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A considerable enhancement of the catalytic activity of graphene oxide (GO) was achieved as a result of plasma treatment in a hydrogen glow discharge. The results obtained for the hydroisomerization of 1-octene, together with the catalyst characterization showed that plasma exposure leads to the formation of defects in the material and of surface acidic species. Optical emission spectroscopy diagnostics of the plasma revealed that the electron temperature and the dissociation of molecular hydrogen are important parameters that can be tuned for optimization of the treatment process.

[EN] H2 plasma has been used to generate carbon vacancies on reduced graphene oxide to increase its catalytic activity as a hydrogenation catalyst. A relationship between the power of the plasma treatment and the exposure time with the activity of the material was observed for CvC double bond hydrogenation. The activity data in the case of 1-octene, showing skeletal isomerization besides hydrogenation, indicate that H2 plasma treatment can introduce hydrogenating and acid sites rendering a bifunctional catalyst that is reminiscent of the activity of noble metals supported on acid supports., Financial support from the Spanish Ministry of Economy and Competitiveness (Severo Ochoa, CTQ2015-69563-CO2-R1 and Grapas) is gratefully acknowledged. AP thanks the Ministry for a Ramon y Cajal research associate contract. AFG thanks the Center of Supercomputing of Galicia (CESGA) for the computational facilities. MM acknowledges financial support from the PN 16 47 01 04 project. VIP kindly acknowledges UEFISCDI for financial support (project PN-III-P4-ID-PCE-2016-0146, No. 121/2017).

Graphene oxide (GO) and N-doped graphene [(N)G] graphenes were submitted to H glow discharge under different discharge regimes, in both the negative glow and positive column plasma regions. The resulted catalysts were fully characterized using several techniques such as Raman, DRIFT and XPS spectroscopy, powder X-ray diffraction, H pulse chemisorption and H-, CO- and NH-TPD experiments. Density functional theory calculations were performed taking a slab model of graphene sheet with an optimized C[sbnd]C bond length (1.426 Å) and a 16 Å vacuum layer between sheets. An overview of these characterizations showed that the O/C atomic ratio of GO is influenced by the plasma regime, indicating the occurrence of O removal, as also predicted by DFT calculations. In the case of (N)G, the plasma treatment also removes pyridinic N with an increase of the C/N ratio. The efficiency of the plasma modification has been checked through catalytic tests in hydroisomerization of 1-octene and hydrogenation of α-methyl-styrene. Contrarily to classical thermal activation requiring high temperatures, the generation of the defects by treating with plasma occurs at voltages in the range of 2−5 kV. In consequence, the hydrogenation and isomerization of alkenes resulted with high yields and good selectivities. Graphene prepared from sodium alginate from brown algae was considered as reference in these investigations., This work was supported by the Romanian Ministry of Education and Research UEFISCDI (projects PN-III-P4-ID-PCE-2016-0146, nr. 121/2017, PN-III-P1-1.1-TE-2016-2191, nr. 89/2018 and 16N/2019) and by the Spanish Ministry of Science and Innovation (Severo Ochoa and RTI2018-89237-CO2-R1). MM thanks Dr. F. Gherendi for the calibration of the OES system.

A novel advanced oxidation process based on the combination of ozonation with non-thermal plasma generated in a pulsed corona discharge was developed for the oxidative degradation of recalcitrant organic pollutants in water. The pulsed corona discharge in contact with liquid, operated in oxygen, produced 3.5 mg L −1 ozone, which was subsequently introduced in the ozonation reactor. The solution to be treated was continuously circulated between the plasma reactor and the ozonation reactor. The system was tested for the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) and considerably improved performance as compared to ozonation alone, both with respect to the removal of the target compound and to mineralization. The apparent reaction rate constant for 2,4-D removal was 0.195 min −1 , more than two times higher than the value obtained in ozonation experiments. The mineralization reached more than 90% after 60 min treatment and the chlorine balance confirms the absence of quantifiable amounts of chlorinated by-products. The energy efficiency was considerably enhanced by shortening the duration of the discharge pulses, which opens the way for further optimization of the electrical circuit design.

The objective of these investigations is to understand in more detail how organic compounds in water are degraded during plasma treatment. The formation of oxidizing species (ozone (O3), hydrogen peroxide (H2O2) and hydroxyl radicals (OH)) in a pulsed corona discharge in contact with liquid is investigated. The degradation of a target organic compound (methylparaben) in aqueous solution was increased when combining plasma treatment with ozonation, using the O3 generated in the discharge. Enhanced mass transfer of O3 obtained in this plasma+O3 configuration leads to a six fold increase of MeP oxidation rate. The evolution of oxidants concentration during treatment of MeP solutions provides information on their consumption in reactions with MeP and its oxidation products. The correlation of MeP degradation results (MeP removal and mineralization) with O3 consumption and the identified reaction products confirms that although O3 plays an important role in the degradation, for the mineralization OH radicals have an essential contribution. The concentration of OH radicals is diminished in the solutions containing MeP as compared to plasma-treated water, indicating OH consumption in reactions with the target compound and its degradation products. The concentration of H2O2 in the liquid can be either increased or reduced in the presence of MeP, depending on its initial concentration. On the one hand, decomposition of H2O2 by OH or O3 is suppressed in the presence of MeP, but on the other hand less OH radicals are available for its formation.

A pulsed corona discharge above liquid combined with ozonation has been investigated for the degradation of organic pollutants in water, as well as regarding the generation of several oxidizing species: ozone in gas phase, hydrogen peroxide and hydroxyl radicals in the liquid. A considerable improvement in the energy efficiency for organic compounds removal has been observed when reducing the width of the discharge pulses. This finding was correlated with the efficient formation of oxidizing species in case of short pulses. Recycling of the effluent gas from the plasma also enhances contaminants degradation. This was mainly attributed to an in situ peroxone process, i.e. the reaction between plasma-generated O3 and H2O2, forming highly reactive OH radicals, largely responsible for organic compounds degradation. This assumption is supported by the decline in O3 and H2O2 concentrations and simultaneous increase in OH concentration detected in plasma-ozonation experiments as compared to results obtained with plasma alone.

The interest in plasma-activated water (PAW) has been greatly increasing during the last few years due to its potential applications in biological and medical sciences, as well as in agriculture and food industry. The effect of PAW is caused by the reactive oxygen and nitrogen species (RONS) generated in the liquid exposed to plasma. This work reviews recent research on the formation of reactive nitrogen species (RNS) in aqueous solutions treated by non-thermal plasma. The most important chemical reactions leading to the production of these active species in the gas and liquid phase, as well as their chemistry in the liquid, correlated with their lifetime are addressed. The literature data on the most important long-lived RNS in PAW (nitrite and nitrate) and the short-lived ones (peroxynitrite and peroxynitrate) are reviewed. The reported results show that their concentrations strongly depend on the type of electrical discharge, gas composition, liquid properties and treatment conditions, and thus tuning the PAW composition over a relatively wide range can be achieved. Results on the possible application of PAW in agriculture are also reviewed. The role of RNS in this area is related to their participation in various signalling pathways in plants, which regulate metabolic processes, plant development, response to stress, etc, and thus can finally lead to enhanced germination and/or faster germination process and increase in plant growth.

The influence of non-thermal plasma treatment on wheat seeds ( Triticum aestivum ) has been investigated using a surface discharge reactor at atmospheric pressure and room temperature. Growth parameters, like roots and sprouts length and dry weight were measured on the fourth day of germination and a Gaussian distribution was used for curve-fitting of the obtained results. It was found that plasma had little effect on the germination rate, but influenced growth parameters. In the case of plasma treated seeds, the distribution of roots was shifted towards higher lengths as compared with the untreated samples. The distribution of the sprouts length was about two times narrower for the treated samples as compared with the control seeds. The sprouts and roots of the plasma treated seeds were heavier than those of the control samples. The root-to-shoot (R/S) ratio differed substantially, being 0.88 ± 0.016 for the untreated seeds and reaching 1.2 ± 0.005 for the treated samples. Industrial relevance The results obtained in this research demonstrate that non-thermal plasma treatment has a positive effect on wheat early growth. Due to its advantages (uniform treatment, no destruction of seeds, no requirement for chemicals), plasma might become an effective alternative to traditional pre-sowing seed treatment used in agriculture.

The degradation of methylparaben (MeP) in water was investigated using a pulsed corona discharge generated in oxygen, above the liquid. A comparison was made between results obtained in semi-batch corona (SBC) configuration (stationary solution, continuous gas flow) and results obtained in a semi-batch corona with recirculation combined with ozonation (SBCR + O3), where the liquid is continuously circulated between a solution reservoir and the plasma reactor and the effluent gas containing ozone is bubbled through the solution in the reservoir. It was found that MeP was completely degraded after 10-15 min of treatment in both configurations. Oxidation by ozone alone, in the absence of plasma, was a slower process. The energy efficiency for MeP removal (Y MeP) and for mineralization (Y TOC) was significantly higher in the SBCR + O3 configuration (Y MeP = 7.1 g/kWh at 90 % MeP removal and Y TOC = 0.41 g/kWh at 50 % total organic carbon (TOC) removal) than in the SBC configuration (Y MeP = 0.6 g/kWh at 90 % MeP removal and Y TOC = 0.11 g/kWh at 50 % TOC removal).

A pulsed dielectric barrier discharge was used for the decomposition of enalapril, its metabolite, enalaprilat, its degradation by-product, diketopiperazine, aswellastheircombination, in aqueous solution. The discharge was generated at the interface between gas and the solution which flows as a film on the surface of the inner electrode of the plasma reactor. The degradation mechanism of the studied compounds and the temporal evolution of the reaction intermediates were established from LC‐MS analysis. A wide variety of degradation by-products were formed; at least six new derivatives, not mentioned in literature, were observed. However, most of these by-products were subsequently degraded to small molecules. The mineralization degree, determined from TOC and COD measurements, was approximately 40%.

A pulsed corona discharge in multiwire-plate geometry, generated above water was studied for the removal of organic compounds in liquids. The degradation of methylene blue (MB) and the formation of hydrogen peroxide (H2O2) were investigated. The MB solution was rapidly decolorized, evidencing the degradation of the dye after approximately 10 min plasma treatment. Nitrate, formate, sulphate and chlorine ions have been detected in the treated solution, explaining partly the change in the solution properties with plasma exposure, i.e. increase of electrical conductivity and decrease of pH. It was found that the concentration of H2O2 generated in water increased with plasma exposure time, reaching 200 mg/L after 30 min treatment. In the MB solution less hydrogen peroxide was detected, suggesting reactions with the dye and its degradation products. The addition of FeCl2 catalyst had a slight favorable effect on methylene blue degradation due to Fenton’s reaction. It was observed that MB and H2O2 concentrations continue to decrease after the plasma treatment was stopped, suggesting that active species which accumulate in the solution may react post-plasma with methylene blue and its degradation products.

Silver colloids have been prepared by reducing AgNO3 in aqueous solution and embeded in alumina following a sol–gel procedure in the presence of Pluronic 84 ((EO)19(PO)39(EO)19), as surfactant. Plasma-catalytic experiments aimed at the mineralization of toluene showed that the selectivity to CO2 was significantly increased in the presence of Ag catalysts compared with results obtained using the plasma alone. In-situ studies of the ozone interaction with catalysts provide an insight into the nature of the active sites of supported silver colloids for mineralization reactions. It is noticeable that when ozone is chemisorbed on embedded Ag colloidal catalysts no change in the silver oxidation state or size is found. The population of the chemisorbed species is higher at lower temperatures, where the non-selective decomposition of ozone is smaller. The catalysts exhibit high stability, preserving the structural and textural properties after the catalytic tests, that is indeed very important in the presence of ozone.

The decomposition of methylene blue (MB) in aqueous solution was investigated using a pulsed corona discharge. The discharge was ignited in the gas bubbled in the solution through several needle electrodes. The influence of treatment time, volume of the treated solution and initial concentration of the dye in solution on MB degradation was studied. The effect of the nature of the gas introduced was also investigated. For the same energy input, MB conversion increased in the order air < argon < oxygen. When using oxygen, the decomposition of MB exceeded 95% after ~20 min plasma treatment. Higher efficiency was obtained for higher treated volume and higher initial concentration. At 90% conversion the yield obtained with oxygen was ~5 g/kWh for an initial concentration of 150 mg/l and a treated volume of solution of 100 ml.

The decomposition of chlorinated volatile organic compounds by non-thermal plasma generated in a dielectric barrier discharge was investigated. As model compounds trichloroethylene (TCE) and 1,2-dichloroethane (DCE) were chosen. It was found that TCE removal exceeds 95% for input energy densities above 0.2 eV/molecule, regardless of the initial concentration of TCE, in the range 100–750 ppm. On the other hand, DCE was more difficult to decompose, the removal rate reached a maximum of 60% at the highest input energy used. For both investigated compounds the selectivity towards carbon dioxide was significantly influenced by their initial concentration, increasing when low concentrations were used. The gas flow rate had also an effect on CO2 selectivity, which is higher at low flow rate, due to the higher residence time of the gas in the plasma. The best values obtained in these experiments were around 80%.

The oxidative decomposition of trichloroethylene (TCE) in dry air was investigated in non-thermal plasma at atmospheric pressure and room temperature, both in the absence and in the presence of gold containing mesoporous silica (GMS) catalysts. In the absence of catalyst, TCE removal reached 100% for average powers dissipated in the plasma above 3 W, for a TCE concentration of 430 ppmv. Carbon monoxide and carbon dioxide were the major reaction products with CO2 selectivity up to 25% and CO selectivity up to 70%. In the presence of gold containing mesoporous catalysts, the concentrations of CO and CO2 increased as compared to those obtained with plasma alone. The GMS catalysts can dissociate ozone produced in plasma to oxygen radicals that decompose TCE. Among these catalysts, the one containing the least amount of Au (0.5% GMS) showed the best catalytic performance. In the presence of ozone generated in the plasma, isolated gold cations might play a critical role for the catalytic behavior.

The degradation of several organic compounds in aqueous solution: methyl yellow (C14H15N3), methyl red (C15H15N3O2), methyl orange (C14H14N3NaO3S), phenol red (C19H14O5S) and methylene blue (C16H18ClN3S), was investigated in a pulsed corona discharge. High voltage pulses of 17 kV amplitude, 24 ns rise time and approximately 200 ns duration (full width at half maximum––FWHM) were applied to an array of six hollow needles. When oxygen was bubbled into the solution through the needle, current pulses of 90 A amplitude were obtained and the average power dissipated in the discharge was 19 W at 100 Hz pulse repetition rate. UV-visible spectra of the aqueous solutions show a significant reduction of the absorbance in the visible range, up to 90%, after plasma treatment, suggesting fragmentation of the compounds. Several aliphatic compounds were identified as oxidation products of methyl yellow, methyl red and methyl orange. For methylene blue and phenol red aromatic reaction products were detected as well.

A novel catalytic reactor with dielectric barrier discharge (DBD) at atmospheric pressure was developed for the abatement of volatile organic compounds (VOCs). The novelty of DBD reactor is the metallic catalyst serving also as the inner electrode. The catalytic electrode was prepared from sintered metal fibers (SMF) in the form of a cylindrical tube. Oxides of Mn and Co were deposited on SMF by impregnation. Decomposition of toluene taken as the model VOC compound (

A dielectric barrier discharge (DBD) combined with Mn-based phosphate catalysts placed downstream of the plasma reactor was investigated experimentally for total oxidation of toluene in air. The discharge was initiated by high voltage pulses of 18 kV amplitude and 1213 ns rise time. The pulse frequency increased from 14 to 80 Hz, for applied voltages in the range 18-28 kV. Discharge currents up to 100 A and approximately 50 ns duration were obtained. No other hydrocarbons except toluene were detected in the effluent gas. The yield of carbon dioxide formed in the discharge was up to 24%. As catalysts, MnPO4, Mn-APO-5 and Mn-SAPO-11 were tested, for temperatures up to 400 degrees C. Under purely catalytic conditions, the best behavior for toluene total oxidation was found for Mn-SAPO-11, with a CO2 yield up to 33%, at 400 degrees C. The combined application of plasma and catalysis showed a remarkable synergetic effect, even at low temperature, up to 100 degrees C, where the catalysts alone are not active. In this range, the CO2 yield increased up to 41%, for the Mn-SAPO catalyst. At 400 degrees C the highest CO2 yield was obtained for MnPO4, reaching 68%. The synergetic effect observed for the plasma-catalyst combination is attributed to ozone radicals formed in the discharge, which decompose on the catalyst surface, greatly contributing to toluene total oxidation. (c) 2005 Elsevier B.V. All rights reserved.

Thin films of zirconium tin titanate, (Zr 0.8 Sn 0.2 )TiO 4 (ZST) were deposited using a pulsed electron beam source based on a channel-spark discharge for target ablation. An advanced degree of crystallization was obtained for the films deposited on alumina substrate post-annealed at 1000 °C. The crystalline lattice constants of the films are very close to those of the target material, which confirms the same stoichiometry in ZST films and in the bulk.

The conversion of methane to aromatic hydrocarbons was investigated in a pulsed microwave plasma at atmospheric pressure in the presence of a heterogeneous catalyst. The influence of the microwave power and methane flow rate or residence time, respectively, on the conversion degree and product concentration was analyzed. The methane conversion reached 60–70%. Higher hydrocarbons were produced, with C 2 being the most abundant. Only after initial carbon formation in the discharge were aromatic products observed. The solid carbon catalyzed the methane aromatization. Benzene was the main aromatic product formed, in concentrations up to 0.6%, with selectivities up to approximately 30%.

Non-thermal plasma generated in a pulsed corona discharge in contact with liquid was used for the degradation of methyl paraben (MeP) in water. In the combined NTP-ozonation system the liquid is recirculated between a reservoir and the plasma reactor and the effluent gas containing ozone is passed through the solution in the reservoir. The comparison between results obtained by plasma treatment and by NTP-ozonation showed considerably higher efficiency for MeP removal and for mineralization in the latter case.

The oxidation of toluene in air was investigated using a dielectric barrier discharge (DBD) combined with a Pd/Al2O3 catalyst. When using only plasma, rather low selectivity towards CO2 was obtained: 32-35%. By filling the DBD reactor with Pd/Al2O3 catalyst the CO2 selectivity was significantly enhanced (80-90%), however, a large amount of toluene was desorbed from the catalyst when the discharge was operated. By filling a quarter of the discharge gap with catalyst and placing the rest of the catalyst downstream of the plasma reactor, an important increase of CO2 selectivity (~75%) and a 15% increase in toluene conversion were achieved as compared to the results with plasma alone. The catalyst exhibited a very good stability in this reaction.

The decomposition of the azo dye methyl red in aqueous solution was performed using a pulsed dielectric barrier discharge reactor (DBD) in coaxial configuration. The solution was made to flow as a thin layer on the surface of the inner electrode of the DBD reactor and the discharge was generated at the gas-liquid interface. In this way the oxidizing species formed in the discharge can easily penetrate the solution and react with the dye molecules in order to decompose them. After 10 minutes plasma treatment 93% removal of the dye was reached for 50 mg/L initial concentration of methyl red in solution. The corresponding removal yield was 52.5 g/kWh. Lower concentrations of the dye are removed faster, however the efficiency is lower in this case. It was found that the degradation of methyl red depended on the initial dye concentration, being faster for lower concentration, but the energy yield was higher for the higher initial concentration. Methyl red was degraded faster when decreasing the solution pH. Several degradation products, investigated by gas chromatography-mass spectrometry (GC-MS), were identified and discussed.

Oxidative removal of toluene in a dielectric barrier discharge reactor combined with manganese catalysts downstream was investigated. Toluene input concentration was varied in the range of 415-2227 ppm. The discharge was operated in pulsed mode, with short pulses of 23-35 kV peak voltage. At 7 W average power, toluene conversion was 60%-70%, independent on the toluene input concentration and on the total gas flow rate in the range of 110-330 SCCM (SCCM denotes cubic centimeter per minute at STP). Toluene total oxidation was favored at high residence time of the gas in the discharge zone and low toluene concentration, when the main reaction product was CO2 with selectivities of 80%-85%. The addition of the catalysts led to a 15%-20% increase in toluene conversion with respect to the values obtained in the plasma, due to oxidation with ozone on the catalyst surface. (c) 2006 American Institute of Physics.

The decomposition of trichloroethylene ITCE) by non-thermal plasma was investigated in a dielectric barrier discharge (DBD) reactor with a copper rod inner electrode and compared with a plasma-catalytic reactor. The particularity of the plasma-catalytic reactor is the inner electrode made of sintered metal fibers (SMF) coated by transition metal oxides. In order to optimize the geometry of the plasma reactor, the efficiency of TCE removal was compared for different discharge gap lengths in the range of 1-5 mm. Shorter gap lengths (1-3 mm) appear to be more advantageous with respect to TCE conversion. In this case TCE conversion varies between 67% and 100% for input energy densities in the range of 80-480 J/l, while for the 5 turn discharge gap the conversion was lower (53-97%) for similar values of the input energy. As a result of TICE oxidation carbon monoxide and carbon dioxide were detected in the effluent gas. Their selectivity was rather low, in the range 14-24% for CO2 and 11-23% for CO, and was not influenced by the gap length. Several other chlorinated organic compounds were detected as reaction products. When using MnOx/SMF catalysts as the inner electrode of the DBD reactor, the TCE conversion was significantly enhanced, reaching similar to 95% at 150 J/l input energy. The selectivity to CO2 showed a major increase as compared to the case without catalysts, reaching 58% for input energies above 550 J/l. (C) 2007 Elsevier B.V. All rights reserved.