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STSM Reports

Below are listed Short-Term Scientific Missions carried out in the frame of the TD1208 COST Action with brief summary of the content and results of each STSM. For quick access to the particular report you may use list of STSM Grantees. If you wish to print this page, click the printer icon at the top right corner. You may also see an interactive map of STSMs.

 

 



Hot arc - plasma activated water: RNOS quantification, synthesis optimization and activity mapping

Hoeben Wilfred

Early-Stage Researcher

STSM period: from 09/03/2017 to 24/03/2017

Home institution: Eindhoven University of Technology, Eindhoven, The Netherlands

Host institution: Institute of Plasma Physics CAS, Prague, Czech Republic

 

Plasma activated water from a hot arc PAW generator has been analyzed for nitrite, nitrate and peroxide densities. Observed nitrite and nitrate levels are impressive, reaching several millimoles per liter. Nitrate levels appear positively influenced by the applied energy density, together with a less pronounced increase in nitrite levels and limiting energy density for maximum peroxide levels. Active cooling during synthesis appears to be necessary for obtaining relevant peroxide levels. Additionally, the influence of several reactor parameters on PAW activity has been studied. Together with solid ion chromatographic detection, sensor-based PAW probing has been examined: acidity, oxidizingreduction potential and electrical conductivity have been concerned. UV absorbance spectrometry has been applied to investigate the possibilities of rapid nitrite screening. Low level access diagnostics have appeared to be a reasonable alternative to ion chromatography in situations, where the latter advanced diagnostic tool is not available; an exception are colorimetric indicator strips, with unacceptable performance for PAW applications. Finally, several PAW recipes have been submitted to acid-base titrimetry using combined pH and ORP electrodes. The pH titration curves exhibit typical features of weak acid presence and ORP versus pH titrimetric curves appear as recipe-characteristic.

Arc-water vortex interaction.




Experimental optical spectroscopic analysis of surface wave sustained plasma with liquids

Zhekova Maya

Early-Stage Researcher

STSM period: from 18/02/2017 to 04/03/2017

Home institution: Sofia University, Sofia, Bulgaria

Host institution: Faculty of Chemistry, Brno University of Technology, Brno, Czech Republic

 

The main goal of this STSM was the investigation of Surface wave sustained discharge (SWDs) - liquid interaction. SWDs operating at atmospheric pressure at 2.45 GHz in argon with different discharge conditions (power, radius, gas flow) was used. The influence of adding small amounts (up to 10%) of Nitrogen, Oxygen and water vapours to the gas flow, on the plasma parameters was be investigated. The optical emission spectroscopy of plasma torch was applied to determine gas and electron temperatures. Hydrogen peroxide and nitrogen oxide created in the liquid by plasma treatment was determined and their relative concentrations were obtained.

Plasma jet at 3 l/min Argon flow at 20 W of applied MW power.




Schlieren imaging of helium plasma jet interacting with liquid

Kovacecic Vesna

Early-Stage Researcher

STSM period: from 02/02/2017 to 19/02/2017

Home institution: University of Belgrade, Faculty of Physics, Belgrade, Serbia

Host institution: Laboratoire de Physique des Plasmas, Ecole Polytechnique, Paris, France

 

Application of non-thermal plasma jets and their interesting physics motivate researchers in the field of plasma physics to perform complex studies and create advanced models in order to understand their nature. The addition of the conductive or dielectric target transforms plasma jet discharge from the emission of single guided ionization waves to the transient glow discharge. One of the most complicated cases is addition of liquid target, when discharge physics and chemistry greatly change. The aim of the STSM was Schlieren imaging of plasma jet liquid target interaction. Standard Schlieren setup was built in order to perform parametric measurements where distance between plasma jet and the target and helium flow were variable parameters. It was found that at lower helium flows the effluent of the plasma jet remains in laminar flow regime with and without plasma. On the contrary, when helium gas flow was high turbulences in the effluent induced by plasma were obvious. Significant influence of water conductivity on plasma jet propagation was not observed. Interesting phenomena of changes of the refractive index in the liquid phase was observed and analyzed. Observed vortexes in the liquid are attributed to temperature changes and heating effects.

The effluent of the jet interacting with distilled water obtained by Schlieren imaging when the capillary was positioned 10 mm from the liquid surface- Horizontal blade position. Top row shows images of He jet with gas flow set to 500 SCCM (a) and 500 SCCM with plasma (b). The bottom row shows images when gas flow was set to 2000 SCCM (c) and 2000 SCCM with plasma (d).




FTIR spectroscopy of chemical species produced in plasma jet interaction with liquid target

Sretenovic Goran

Early-Stage Researcher

STSM period: from 02/02/2017 to 19/02/2017

Home institution: University of Belgrade, Faculty of Physics, Belgrade, Serbia

Host institution: Laboratoire de Physique des Plasmas, Ecole Polytechnique, Paris, France

 

The focus of the research performed during this STSM was investigation of chemical species produced in the free expanding helium plasma jet and plasma jet in contact with liquid target using Fourier transform infrared spectroscopy (FTIR). The experiment is organized as an extension of the collaboration that was previously established. Optical emission spectroscopy measurements that are previously done for plasma jet - liquid sample interaction are meant to be accomplished by absorption detection of produced species in such an interaction. Dielectric barrier discharge plasma jet in helium supplied by sinusoidal high voltage signal is used in the study. Plasma jet expanded into the different environments, such as ambient air and nitrogen, with and without water as a target. The spectra of reactive species NO, N2O, NO2, HNO3 and HNO2 are found under all discharge conditions. Production of ozone is noticed in presence of air, but also in plasma jet in nitrogen environment in contact with water.

IR absorption diagram of He plasma jet with nitrogen shielding, with liquid target.




High Speed Schlieren imaging of a plasma jet generated in a polymeric solution

Grande Silvia

Early-Stage Researcher

STSM period: from 01/02/2017 to 10/03/2017

Home institution: Department of Applied Physics, Ghent University, Ghent, Belgium

Host institution: Department of Industrial Engineering, Alma Mater Studiorum Universita di Bologna, Bologna, Italy

 

The research was focused on the investigation of fluid-dynamics of an atmospheric pressure plasma jet (APPJ) generated directly in a polymer solution. This APPJ is designed to improve the electrospinnability of polymer solution and the quality of electrospun nanofibers. The investigated plasma jet set-up ensures a close and intense interaction between the polymer solution and plasma plume, which can modify the chemical and physical parameters of the solution itself. During the STSM in Bologna, Schlieren imaging was used to investigate distilled water for different plasma exposure time. Unfortunately, the Schlieren imaging did not result in a suitable technique for the set-up under test, because the refraction index gradient was probably below the sensitivity of the system. The use of a backlight allowed to track the movement of each bubble inside the liquid with a comparable higher time resolution than HSI. On the other hand some treated liquid solution damped all the light due to bubbles formation and to change in color. As next step, High Speed Imaging (HSI) was applied to investigate the treatment of distilled water and a polymer solution of 1 % of Polyethylene Oxide dissolved in H2O. As a result, the treatment of distilled water with or without plasma does not present any noticeable differences. On the contrary, the polymer solution presents a large number of small bubbles when the solution is treated with just argon, while during the plasma treatment the bubbles are less in number. This behavior can be explained considering the increasing temperature of the liquid due to the plasma.

High Speed imaging: a) plasma afterglow jet without any liquid inside the reactor chamber; b) Argon streaming inside the distilled water with a flow rate of 0.9 slm; c) distilled water exposed to Argon-plasma with flow rate of 0.9 slm and ignited with 7.8 kV p.t.p.




Interaction of chemical species with liquids enhanced by the EHD effect

Shaw Alex

Early-Stage Researcher

STSM period: from 30/01/2017 to 17/02/2017

Home institution: Loughborough University, Loughborough, United Kingdom

Host institution: Department of Industrial Engineering, Alma Mater Studiorum Universita di Bologna, Bologna, Italy

 

Surface dielectric barrier discharges (S-DBDs) have received growing attention in recent years as a source of highly reactive species that can trigger chemical and biological processes in liquids. Key to their efficacy is the need to maximize the flux of reactive species reaching the liquid. In remote treatments, the transport of these reactive species has typically been assumed to be dominated by diffusion. However, recent work has demonstrated the importance of electrohydrodynamic effects and the significance of induced synthetic jets. In particular, the efficacy in degrading potassium indigotrisulphonate dye (indigo) in water solutions using single annular electrode S-DBDs was found to be most efficient when the inner diameter of the electrode was 30mm. Previous studies, however, have been limited to single annular electrode S-DBDs and did not consider scaling-up and interaction between adjacent electrodes. In this Short Term Scientific Mission (STSM) different scaling-up approaches were investigated and different electrode configurations evaluated with the goal to provide some guidelines for the scaling up of annular S-DBDs. As an example, figure below shows one of the designs considered in this study. Schlieren imaging, Pitot tube measurements and degradation of indigo in water were performed. Tallying with previous results, 30 mm diameter electrodes were found to be the most efficient and a hexagonal arrangement of these electrodes was found to be more energy efficient than concentric arrangements.

Example of a Surface dielectric barrier discharge (S-DBD) formed using 2 concentric electrodes.




Study the effect of cold atmospheric plasma (CAP) by using the COST reference jet on procedures for the decontamination of tooth root canals

Mohamed Mokhtar Hefny

PhD Student

STSM period: from 30/01/2017 to 24/02/2017

Home institution: Faculty of Physics and Astronomy, University of Bochum, Germany

Host institution: Department of Industrial Engineering, Alma Mater Studiorum Universita di Bologna, Bologna, Italy

 

The COST-jet, RF-driven microscale atmospheric pressure plasma jet, has been used for inactivation of Enterococcus faecalis bacteria, which is the main cause of the endodontic failures because of its high resistance to conventional cleaning methods. Four plasma conditions were used in the inactivation on agar: 1.4 slm He, 1.4 slm He/1700 ppm H2O, 1.4 slm He/ 0.6% O2 and 1.4 slm He/ 0.6% O2/1700 ppm H2O. From agar treatment, we realized that He/O2 plasma was the most powerful in the inactivation, so we used it to inactivate the bacteria on liquid suspension and on a realistic tooth model. To study the gas flow during the treatment with the COST-jet and to study the behavior of this flow with different targets, Schlieren's method was used with He as a working gas at three different helium flows 1.4, 2.8, and 5.6 slm. A chemical analysis by commercial test strips (Quantofix) was performed for distilled water (DW) treated by four types of plasma, resulting into: 10-500 mg/L for NO3-, 1-80 mg/L for NO2- and 1-100 mg/L for H2O2. A commercial pH probe (pH 7110 onoLab) was used for measuring pH changes in the plasma activated medium.

A photograph of the COST-jet with the realistic tooth model.




Effects of different waveforms on a DBD Plasma microbubble reactor

Seri Paolo

Early-Stage Researcher

STSM period: from 09/01/2017 to 27/01/2017

Home institution: Department of Industrial Engineering, Alma Mater Studiorum Universita di Bologna, Bologna, Italy

Host institution: Loughborough University, Loughborough, United Kingdom

 

The influence of different waveforms and duty cycle modulation frequency on the chemical yield of a bubbling reactor has been investigated during this short term scientific mission. In order to do so, a multilevel inverter power supply, capable of generating arbitrary waveforms with constant average power, frequency, no matching issues and engineered by the University of Bologna has been used. Absorption spectroscopy in liquid phase has been carried to estimate the Ozone production inside the reactor. Results from conventional methods (256 nm UV absorption) have been compared to the innovative chemical probe (Potassium Indigo Trisulfonate) partially developed by the Loughborough University. Optical Emission Spectroscopy (OES) and water PH and conductivity measurements have been used to help interpreting data. Results from this work show how not only waveforms with higher instantaneous powers (square waves) usually perform better in Ozone production, but also that faster duty cycles modulation frequencies can deeply influence the chemical yield of a plasma discharge, further enhancing the Ozone production.

Treated water's reduction in PH and increase in conductivity for different waveforms.




Investigation of the influence of different components of plasma afterglow on GapDH activity

Giardina Agata

Ph.D. Student

STSM period: from 01/01/2017 to 31/03/2017

Home institution: University of Padova, Padova, Italy

Host institution: University of Bochum, Bochum, Germany

 

Cold plasma has been attracting growing interest over the past decade due to its sterilization properties. However the study of inactivation mechanisms results challenging because of the diverse nature of plasma and biological systems treated. Here the impact of two different plasma discharges, dielectric barrier discharge and the plasma jet μ-APPJ (microscale atmospheric pressure plasma jet), was investigated on a molecular level. Glyceraldehyde-3-phosphate dehydrogenase (GapDH) was used as a model protein in vitro. Contribution of different components of plasma to this enzyme inactivation was then assessed using a modified version of the μ-APPJ, achieving the separation of charged and uncharged species. The same approach was applied to Escherichia coli, considered as a model living system of low complexity.

Effect of DBD on glyceraldehyde 3-phosphate dehydrogenase. (a) Activity of GapDH for jet exposures at different time. All relative activities are normalized to the dry control. (b) SDS-PAGE of GapDH samples exposed to plasma. (c) Decrease of free thiol groups in GaPDH after DBD treatment. The amount of thiols in the dry control is set to 1 and other results are normalized to it.




Enhanced plasma jet LIBS spectroscopy

Maletic Dejan

Early-Stage Researcher

STSM period: from 28/11/2016 to 19/12/2016

Home institution: Institute of Physics, Belgrade, Serbia

Host institution: Institute of Physics, Zagreb, Croatia

 

We investigated the mutual interaction of the laser induced plasma with the plasma jet at atmospheric pressure in interaction with water surface. The two plasma jets were used, sine wave at 80 kHz and the pulsed plasma jet with the pulse width of 6.125 μs and repetition rate 10 kHz. We performed optical emission measurements for several gases (Helium, Argon) and gas mixtures (Helium-Argon, Helium-Nitrogen) at flow rates 2 and 4 slm. The plasma jet was placed at 15 mm from the three various targets (water, metal and dielectric). The laser beam was focused in the middle between the je jet nozzle and the target. We also performed time resolved line emission measurements of the laser-jet interaction for the excited He 388.86 nm (1s3p) for metal and water targets. We have managed to produce laser and plasma jet plasma under the water and at the water surface. Plasma under the water is unstable and optical emission signal was very low. We recorded the emission of the laser and jet plasma on the surface of the water. The laser plasma and the plasma jet can interact with each other and change the intensity of some spectral lines especially argon and helium lines. Plasma jet in interaction with water surface produces high intensity of NO and OH bands in the OES spectra. Changing the composition of the buffer gas has a high impact on the concentration of produced radicals that has a key role in biomedical application and water treatment.

(a) Sinewave plasma jet with laser plasma in He/Ar 0.5% mixture on the water surface b) pulsed helium plasma jet and laser plasma under the water and c) pulsed helium plasma jet and laser plasma at the water surface.




Quantitative analysis of ROS concentration in gas phase produced by two different non-equilibrium atmospheric pressure plasma sources by means of absorption spectroscopy techniques

Simoncelli Emanuele

Early-Stage Researcher

STSM period: from 25/11/2016 to 25/01/2017

Home institution: Department of Industrial Engineering, Alma Mater Studiorum Universita di Bologna, Bologna, Italy

Host institution: Department of Applied Physics, Ghent University, Ghent, Belgium

 

ThiS STSM was focused on the investigation of the gas phase chemistry produced by two cold atmospheric pressure plasma (CAP) sources (a surface dielectric barrier discharge and a RF plasma jet) in a controlled atmosphere with different relative humidity (from 0% to 100%). The experimental setup was arranged to detect reactive species produced by plasma sources by means of absorption spectroscopy; in particular, the concentrations of Reactive Oxygen Species (RONS), such as OH(X), O3, NO, NO2, NO3 (molecules extremely relevant in the field of plasma treatment of water due to their antibacterial and oxidant properties), were quantitatively measured. Moreover, through the analysis of emission spectra, the rotational and vibrational temperature of plasma were evaluated with Boltzmann plot method. This experimental study, performed during the STSM in Ghent, will be coupled with chemical analysis of treated liquids and microbiological inactivation experiments on bacterial suspensions, carried out in Industrial Applications of Plasmas (IAP) group's laboratories in Bologna.

(A) Evaluation of O3 density by means of single mode method; (B) identification of the O3 and NO absorption contributions.




Use of DBD non-thermal plasma in oil liquids for food and biomedical applications

Vandamme Jeroen

Early-Stage Researcher

STSM period: from 14/11/2016 to 25/11/2016

Home institution: KU Leuven, Gent, Belgium

Host institution: Leibnitz Institute for Plasma Science and Technology, ZIK plasmatis, Greifswald, Germany

 

This STSM was aimed at the study of dielectric barrier discharge (DBD) generated plasma chemistry and its effect on oil. During this project, a 50 kHz DBD non-thermal plasma reactor (helium-oxygen gas mixture) was used for accelerated oxidation in canola oil. The impact of various parameters, including molecular oxygen concentration, applied voltage, distance between electrodes and gas flow, was evaluated. During these experiments, densities of singlet delta oxygen and ozone were determined in the gas effluent, in order to evaluate their impact on the oxidative degradation of the oil. Treated oil samples were analyzed afterwards, using FTIR for the determination of the oxidative status. Results showed that a maximum density of singlet delta oxygen is formed when 0.2 % of molecular oxygen is added to the helium gas flow. Ozone, however, shows higher concentrations when molecular oxygen concentration is increased up to 1.0 %. Other parameters, such as gas flow, inter-electrode distance and applied voltage, also proved to have significant impact on the formation of singlet delta oxygen and ozone. Furthermore, adding a sample of oil between the two electrodes drastically changed the plasma chemistry. The whole set of results will be correlated to the FTIR results, in order to gain insight into the oxidative reactions of the canola oil caused by singlet delta oxygen and ozone.

Ozone density as a function of the gas flow (with glass container; molecular oxygen fraction: 0.5%; applied voltage: 3kV; inter-electrode distance: 1cm), with and without oil in the glass container.




The effect of the pH value on the gold nanoparticle synthesis at plasma liquid precursor interaction

Vlad Iulia-Elena

Early-Stage Researcher

STSM period: from 22/06/2016 to 05/07/2016

Home institution: Babes-Bolyai University, Cluj-Napoca, Romania

Host institution: University of Ulster, Newtonabbey, United Kingdom

 

The purpose of this STSM was to investigate the effect of the pH value on gold nanoparticle synthesis at plasma liquid precursor interaction. Solutions of four different precursor (HAuCl4) concentrations, each with 5 different pH values (2, 3, 10, 12 and a not modified value), underwent plasma treatment for 10 minutes. The formed colloidal solutions were investigated by means of UV-vis spectroscopy and TEM. Moreover the H2O2 was also measured. The results showed that the pH value has a strong influence on the final properties of the gold nanoparticles. Low pH values can be associated with low concentrations of hydrogen peroxide formed in the solution and lead to a partial reduction of the precursor. Moreover, the modifications of the pH value affect the position of absorption maximum. Furthermore, it was showed that extreme pH values lead to narrow size and shape distributions for all investigated precursor concentrations as the nanoparticles have small sizes and tend to become spherical in shape.

Size distribution of the gold nanoparticles obtained using a 0.05 mM precursor solution, for different pH values.




Spectroscopic investigation of surface dielectric barrier discharge with liquid electrodes

Nikola Cvetanovic

Early-Stage Researcher

STSM period: from 28/05/2016 to 11/06/2016

Home institution: University of Belgrade, Faculty of Physics, Belgrade, Serbia

Host institution: Masaryk University, Brno, Czech Republic

 

This STSM was dedicated to the spectroscopic investigation of surface dielectric barrier discharge with liquid electrodes. This specific surface discharge configuration was developed at Masaryk University and has shown potential for treatment of dielectric surfaces. The discharge was operated in argon at atmospheric pressure with oxalic acid solution as a liquid electrode. It is formed as a number of short-lived, filamentary microdischarges, appearing randomly at both polarities of the applied voltage. Space and time resolved (according to polarity) emission spectroscopy measurements were done. The OH (A2Σ+ → X2Π) band was used for gas temperature estimation and compared to the new method that uses resonant broadening of argon lines. The broadened Balmer hydrogen lines were used for electron density measurements while broadening of Ar lines is also analyzed in terms of pressure broadening and shift. The measurements performed during the STSM show interesting results. More detailed analysis of the attained data and possibly additional measurements will produce results for an article in a scientific journal.

Appearance of the surface dielectric barrier discharge with liquid electrodes.




Fast Imaging of the creation of vapour layers and discharge on a flat ended electrode in saline solution

Karim Lutful Mohammad

Early-Stage Researcher

STSM period: from 23/05/2016 to 30/05/2016

Home institution: Queens University Belfast, Belfast, United Kingdom

Host institution: Faculty of Chemistry, Brno University of Technology, Brno, Czech Republic

 

The main objective of this STSM was to capture the whole events of breakdown mechanism in saline, viz. creation of bubble, expansion of vapour layers and ignition of plasmas by using a fast framing camera with framing rate up to 540 kHz. For this purpose, a set of experiments with varies discharge geometries have been performed to characterise the pre-and-post breakdown phenomena in saline. Pulses of 500 μs to 10 ms long and up to -300V were applied to generate the discharges with 1 - 20Hz repetition rate in this investigation. In these experiments shadowgraphy, Photo-emission, electrical response (I-V characteristic) and fast imaging observations were made. The fast images of tip surface visualized the structure of bubbles and vapour layers which are correlated with the electrical signal of the system. The decrease in current signal as the bubble grows and expands rapidly. At the point of breakdown the tip is isolated by the vapour layers from the conducting saline. After the first discharge, the vapour layers re-developed again to get some subsequent secondary discharges were observed in the same voltage pulse.

Electrical response of the system with an applied potential of -300V of 1 ms long pulse in 0.9% NaCl at room temperature. The current and voltage signals indicate the vapour layer development, deformation and light emission.




Characterization of gas dynamics in plasma jets by Schlieren photography and numerical modelling

Obrusnik Adam

Early-Stage Researcher

STSM period: from 22/05/2016 to 26/06/2016

Home institution: Masaryk University, Brno, Czech Republic

Host institution: Department of Industrial Engineering, Alma Mater Studiorum Universita di Bologna, Bologna, Italy

 

The aim of this STSM was to investigate the onset of turbulence in atmospheric pressure plasma jets (APPJ) ignited in helium and impinging on a flat surface. This geometrical configuration is very common in a range of biomedical and material applications of APPJs and, depending on the application, the onset of turbulence can be either welcome or undesirable. We have used high speed Schlieren imaging (4000 to 40000 frames per second) in order to assess the flow regime. The flow regime was investigated across a wide range of operating conditions gas flow rate through the jet, total input power and the frequency of the pulsed kHz power supply. The data that were obtained illustrate, among other things, the importance of frequency for the turbulence onset. Additionally, we have compared how the flow changes when a solid conductive substrate is replaced by a liquid substrate (phosphate buffered saline) and how the presence of the liquid influences the stabilization of the flow.




Fast imaging of the creation of discharges at a sharp tipped electrode

Asimakoulas Leonidas

Early-Stage Researcher

STSM period: from 20/05/2016 to 30/05/2016

Home institution: Queens University Belfast, Belfast, United Kingdom

Host institution: Faculty of Chemistry, Brno University of Technology, Brno, Czech Republic

 

The aim of this short term scientific mission, supported by the COST action, was to investigate discharges in saline solutions produced by pulsed low voltages with different types of electrodes (various materials and tip profiles were used). For this reason, the Photron SA-X2 fast-framing camera was used for the record of the vapour formation and the discharge propagation. This camera can achieve rates up to 1 MHz providing information of the phenomena that take place before/during and after the discharge. Data were also acquired with an oscilloscope, of the voltage, current and light emission from the plasma formed. The data are being analysed. The image below shows some frames from the film of a -270 V and 1ms duration voltage pulse applied to a 1 μm diameter tungsten tip immersed in saline. These images are backlit and the growth of a vapour layer around the tip is clearly observed during the pulse. The final image shows the collapse of this layer after the end of the pulse and the apparent formation of shockwaves.

Tungsten tip of 1um diam. Frames acquired during a voltage pulse of -270V a) beginning of pulse, b) 520 μs, c) end of pulse (1ms), d) 1.28ms.




Gas-phase characterization of atmospheric pressure plasma jet in contact with liquids by OES

Fontelo Rodriguez Raul

Early-Stage Researcher

STSM period: from 25/04/2016 to 29/04/2016

Home institution: School of Industrial Engineering of Barcelona, Barcelona, Spain

Host institution: University Pierre and Marie Curie, Paris, France

 

The main goal was to study the composition of a gas phase produced by an atmospheric pressure plasma jet in contact with liquids in views biological applications. The liquid employed was a cell culture medium. Different conditions for the analysis were assessed, the spectra obtained were measured at a discharge situation (0 mm) and in a post-discharge situation (10 mm). The different plasma jets were analyzed by Optical Emission Spectroscopy. We could define more how the plasma could interact with the liquid taking into account a possible future cell culture on the liquid treated. The results show that the composition in all cases is very similar, despite the fact that when Helium mixed with Nitrogen was used, the Nitrogen species took more importance making the Helium species undetectable. Studying the evolution of the intensity of each peak, the strongest changes on the liquid by the plasma action could be defined. In the cases of the discharge situation, the intensity of the peaks was increased with the Helium flow, however, in the post-discharge situations, the evolution of the peaks has different variations in the plasma Helium case and is even decreased with Helium and Nitrogen mixtures when the Helium flow was increased.

Peak intensity evolution of the most significant species for the Helium plasma at a discharge situation (0 mm).




Water plasmas for bacterial inactivation

Field Thomas

Professor

STSM period: from 25/04/2016 to 29/04/2016

Home institution: Queen's University Belfast, Belfast, United Kingdom

Host institution: Comenius University, Bratislava, Slovakia

 

The purpose of this STSM was to explore possible modifications to the electrospray water plasmas in the group of Zdenko Machala, Karel Hensel and Mario Janda; e.g. electrode gap distance and the HV DC self-pulsing circuit. Ultimately the aim of this research is to produce an effective plasma tool for destruction of bacterial infection, but within the time-frame of this visit the aim was to explore the effect of modifications and observe the electrical characteristics of the plasma and perform preliminary chemical analyses. Different plasmas modes were observed. With a lower valued resistor of ~ 5MΩ in the self-pulsing circuit it was possible to observe a "glow" type discharge mode that produced a higher ratio of hydrogen peroxide to nitrites than "transient spark" type discharge which was typically generated with resistance of ~ 10MΩ or more. Pictures of these two modes are shown below. The left hand picture show more filamentary transient spark type discharge, whereas the right hand picture shows the glow mode.




Growth of copper oxide nanostructures in chemical solution under the influence of plasma liquid discharge

Filipic Gregor

Early-Stage Researcher

STSM period: from 18/04/2016 to 29/04/2016

Home institution: Jozef Stefan Institute, Ljubljana, Slovenia

Host institution: Institute of Physics, Zagreb, Croatia

 

Copper oxide nanostructures are very interesting materials for different applications (photovoltaic cells, catalysts, gas sensors) due to their excellent properties, due to narrow band gap, electron confinement and possibility to offer more than single active crystal plane exposure. Copper oxide nanodots, nanosheets, nanoflowers, nanowires can be grown as a powder, on different substrates or on a copper surface itself. The most versatile class of methods in terms of the structure shape and crystallinity is wet chemical class. These methods utilise chemical solutions. In addition, typically heating is necessary to form the nanostructures and the treating time can be relatively long. Recently, a new approach to copper oxide nanowires has been demonstrated combining two steps. First, copper hydroxide nanostructuring is done on the surface in a chemical bath, and then atmospheric plasma is used to grow the copper oxide nanowires. The purpose of my mission would be to reduce the time needed for copper oxide nanostructure growth on the surface of copper sample and increase its versatility by introducing a single step plasma enhanced chemical method. The copper samples will be submerged in chemical bath with simultaneous plasma discharge. Plasma is a He atmospheric plasma jet, and chemical bath would contain aq.(NH4)2S2O8. Similar solution was already used in two step process of copper oxide nanostructure growth on copper surface, where the dipping of copper to the solution was followed by exposure to atmospheric microwave plasma.




Peroxynitrite detection in PAW simultaneously by fluorescent dye H2DCFDA and by kinetic study of postdischarge processes

Barbora Tarabova

PhD Student

STSM period: from 17/04/2016 to 30/04/2016

Home institution: Comenius university, Faculty of mathematics, physics and informatics, Bratislava, Slovakia

Host institution: Institute of Plasma Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic

 

Peroxynitrites are postulated to be the key antimicrobial agent in plasmas activated liquids. Their detection is very difficult due their short life-time and very low steady-state concentrations. We have already proposed the fluorescent method for peroxynitrites detection using fluorescent dye 2,7-dichlorofluoresceine diacetate (H2DCFDA). It was shown by using different specific scavengers of reactive species, that the H2DCFDA is sensitive to peroxynitrites and can be used for their qualitative detection. In this STSM we focused on the detection of post-discharge kinetics of peroxynitrites formation in aqueous solutions electro-sprayed through the cold air plasma generated by DC transient spark discharge. Kinetic study of nitrites and hydrogen peroxide showed exponential decrease of their concentrations in PAW post-discharge processes due to the formation of peroxynitrous acid O=NOOH. The rate of peroxynitrites formation rONOOH was determined through the pseudo-second order kinetics. Initial rate (t = 0 min) of post-discharge peroxynitrite formation was determined rONOOH = 87 nM/s and it was decreasing exponentially. Furthermore, we performed parallel detection of peroxynitrites by the H2DCFDA. The decrease of the peroxynitrite formation rate rONOOH was compared with the decrease of the fluorescent signal of H2DCFDA dye induced by peroxynitrite. The comparison showed that the H2DCFDA fluorescent is suitable for peroxynitrite detection in PAW.




Optical characterization of high pressure microdischarges in Air with water vapor admixture

Klas Matej

Early-Stage Researcher

STSM period: from 17/04/2016 to 30/04/2016

Home institution: Comenius University, Bratislava, Slovakia

Host institution: Brno University of Technology, Faculty of Chemistry, Brno, Czech Republic

 

Generation of AC and DC microdischarges in Air are promising method to sustained nonthermal plasma at atmospheric and above pressure. However, the mechanism of breakdown at high pressure and very high electric fields are still not well known. Purpose of this STSM was to uncover some of the plasma behavior by experimentally estimate properties of the plasma from emission spectra measured at various discharge conditions. CCD spectrometric study of microdischarges fed by various admixture of water vapor was carried out in a flowing regime of 200 sccm at room temperature and pressure of 1.3 Bar. We investigate the influence of electrode distance from 10 up to 100 μm and frequency from DC to RF on the emission spectra for dry air and air with relative humidity up to 100%.




Diagnostics and analysis of processes in discharge in water-ethanol mixture - FTIR analysis of gaseous products

Hlochova Lenka

Early-Stage Researcher

STSM period: from 17/04/2016 to 30/04/2016

Home institution: Brno University of Technology, Faculty of Chemistry, Brno, Czech Republic

Host institution: Comenius University, Bratislava, Slovakia

 

This STSM was focused on the processes in the discharge ignited in ethanol, ethanol-water mixture and in water solution with the conductivity of 200 μS/cm. In this unique environment are generated some gaseous products by the discharge, which are analyzed by FTIR. In the case of ethanol and ethanol-water mixture we can observe ethanol, methanol, carbon dioxide, ethane and ethane spectra. In the case of the discharge in water solution we can see the water and carbon dioxide, only and moreover, the intensity of absorbance is much lower than with the discharge in ethanol or ethanol-water mixture.

FTIR spektra of the ethanol with the discharge.




RNase inactivation by air spark discharge

Krewing Marco

Early-Stage Researcher

STSM period: from 17/04/2016 to 30/04/2016

Home institution: University of Bochum, Germany

Host institution: Comenius University, Bratislava, Slovakia

 

The RNase A is one of the most stabile enzymes in nature. It is ubiquitous and especially when working with RNA in experimental setups, it becomes very difficult to inactivate and remove the enzyme completely. In our group we were able to show, that a dielectric barrier discharge can fully inactivate RNase A within minutes of treatment. In this STSM the impact of other plasma discharges on RNase A was investigated. With transient spark discharge in direct contact to the surface of an RNase A solution the inactivation rate was 70% within 10 min of treatment. Additionally, a streamer corona discharge was applied on dried RNase A with electrospraying of little amounts of deionized water. With 81% within 10 min the inactivation rate was even higher compared to transient spark discharge, probably due a more favorable ratio of sample volume and contact area to the plasma. Using both discharges on dried RNase A without any water in the setup even after 20 min of treatment no significant inactivation was observed indicating that generation of reactive species inside the water is essential for enzyme inactivation.




Processing of selected organic polymers using RF plasma jet

Pawlat Joanna

Professor

STSM period: from 16/04/2016 to 22/04/2016

Home institution: Lublin University of Technology,Lublin, Poland

Host institution: Jozef Stefan Institute, Ljubljana, Slovenia

 

RF atmospheric pressure plasma jet was used to enhance wettability of organic polymers. Cellulose-based paper of 90 g/mm2 grammage as a perspective platform for antibiotic sensitivity tests was selected as a model material. Helium was the carrier gas for oxygen and nitrogen; pure water was used for goniometric tests. Influence of the flow rate and gas type, power of the discharge, and distance from the nozzle was examined. Dry-treated and wet-treated paper properties were compared using goniometric tests, XPS and AFM tools. RF plasma jet allowed to decrease surface contact angle in both cases without drastic changes in other features of tested material.

The contact angle change after 60 s dipping in pure water prior to 1 min plasma treatment in dependence of substrate gas, distance 3 cm).




Plasma assisted synthesis and modification of carbon and composite nanoparticles in liquids

Tarasenka Natalie

Early-Stage Researcher

STSM period: from 10/04/2016 to 30/04/2016

Home institution: B.I. Stepanov Institute of Physics, Minsk, Belarus

Host institution: Ulster University, Newtownabbey, United Kingdom

 

The aim of this STSM was to contribute to the on-going research on the synthesis and surface engineering of advanced nanoparticles (NPs) that may have potential biomedical and photovoltaic applications. The first part of the work was focused on the evaluation of the capabilities of the liquid assisted electrical discharge and laser ablation techniques for synthesis of luminescent carbon nanocrystals. The NPs were produced by electrical discharge and laser ablation in liquid with subsequent surface engineering by atmospheric pressure dc microplasma or by laser irradiation directly in solution with the purpose of their surface functionalization and luminescence enhancement. Experiments on laser-induced modification of C dots under irradiation of the colloids with radiation of different wavelengths (266, 355, 532 nm) were carried out aiming to elucidate the optimal conditions of laser-induced modification. In order to study the chemical composition, structure and morphology of the prepared nanoparticles HRTEM, SAED, Raman, FTIR, and XPS techniques were used. The results of the characterization proved the formation of near-spherical carbon NPs with graphite-like inner structure. The analysis of the photoluminescence (PL) properties highlighted an improvement of surface and optical NPs characteristics after the plasma and laser treatment. The surface chemistry induced by the plasma treatment was analyzed. It was suggested that the plasma induced non-equilibrium liquid chemistry results in nanocrystal surface modification and in the enhancement of photoluminescence properties of the synthesized nanoparticles. The second part of the work was focused on the characterization of the binary Gd5Si4 and ternary Gd5Si2Ge2 NPs prepared by electrical discharge treatment of the mixture of powders, suspended in ethanol. For determination of the optimal conditions for the binary and ternary compound nanoparticles formation, the characterization of inner structure, phase composition and morphology of nanoparticles prepared by means of HRTEM, SAED, XPS, Raman and FTIR techniques was performed. The characterization performed underlined the effectiveness of the plasma treatment for compound NPs preparation.




On the simulation of electrical discharges within cavitation bubbles in transformer oil

Aljure Rey Mauricio

Ph.D. Student

STSM period: from 02/04/2016 to 14/04/2016

Home institution: KTH - Royal Institute of Technology, Stockholm, Sweden

Host institution: Institute of Physics Belgrade, Belgrade, Serbia

 

The goal of this STSM was to initiate the development of numerical model which will be used to understand the first stages of electrical discharges in point-to-plane systems immersed in mineral oil. In most of the cases a bubble preludes the electrical discharge. Electrical discharges within the bubble have been considered in this STSM as a possible key mechanism for the channel expansion of the electrical discharge. Two methods have been proposed, including fluid models derived as velocity moments of the Boltzmann equation and Monte Carlo models. Due to the large background electric field and its spatial gradients, it has been found that fluid models are not generally adequate for electrical discharges within the hydrogen bubble and that much better option would be the use of the current Monte Carlo code of the host institution. The preliminary Monte Carlo simulations revealed the presence of highly energetic runaway electrons. In order to properly model the runaway electrons and development of an electrical discharge within the bubble under these conditions, the following new elements in Monte Carlo codes of the host institution must be introduced: (1) the full anisotropic representation of electron scattering; (2) due to large spatial gradients in the electric fields, the positions and the velocities of the electrons should be updated with the leap-frog method, and (3) due to the presence of runaway electrons, the appropriate technique for sampling their positions and velocities is required.

Geometry and electric field at the tip electrode




Generation and diagnostics of surface-wave-sustained plasma in contact with liquids

Marinova Plamena

Early-Stage Researcher

STSM period: from 28/03/2016 to 30/04/2016

Home institution: Sofia University, Sofia, Bulgaria

Host institution: Faculty of Chemistry, Brno University of Technology, Brno, Czech Republic

 

The main goal of this STSM was investigation of the effects of plasma-liquid interaction. The plasma source used in these investigations is surface-wave-sustained discharge operating at 2.45 GHz and atmospheric pressure produced by an electromagnetic wave launcher surfatron type in Argon. Experiments of plasma torch acting on water were performed and also measurements of the plasma parameters were carryed out under various discharge conditions, including different tube diameters, input power and gas flow. The discharge radii considered in the study are: 0.05 cm, 0.1 cm and 0.15 cm. During the STSM estimation of the changes in the characteristics concentration of hydrogen peroxide of plasma treated liquids has been performed as well as optical emission spectroscopy and ultra-fast camera observations. In presence of water the geometrical dimensions of the plasma have been measured and compared to these without the water at the same discharge conditions (wave power, gas flow and plasma radius). For the tube with diameter 3 mm for all the discharge configurations the plasma torch is longer especially at higher power when water surface is placed bellow.




Decontamination of E. coli by using mini gliding arc plasma reactor

Terebun Piotr

Early-Stage Researcher

STSM period: from 21/03/2016 to 08/04/2016

Home institution: Lublin University of Technology, Lublin, Poland

Host institution: Comenius University, Bratislava, Slovakia

 

The glide arc plasma reactors are generally known in practice as a source of non-equilibrium plasma. The aim of STSM was repeating and extending measurements with mini glide arc reactor performed during the previous internship in Bratislava. Conducted studies included determination of impact of non-thermal plasma generated in the reactor on the colonies of bacteria E. coli and concentrations of compounds that are formed in the water after treatment with plasma. The study confirms the effectiveness of the use of plasma in the decontamination of bacteria E. coli in liquid and formation of H2O2, NO2-, NO3- compounds in solution. The results indicate that important role is played by the composition of working gas flowing through the discharge chamber.

Gliding arc interacting with liquid surface.




Liquid phase polymerization on titanium by atmospheric pressure discharges

Buxadera-Palomero Judit

Early-Stage Researcher

STSM period: from 15/03/2016 to 30/04/2016

Home institution: Catalunyan University, Barcelona, Spain

Host institution: Leibniz Institute for Plasma Science and Technology, Greifswald, Germany

 

The research topic of the STSM was the generation of coatings with antifouling properties on titanium substrates by a direct plasma treatment of 2-hydroxyethyl methacrylate (HEMA) with an atmospheric pressure Ar plasma jet operated at 27.12 MHz. The influence of volume (5-10 μL), input power of the discharge (3-10 W), Ar gas flow (0.5-1 slm), treatment time (2-10min), and distance between the substrate and the jet (3-5mm) on pHEMA film compositions have been investigated by applying Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and contact angle measurements. Plasma polymerized HEMA coatings have been produced by the direct treatment of the liquid precursor with argon jet plasmas. The parameters of the plasma treatment have been varied in order to obtain stable coatings with a high retention of the monomer structure which was confirmed by XPS and FTIR studies. Future studies will be focused on in vitro cell tests to analyze the antifouling properties of the produced pHEMA films.

A) Elemental composition of pHEMA as deposited and after 5 min ultrasonic treatment in deionized water. High resolution C1s XPS spectra of pHEMA B) as prepared and C) after USB.




LIF (TALIF) of atmospheric pressure plasma jet

Selakovic Nenad

Early-Stage Researcher

STSM period: from 07/03/2016 to 25/03/2016

Home institution: Institute of Physics Belgrade, Belgrade, Serbia

Host institution: Faculty of Science, Masaryk University, Brno, Czech Republic

 

In collaboration with colleagues from Masaryk University (Brno) we have performed the set of laser induced fluorescence measurements of atmospheric pressure plasma jet (APPJ) in order to obtain concentrations of OH and NO radicals generated in plasma. Knowing the amount of mentioned species, and their reduction or increase by varying the parameters, gives us a great advantage in the possible biomedical application of this plasma source which was the main goal of this STSM. The measurements were performed for different setups of plasma source (with and without contact of plasma plume with conductive water) and variation of parameters (varying humidity, power delivered to the plasma and the distance from the plasma body to the liquid surface).

OH concentration (left) and lifetime of laser excited OH (right) for 6 μs delay time, 2.7 W of plasma power, 4 slm flow of helium, 232 ppm of humidity. Plasma jet in contact with water 25 mm from the edge of the glass tube to the water surface.




Dielectric barier discharge plasma jet for surface decontamination

Kwiatkowski Michal

Early-Stage Researcher

STSM period: from 29/02/2016 to 11/03/2016

Home institution: Lublin University of Technology,Lublin, Poland

Host institution: Comenius University, Bratislava, Slovakia

 

The aim of cooperation during the internship was the opportunity to explore the influence of non-thermal plasma generated in a jet type reactor with dielectric barrier discharge to the colony of bacteria E. coli placed on a dry PTFE surface and in aqueous solution. Subsequent measurements related to the impact of non-thermal plasma to buffer solution of water (Na2PO4), the resulting chemical compounds (H2O2, NO2-) by reacting the surface of the liquid were performed.

The reduction of bacteria in an aqueous solution, 5 min treatment time of Na2PO4 solution




Comparison of advanced plasma sources for fungal decontamination in liquid media

Walsh James

Early-Stage Researcher

STSM period: from 24/02/2016 to 09/03/2016

Home institution: University of Liverpool, Liverpool, United Kingdom

Host institution: Jozef Stefan Institute, Ljubljana, Slovenia

 

The SSTM has been a complete success; while some of the planned objectives were not met due to technical challenges a great deal of high-quality data was obtained which can be used for a joint publication. This publication is currently under preparation and will be submitted shortly. The nanosecond pulsed power source developed for this project was employed in an exciting new application area which holds great promise for future collaborative activities. Discussions are currently underway to organise another research visit to IJS in the coming months to further explore this area. Overall, the activities undertaken have produced some nice data but more importantly they have helped cement a lasting collaborative activity between researchers at the University of Liverpool and those at the IJS.




Chemical and biological study of the effects of a plasma jet on bacterial cell membrane integrity

Breton Marie

Early-Stage Researcher

STSM period: from 22/02/2016 to 03/06/2016

Home institution: CNRS, Villejuif, France

Host institution: Institute of Plasma Physics CAS, Prague, Czech Republic

 

The purpose of this STSM was to study the interactions of the plasma-produced reactive species with biological matter in liquid with emphasis on the mechanism by which the plasma affects the bacterial cell membrane integrity. In this work we have assessed plasma-induced chemical modifications of DOPC lipid (1,2-dioleoyl-sn-glycero-3-phosphocholine) in vesicles as a model of bacterial membrane. A non-thermal atmospheric pressure plasma jet (kINPen, INP Greifswald, Germany) was used as a plasma source generated in contact with liquid. First, the effects of plasma treatments on various aqueous buffers were characterized in terms of pH change, volume decrease and peroxide and nitrate concentration. Then, aqueous suspensions of giant unilamellar vesicles (GUV) prepared from DOPC were used to detect chemical changes of membrane phospholipids by plasma treatment. GUVs were treated by argon APPJ in a reaction vessel under a controlled atmosphere of dry air, nitrogen or oxygen. After APPJ treatment, phospholipids were extracted and a transmethylation reaction was carried out to allow gas chromatography-mass spectrometry (GC-MS) analyses. The transmethylation reaction had to be investigated since some of the literature-based protocols proved to be damaging for phospholipid molecules. No chemical modifications appeared after plasma treatment of this lipid, which has a low sensitivity to oxidation and nitration. Further inquiries are being conducted with the DLPC lipid, which is more sensitive to oxidation and nitration. Finally, bacterial suspensions of E. coli were also treated by argon APPJ in a reaction vessel under a controlled atmosphere of dry air, or oxygen, and the isolated lipids were analyzed to investigate variations in proportions of various types of phospholipids. The plasma treatment clearly affected the lipids proportions in two ways. First, the proportion of short chain lipids dramatically decreased. Second, the proportion of lipids presenting a high number of carbon double bonds also decreased. These results demonstrate that plasma treatments of bacteria induce a major modification of the composition of the bacterial membrane, which would represent an explanation of the bacterial permeabilization induced by plasma treatment.




Antibacterial tretment of PTFE tubes

Galmiz Olexander

Early-Stage Researcher

STSM period: from 18/01/2016 to 18/02/2016

Home institution: Faculty of Science, Masaryk University, Brno, Czech Republic

Host institution: Comenius University, Bratislava, Slovakia

 

By using water solution as a discharge electrode it is possible to combine basic features of both water discharges and SDBD (Surface Dielectric Barrier Discharge). The benefit of such combination lies in obtaining highly oxidative plasma without problems of electrode erosion. This study investigates the plasma treatment of polyvinyl chloride (PVC) and polytetrafluoroethylene (PTFE) tubes as a possibility to alter properties of Pseudomonas aeruginosa cell biofilms formatted on the inner surface of tubes. In the first step we observed the ability of plasma treatment to eradicate formed biofilms and inactivate the formed biofilm cells. In the next step we supposed, that plasma treatment of tubes changes the tubes surface properties and causes differences of intensity of formed biofilms during static and dynamic conditions.




Time resolved diagnostics on PEO discharges

Nomine Alexandre

Early-Stage Researcher

STSM period: from 14/11/2015 to 29/11/2015

Home institution: The Open University, Milton Keynes, United Kingdom

Host institution: Institut Jean Lamour - CNRS - Universite de Lorraine, Nancy, France

 

The new set-up for single PEO discharge consists in using a high voltage power supply (up to 30 kV) combined with a nanosecond rise time switch that allows the control of the shape and duration of the pulse. The cathode is an Aluminium wire while the sample is an Aluminium wire separated from a larger sample by resin (see figure). One of the first noticeable result is that within the new set-up the breakdown voltage is relatively high (above 1 kV) as compared to the apparition voltage in conventional PEO (400 - 800 V). This could be explained by the fact that charge accumulation will be affected by the small size of the sample. Indeed in a large sample, breakdown do not occur simultaneously all over the sample, the place where breakdown (resp. do not) occur are likely (resp. low) high voltage. If one averages over the total sample surface, the operating voltage is likely to be lower than the real breakdown voltage of a discharge. It is also worth noting that the breakdown voltage increases with the coating thickness. The perspective of this work is to obtain the breakdown voltage depending on different process parameters (substrate nature, coating thickness, electrolyte conductivity, composition and pH) which should provide important information about the breakdown mechanism.

Photograph of the experimental set-up.




Characterisation of single PEO discharge

Nomine Anna

Early-Stage Researcher

STSM period: from 14/11/2015 to 29/11/2015

Home institution: The Open University, Milton Keynes, United Kingdom

Host institution: Institut Jean Lamour - CNRS - Universite de Lorraine, Nancy, France

 

Plasma Electrolytic Oxidation (PEO) encounters an increasing interest in many fields of industry as it makes it possible to grow thick oxide coatings on light alloys (Al, Ti, Mg). Among many advantages, PEO is eco-friendly, single step and rapid process. However, the high energy consumption remains problematic in sight of a future large scale production. Recent work undertaken during Gerard Henrion's STSM in University of Cambridge have allowed the establishment of an preliminary audit of the energy dissipation in a single PEO discharge and it has been shown that a large part of the energy injected in a discharge is dissipated in water vaporisation and only a few in percent in plasma ignition, sustaining and coating phase transition. Hence it justifies the study of single PEO discharges in order to be able to optimise the energy consumption. During this STSM, it has been made possible to isolate a single PEO micro-discharge (see figure). However the time-resolved plasma diagnostics on these discharges has not been made possible due to high level of noise induced by the power supply and the low level of light emission of a single discharge. It has been then decided to develop a new set-up for time resolved diagnostics on PEO discharges.

Photograph of (a) micro-discharges on large sample and (b) of a single discharge on a 300 μm diameter wire sample.




Single step solubilization of carbon nanotubes in water by plasma liquid discharge

Harinarayanan Puliyalil

Early-Stage Researcher

STSM period: from 12/11/2015 to 20/12/2015

Home institution: Jozef Stefan Institute, Ljubljana, Slovenia

Host institution: Institute of Physics Belgrade, Belgrade, Serbia

 

Large scale production of carbon nanotube (CNT) dispersion in various liquids is essential for fabricating suitable nanocomposites for many important applications. The major challenge in creating such stable dispersion in water is the fast agglomeration of CNTs due to high extend of secondary interactions. Conventional methods includes various pre-treatments and further addition of suitable surfactants in to the liquid phase. However, this has the disadvantages of impurities in the final composite materials. Thus to avoid such disadvantages, here we presented an atmospheric pressure He plasma treatment at the liquid-gas interphase to improve the dispersion of CNTs in water. From the plasma treated dispersion, entangled CNT network was constructed. The effects of plasma treatment on the stability of the dispersion was monitored by UV-Vis spectroscopy. Further, various spectroscopic studies including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) were carried out.




Post-discharge kinetics of peroxynitrites produced in liquids treated by gas phase plasma discharges

Romolo Laurita

Early-Stage Researcher

STSM period: from 15/11/2015 to 21/11/2015

Home institution: University of Bologna, Department of Industrial Engineering, Bologna, Italy

Host institution: Institute of Plasma Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic

 

The aim of this short term scientific mission was to investigate post-discharge kinetics of peroxynitrite formation in aqueous liquid treated by atmospheric pressure dielectric barrier discharge (DBD) driven by nanosecond pulses. This plasma source has been developed by the group for Industrial Application of Plasma at Alma Mater Studiorum - Università di Bologna and was already investigated during a previous STSM performed in hosting laboratory at the Institute of Plasma Physics CAS. It is a DBD air plasma reactor, with aluminum electrodes and 1 mm thick layers of borosilicate glass as dielectrics, which was used to produce plasma activated water (PAW). This STSM was continuation on the previous work focused on the kinetics of NO2- and H2O2 decay in plasma activated water. Evolution of nitrites and nitrates concentrations in PAW after treatment by plasma have been measured by means of an ion chromatography, while H2O2 concentration using the titanium sulfate method. From the kinetics of NO2- and H2O2 decay the rates of ONOOH formation in PAW were determined for various acidic pH values. The rate of ONOOH formation increased with [H+] and was more than 4 times higher by lowering the pH of the solution from 2.9 to 2.3. These findings contribute significantly to the understanding of the chemistry of peroxynitrite formation in air plasma - treated water, i.e. dominant pathway ONOOH formation is through the post-discharge reaction between H2O2 and HNO2.

Schematic and picture of DBD reactor used for investigation of post-discharge kinetics of peroxynitrite formation in aqueous liquid after treatment by air plasma.




Synthesis, plasma modification, and characterization of nanomaterials for water purification

Sasa Lazovic

Early-Stage Researcher

STSM period: from 19/10/2015 to 08/11/2015

Home institution: Institute od Physics, Belgrade, Serbia

Host institution: Jozef Stefan Institute, Ljubljana, Slovenia

 

The main objective of this STSM was to investigate simple and cost effective method for synthesis of TiO2 nano tubes which can be used for photocatalytic applications. Furthermore, N2 plasma was used to shift the activation of the TiO2 NT from UV to visible. The aim of this work was to optimize material synthesis and doping processes in order to identify best candidates for photocatalytic removal of organic pollutants from water by tuning material optical properties. XRD, XPS, and Raman measurements were used for detailed sample characterization.

Raman spectra of N2-plasma doped TiO2 samples. Enlarged view of the Eg mode at ~144 cm-1 is shown in the inset.




Spectroscopic measurements of electric field in a He plasma jet

Ana Sobota

Early-Stage Researcher

STSM period: from 08/10/2015 to 18/10/2015

Home institution: Eindhoven University of Technology, The Netherlands

Host institution: University of Belgrade, Faculty of Physics, Serbia

 

The focus of research of the applicant is the electric field and the charge in plasma bullets and their dependence on the substrates, dielectric and polar liquid. This STSM was a part of a polydiagnostic study she is currently undertaking on this subject. The group of Prof. Bratislav Obradovic at the host institution has a tradition in electric field determination by optical emission spectroscopy on helium transitions by observing the Stark-induced splitting of the spectral lines and observing the relative behaviour of the forbidden and the allowed counterparts. The measurements performed in Beograd have resulted in numerous high-quality measurements of the electric field of the jet in free expansion as well as its interaction with dielectric and liquid substrates and as such is a valuable addition to the efforts already done in Eindhoven. The electric fields that were measured were in the range from 5 to 30 kV/cm. We have shown that the presence of a dielectric target significantly influences (increases) the electric field, while the liquid targets have shown that the conductivity of the liquid in the range from 15 μS/cm to 13.9 mS/cm does not show a significant influence. The analysis is still ongoing, however it is already clear that the results are of high quality and a high degree of novelty.




Spectroscopic investigation of the underwater diaphragm discharge

Nikola Cvetanovic

Early-Stage Researcher

STSM period: from 16/09/2015 to 30/09/2015

Home institution: University of Belgrade, Faculty of Physics, Belgrade, Serbia

Host institution: Brno University of Technology, Faculty of Chemistry, Brno, Czech Republic

 

The STSM was dedicated to the investigation of diaphragm underwater discharge. This discharge was designed and made at the Faculty of Sciences, Masaryk University, Brno preferably for application of textile plasma H2O treatment. Spectroscopic investigations were performed by focusing radiation from different axial positions to the optical fiber connected to the high resolution spectrometer. Gas temperature was estimated by measuring rotational temperature from the N2 second positive system. The broadened Balmer alpha line was used for electron density measurements. The fitting procedure of time unresolved profiles included all the possible broadening mechanisms. The analysis of the line profiles indicates that the breakdown occurs within an air microbubble. In addition to the underwater diaphragm discharge, during the STSM the surface barrier discharge with liquid electrodes was also spectroscopically examined for varying input powers from 20 W to 60 W. Time integrated spectroscopy was accompanied with electrical measurements. This discharge operated in atmospheric pressure argon as a working gas and with oxalic acid solution as a liquid electrode. The investigations made during the STSM show interesting results with a potential for publishing and for further collaboration.




Plasma jet discharge in contact with water solutions and chemical and biological analysis of water solutions

Kwiatkowski Michal

Early-Stage Researcher

STSM period: from 11/05/2015 to 25/05/2015

Home institution: Lublin University of Technology,Lublin, Poland

Host institution: Comenius University, Bratislava, Slovakia

 

The aim of cooperation during the internship was to perform studies on the impact of non-thermal plasma generated in the plasma jet type reactor with barrier discharge on the properties of water and on the colonies of bacteria E. coli . Bacteria E. coli was placed in deionized water (DI), DI + Na2PO4/KH2PO4, and DI + Na2PO4. The measurements were repeated for verification of the results. In addition measurements of water conductivity and pH were performed. The second part of the measurements was to study compounds that are formed in the water after treatment with a plasma (O3, NO3-, H2O2, NO2-).




Characterization of an Ar plasma jet and its interaction with liquids

Jakob Jogi

Early-Stage Researcher

STSM period: from 14/04/2015 to 25/04/2015

Home institution: Institute of Physics, University of Tartu, Estonia

Host institution: Comenius University, Bratislava, Slovakia

 

The goal of the STSM was the characterization of an atmospheric pressure argon plasma jet and subsequent investigation of the treatment of amino acids by the plasma jet. The argon plasma jet was ignited in a hollow needle-to-cylinder electrode configuration with a high-voltage power supply (kHz frequencies). The discharge was created in a quartz capillary (0.5 mm inner diameter) and the formed plasma jet was flowing into the ambient air. First part of the studies was devoted on the characterization of the specific atmospheric pressure argon plasma jet. The optical emission of the plasma jet along the axis of argon flow was used to obtain the distribution of relative density of excited argon states and reactive species of N2 and OH along the tube axis. The electrical characterization was carried out by registering the applied voltage and current. Longest jet was obtained at 40 sccm flow rate while at higher flow rates the flow became turbulent. The contact of plasma jet with liquid increased the intensity of optical emission near the liquid surface. Plasma treatment of phenyl-alanine solution in water resulted in decreased phenyl-alanine concentration and there appeared new species according to UV-VIS absorption and capillary electrophoresis.




High-speed video imaging of Plasma Electrolytic Oxidation (PEO) discharges

Gerard Henrion

Professor

STSM period: from 18/04/2015 to 24/04/2015

Home institution: University of Cambridge, Cambridge, United Kingdom

Host institution: Engineering Research Institute, University of Ulster, Newtownabbey, United Kingdom

 

Objective of the STSM was to get high speed video imaging of single discharges alongside synchronized time resolved measurements of current and voltage to help understand the sequence of events that occur during the plasma electrolytic oxidation (PEO) process. Dedicated small area samples allowing single discharges ignition developed at University of Cambridge (UK) were used together with high speed video camera provided by the group from Institute Jean Lamour in Nancy (France). Video pictures have been recorded with an acquisition rate of 125 000 frames per second and spatial resolution of 9 μm. Correlations have been established between discharge current, light emission from the discharge and behaviour of the bubble. It has been particularly shown that bubble growth occurs after the discharge emerges from the discharge channel. Then the gas bubble expands with a growth peak velocity about 10 m/s until it reaches a maximum size (typ. 500 μm in diameter). The increase in electrical resistance as the bubble grows is likely responsible of the current cut off, which makes the bubble shrink. A semi-quantitative energetic audit has been carried out. It has been concluded that most of the injected energy is absorbed in the form of vaporisation of water, which is believed to be responsible of the bubble growth, although its temperature and pressure remain relatively low.




Non-equilibrium plasma induced liquid chemistry for synthesis of advanced nanocomposites

Anna Liguori

PhD Student

STSM period: from 11/04/2015 to 01/05/2015

Home institution: Department of Industrial Engineering, Alma Mater Studiorum-Universita di Bologna, Bologna, Italy

Host institution: Engineering Research Institute, University of Ulster, Newtownabbey, United Kingdom

 

The aim of the STSM was to contribute to the on-going research on the synthesis and surface engineering of advanced nanoparticles (NPs) that can be used for optoelectronic components (e.g. as a down-conversion layer for photovoltaic devices). The first part of the work was focused on the plasma surface engineering of pre-synthesized silicon NPs in ethanol in order to tailor their surface and optical properties. Preliminary characterization performed by means of photoluminescence (PL) measurements highlighted an improvement of surface and optical NPs characteristics. The second part of the work was aimed at inducing the synthesis of copper and cuprous nanoparticles by using a copper road as counter-electrode of the DC plasma system and generating plasma on the surface of a specific solution. The characterization carried out by means of PL, UV-VIS and FTIR measurements underlined the effectiveness of the plasma system in NPs synthesis.

6 ml electrolyte solution (a), 4.5 ml electrolyte solution + 1.5 ml ethylene glycol (b), 3 ml electrolyte solution + 3 ml ethylene glycol (c), 1.5 ml electrolyte solution + 4.5 ml ethylen glycol (d) after plasma exposure and subsequent centrifugation and washing of the synthesized sediments.




Corona discharges in liquids

Robert Banaschik

Early-Stage Researcher

STSM period: from 08/04/2015 to 21/04/2015

Home institution: Leibniz Institute for Plasma Science and Technology, Greifswald, Germany

Host institution: Institute of Plasma Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic

 

At the INP Greifswald we have developed an underwater pulsed corona discharge plasma system, consisting of a wire-cylinder geometry that is operated with high voltage pulses of sub-microsecond duration. During this STSM we focused on the plasma-chemical degradation of phenol, comparing three different ground electrode materials (stainless steel, brass and titanium). Phenol degradation was resulting in specific degradation products. In particular catalytic effects from ions released from the ground electrode were contributing to the degradation. According to our experiments, titanium electrodes have the smallest effect for phenol degradation, whereas steel electrodes strongly affect decomposition efficiency. In conclusion, this would mean that after normalizing degradation efficiencies with respect to the degradation observed for titanium electrodes (i.e. set to 100%), steel electrodes are increasing decomposition efficiency by 74% and brass electrodes by 37%, respectively. Hydrogen peroxide production couldn't be correlated with degradation efficiencies that were observed for different electrode materials. Catalytic effects, reactor materials and maybe reactor design are not reflected in the formation of H2O2.




Measurement of peroxynitrites in water solutions activated by air transient spark discharge

Barbora Tarabova

PhD Student

STSM period: from 03/11/2014 to 22/11/2014

Home institution: Comenius University, Faculty of Mathematics, Physics and Informatics, Bratislava, Slovakia

Host institution: Leibnitz Institute for Plasma Science and Technology, ZIK plasmatis, Greifswald, Germany

 

Peroxynitrites are postulated to be the key antimicrobial agent in plasma activated water, but their detection is generally difficult. During this STSM the selectivity of the fuorescent dye 2',7'-dichlorodihydrofluorescein diacetate (H2DCFDA) was investigated with the respect to peroxynitrites detection in plasma activated water (PAW) by air transient spark by using scavengers of reactive oxygen and nitrogen species (RONS) and dyes selective for other RONS. The aim of the study was to distinguish the part of the fluorescence signal that is due to the peroxynitrites presence in PAW. Due to the fact that air plasmas generate a great number of various RONS in plasma treated liquids, we tested the possible cross-reactivities of RONS with the H2DCFDA dye. Except the OCl- ions, the fluorescent response of species like H2O2, NOx or O2.- was not significant. Despite this fact, even the low concentration of ONOO- created higher fluorescence signal than the same concentrations of OCl-. The efficiency of used scavengers (taurine, hypotaurine, ebselen, catalase, azide) was tested on different plasma activated solutions and on different RONS. We demonstrated that at least in plasma activated solution with no Cl- presented and therefore no OCl- anions created, the H2DCFDA signal is mostly due to the peroxynitrites.




Chemical analysis of the reactive species produced in water treated by plasma produced radicals or VUV photons

Mohamed Mokhtar Hefny

PhD Student

STSM period: from 02/03/2015 to 20/03/2015

Home institution: Faculty of Physics and Astronomy, University of Bochum, Germany

Host institution: Institute of Plasma Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic

 

The RF-driven microscale atmospheric pressure plasma jet (μ-APPJ) has been used for treating water, where the presence of reactive species in it after treatment has been analyzed using ion and liquid chromatography, spectrophotometric methods and pH measurements. The used μ-APPJ is a remote cold plasma was implemented into a small glass reactor with 6 ml volume, where 3 ml of liquid can be treated with plasma with jet nozzle at 4 mm distance to liquid surface. Treatments have been performed with plasma containing only He, He with 0.6% O2, and He with 0.25% N2, where all these mixtures have been applied with water vapor (~864 ppm) and without water vapor. During the STSM we focused on the study of aqueous-phase chemistry of reactive oxygen species (ROS) and reactive nitrogen species (RNS) generated by plasma jet in the treated water. We made a lot of studies of OH, H2O2, NO2-, NO2- synthesize in the treated water, we also studied the reaction pathways of phenol degradation induced by our plasma in deionized water and we used phenol as a chemical probe. Additionally, the change of the pH has been monitored as well.




Influx mechanisms of plasma-generated RONS into model membranes

Simon Maheux

PhD Student

STSM period: from 26/01/2015 to 31/03/2015

Home institution: Luxembourg Institute of Science and Technology (LIST), Belvaux, Luxembourg

Host institution: Leibniz Institute for Plasma Science and Technology, Greifswald, Germany

 

In order to better understand complex inactivation mechanisms occurring in plasma-treated bacteria, simplification of the interacting systems (plasma, physiological liquid and bacteria) is desirable. Therefore, the use of liposomes encapsulating a RONS-sensitive fluorescent probe may be a valid bacterial model plasmic membrane. This STSM was focused on the study degradation mechanisms occurring in pH-buffered DOPC-based liposome suspensions treated by two different sources of cold atmospheric plasma (CAP): a He/N2 CAP in N2 controlled atmosphere and an Ar CAP in air. Although a lack of control over the size of the liposomes synthesized prevented to assess accurately the effect of plasma treatment on their size distribution, zeta potential measurements showed that none of these plasma treatments do not induce any significant change in the hydration layer surrounding the liposomes. Aggregation, favoured between liposomes with low zeta potential, might explain the issues encountered. On the other hand, fluorescein buffered solutions exposed to the same plasma treatments displayed a different outcome. Whereas Ar CAP in air only induced an UV-triggered bleaching of the fluorescent dye, fluorescein solution treated by He/N2 CAP in N2 atmosphere turned orange over time. Fluorescence and absorption spectra of the dye were altered accordingly.




Electrospraying effect of water in combination with DC corona discharge

Branislav Pongrac

Early-Stage Researcher

STSM period: from 12/01/2015 to 03/04/2015

Home institution: Comenius University, Faculty of Mathematics, Physics and Informatics, Bratislava, Slovakia

Host institution: Brno University of Technology, Faculty of Chemistry, Brno, Czech Republic

 

The effect of the electrospraying of various water solutions in combination with a direct current (DC) corona discharge generated in atmospheric air or SF6 background gas was investigated. In particular, we tried to verify the hypothesis; if the shape of the water filament created from the HV anode or HV cathode looks different as a result of the movement of positive and negative ions of different mobility dissociated in the water, or rather as a result of the atmospheric corona space charge which can locally reduce the external electric field. We employed high-speed camera and conventional digital camera visualizations, and oscilloscopic discharge current measurements. We observed mainly intermittent electrospraying modes where process of filament formation and droplet formation from the mass fragments of water was repetitive. In some cases also continuous electrospraying modes were observed where the filament was constantly connected with the nozzle electrode. In the atmospheric air, the corona discharge was always present during the electrospraying. When the SF6 background gas was present, the generation of corona discharge was significantly suppressed. The results clearly show that the effect of ion mobility is negligible, and rather the effect of corona space charge is dominant.




Comparison of liquid and gas phase plasma reactors for decolorization of reactive azo dyes

Bratislav Obradovic

Professor

STSM period: from 21/11/2014 to 07/12/2014

Home institution: University of Belgrade, Faculty of Physics, Belgrade, Serbia

Host institution: Brno University of Technology, Faculty of Chemistry, Brno, Czech Republic

 

The first part of STSM was dedicated to comparison of liquid and gas phase plasma reactors for decolorization of Reactive Azo Dyes. The DC diaphragm discharge is compared with water falling film DBD according to degradation efficiency and different dye’s degradation products. To the purpose of comparing the two plasma sources, the same azo-dyes (Direct Red 79 and Reactive Yellow 125) have been treated and used the same diagnostics methods for monitoring of degradation products. The HPLC-MS analyzes of the discharges products were carried out as well as reaction mechanisms leading to their formation under plasma conditions. The second part of STSM was focused on the optical diagnostics of newly developed plasma jet generated directly in liquid. Based on overview spectra, the selected parts were measured in detail with respect to estimate plasma parameters in dependence on solution conductivity. Figure below shows LC/MS ESI (+) chromatograms of untreated, DBD and DD treated samples of 300 ppm Reactive Yellow 125 solutions.


 

Chemical and bactericidal effects induced in water solutions by transient spark discharge treatment

Barbora Tarabova

PhD Student

STSM period: from 03/11/2014 to 22/11/2014

Home institution: Comenius University, Faculty of Mathematics, Physics and Informatics, Bratislava, Slovakia

Host institution: Institute of Plasma Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic

 

The STSM was focused on detection of nitrites and nitrates created in the plasma activated water, the study of the chemistry pathways of reactive species induced in liquid phase by air plasma by phenol as the chemical probe and the plasma effects on Escherichia coli. The comparison of the measured nitrites concentration by Griess reagents (colorimetric method) and by the high precision ion chromatography (IC) showed no significant difference in the nitrite concentration. We attempted to increase the detection limit of Griess assay by addition of the catalase to decompose hydrogen peroxide thus avoid its potential effect on the nitrite detection. The results showed no significant difference between the samples with or without added catalase (see figure). We detected the product of phenol degradation – hydroxylated degradation products, nitrated by-products, but no muconic acid as a specific product of the reaction of ozone and phenol. The fluorescence-based staining showed no membrane damage of treated bacteria. Bacteria in buffered solution were able to recovery after plasma treatment unlike the bacteria in acidic environment. The results showed that the discharge did not break the cells integrity but their inactivation is caused by the acidic environment and the presence of RONS which started the intracellular processes leading to DNA damage and loss of the metabolic activity.


 

Chemical analysis of the reactive species produced in water by liquid and gas phase plasma discharge

Romolo Laurita

PhD Student

STSM period: from 02/11/2014 to 22/11/2014

Home institution: University of Bologna, Department of Industrial Engineering, Bologna, Italy

Host institution: Institute of Plasma Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic

 

The purpose of this STSM was the investigation of the reactive species produced in water by air plasma generated by dielectric barrier discharge (DBD) driven by nanosecond pulses. Three different liquids have been used (deionized water, DIW, phosphate buffer solution, PB, and deionized water with phosphate electrolyte) in order to investigate the effect of pH and conductivity on the production of reactive species by DBD in plasma activated water (PAW). Nitrites and nitrates concentrations in PAW have been measured by means of an ion chromatography, while H2O2 concentration using the titanium sulfate method. Reactive species concentrations have been also measured using analytic strips. It was determined that pH and electrolytic conductivity had great effect on the chemistry induced by air DBD plasma in water. Already one minute treatment of DIW and electrolyte solution induced a significant reduction of the pH (lower than 4) and post-discharge decomposition of peroxides and nitrites formed in plasma treated water by DBD. This effect greatly accelerated with longer DBD exposures of PAW. If DIW was treated for 10 minutes, pH of PAW decreased to 2.4 and almost all the produced nitrites vanished from PAW within 6 minutes of post-discharge time via peroxynitrite reaction mechanism with H2O2 (see figure). This was accompanied with higher degradation of phenol and formation of hydroxylated and nitrated products of phenol.


 

Oxidation of organic pollutants by electrical discharges

Joana Madureira

Early-Stage Researcher

STSM period: from 06/10/2014 to 31/10/2014

Home institution: Instituto Superior Tecnico, Loures, Portugal

Host institution: University of Padova, Padova, Italy

 

Clofibric acid (CFA) is the active metabolite of the lipid regulator clofibrate used to decrease the level of cholesterol and triglycerides. This drug appears in wastewater effluents because of its high persistence and the inability of conventional treatments to degrade it. In this work we have studied the degradation of CFA in liquid samples, through advanced oxidation processes (AOP), using either ionizing radiation from a 60Co source (IST, Lisbon, Portugal) or a DBD discharge in contact with water (University of Padova, Italy). The results of both technologies are compared in terms of effectiveness for CFA degradation and the products formed. The results show that in both technologies CFA degradation follows an exponential decay with time and depends on the initial concentration of the compound, being faster for lower concentrations. The main degradation by-products, analyzed by LC-MS, are different for the two technologies, indicating that probably the reactive species formed during the processes and the degradation paths are different. The degradation rate was found to be higher for gamma radiation. Among other reasons, this is probably due to the higher penetration of gamma rays in the solution thus increasing the effective volume under treatment. The treatment by a lower penetrating ionizing radiation, e-beam, is envisaged as further work.


 

Study of reaction chemistry by plasma-liquid interactions

Jenish Patel

Early-Stage Researcher

STSM period: from 16/06/2014 to 13/07/2014

Home institution: University of Ulster, Newtonabbey, United Kingdom

Host institution: Case Western Reserve University, Department of Chemical Engineering, Cleveland, USA

 

The role of reductants in the synthesis of various chemical compounds (i.e. gold nanoparticles, silver nanoparticles, hydrogen peroxide) is critical to understand the reaction chemistry occurring at interface and/or inside the liquid. Different concentrations of propanol (up to 33%) were added to gold and silver precursor solutions with 1% polyvinyl alcohol before plasma treatment to study the behaviour of characteristic absorption peaks of the nanoparticles. The addition of propanol causes the reduction in the characteristic absorbance of the nanoparticles; the absorbance reduces to about 40% and 21% for silver (see figure) and gold nanoparticles respectively when the amount of propanol added is increased up to 33%. These results strongly suggest that the OH radicals scavenged by the propanol affects the reduction mechanism of the silver atoms. The reduction mechanism of gold nanoparticles is associated with hydrogen peroxide which was found to be present in the plasma processed deionized water in our set-up.


 

Electrical discharges with liquids for future applications

Branislav Radjenovic

Researcher

STSM period: from 18/05/2014 to 31/05/2014

Home institution: Institute of Physics, Belgrade, Serbia

Host institution: Comenius University, Bratislava, Slovakia

 

Although the physics for breakdown initiation in gases in generally well understood, the process of breakdown initiation in liquids is much less clear. A large number of experimental data on the breakdown in water revealed that the breakdown voltage in water is of the same magnitude as in the case of gases. This means that the breakdown in liquids may occur not at the extremely high electric fields required by the Paschen curve. Considering that the atmospheric pressure sources operate in ambient air which unavoidably contains water vapor it is of great importance to investigate the basic processes and properties of discharges in water vapor. In this STSM we performed experimental and theoretical studies on electrical breakdown characteristics in water vapor in microgaps between two parallel electrodes. Measurements were carried out for the pressures of 24.15 torr, 20.85 torr and 14.55 torr with the gap size ranging from 40 μm to 900 μm. In figure below we show the volt-ampere characteristics recorded in water vapor microdischarges.


 

Interaction of plasma with biological liquids

Agata Giardina

PhD Student

STSM period: from 04/05/2014 to 24/05/2014

Home institution: University of Padova, Padova, Italy

Host institution: Centre for Innovation Competence (ZIK) plasmatis, Greifswald, Germany

 

The field of research of this short term scientific mission has dealt with the interaction of plasmas with biologically relevant systems (biophysical models, bioharming materials,…). Specifically, assays were performed to study possible interactions of different liposomes with a reactive environment, a subphase previously treated with cold plasma. Two plasma sources were compared: plasma jet and transient discharge. This type of treatment allows long lived plasma generated species or metastable species produced in reactions of the plasma with the liquid to interact with the cells (effects of electric fields, UV light, etc. are shunned). These reactive species are the main actors of plasma–cell interaction. The effect of interaction with cold plasma was evaluated through fluorescence imaging. Also an investigation of the time dependence was performed incubating cells with sample for 24 h before carrying out the measurements. The STMS allowed Agata to extend her experience to include plasma application in the biomedical field and established a first step towards a possible future research collaboration of the ZIK plasmatis at the INP Greifswald with the Chemistry Department at the University of Padova. Figure below shows GUV after 30 min kINPen treatment.


 

Corona discharges in liquids - Investigation of reaction mechanisms that are responsible for the degradation of pharmaceutical residues

Robert Banaschik

Early-Stage Researcher

STSM period: from 06/04/2014 to 18/04/2014

Home institution: Leibniz Institute for Plasma Science and Technology, Greifswald, Germany

Host institution: Institute of Plasma Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic

 

In our preliminary investigations at the INP Greifswald we have developed an underwater pulsed corona discharge plasma system, consisting of a wire-to cylinder geometry that is operated with high voltage pulses of sub microsecond duration. In this STSM we investigated basic plasma chemical processes which occur during and follow the discharges in water, especially focusing on the formation of hydroxyl radicals, hydrogen peroxide, ozone, and reactive nitrogen species. These processes were studied for the degradation of phenol, which was used as chemical model system for different reaction pathways of OH, O3 and RNS. The obtained data suggest that the attack of hydroxyl radicals was mainly responsible for the decomposition of phenol. Typical reaction products, such as benzoquinone (BQ), hydroxybenzoquinone (HBQ), catechol (CC), and hydroquinone (HQ), were identified (see figure). There was no evidence for chemical reactions involving ozone due to the absence of muconic acid, which is a typical product formed after benzene ring cleavage by ozone attack.


 

Degradation of amoxicillin under DBD plasma discharge

Tomasz Izdebski

Early-Stage Researcher

STSM period: from 28/03/2014 to 18/04/2014

Home institution: Szewalski Institute of Fluid-Flow Machinery, Center for Plasma and Laser Engineering, Gdansk, Poland

Host institution: University of Padova, Padova, Italy

 

The purpose of this STSM was to recognize a mechanisms of antibiotics destruction in relation to their chemical structure. The question is not about ability of electrical discharges to destruct pharmaceuticals in water because it is already proven by other researchers but it is necessary to know what parameters of the process are responsible for the destruction of pharmaceuticals. This research was focused on the diagnostics of the degradation products of amoxicillin treated with the DBD electrical discharge above water, investigation of the amoxicillin removal efficiency and determination of the degradation mechanism. The experiment was performed with two initial concentration values: 3×10-4 M and 1×10-5 M. Amoxicillin degradation rate constants for the two plasma discharge experiments were extrapolated from the plots shown in figure below. These plots were made using HPLC analysis of samples taken during the treatment. It is seen that there is a 100% degradation of amoxicillin after 120 min of discharge time, but we still have large amounts of degradation intermediates in the solution. On the other hand lower concentration of amoxicillin is degrading at much faster rate. This means that advanced oxidation processes are influenced by the initial concentration of the solution.


 

Study of the influence of Ar/He/O2 plasma on the removal of organic pollutants from the water

Sasa Lazovic

Early-Stage Researcher

STSM period: from 20/01/2014 to 19/02/2014

Home institution: Institute od Physics, Belgrade, Serbia

Host institution: Jozef Stefan Institute, Ljubljana, Slovenia

 

The main objective of this STSM was to investigate the interaction between the Ar/He/O2 plasma reactive species and water contaminated with the organic pollutants (such as dyes) and to confirm and verify our preliminary data that show that atmospheric pressure plasma can lead to degradation of organic pollutants. The results are comparable to the results from the literature of joint application of Degussa TiO2 and UV light. Plasma parameters such as gas flow rate and composition, power, etc. are optimized to provide abundant radical production and delivery to the liquids. Furthermore, photo-catalysts are used to support the generation of the radicals in the liquids and further improve the degradation effects. Special attention is dedicated to the synergetic effects of the radicals generated by the plasma and catalyst and to the optimization of pollutant decolorization/degradation rates. Figure shows decolorization of RO 16 by plasma, TiO2, and plasma + TiO2.


 

Plasma-assisted decomposition of micropollutants in water by DBD and diaphragm discharge

Patrick Vanraes

Early-Stage Researcher

STSM period: from 06/01/2014 to 07/02/2014

Home institution: Ghent University, Department of Applied Physics, Ghent, Belgium

Host institution: Brno University of Technology, Faculty of Chemistry, Brno, Czech Republic

 

The herbicide atrazine takes a prominent place amongst contaminants of emerging concern. It is hazardous in relatively small concentrations, to humans, animals and aquatic life. As modern wastewater treatment plants are not able to sufficiently remove or decompose it, more efficient and cheaper water treatment techniques need to be developed. Amongst various proposed advanced oxidation processes, plasma discharge in or in contact with water is a promising new technique for water treatment applications. We have investigated an AC-driven diaphragm discharge reactor in terms of performance of hydrogen peroxide production and atrazine decomposition. Energy yield for hydrogen peroxide generation is 2.89 g/kWh. From HPLC-MS analysis, energy yield of 0.024 mg/kWh for atrazine degradation is determined. Correspondingly, the reactor is interesting for hydrogen peroxide production, but has relatively low energy efficiency for atrazine degradation. Figure below shows HPLC-MS chromatogram of initial sample and samples from both reactor halves after 60 min of plasma treatment.


 

Plasma generation in water solutions of selected organic acids

Edita Vyhnankova

PhD Student

STSM period: from 04/11/2013 to 29/11/2013

Home institution: Brno University of Technology, Faculty of Chemistry, Brno, Czech Republic

Host institution: Leibniz Institute for Plasma Science and Technology, Greifswald, Germany

 

In this STSM a diaphragm discharge in solutions of five simple organic acids (formic, acetic, propionic, oxalic and malonic) in two concentrations was studied. The discharge was generated in a polycarbonate batch reactor divided into two electrode parts by a dielectric barrier with a pin-hole in its centre. Hydrogen peroxide concentration, pH changes and optical emission spectra (OES) were the focus of the work. The H2O2 measurements were conducted with specific titanium reagent using absorption spectroscopy, pH changes were followed on an automatic titration manager. Result show the slight increase in H2O2 concentration in presence of the acids in higher of the chosen initial concentrations (1.0 mmol/l, compared to 0.1 mmol/l or reference NaCl solution). pH progression also differs with initial value of the solution – in absence or low concentrated acid, the pH rises significantly in cathode part of the reactor, while this effect is supressed with lower initial pH. OES recorded as overview and detailed OH band did not reveal any substantial differences when acids were used in the solution.


 

Reduction of corrosion layers on various metals using underwater discharge

Lenka Hlochova

Early-Stage Researcher

STSM period: from 01/11/2013 to 30/11/2013

Home institution: Brno University of Technology, Faculty of Chemistry, Brno, Czech Republic

Host institution: Queens University Belfast, Belfast, United Kingdom

 

This STSM was focused on the plasma removal of corrosion layers on the different archaeological samples. These samples were made from glass and ceramics. A multi-electrode system was used for the treatment. The treatment was carrying out under different experimental conditions, including different distances from the discharge, different sodium chloride concentrations in the liquid. The optimal setup for cleaning of the archaeological artefacts was with 0.9% solution sodium chloride (conductivity about 13 mS/cm) at a distance of about 1 mm from the multi-electrode head. At this distance, the sample is in the bubble in which the plasma and hence reactive species were created. I also made optical emission spectroscopy measurements of the discharge with different powers and with and without the sample and with the sample at different distances from the head. After treatment the sample surfaces were analysed using a SEM/EDS. Figure below shows scheme of experimental setup: 1-spectrometer, 2-optical fibre, 3-power electrode, 4-liquid medium, 5-insulator, 6-grounded electrode, 7-treated sample.


 

Discharges generated by sub-ns pulses

Hans Hoeft

Early-Stage Researcher

STSM period: from 24/07/2013 to 02/11/2013

Home institution: Leibniz Institute for Plasma Science and Technology, Greifswald, Germany

Host institution: Eindhoven University of Technology, Eindhoven, Netherlands

 

For the generation of HV pulses for various applications pulse forming lines switched by a spark-gap were often used. The use of oil instead of gas under high pressure (i.e. N2 or SF6) in the spark-gap switch enables very high voltages across small gaps. Fast rising HV pulses are often used to generate discharges in liquids, i.e. for water purification. The purpose of this STSM was to combine the knowledge of electrical engineering and plasma physics to get insight in the plasma generated in pulsed spark and dielectric barrier discharges (DBDs) at atmospheric pressure in N2-O2 mixtures. Therefore fast gated iCCD camera images were recorded to analyse the influence of the sub-ns rise time on the discharge characteristics. Moreover the effect of O2 concentration and pulse repetition rate was examined. To sum up, it can be stated that the dielectric barrier suppresses the influence of the repetition rate due to the lack of high currents and consequently thermalisation of the plasma contrary to the spark discharge. Figure below shows reignitions during the pulse reflections for a pulse with (21 ± 1) kV amplitude and 10 Hz repetition rate in 0.1 and 10 vol% O2 in N2 (iCCD gate 25 ns for 0.1 and 10 ns for 10 vol% O2 in N2, respectively; due to increasing discharge jitter 100 ns for the eighth and tenth reflection for 10 vol% O2 in N2).


 

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