZ) containing wastewater. Pulse duties of 1:5 and 5:1 (on : off) were tested using the high frequency sonication system in the sono-photocatalytic oxidation of CBZ. The effects of frequency, power density measured from calorimetry by changing amplitudes were discussed in the sono-photocatalytic oxidation of CBZ. Complete carbamazepine removal was achieved at the optimum conditions of 5 ppm CBZ initial concentration with 1.5 g/L of catalysts loading and at an alkaline pH of 10 at the end of 4 h of photocatalytic reaction under visible LED light irradiation. Both low frequency and high frequency sonication systems caused an increase in photocatalytic efficiency in a shorter treatment time of 60 min. CBZ removal increased from 44% to 65.42% in low frequency sonication of 20 kHz at the amplitude of 20% (0.15 W/mL power density). In the case of high frequency ultrasonic system (850 kHz), CBZ removal increased significantly from 44% to 89.5 % at 75% amplitude (0.12 W/mL power density) within 60 min of reaction. Continuous mode sonication was observed to be more effective than that of pulse mode sonication not only for degradation efficiency and also for electrical energy consumption needed to degrade CBZ. Sono-catalytic oxidation was also conducted with simulated wastewater that contains SO₄^2-, CO₃^2–, NO^3–, Cl^- anions and natural organic component of fulvic acid. The CBZ degradation was inhibited slightly in the presence of NO₃^– and Cl^-, and fulvic acid, however, the existence of SO₄^2- and CO₃^2– increased the degradation degree of CBZ. Toxicity tests were performed to determine the toxicity of untreated CBZ, and treated CBZ by photocatalytic, and sono-photocatalytic oxidations.     

Development of high durability plasma filter for air circulating disinfection system

Deadly diseases are caused by pathogenic bacteria and viruses that spread, among other means, through air circulating systems; hence, it is important to focus on pathogen removal from the air before circulating air through the system. Our paper introduces a novel plasma-based filter that, when used in an air circulating system with particulate air filter, disinfects the air flow. This device, based on dielectric filter discharge (DFD) structure with low pressure drops, indicates easy installation into existing air circulating system. Its performance was evaluated in accordance with the specifications of duct used in hospitals, with consistent O₃ generation during 200 h showing high durability. Escherichia coli and Micrococcus luteus were used as the target airborne bacteria; the system exhibited a removal efficiency of approximately 99.99% on bacterial aerosols and continuous bactericidal action, demonstrating that the DFD system can be directly applied to existing air circulating systems.     

Optimization of gas–liquid hybrid pulsed discharge plasma for p-nitrophenol contaminated dredged sediment remediation

p-Nitrophenol (PNP) removal in dredged sediment during pulsed discharge plasma process was studied in terms of adjustable trim capacitance, electrode distance and gas-flow rate. PNP degradation efficiency reached up to 88.5% under the conditions of adjustable trim capacitance of 2.0 nF, electrode distance of 16 mm, and air flow rate of 0.8 L min⁻¹. To a certain extent, increasing the adjustable trim capacitance and decreasing the electrode distance leaded to high PNP degradation efficiency. An appropriate air flow rate was determined for gaining relatively high PNP removal efficacy. PNP mineralization was analyzed by UV–Vis spectrum, COD, and TOC evolution.     

Combination of spontaneous polarization plasma and photocatalyst for toluene oxidation

In this paper, we report toluene destruction using a spontaneous polarization plasma and photocatalyst reactor in air at atmospheric pressure and room temperature. A spontaneous polarization material (BaTiO₃) and photocatalyst (TiO₂) were added to the plasma system simultaneously. Three types of catalyst, i.e., TiO₂, BaTiO₃, or TiO₂/BaTiO₃, were used for toluene removal. The catalyst carrier, type, and amount were important factors in the toluene removal efficiency. The specific energy density and energy yield during the discharge process were investigated. The toluene removal efficiency increased when a spontaneous polarization plasma was combined with the photocatalyst. In terms of toluene removal efficiency, the activity order was TiO₂/BaTiO₃ > BaTiO₃ > TiO₂ > none. Large amounts of BaTiO₃ in the TiO₂/BaTiO₃ catalyst gave slightly better conversion. The TiO₂/BaTiO₃ catalyst not only enhanced the toluene removal efficiency, but also saved energy, making it useful for industrial applications.     

CO2 sensing properties of semiconducting copper oxide and spinel ferrite nanocomposite thin film

A new active layer for CO₂ sensing based on semiconducting CuO-Cu_xFe_3−xO₄ (with 0 ≤ x ≤ 1) nanocomposite was prepared by radiofrequency sputtering from a delafossite CuFeO₂ target using a specific in situ reduction method followed by post annealing treatment in air. The tenorite-spinel ferrite nanocomposite layer was deposited on a simplified test device and the response in a carbon dioxide atmosphere was measured by varying the concentration up to 5000 ppm, at different working temperatures (130-475 °C) and frequencies (0.5-250 kHz). The results showed a high response of 50% (Rair/RCO₂=1.9) at 250 °C and 700 Hz for a CO₂ concentration of 5000 ppm.     

Influence of co-existing cations and anions on removal of direct red 89 dye from synthetic wastewater by hydrodynamic cavitation process: An empirical modeling

In the present study the evaluation of Direct Red 89 (DR89) dye removal from synthetic wastewater by a lab-scale hydrodynamic cavitation (HC) process has been investigated under different operational conditions; the influence of co-existing cations and anions was applied using synthetic wastewater to assess whether the DR89 removal was enhanced. To study the effect of operational parameters, an empirical approach was adopted for the modeling of the HC process. The results showed that the DR89 degradation rate was strongly influenced by solution pH, reaction time and initial DR89 concentration. The removal efficiencies of DR89 were enhanced remarkably with the reaction time increment. When the initial concentration of DR89 increased from 30 to 90 mg/L, the DR89 removal efficiency decreased from 36.3 ± 3.8% to 17.5 ± 2.5%. In addition, the highest DR89 removal efficiency (75.4 ± 3.4%) was observed at a solution pH of 3. At a solution pH of 8, the DR89 removal efficiency was 18.4 ± 1.1%. An initial DR89 concentration of 80 mg/L was 75.4 ± 5.1% degraded after 130 min at a solution pH of 3. The results indicated that a synergistic effect occurred due to the added ions except for HCO₃^–. The removal of DR89 by the HC process was extremely enhanced with NO₃‾ ions with synergetic index higher than 2.5. Kinetic studies revealed that the decolorization of DR89 by HC followed a first order kinetic mechanism. The comparison between the predicted results of the empirical model and experimental data was also conducted. The empirical model described the DR89 removal efficiency under different conditions (R²: 0.93) and the results showed the HC reaction to be a useful technology for the treatment of dye in the textile wastewater.     

Very rapid synthesis of highly efficient and biocompatible Ag2Se QD phytocatalysts using ultrasonic irradiation for aqueous/sustainable reduction of toxic nitroarenes to anilines with excellent yield/selectivity at room temperature

There are many problems associated with the synthesis of nanocatalysts and catalytic reduction of nitroarenes - e.g., high temperatures, costs, long reaction/synthesis process times, the toxicity of chemicals/solvents, undesirable byproducts, the toxic/harmful wastes, low efficiency/selectivity, etc. This study represents an attempt to overcome these challenges. To this purpose, biocompatible and highly efficient Ag₂Se quantum dots (QDs) catalysts with antibacterial activity were synthesized in a very rapid (30 sec, rt), simple, inexpensive, sustainable/green, and one-pot strategy in water using ultrasonic irradiation. Characterization of the QDs was performed using different techniques. UV–Vis absorption and fluorescence spectroscopic studies showed an absorption peak at 480–550 nm and a maximum emission peak around 675 nm, which confirmed the successful synthesis of Ag₂Se QDs via the applied biosynthetic method. Subsequently, catalytic reduction of nitroarenes by them was carried out under safe conditions (H₂O, rt, air atmosphere) in ∼ 60 min with excellent yield and selectivity (>99%). Their catalytic activity in the reduction of various toxic nitroarenes to aminoarenes under green conditions was investigated. Thus, a rapid and safe ultrasound-based method was employed to prepare stable and green Ag₂Se QDs phyto-catalysts with unique properties, including exquisite monodispersity in shape (orthorhombic) and size (∼7 nm), air-stability, and good purity and crystallinity. Importantly, instead of various toxic chemicals, the plant extract obtained by rapid ultrasonic method (10 min, rt) was used as natural reducing, capping, and stabilizing agents. Moreover, antibacterial assays results showed that Ag₂Se-QDs catalysts at low concentrations (ppm) have high activity against all tested bacteria, especially E. coli (MIC:31.25 ppm, MBC:125 ppm) which were significantly different from those of Fig extract (MIC = MBC:500 ppm). The data reflect the role of these bio-synthesized Ag₂Se-QDs catalysts in the development of versatile and very safe catalysts with biomedical properties.     

Thermally Evaporated Ag–Au Bimetallic Catalysts for Efficient Electrochemical CO2 Reduction

CO₂ reduction reaction (CO₂RR) has indispensable significance for carbon recycling and renewable energy production. As typical electrochemical catalysts, Au and Ag show relatively high reaction activity and selectivity in CO₂RR. In this study, a series of Ag–Au bimetallic catalysts are designed and synthesized through the thermal evaporation method for efficient yet massive production of electrochemical catalysts. The Ag–Au catalysts show significantly enhanced activity and selectivity in CO₂RR, which is mainly attributed to the increased grain boundaries with well-dispersed single Ag atoms. After the optimization, Au20Ag10 exhibits the best performance with a CO Faraday efficiency of 89% at −0.9 V (vs the reversible hydrogen electrode) with good stability.     

A multi-wire-to-cylindrical type packed-bed plasma reactor for the inactivation of M. aeruginosa

Eutrophication in drinking water supplies brings about serious impact on the drinking water safety. In this study, a new multi-wire-to-cylindrical type packed-bed plasma reactor has been proposed and experimentally investigated its ability to control excessive growth of Microcystis aeruginosa (M. aeruginosa). Experimental results show the removal efficiency of M. aeruginosa and the inactivation constant were increased with the increased electrode number and air flow rate. More than 93% of optical density was removed at an air flow rate of 0.75 m³/h with treatment for 40 min at the end of the fifth day and the inactivation constant 16.20 was obtained in the multi-wire-to-cylindrical type packed-bed plasma reactor with 3 mm diameter 6-wire high-voltage electrodes; the difference in the electrode material on the removal efficiency of M. aeruginosa was unobvious, but the effects of pulse repetitive rate and applied peak pulse voltage on the inactivation of M. aeruginosa were significant. The changes in the visible spectra of M. aeruginosa solution demonstrated that photosynthetic pigments, such as chlorophyll-a, phycocyanins, carotenoids have been damaged, indicating the inhibitive behaviors of discharge on the algal growth. These results implicate that M. aeruginosa cells were inactivated by a multi-wire-to-cylindrical type packed-bed plasma reactor, demonstrating the considerable potential of such an alternative process for efficient water purification.     

Preparation of zeolite nanorods by corona discharge plasma for degradation of phenazopyridine by heterogeneous sono-Fenton-like process

The plasma-modified clinoptilolite (PMC) nanorods were prepared from natural clinoptilolite (NC) utilizing environmentally-friendly corona discharge plasma. The PMC and NC were characterized by XRD, FT-IR, SEM, EDX, XPS and BET, which confirmed the nanocatalyst formation. The catalytic performance of the PMC in the heterogeneous sono-Fenton-like process was greater than the NC for treatment of phenazopyridine (PhP). The desired amounts were obtained for experimental parameters including initial pH (5), PMC dosage (2 g/L), K₂S₂O₈ concentration (2 mmol/L), ultrasonic power (300 W) and PhP concentration (10 mg/L). Reactive oxygen species scavengers decreased the removal efficiency of the PhP. The treatment process followed pseudo-first order kinetic and seven degradation intermediates were identified by the GC–MS technique.     

Analysis of sterilization effect by pulsed dielectric barrier discharge

Atmospheric pressure (AP) plasmas can sterilize against almost all kinds of bacteria because many ions and reactive species, such as oxygen atoms and ozone, etc., are generated during AP plasmas. So AP plasmas are proper processes for application to air cleaners and sterilizers. The aim of this paper is to evaluate a germicidal effect caused by pulsed plasma system in air utilizing a dielectric barrier discharge (DBD) type reactor incorporating alumina, glass, etc. Escherichia coli, Bacillus subtilis and Pseudomonas aeruginosa bacteria were used for this sterilization experiment. For analysis of the relationship between sterilization results and chemical species generated in the discharge, we used optical emission spectroscopy and we checked emission spectra by atomic oxygen (394.2 and 436.8 nm) and second positive system of nitrogen (337.1 nm). Experimental results showed that DBD treatment during 70 s sterilized E. coli with 99.99% effectively and ozone molecules were the dominant germicidal species. From these results we concluded that the pulsed DBD system is very effective for sterilization.     

Determination of the OH radical in atmospheric pressure dielectric barrier discharge plasmas using near infrared cavity ring-down spectroscopy

The hydroxyl radical (OH) plays an important role in combustion systems, atmospheric chemistry and the removal of air pollutants by non-thermal plasmas. The present work reports the determination of the hydroxyl radicals in atmospheric dielectric barrier discharge plasmas via near infrared continuous wave cavity ring-down spectroscopy. The P-branches of OH X²Π_i (ν' = 2 ←ν^′′ = 0) bands were used for its number density measurements. The minimum measurable absorption coefficient is about 3 × 10^-8 cm^-1 in DBD plasmas. At certain experimental conditions (a.c. frequency of 70 kHz, 6700 ppm H₂O in He, 1 atm), when the peak-to-peak discharge voltage varied from 6 kV to 10.4 kV, the determined OH radical concentration increased from (2.1 ± 0.1) × 10¹³ molecules cm^-3 to (3.7 ± 0.1) × 10¹³ molecules cm^-3. The plasma gas temperature, derived from the Boltzmann plots of OH rotational population distributions, ranged from 312 ± 10 K to 363 ± 10 K when the discharge voltage was raised in the above range. The influences of O₂ and N₂ addition on the production of OH radicals have been also investigated.     

Experimental proof on two-cone axisymmetric-folded combination CO2 laser

The experimental proof of the light output on the two-cone axisymmetric-folded combination (ASFC) CO₂ laser has been performed. The output power from the centre discharge tube is 26.7 W, and that of one couple of folded discharge tubes is 40.5 W. Seventeen beams can be obtained from the device, which are from the folded cavities with axes placed in the inner and outer cones, respectively. Therefore, the ASFC CO₂ laser with more discharge tubes can be fabricated and much higher output power can be obtained.     

Mechanism analysis of hydroxypropyl guar gum degradation in fracture flowback fluid by homogeneous sono-Fenton process

An effective hybrid system was applied as the first report for the successful treatment of key pollutants (hydroxypropyl guar gum, HPG) in fracturing flowback fluid, and the synergistic index of the hybrid system was 20.45. In this regard, chemical oxygen demand (COD) removal ratio was evaluated with various influencing operating factors including reaction time, H₂O₂ concentration, Fe²⁺ concentration, ultrasonic power, initial pH, and temperature. The optimal operating parameters by single-factor analysis method were: the pH of 3.0, the H₂O₂ concentration of 80 mM, the Fe²⁺ concentration of 5 mM, the ultrasonic power of 180 W, the ultrasonic frequency of 20–25 kHz, the temperature of 39 ℃, the reaction time of 30 min, and the COD removal rate reached 81.15 %, which was permissible to discharge surface water sources based on the environmental standards. A possible mechanism for HPG degradation and the generation of reactive species was proposed. Results of quenching tests showed that various impacts of the decomposition rate by addition of scavengers had followed the order of EDTA-2Na < BQ < t-BuOH, therefore OH radicals had a dominant role in destructing the HPG. Based on the kinetic study, it was concluded that Chan Kinetic Model was more appropriate to describe the degradation of HPG. Identification of intermediates by GC–MS showed that a wide range of recalcitrant compounds was removed and/or degraded into small molecular compounds effectively after treatment. Under the optimal conditions, the sono-Fenton system was used to treat the fracturing flowback fluid with the initial COD value of 675.21 mg/L, and the COD value decreased to 80.83 mg/L after 60 min treatment, which was in line with the marine sewage discharge standard. In conclusion, sono-Fenton system can be introduced as a successful advanced treatment process for the efficient remediation of fracture flowback fluid.     

Ultrasonically enhanced extraction of luteolin and apigenin from the leaves of Perilla frutescens (L.) Britt. using liquid carbon dioxide and ethanol

The present study reports on the ultrasonic enhancement of the liquid carbon dioxide (CO₂) extraction of luteolin and apigenin from the leaves of Perilla frutescens (L.) Britt., to which ethanol is added as a cosolvent. The purpose of this research is also to investigate the effects of the particle size, temperature, pressure, irradiation power, irradiation time, and ethanol content in the liquid CO₂ solution on the extraction yield using single-factor experiments. We qualitatively and quantitatively analyzed the yields in the extract using HPLC (high-performance liquid chromatography). The liquid CO₂ mixed with ethanol was used at temperatures of 5, 20 and 25 °C with extraction pressures from 8 to 14 MPa. The yields of luteolin and apigenin in the extraction were clearly enhanced by the ultrasound irradiation, but the selectivity of the extract was not changed. The yields of luteolin and apigenin in the extract were also significantly improved by adjusting the operating temperature, the irradiation time, and the ethanol content in the liquid CO₂ solution, but no change in the selectivity of the extract was observed.