Tesis sobre el tema "Non thermal plasma (NTP)"

Le travail de cette thèse vise à étudier un procédé hybride pour le traitement de molécules organiques dans l’eau. Il s’agit du procédé Plasma Non Thermique (NTP) couplé à la catalyse hétérogène de type (Fenton-like). Le paracétamol est utilisé comme la molécule modèle pour cette étude. Deux configurations différentes de réacteur plasma de type Décharge à Barrière Diélectrique (DBD) ont été utilisées : (i) un réacteur multipointes-plan en mode statique ; (ii) un réacteur coaxial tubulaire avec écoulement de la solution à traiter. Afin d’évaluer la synergie entre les deux procédés (plasma et catalyse), les traitements ont été appliqués séparément puis couplés. Les effets synergiques du procédé couplé plasma-catalyse ont été démontré en termes de taux de dégradation, de rendement énergétique et également en termes de la minéralisation de polluant, correspondant à une diminution de la charge organique de la solution avec la conversion du carbone organique en carbone inorganique. La première partie du travail réalisée avec le réacteur multipointes-plan a permis d’établir le rôle efficace du couplage plasma-catalyse en comparaison avec le procédé de plasma seul. En effet, en couplage, une minéralisation de 54 % a été atteinte après traitement de 60 minutes et que le rendement énergétique est augmenté d’un facteur de deux, réduisant ainsi le coût du traitement. Les travaux réalisés sur le réacteur coaxial ont permis d’étudier l’effet de nombreux paramètres sur le couplage plasma-catalyse comme la composition du gaz injecté, du débit de gaz et de liquide, la position du catalyseur par rapport à la décharge plasma, etc. Nous avons ainsi pu montrer l’intérêt de travailler dans un gaz riche en oxygène sur les cinétiques de dégradation et de minéralisation ainsi que le rôle de la puissance électrique appliquée sur les mécanismes d’oxydation. Par exemple, il a été possible d’obtenir une minéralisation de 70 % après 90 min de traitement sous air alors que sous O₂/N₂ (80/20 sccm), la minéralisation atteignait 95 %. La stabilité du catalyseur a également été étudiée en termes de minéralisation après plusieurs réutilisations du catalyseur. Nous avons également démontré le rôle du radical hydroxyle (·OH) sur le traitement avec l’utilisation de piégeurs de radicaux. Effectivement, en présence du méthanol, consommateur des radicaux hydroxyles, une diminution de la dégradation de près de de 50 % a été obtenue et aucune minéralisation n’a été observée
The work of this PhD thesis aims at studying a hybrid process for the treatment of organic molecules in water. It consists of the Non Thermal Plasma (NTP) process coupled with heterogeneous catalysis (Fenton-like type). Paracetamol is used as the target molecule for this study. Two different configurations of Dielectric Barrier Discharge (DBD) plasma reactor were used: (i) a multi-needles-to-plane reactor in static mode; (ii) a coaxial tubular reactor with flow of the solution to be treated. In order to evaluate the synergy between the two processes (plasma and catalysis), the treatments were applied separately and then coupled. The synergistic effects of the coupled plasma-catalysis process were demonstrated in terms of degradation rate, energy yield, and also in terms of pollutant mineralization, corresponding to a decrease of the organic molecules load in the solution with the conversion of organic carbon into inorganic carbon. The first part of the work carried out with the multi-needles-to-plane reactor allowed to establish the effective role of the plasma-catalysis coupling in comparison with the plasma process alone. Indeed, in coupling, a mineralization of 54% was reached after the 60 minutes of treatment and the energy yield was increased by a factor of two, thus reducing the cost of treatment. The work carried out on the coaxial reactor allowed us to study the effect of many parameters on plasma-catalysis coupling efficiency such as the composition of the injected gas, the gas and liquid flow rate, the position of the catalyst in relation to the plasma discharge, etc. We were thus able to show the interest of working in an oxygen-rich gas on kinetics of degradation and mineralization as well as the role of applied electrical power on the oxidation mechanisms. As an example, it was possible to obtain a mineralization of 70 % after 90 minutes under air, whereas under O₂/N₂ (80/20 sccm), the mineralization reached 95 %. The stability of the catalyst was also studied in terms of mineralization after several reuses of the catalyst. We also demonstrated the role of the hydroxyl radical (·OH) on the treatment with the use of radical scavengers. Indeed, the presence of methanol, known as a scavenger of hydroxyl radicals, a decrease of the degradation of nearly 50% was obtained and no mineralization was observed

Les plasmas froids d’air à pression atmosphérique sont très utiles pour un grand nombre d’applications grâce à leur chimie hors-équilibre et leur souplesse d’utilisation. Leur intérêt réside dans la production de certaines espèces réactives ou chargées avec un coût énergétique plus avantageux que la chimie à l’équilibre. L’objectif de cette thèse est de combiner les décharges nanosecondes répétitives pulsées (NRP) avec une géométrie micrométrique. Par cette combinaison, nous souhaitons palier au chauffage excessif des étincelles qui génèrent pourtant des fortes densités d’espèces. Notre étude se concentre en trois points principaux. Dans un premier temps la phase de claquage est étudiée ; c’est pendant cette étape que l’énergie est déposée et que les espèces sont produites. La combinaison des diagnostics électriques et de spectroscopie d’émission optique montrent que l’air est presque complètement dissocié et ionisé. Ensuite, nous nous intéressons à la phase de recombinaison qui conditionne la durée de vie de ces espèces. Les résultats mettent en évidence une réaction à trois corps comme mécanisme de recombinaison principal. Et enfin, le dernier point concerne le transport des espèces vers un substrat conducteur. En lui appliquant une tension, celui-ci nous permet de générer un écoulement de vent ionique provenant de la décharge. L’écoulement est étudié par vélocimétrie d’images de particules et imagerie Schlieren. Ce travail a permis de démontrer la capacité des NRP micro-plasmas dans la production contrôlée d’espèces réactives et chargées, mais aussi dans leur transport vers une surface par panache électro-aérodynamique
Non-thermal plasmas generated in air at atmospheric pressure have numerous potential applications due to their non-equilibrium chemistry and ease of use. Their main advantages lie in the cost-efficient production of reactive and charged species compared to that of equilibrium chemistry. The aim of this thesis is to combine nanosecond repetitively pulsed discharges (NRP) with a microscale geometry. Using this combination, we seek to reduce the excessive heat release of NRP sparks, while nonetheless reaching high densities of reactive species and electrons. This work is comprised of three main parts. Our first goal is to study the breakdown phase, in which energy is deposited and charged species are produced. We employ both electrical characterization and optical emission spectroscopy in order to show that the NRP microplasma fully ionizes and dissociates the gas. The second part consists of the study of the recombination phase, in which the produced species recombine or survive. Results show that three-body recombination can explain the electron lifetime in this phase. Finally, we study the transport of plasma chemical species from the microplasma to a DC-biased conductive plate representing a substrate. By applying a voltage to this third electrode, we drive an electro-thermal plume via an ionic wind from the microplasma to the plate. This flow is investigated mainly by particle image velocimetry as well as Schlieren imaging. This work shows the capability of NRP microplasmas to produce high densities of reactive and charged species and transport them to a surface using an electrohydrodynamic plume

Plasma generated in contact with water has been extensively investigated in various electrode geometries and various discharge types for water treatment, of which the applications have been employed industrially on different scales. The reactive species such as OH radicals, O3, H2O2 and HO2 can be generated from the reactions that occur at the plasma-water interface. For discharges above water, the effect of positive gas ions, which lead to the formation of positive water ions, is considered the main pathway for OH radical formation; while for the discharge under water, the water dissociation by electron collisions is considered as the main pathway. However, the reaction zone for the production of reactive species (gas or liquid phase) is still controversial. This thesis presents a study of the plasma generated in the gas phase in contact with water by various discharge types for water treatment. The discharge characteristics, OH radical and H2O2 production, and solution conductivity and pH variation were investigated and compared under different experimental conditions. The degradation of methylene blue dye was investigated under DBD. The transition of impulsive current discharges into impulsive-diffuse discharges was recorded by increasing the solution conductivity; a further transition of the discharge type into a spark was recorded when the solution conductivity was increased to >2.4 mS/cm. The H2O2 energy efficiency of 1.1 g/kWh was recorded under positive impulsive current discharges in N2 and helium. The highest charge/H2O2 ratio of 1:1.26 was recorded under positive impulsive current discharges in O2 and N2. Under positive DC glow discharges, the H2O2 energy efficiency of 1.9 g/kWh was recorded in air discharges, and was slightly increased to 1.95 g/kWh when using a flow liquid electrode. Increased solution acidity and basicity from neutral solution have negative effects on H2O2 production. A significant amount of water vapour was observed under DC glow discharges, resulting in a negative effect on H2O2 production. Under negative discharges, no H2O2 production was detected in water after O2, N2, air and helium discharge treatments. In DBD, a threshold voltage is required to initiate electrical discharges between the glass plate and the water, through the micro-pores. The H2O2 production yield of 1.1 g/kWh was recorded in O2 discharge treatment. The degradation yield of methylene blue dye of 310 g/kWh was achieved within the first minute of O2 discharge treatment.

This thesis reports a pure and applied study on non-thermal plasmas (NTPs) produced using Dielectric Barrier Discharge (DBD) generators of various forms. The main aim of the pure aspect of the study was to obtain a better understanding of the chemistry taking place within the NTP in an air-fed DBD and to what extent the plasma output varies from the glow to the downstream regions under various operational conditions. Thus, a DBD plasma jet generator was designed and employed for the investigations of these regions. The analyses of the plasma glow region and the downstream exhaust were carried out using Fourier Transform InfraRed (FTIR) and UV–Vis absorption spectroscopies. The applied studies focussed on the development of a novel, dielectric barrier discharge-packed bed reactor (DBD-PBR) for effective ozone generation from oxygen or air, and its application to the remediation of Cu(II)-EDTA and Fe(III)-EDTA containing water in combination with an oscillatory baffled reactor (OBR) and a UV irradiation reactor (UVR). In-situ analysis of the plasma glow region of the plasma jet identified: O3, N2O5, N2O, NO2 HNO3, CO2, CO and, for the first time, a vibrationally excited form of CO2 (i.e. CO2*(v)), while O3, N2O5, HNO3 and N2O were detected in the downstream exhaust. The behaviour of these species was monitored as a function of a range of experimental conditions including: input power, gas flow rate, relative humidity, gas temperature and feed gas composition, and mechanisms postulated based on literature precedent. It is clear from this work that the feed gas composition, input power, gas temperature and relative humidity have a significant effect upon the NTP chemistry in the glow and post glow regions. Unexpectedly, the spectroscopic analyses of O3, NO2 and N2O in the plasma glow region and in the downstream exhaust suggested the occurrence of chemical reactions in the afterglow region rather than simple diffusion. This behaviour rules out the general assumption that reactive chemistry is confined to the glow region. The DBD-PBR was designed, fabricated, characterized and optimized for ozone generation from oxygen and air. The effects of reactor arrangement, feed gas flow rate, coolant temperature, input power and dielectric material on ozone generation were investigated. The highest ozone concentration of 152 g m-3 was obtained using 2.0 mm glass beads and an oxygen feed at 5 oC, and 0.06 dm3 min-1, while the highest ozone yield efficiency was 210 g kW-1 h-1 at an oxygen feed rate of 15 dm3 min-1 this compares to 173 g kW-1h-1 reported in the literature. The highest ozone concentration produced from air was 15.5 g m-3 at flow rate Preface v of 0.06 dm3 min-1 with Al2O3 beads as the dielectric. It was found that the dielectric employed in the DBD-PBR had a significant effect upon the selectivity towards ozone at low feed gas flow rates. Different NOx by-products were formed along with ozone when the DBD-PBR was fed with air depending on the coolant temperature and the dielectric material. The efficiency of ozone generation via DBR-PBRs was significantly enhanced reducing the discharge current during the generation of NTP by decreasing the capacitance of the dielectric and by effective heat removal. Finally, a MnO2-based catalyst (CARULIT 200) tested for DBD-PBR exhaust control, and was found to be effective for simultaneous ozone and NOx removal at room temperature. The DBD-PBR was coupled to an OBR to intensify ozone-to-water mass transfer. The OBR was operated as a semi-batch and as a co-current, up-flow continuous reactor. The effect of input ozone concentration, input gas & water flow rates, and oscillation amplitude and frequency on gas hold up, volumetric mass transfer coefficient and mass transfer efficiency were determined. The same reactor was operated as a bubble column (i.e. without baffles or oscillation) and as a baffled column (without oscillation) to assess the effect of the reactor arrangement on the mass transfer. The results show that the OBR was 5 and 3 times more efficient for ozone-water mass transfer than the baffled and bubble columns, respectively. The enhancement obtained with the OBR over the baffled column reactor was found to decrease with gas flow rate due to changes in bubble flow pattern from homogenous to heterogeneous. Under continuous flow conditions, the performance of the baffled reactor and the OBR were found to be twice as efficient for ozone-water mass transfer than when operating under semi-batch conditions. The mass transfer efficiency (MTE, %) was found to increase from 57 % using the baffled reactor to 92 % with OBR under continuous flow at water and gas superficial velocities of 0.3 and 3.4 cm s-1, respectively. From these results it is clear that the OBR and baffled reactor are promising approaches for enhancing ozone-water mass transfer and its application in water treatment. One of the targeted fields of the DBD-PBR/OBR/UVR system is in water treatment, and hence it was important to evaluate its performance in such application. Therefore, the system was employed for the treatment of water samples contaminated with Cu(II)-EDTA and Fe(III)-EDTA. These compounds were chosen because they are difficult to remove from water using conventional methods. The effects of reactor arrangement, ozonation time and ozonation plus UV irradiation on remediation of the complexes were investigated under Preface vi continuous flow conditions. The results suggest that Cu(II)-EDTA was decomposed completely by ozonation within 17 minutes using the OBR, with no significant enhancement by UV irradiation. However, the Fe(III)-EDTA was converted to other stable complexes (i.e. Fe(III)-ED3A and Fe(III)-IDA) by ozonation, and hence following the ozonation by UV irradiation was essential to ensure complete degradation. The total organic carbon (TOC) of the Fe(III)-EDTA and Cu(II)-EDTA solutions was reduced by 50% after 17 minutes of O3/UV treatment using the OBR. Some of the final products were identified using Ion Chromatography and included: oxalic acid, formic acid, acetic acid, glycolic acid, nitrate and nitrite ions. From these results, it is clear that the enhancement in ozone-water mass transfer using the OBR or the baffled reactor was essential for reducing the treatment time and ozone dosage required for the remediation of Cu(II)-EDTA and Fe(III)-EDTA over conventional bubble column reactors.

In this study, an in-house built atmospheric. pressure non-thermal plasma jet has been investigated for its potential utilisation as a new alternative antimicrobial tool for a variety of medical applications. Anti - biofilm activity of this plasma jet has been evaluated against biofilms of a selected panel of bacterial species, grown on different abiotic surfaces, where complete eradication of all tested bacterial biofilms was achieved after relatively short plasma exposures of up to 10 minutes. Multiple approaches of cell viability evaluation were adopted to show the nature, extent and distribution of the remarkable anti-biofilm activity of the plasma jet including colony counting, XTT metabolic assay, scanning electron microscopy examination and differential Live/Dead fluorescent staining followed by confocal laser scanning microscopy examination. Antibacterial efficacy of the plasma jet has also been evaluated against similar bacterial species in their planktonic mode of growth where plasma exposures even shorter than those required for biofilm eradication were sufficient to cause complete inactivation of these planktonic bacteria. Such excellent bactericidal activity resulted from the ability of plasma exposure to mediate an oxidative damage to multiple cellular targets including cellular membrane, DNA and proteins of bacterial cells. However, damage of cellular membrane and the resultant disruption of its integrity and permeability were shown to be the primary rate-determining step in the plasma mediated bacterial cell death. Furthermore, in depth investigation of the plasma- mediated bacterial destruction mechanism has been carried out to identify the plasma-produced reactive species that were responsible for mediating its bactericidal activity. Based on the findings of this study, a hypothesis was formulated to describe the mechanism of bacterial cell destruction after plasma exposure. This hypothesis assumed a two-part mechanism; one part was a rapid H20 2-dependent mechanism associated with Fenton's or Fenton's-like reaction that was catalysed by metal ions released from the bacterial cells initially damaged by another proposed H20 2 - independent mechanism.

Non-thermal plasma, as a potential nitric oxide (NO) removal technology, has been researched for more than one decade. The advantage of direct non-thermal plasma treatment is that it is able to generate reactive species from the existing components in the flue gas without additional catalyst, oxidant or reductant, so any NO removal system based upon this technology is simple and easy to operate. However, the energy efficiency of non-thermal plasma technology is lower than the most commonly used selective catalytic reduction system for NO removal. In order to understand the possible reasons, it is important to investigate the mechanism of NO removal by direct non-thermal plasma treatment. Two of the most commonly used non-thermal plasma sources, dielectric barrier discharge (DBD) and corona discharge, are investigated. The most important reactive species include oxygen atom (O), ozone (O3) and hydroxyl radical (OH). Different reactive species lead to different chemical reaction pathways for NO removal. Under different NO concentration and discharge configurations, the dominant reactive species was found to change from one to another. For dielectric barrier discharge, when the initial NO concentration was higher than 420 ppm under dry condition, it was found that O was the dominant reactive species for NO oxidation and NO oxidation was independent on O2 concentration. When initial NO concentration was lower than 100 ppm under dry condition, it was found that O3 was the dominant reactive species and NO oxidation was dependent on O2 concentration. When NO concentration was in the range of 120 ppm to 190 ppm, there was a synergistic effect of O and O3 on NO oxidation. NO removal depended on the initial NO concentration. However, no matter what the initial NO concentration was, the NO removal energy efficiency was lower than 25g/kWh. When water vapour (H2O) was introduced into the gas mixture, reactive species OH was generated and provided an alternative chemical reaction pathway for NO removal. When initial NO concentration was 1000 ppm, NO removal was in the range of 150 ppm to 200 ppm, but the energy efficiency was in the range of 7 to 12 g/kWh. With an increase of temperature in DBD reactor, the effect of OH on NO removal was promoted. To further investigate the OH effect, a novel pin to water corona discharge configuration was used. The effect of discharge modes from Trichel pulse, pulseless and arc discharge was investigated. Under arc discharge mode, 200 ppm NO was generated at 6W discharge power. Under Trichel and pulseless discharge modes, NO removal increased with increasing discharge power. When initial NO concentration was 1000 ppm, the highest NO removal achieved was 715 ppm with 5.5 g/kWh energy efficiency. In addition, it was found that the energy efficiency did not reduce with increasing discharge power. In order to increase the possibility of chemical reaction between NO and reactive species, higher initial NO concentration was used. To obtain higher NO concentration a process of NO absorption by activated carbon and thermal desorption was used. This increased the NO concentration from 1000 ppm up to 6%. It is found that at 6% level, NO could be partially oxidized by oxygen molecule (O2) and higher O2 concentration would obtain higher NO oxidation rate. Direct non-thermal plasma treatment can be used for NO removal but the energy efficiency (less than 30g/kWh) is too low to compete with the mature technologies including selective catalytic reduction (SCR) and low temperature oxidation (LoTOx) whose energy efficiencies are higher than 60 g/kWh. Although the energy efficiency is not improved in this research, the mechanism and chemical reaction pathways of NO removal are quantitatively analysed under different initial NO concentration levels by two different non-thermal plasma technologies (DBD and corona discharge). The dominant reactive species for NO removal can shift from O, O3 to OH. In addition, a novel technology which is a combination of non-thermal plasma, NO absorption and desorption processes is developed in this research. It offers a new mechanism for NO removal, because increasing the concentration of NO from ppm level to a few percentages creates a regime where NO removal can be effectively done by O2 rather than strong oxidants like O and O3. As the formation of O and O3 is more expensive than that of O2, this is a promising research direction for NO removal. However, based on the investigation in this research, some challenges are found. One is the poor selection between NO and H2O for activated carbon and the other one is high energy consumption for the desorption process.

This thesis focuses on the process of nanoparticle generation using new source of nonthermal plasma combining corona and pin-hole discharge in liquids. The theoretical part is focused on generation of metallic nanoparticles using various types of plasma discharge, the properties of metallic nanoparticles, their preparation by other methods and methods of characterization of nanoparticles. The experimental part deals with the preparation of copper, silver and gold nanoparticles from solutions of their precursors. The influence of experimental conditions, such as the influence of voltage polarity, effect of precursor concentration, effect of added electrolyte or reducing agent were investigated. All samples were analyzed by UV-VIS spectroscopy. Dynamic light scattering was used to determine the sice of nanoparticles. To confirm the presence of nanoparticles, samples were analyzed using scanning microscope with and energy dispersion spectrometer for elemental analysis.

The original work presented in this thesis provides examples of the unique chemistry of a helium/oxygen Kilohertz plasma jet and its antimicrobial activity against a cohort of clinically relevant microorganisms termed the ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter cloacae). The potential of non-thermal plasma to attenuate quorum sensing controlled bacterial virulence is demonstrated in Gram-negative bacteria with further elucidation undertaken to examine how examples of plasma produced reactive species; the hydroxyl radical and peroxynitrite anion affect acyl homoserine lactones (extra-cellular molecules utilised by Gram-negative bacteria in quorum sensing). This thesis provides further evidence of non-thermal plasmas antimicrobial efficacy and presents new evidence of how non-thermal plasma may attenuate bacterial quorum sensing controlled virulence through modification of acyl homoserine lactones in a chain length-dependent manner. This work contributes new knowledge and understanding of non-thermal plasmas interaction with bacteria and its potential for the amelioration of hospital acquired infections.

Recent interest in hydrogen as an energy source has resulted in development of new technologies such as non-thermal plasma processing of natural gas. We report the development of a process yielding hydrogen from natural gas that generates no green house gases and thus meets the Kyoto accord targets.
In this process, natural gas is treated in a dielectric barrier discharge (DBD) yielding hydrogen and solid carbon according to the following reaction: CH4 (g) → 2H2 (g) + C (s). The direct cracking of the hydrocarbon is possible if the natural gas is injected in the plasma zone, created by the presence of a dielectric ceramic material.
It was found that the dielectric material plays an important role on plasma intensity. The change in ceramic properties affects the parameters of the discharge. It was discovered that the number of micro-discharges increased when a ceramic with a higher dielectric constant was used. Furthermore, the ceramic relative permittivity or dielectric constant has a direct influence on the hydrogen yield.
However, the challenge is that when using a commercial high dielectric ceramic as barrier they tend to break in the plasma environment. In the attempt of improving the process efficiency medium permittivity dielectric ceramics (9 < K' <166) were fabricated and successfully tested in the discharge reactor. A broad variety of ceramics (from low to high permittivity) were tested and the results suggested that the CH4 conversion using high dielectric constant barrier is much higher than using conventional barrier material such as A12O3.

This thesis has studied CO2 reforming of CH4 in atmospheric pressure, non-thermal plasma discharges. The objective of this research was to improve the current understanding of plasma-catalytic interactions for methane reforming. Chapter 1 introduces the existing and potential applications for methane reforming products. The industrial approaches to methane reforming and considerations for catalyst selection are discussed. Chapter 2 introduces non-thermal plasma technology and plasma-catalysis. An introduction to the analytical techniques used throughout this thesis is given. Chapter 3 investigates the effects of packing materials into the discharge gap. The materials were found to influence the reactant conversions for dry reforming of methane in the following order: quartz wool > no packing > Al2O3 > zeolite 3A > BaTiO3 > TiO2. In addition to the dielectric properties, the morphology and porosity of the materials was found to influence the reaction chemistry. The materials also affected the electrical properties of the plasma resulting in surface discharges, as opposed to a filamentary discharge mode. Chapter 4 investigates the effects of variation in CH4/CO2 ratios on plasma-assisted dry reforming of CH4. Differences in the reaction performance for different feed gas compositions are explained in terms of the possible reaction pathways and the electron energy distribution functions. A NiO/Al2O3 catalyst is introduced for plasma-catalytic dry reforming of CH4, which was found to have no significant effect on the reaction performance at low specific input energies. Chapter 5 presents the plasma-assisted reduction of a NiO/Al2O3 catalyst by CH4 and H2/Ar discharges. When reduced in a CH4 discharge, the active Ni/Al2O3 catalyst was effective for plasma-catalytic methane decomposition to produce H2 and solid carbon filaments. A decrease in the breakdown voltage was observed, following the catalyst reduction to the more conductive Ni phase. Chapter 6 investigates the performance of the plasma-reduced Ni/Al2O3 catalysts for plasma-catalytic dry reforming of methane. Whilst the activity towards dry reforming of CH4 was low, the CH4 plasma-reduced catalyst was found to be effective for catalysing the decomposition of CH4 into H2 and solid carbon filaments; both potentially useful products. Chapter 7 discusses further work relevant to this thesis.

In this report we establish cyclohexasilane (CHS) as a reliable precursor for non-thermal plasma synthesis of high quality photoluminescent silicon nanocrystals (SiNCs). We demonstrate that this synthesis approach can produce high quality, size tunable silicon quantum dots with quantum yields exceeding 60% as synthesized (subsequent work in our group has measured over 70% quantum yield after density gradient ultracentrifugation size purification).After a brief background on non-thermal plasma synthesis, the characterization methods used in this study, and an overview of CHS, we report at length on our development of the apparatus used, and our exploration of the controllable processing parameters of the synthesis method. We describe our successes and challenges with size tuning, sample collection, and passivation. Finally, we discuss preliminary studies we performed to identify promising future research areas. Novel reactor designs, blue light passivation, and magnetic confinement of plasma are described briefly to entice future researchers.

It has been shown that non-thermal plasma has great potential for chemical oxidation and bacterial inactivation. However, the mechanism of plasma-induced oxidation and bactericidal effects is not fully understood, and optimisation of the non-thermal plasma treatment is required to improve the efficiency of this technology. This research presents an investigation into the oxidation and bio-decontamination capabilities of steady-state corona discharges and impulsive transient plasma discharges in atmospheric air. Degree of decolorisation of blue dye by plasma discharges was obtained and used for evaluation of the oxidation efficiency of these discharges. The Gram-positive and Gram-negative bacteria, Staphylococcus aureus and Escherichia coli, respectively, were used for investigation of the bio-decontamination capability of the plasma discharges. It has been shown that conditions such as air humidity, electrode topology, and voltage levels may affect the efficiency of plasma treatment. The obtained results show that the oxidation and inactivation effects depend on the amount of charge delivered by the plasma. The charge-dependent decolorisation and inactivation rates of plasma discharge treatment, which indicate the oxidation efficiency and inactivation efficiency, were obtained and analysed. Different decolorisation and inactivation rates were achieved with various electrode topologies and energisation polarities. This study also investigated the production of reactive species by atmospheric plasma discharges. Ozone concentration was measured during the decolorisation and inactivation tests. The production of OH radicals by the plasma discharges have also been obtained in this study using terephthalic acid as the chemical probe. The obtained results confirm that the reactive oxygen species play a major role in the plasma discharge treatment. In addition, an attempt of using TiO2 as a catalyst to enhance oxidation and bio-decontamination effects of the plasma discharge treatment has been made. TiO2 was revealed to have the potential to improve the oxidation efficiency of atmospheric plasma discharges. The results obtained and presented in this thesis will help in optimisation of non-thermal plasma systems for chemical and biological decontamination.

Plasma chemistry is a rapidly growing field to develop and exploit the great potential of plasma to perform chemical reactions. This thesis deals with the oxidation of organic pollutants in air and water promoted by the action of air non-thermal plasma (NTP). Such plasmas, which are conveniently produced by electric non-thermalizing discharges like corona and dielectric barrier discharges in air at atmospheric pressure and ambient temperature, provide highly reactive oxidizing environments comprising electrons, excited molecules, atomic and radical species (O, OH), ions (O2+, N2+, NO+, O–, O2–, O3–), O3 and NO. Despite the numerous successful applications of NTP in processes of environmental and commercial relevance, the chemistry of organic compounds within air non-thermal plasmas is still not well characterized, both as far as products and mechanisms are concerned. This thesis developed as a contribution to this field of research along three lines dealing, respectively, with plasma processing of: volatile organic compounds (VOCs) in air with plasma alone; VOCs in air with plasma plus an heterogeneous catalyst; organic pollutants in aqueous solutions above which an air plasma is generated. All three projects had a common focus in the mechanistic characterization of the oxidation processes within these very complex and highly reactive systems. The study of VOC oxidation in air NTP was carried out with a large prototype corona reactor developed at the Department of Chemical Sciences in Padova, which can be energized with DC or pulsed high voltage of either polarity. Comparative studies were carried out to evaluate the response of selected model VOCs to different corona regimes (+DC, −DC and +pulsed). The VOCs considered include two alkanes (n-hexane and i-octane), toluene and two halogenated methanes, dibromomethane (CH2Br2) and dibromodifluoromethane (CF2Br2, halon 1202). Remarkably, all these different VOCs, including the highly inert halon, can be oxidized to CO2 at room temperature with efficiencies which depend on VOC type (despite their high reactivity NTPs display some selectivity), on VOC concentration (the efficiency increases linearly with the reciprocal of VOC concentration) but also on the way energy is given to the plasma. Thus, for all VOCs examined the efficiency decreases in the order: +pulsed > -DC > +DC corona. This means that any given amount of energy produces an extent of VOC conversion ([VOC]/[VOC]0) which depends on the corona regime and decreases in the order +pulsed > –DC > +DC. The greater efficiency of +pulsed corona is due to the higher mean electron energy achieved, for any given input of energy, with this type of power supply with respect to DC high voltage. The mean electron energy of the plasma under the different corona regimes was experimentally determined in our reactor by emission spectroscopy measurements following a published procedure. Another important variable tested was the humidity in the air, which is known to produce the strongly oxidizing OH radicals via electron induced dissociation or via reaction with O2+ and N2+ ions. Thus, the greater efficiency in humid with respect to dry air observed for the oxidation of hydrocarbons and of CH2Br2 with –DC and +pulsed corona was attributed to reaction with OH radicals. Surprisingly, in experiments with + DC the same VOCs undergo less efficient oxidation in humid air than in dry air, despite the presence of OH radicals. Analysis of the plasma ionized species, performed by APCI-MS (Atmospheric Pressure Chemical Ionization – Mass Spectrometry), coupled to the determination of current/voltage characteristics of DC coronas, led to the proposal that in the case of +DC corona the oxidation of hydrocarbons and of CH2Br2 is initiated by reactions with ions (O2+, H3O+ and their hydrates, NO+) both in dry as well as in humid air. In contrast, with –DC and +pulsed corona in humid air, OH radicals are involved in the initial stage of hydrocarbons and of CH2Br2 oxidation. Consistent with its very low reactivity with the OH radical, the oxidation of CF2Br2 in humid air proceeds less efficiently with both +DC and –DC corona. It was thus proposed that the oxidation of CF2Br2 occurs via a common mechanism under all corona regimes tested, the initial step being electron induced C-Br dissociation. The process efficiency is lower in humid air because the mean electron energy is lowered due to reaction of the electrons with water molecules. The two halomethanes also form different products: FTIR analysis of post-discharge gas has shown that CH2Br2 produces both CO2 and CO, whereas CF2Br2 forms CO2 and F2C=O. The latter product is a longlived oxidation intermediate due to its low reactivity with atmospheric radicals. It is however very rapidly hydrolized to CO2 and HF as shown by combined ion chromatography and FT-IR analysis of the solution and of the exhaust gas obtained after a water scrubbing step. Other non-carbon containing products of the discharge were analyzed by FT-IR analysis, including ozone, HNO3 and N2O. In experiments with both halomethanes evidence was found for brominesustained catalytic ozone destruction cycles, responsible also for increased conversion of NOx into HNO3. Efficiency and, especially, product selectivity can be improved by the combined action of plasma and heterogeneous catalysts which usually result in synergic effects. The nature and origin of this synergy was the focus of the research I carried out in my second year in graduate school during a stage at the Advanced Industrial Science and Technology Institute (AIST) in Tsukuba (Japan), in the group of dr. Hyun-Ha Kim. As molecular probe to compare the effects of plasma alone and plasma plus catalyst we selected the O-scrambling reaction to form 16O18O starting from a mixture of 16O2 and 18O2. Four different reactors were used and various catalysts, including TiO2, MS-13X and gAl2O3 also containing a few % of Ag. It was possible to conclude that, in the absence of a catalyst the O-exchange reaction occurs in the gas phase and not on the electrodes surface. It was also possible to use the results of these experiments to estimate, for any given energy input the average concentration of O atoms within the plasma. This is a most interesting outcome of these studies since the traditional method for obtaining O atom density involves sophisticated laser spectroscopy instrumentation and procedures. As for the catalyst/plasma interaction, using again a labelled molecular probe, 18O2, it was possible to conclude that the plasma induces oxygen fission on the catalyst surface and that this oxygen is then used in the oxidation of VOCs. The third project dealt with the plasma induced oxidation of phenol in aqueous solution. For these studies two prototype reactors were developed and tested, both characterized by application of electric discharges in the air above the solution. The first is a dielectric barrier discharge reactor which afforded the efficient removal of phenol from the aqueous solution according to an exponential decay as a function of treatment time at constant power. A qualitative analysis of the intermediate and final products of phenol oxidation was performed and the major reactive species formed upon the application of the discharge in air were identified and determined. It is concluded that the decomposition of phenol is initiated by reactions with ozone, taking place on the surface of the solution, and with hydroxyl radicals, both at the surface and within the bulk of the solution. An interesting and most convenient result is the better efficiency of phenol removal in tap water than in milliQ water. After ruling out possible effects due to conductivity, to Fenton’s reaction due to Fe2+ and to active chlorine, it was concluded that the efficiency increase is due to the higher pH of the solution mantained by the presence of bicarbonate salts. The second developed reactor allowed us to perform some interesting comparisons since it can be powered by different types of high voltage for the generation of plasma. The possibility to apply this technology to the treatment of waste water depends on many factors: the process efficiency, the final composition of the treated solution, the general applicability of the system to the organic pollutants. The data obtained so far are very promising due to the efficient oxidation all the way to CO2 and to the absence of any hazardous organic byproduct after a proper treatment time. The results of this thesis confirm that plasma processing is a promising highly efficient means for the advanced oxidation of organic pollutants both in air and in aqueous solution.
Lo studio di processi chimici indotti da plasmi sta suscitando un notevole interesse per il grande potenziale che questi sistemi possono sviluppare. Questa tesi riguarda l’ossidazione di inquinanti organici in aria e in soluzione acquosa promossa dall’interazione con plasma non-termico (NTP). Questi plasmi, che sono convenientemente generati da scariche elettriche non termalizzanti, principalmente scariche corona e a barriera di dielettrico, in aria a temperatura e pressione ambiente, costituiscono ambienti di reazione molto reattivi e fortemente ossidanti per la presenza di elettroni, molecole eccitate, specie atomiche e radicali (O, OH), ioni (O2+, N2+, NO+, O–, O2–, O3–), O3 e NO. Nonostante siano numerose le applicazioni tecnologiche di questi plasmi in processi di rilevanza ambientale e commerciale, la chimica dei composti organici in questi sistemi è tuttora non ben nota sia per quanto riguarda i prodotti che i meccanismi di reazione. Questa tesi è uno studio meccanicistico che si è sviluppato lungo tre linee di ricerca riguardanti l’ossidazione di: i) composti organici volatili (VOC) in aria con solo plasma; ii) VOC in aria con plasma e un catalizzatore eterogeno; inquinanti organici in soluzioni acquose poste a contatto con plasma non termico in aria. I tre progetti hanno un obiettivo comune che riguarda la caratterizzazione dei meccanismi di ossidazione che operano in questi sistemi di enorme complessità chimica. Lo studio dell’ossidazione di VOC in plasmi non termici in aria è stato condotto utilizzando un reattore prototipo a scarica corona sviluppato presso il Dipartimento di Scienze Chimiche a Padova, che può essere alimentato da alta tensione DC o ad impulsi di polarità sia positiva che negativa. Sono stati svolti studi comparativi per valutare la risposta di alcuni modelli di VOC a diversi regimi di scarica corona, precisamente +DC, -DC e +pulsed. I composti studiati sono due alcani (esano ed iso-ottano), il toluene e gli alometani dibromometano (CH2Br2) e dibromodifluorometane (CF2Br2, halon 1202). E’ notevole il fatto che tutti questi VOC, compreso l’halon notoriamente molto inerte, possono essere ossidati a CO2 in questi plasmi a temperatura ambiente con un’efficienza che dipende dal tipo di VOC (nonostante la loro elevata reattività questi plasmi presentano comunque un certo grado di selettività), dalla concentrazione del VOC (l’efficienza aumenta linearmente col reciproco della concentrazione iniziale del VOC) e dal modo in cui l’energia viene fornita al reattore. Infatti, per tutti i VOC considerati, l’efficienza del trattamento aumenta nell’ordine: +DC < -DC < +pulsed. Questo significa che il grado di conversione ([VOC]/[VOC]0) prodotto da una certa quantità di energia fornita al sistema dipende dal tipo di scarica utilizzato, che a sua volta determina la composizione e natura del plasma e quindi la sua reattività. La maggiore efficienza del corona ad impulsi rispetto al corona DC è attribuibile alla maggiore energia media degli elettroni in questo regime di scarica. L’energia media degli elettroni è stata determinata sperimentalmente nel nostro reattore nelle diverse condizioni di scarica mediante esperimenti di spettroscopia di emissione utilizzando un metodo pubblicato in letteratura. Un’altra importante variabile di questi processi è il grado di umidità dell’aria, che determina la formazione di maggiori o minori concentrazioni del radicale OH. Questo radicale si forma dall’acqua attraverso reazione con elettroni ad alta energia o reazione con gli ioni O2+ and N2+. La maggior efficienza dell’ossidazione di idrocarburi e del CH2Br2 osservata con -DC in aria umida rispetto all’aria secca è stata quindi attribuita alla reazione con radicali OH. Sorprendentemente, con +DC l’umidità produce un effetto opposto per gli stessi VOC, nonostante la presenza in aria umida di radicali OH. L’analisi degli ioni del plasma, effettuata mediante spettrometria di massa APCI-MS (Atmospheric Pressure Chemical Ionization – Mass Spectrometry), accoppiata allo studio della caratteristica corrente/tensione del corona DC, ha portato a concludere che nel caso del corona +DC l’ossidazione degli idrocarburi e del dibromometano è iniziata da reazione con ioni (O2+, H3O+ e i loro idrati, NO+) sia in aria secca che in aria umida. Al contrario, nel caso del corona –DC e del corona +pulsed la principale reazione di attacco a questi VOC risulta essere quella del radicale OH. Per quanto riguarda invece l’halon CF2Br2, sia con +DC che con –DC l’ossidazione in aria umida risulta meno efficiente che in aria secca, un risultato coerente con la nota scarsa reattività di questo VOC con il radicale OH. E’ stata quindi avanzata l’ipotesi che l’ossidazione di questo halon proceda attraverso un meccanismo comune, indipendentemente dal regime di scarica applicato, che comporta la dissociazione iniziale del legame C-Br indotta da interazione con elettroni del plasma. Il processo è meno efficiente in aria umida probabilmente perché la reazione di dissociazione dell’acqua provoca una riduzione dell’energia media degli elettroni rispetto a quella in aria secca. L’ossidazione dei due alometani in aria secca dà prodotti diversi: l’analisi FT-IR del gas in uscita dal reattore ha individuato sia CO2 che CO fra i prodotti di CH2Br2 mentre nel caso di CF2Br2 i prodotti sono CO2 e F2C=O. Quest’ultimo è un intermedio di ossidazione con tempo di vita sufficientemente lungo da poter essere rivelato in quanto notoriamente poco reattivo nelle reazioni con radicali. E’ tuttavia idrolizzato molto velocemente a CO2 e HF come dimostrato da analisi integrate di cromatografia ionica e FT-IR della soluzione e del gas ottenuti dopo gorgogliamento del gas trattato in acqua. Altri prodotti di questi trattamenti rivelati e quantificati mediante spettroscopia FT-IR sono l’ozono, l’acido nitrico e l’ossido N2O. Con entrambi gli alometani si è osservato l’intervento di cicli catalitici di distruzione dell’ozono in cui il bromo atomico è la specie propagatrice. Gli stessi cicli sono inoltre responsabili della conversione degli NOx in HNO3. L’efficienza e la selettività dei processi di ossidazione al plasma possono essere migliorati attraverso l’azione combinata del plasma e di catalizzatori eterogenei. Ne deriva un effetto sinergico, la cui origine e natura sono tuttora in fase di studio. Di questo problema mi sono occupato durante un soggiorno presso l’Advanced Industrial Science and Technology Institute (AIST) a Tsukuba (Giappone), presso il gruppo del Prof. Hyun-Ha Kim. Per confrontare gli effetti di solo plasma e plasma più catalizzatore abbiamo utilizzato come sonda molecolare la reazione di scambio di ossigeno che produce 16O18O partendo da miscele di 16O2 e 18O2. Sono stati utilizzati diversi reattori al plasma con diverse alimentazioni elettriche e parecchi catalizzatori fra cui TiO2, MS-13X e gAl2O3 contentente varie modeste percentuali di Ag. Questi studi hanno permesso di concludere che, in assenza di catalizzatore, la reazione di scambio di ossigeno avviene in fase gas e non sulle superfici degli elettrodi. I risultati di questi esperimenti sono stati utilizzati per sviluppare un metodo basato sulla reazione di scambio isotopico al fine di determinare la concentrazione di ossigeno atomico in questi plasmi. Questo è un risultante importante che si propone come alternativa al metodo tradizionale per la determinazione della concentrazione di ossigeno atomico con strumentazioni ottiche laser e procedure piuttosto sofisticate. Per quanto riguarda l’interazione catalizzatore/plasma, è stato possibile concludere, sempre utilizzando la sonda molecolare 18O2, marcata isotopicamente, che il plasma determina la fissazione dell’ossigeno sulla superficie del catalizzatore e che questo ossigeno è quindi trasferito al VOC nel processo di ossidazione. Infine, il terzo progetto ha riguardato l’ossidazione del fenolo in soluzioni acquose esposte all’azione di plasma non-termico in aria. Per questi studi sono stati sviluppati due prototipi di reattore caratterizzati entrambi dall’applicazione di scariche elettriche nell’aria sovrastante la soluzione da trattare. L’ossidazione del fenolo nel primo reattore, che utilizza scariche a barriera di dielettrico, procede efficacemente fino a CO2 seguendo un decadimento esponenziale in funzione del tempo di trattamento a potenza applicata costante. Dall’analisi dei prodotti ed intermedi di ossidazione nonché dalla determinazione delle principali specie reattive è emerso che la decomposizione del fenolo avviene per reazione con l’ozono sulla superficie della soluzione a contatto con il plasma, e con il radicale OH, sia sulla superficie che all’interno della soluzione. Un risultato molto interessante e utile in vista di applicazioni pratiche di questi processi riguarda la maggiore efficienza dell’ossidazione del fenolo in acqua di rubinetto rispetto all’acqua milliQ. Dopo aver escluso che all’origine di questo fenomeno potessero esserci effetti dovuti alla conduttività maggiore, alla presenza di ioni Fe2+ capaci di indurre la reazione di Fenton, e alla presenza di cloro attivo nell’acqua potabile, è stato verificato che l’effetto tampone esercitato dallo ione bicarbonato mantiene un pH elevato e consente al processo di procedere velocemente.

Les plasmas froids produits par les décharges électriques sont des gaz faiblement ionisés, ce qui maintient la température du gaz à une température proche de la température ambiante, contrairement à la température de l'électron qui peut atteindre plusieurs électron-volts. Les applications des plasmas froids en médecine et en agriculture sont des nouveaux domaines de recherche multidisciplinaires basés sur les interactions de ces plasmas avec des organismes vivants. Le champ électrique ainsi que les espèces réactives de l’oxygène et de l'azote peuvent inactiver les bactéries, stimuler la régénération de la peau (dermatologie), la réduction tumorale (oncologie) et la germination des graines (agriculture). Ces nouveaux domaines de recherche, basé sur la chimie produite par l’interaction plasma-liquide est très prometteur et se développe rapidement. L’objectif de ce travail est d’étudier les interactions entre les plasmas froids et l’eau pour les applications biologiques, d’une part la promotion de la germination des graines au moyen d’une décharge à barrière diélectrique (DBD) et, d’autre part, l’effet ex vivo d’un traitement par jet de plasma froid sur la peau.Ce manuscrit est divisé en cinq chapitres: i) On présente tout d'abord une revue de la littérature présentant l'état de l’art concernant l'interaction plasma-liquide et les principales avancées en matière d'applications des plasmas froids à la germination des semences. Ii) Deuxièmement, les dispisitifs expérimentaux sont décrits, en particulier la fabrication de réacteurs à plasma utilisant l’impression 3D. Iii) Ensuite, la production d'espèces réactives gazeuses et aqueuses formées par des plasmas de type DBD a été mesurée quantitativement et l'interaction plasma-liquide a été analysée. Iv) Puis, plusieurs variétés de graines ont été sélectionnées pour évaluer l’effet un traitement par plasma DBD ; l'étude des mécanismes de promotion de la germination du plasma a été spécifiquement étudiée en traitant les graines de soja vert dans différentes conditions de décharge, dans différents milieux, avec un champ électrique seul et dans différentes conditions de cultures ou de niveau d'hydratation des graines.v) Enfin, l'imagerie paramétrique de Muller (MPI) a été appliquée pour la modification de la peau de souris ex vivo traitées par un plasma à jet d'hélium
Non-Thermal-Plasmas (NTP) produced by electric discharges are weakly ionized gases, which keeps the gas temperature at near room temperature contrary to the electron temperature which can reach several electron-Volts. Applications of NTP to medicine and agriculture are new multidisciplinary research fields based on interactions of the Non-Thermal-Plasmas with living organisms. Electric field as well as Reactive Oxygen and Nitrogen Species produced by NTP may inactivate bacteria, stimulate skin regeneration (dermatology), tumor reduction (oncology) and seeds germination (agriculture). These new fields of research are based on the plasma-liquid chemistry. The objective of this work is to study the NTP interacting with water for biological applications including on one hand, the promotion of the germination of seeds using a Dielectric Barrier Discharge (DBD) and on the other hand, the effect of a plasma jet treatment ex vivo on skinThis manuscript is divided in five chapters: i) First a literature review is presented showing the state of the art of the plasma-liquid interaction, and the main advances of the application of non thermal plasmas to seed germination. Ii) Second, experimental set ups are described, in particular the manufacturing of plasma reactors using 3D printing. Iii) then , the production of gaseous and aqueous reactive species formed by DBD plasmas was measured quantitatively and plasma-liquid interaction was analyzed. Iv) Next, different varieties of seeds were selected to evaluate the effect of a DBD plasma treatment and the study of the mechanisms of plasma germination promotion was specifically investigated by treating mung bean seeds in different discharge conditions, in different mediums, in electric field alone and in different hydration levels of seeds.v) Finally, Muller parametric imaging (MPI) was applied to study the modification of ex vivo mice skin treated by a helium jet plasma

The use of cold atmospheric pressure plasma for applications related to microbial decontamination has grown enormously over the last decade. Non-thermal plasmas generated in ambient air contain a wide variety of reactive oxygen and nitrogen species, or RONS. When such species interact with microorganisms they induce a number of biological changes, ultimately resulting in inactivation of the organism. This thesis focuses on the design, development, optimisation and application of air plasma systems for microbial decontamination. The aim of the work is to gain a better understanding of how RONS are produced in air plasma and how they are transported through different phases of matter, including gases and liquids. It is shown that RONS generation is highly dependent on the discharge conditions and two distinct modes of operation are observed. Downstream of the discharge, the transport of RONS to the sample region is of paramount importance as many highly-reactive species are lost. To address this challenge, the structure of the plasma generating electrodes was systematically studied to optimise the plasma generated air flow and therefore the transport of species downstream. Optimised electrode structures were shown to generate flow velocities in excess of 1m/s which is an order of magnitude improvement over transport by diffusion alone. Using the optimised plasma system, the impact of RONS in real decontamination scenarios linked to food and water security were considered. This included investigation of plasma decontamination of liquid samples, solid surfaces and tissues. It was shown that plasma decontamination can be extremely effective but many factors influence the efficacy of the approach. Microorganisms shielded within a liquid layer or by a complex surface morphology were shown to be particularly difficult to inactivate. Overall, this work has demonstrated that plasma can be a highly effective tool for microbial decontamination but careful consideration of both the discharge parameters and the sample properties is required to achieve the highest level of decontamination.

Non-thermal plasma generated in a dielectric barrier packed-bed reactor has been used for the remediation of chlorinated volatile organic compounds. Chlorinated VOCs are important air pollutant gases which affect both the environment and human health. This thesis uses non-thermal plasma generated in single and multiple packed-bed plasma reactors for the decomposition of dichloromethane (CH2Cl2, DCM) and methyl chloride (CH3Cl). The overall aim of this thesis is to optimize the removal efficiency of DCM and CH3Cl in air plasma by investigating the influence of key process parameters. This thesis starts by investigating the influence of process parameters such as oxygen concentration, initial VOC concentration, energy density, and plasma residence time and background gas on the removal efficiency of both DCM and CH3Cl. Results of these investigations showed maximum removal efficiency with the addition of 2 to 4 % oxygen to nitrogen plasma. Oxygen concentrations in excess of 4 % decreased the decomposition of chlorinated VOCs as a result of ozone and NOx formation. This was improved by adding an alkene, propylene (C3H6), to the gas stream. With propylene additives, the maximum remediation of DCM was achieved in air plasma. It is thought that adding propylene resulted in the generation of more active radicals that play an important role in the decomposition process of DCM as well as a further oxidation of NO to NO2. Results in the single bed also showed that increasing the residence time increased the removal efficiency of chlorinated VOCs in plasma. This was optimized by designing a multiple packed-bed reactor consisting of three packed-bed cells in series, giving a total residence time of 4.2 seconds in the plasma region of the reactor. This reactor was used for both the removal of DCM, and a mixture of DCM and C3H6 in a nitrogen-oxygen gas mixture. A maximum removal efficiency of about 85 % for DCM was achieved in air plasma with the use of three plasma cells and the addition of C3H6 to the gas stream. Nitrogen oxides are air pollutants which are formed as by-products during the decomposition of chlorinated VOCs in plasmas containing nitrogen and oxygen. Results illustrate that the addition of a mixture of DCM and C3H6 resulted in the formation of the lowest concentration of nitric oxide, whilst the total nitrogen oxides concentrations did not increase. A summary of the findings of this work is presented in chapter eight as well as further work. To conclude, the maximum removal efficiency of dichloromethane was achieved in air plasma with the addition of 1000 ppm of propylene and the use of three packed-bed plasma cells in series. The lowest concentration of nitric oxide was formed in this situation.

Non-thermal plasma (NTP) is a promising candidate for controlling engine exhaust emissions. Plasma is known as the fourth state of matter, where both electrons and positive ions co-exist. Both gaseous and particle emissions of diesel exhaust undergo chemical changes when they are exposed to plasma. In this project diesel particulate matter (DPM) mitigation from the actual diesel exhaust by using NTP technology has been studied. The effect of plasma, not only on PM mass but also on PM size distribution, physico-chemical structure of PM and PM removal mechanisms, has been investigated. It was found that NTP technology can significantly reduce both PM mass and number. However, under some circumstances particles can be formed by nucleation. Energy required to create the plasma with the current technology is higher than the benchmark set by the commonly used by the automotive industry. Further research will enable the mechanism of particle creation and energy consumption to be optimised.

This project studies the conversion of CO2 into fuels and chemicals in a dielectric barrier discharge (DBD) reactor. CO2, H2 and CH4 have been used as reactants, and special attention has been paid on understanding the plasma-catalytic synergy when a catalyst is placed in a plasma discharge. CO2 and CH4 are major greenhouse gases, responsible for the global greenhouse effect and climate change. The overall aim of this project is to initiate CO2 hydrogenation and biogas reforming at ambient temperature and atmospheric pressure by using plasma-catalysis. In this project, non-thermal plasma has been generated in a DBD reactor with and without a packed-bed of catalyst, enabling the CO2 conversion to be investigated under three conditions: Plasma alone, thermal catalysis and plasma-catalysis. Transitional metal catalysts such as Cu, Co, Mn, and Ni supported on Al2O3 and SiO2 have been screened, and their performance in the CO2 hydrogenation and biogas reforming have been compared under the three conditions. The synergy between non-thermal plasma and catalysts has been clearly identified. The effects of a catalyst’s properties and operational parameters on the reactions have also been studied. The project starts by the investigation of CO2 hydrogenation with H2. Results showed that reverse water-gas shift reaction and CO2 methanation were dominant in the plasma CO2 hydrogenation process. Compared to plasma CO2 hydrogenation without a catalyst, the combination of plasma with Cu/Al2O3, Mn/Al2O3 and Cu-Mn/Al2O3 catalysts enhanced the conversion of CO2 by 6.7% to 36%. The Mn/Al2O3 catalyst showed the best catalytic activity, as it increased the CO yield by 114% and the energy efficiency of CO production by 116%. The Ni/Al2O3 was even better than the Mn/Al2O3 catalyst, while its presence in the DBD reactor has clearly demonstrated a plasma-catalytic synergy at low temperatures. In addition, the introduction of argon in the reaction has enhanced the conversion of CO2, the yield of CO and CH4 and the energy efficiency of the plasma process. The formation of metastable argon (Ar*) in the plasma has created new reaction-routes which made a significant contribution to the enhanced CO2 conversion and CH4 yield. Biogas reforming has also been initiated at ambient temperatures by non-thermal plasma. The combination of plasma with the Co/Al2O3, Cu/Al2O3, Mn/Al2O3 and Ni/Al2O3 catalysts significantly enhanced CH4 conversion and showed a plasma-catalytic synergy for CH4 conversion and overall energy efficiency of the process. The best CH4 conversion of 19.6% and syngas production have been achieved over the Ni/Al2O3 catalyst at a discharge power of 7.5 W and a gas flow rate of 50 ml min-1. Moreover, the addition of K-promoter into the catalyst has further improved the performance of the Ni/Al2O3 catalyst. A conclusion of the findings of this project and outlook for further work is presented in Chapter seven, where it is concluded that non-thermal plasma has initiated the CO2 hydrogenation and biogas reforming at lower temperatures, comparing with thermal catalytic processes. The combination of plasma and catalyst has further improved the performance of the hydrogenation processes, in terms of conversion, yield, and energy efficiency, while significant synergy between DBD plasma and catalysts has been observed. By upgrading the catalyst and adjusting the operational parameters (e.g. molar ratio of feed gas, preparation method of catalyst, composition of catalyst, and promoters), the plasma-catalytic CO2 hydrogenation and biogas reforming processes can be further optimised.

This thesis focuses on the utilisation of mid-infrared techniques in technological atmospheric pressure, non-thermal plasma (NTP) diagnostics. Two mid-infrared techniques were demonstrated in this work namely laser absorption and Fourier transform infrared (FTIR) spectroscopy. The performance of external-cavity quantum cascade laser (EC-QCL), a relatively new laser type with broad tuning capability was also demonstrated as potential diagnostics tool for technological NTP applications. A dual plate dielectric barrier discharge (DBD) and a packed-bed NTP reactor were designed and fabricated to perform plasma process. Quantitative analysis of the laser absorption and FTIR spectroscopy techniques for gas detection were validated by using standard gas samples. Real-time CO monitoring by means of in-situ laser absorption spectroscopy measurements were performed for gas phase diagnostics in the decomposition of TEOS by means of plasma-enhanced chemical vapour deposition (PE-CVD) and in CO2 reforming of CH4 by means of NTP. In-line FTIR measurements simultaneously recorded the gas spectrum at the exhaust of the plasma reactors. Information from both measurements was found to provide useful information on the plasma processes and chemistry for the NTP applications. Finally, wavelength stability and linearity performance of a broad tuning range EC-QCL were evaluated by using the Allan variance technique. (LOD) at SNR = 1 was estimated to be ~ 2 ppm, achieved under atmospheric pressure, at the room temperature, and a path length of 41 cm for NO detection produced from the decomposition of dichloromethane (DCM) by means of NTP.

Thesis (M.S.)--Southern Illinois University Carbondale, 2008.
"Department of Molecular Biology, Microbiology and Biochemistry." Includes bibliographical references (pages 46-50). Also available online.

This dissertation was undertaken to study two different subjects both related to molecular decomposition by applying a shock tube and non-thermal plasma to decompose selected hydrocarbons. The first approach to molecular decomposition concerned thermal decomposition and oxidation of highly diluted nitromethane (NM) in a shock tube. Reflected shock tube experiments on NM decomposition, using mixtures of 0.2 to 1.5 vol% NM in nitrogen or argon were performed over the temperature range 850-1550 K and pressure range 190-900 kPa, with 46 experiments diluted in nitrogen and 44 diluted in argon. By residual error analysis of the measured decomposition profiles it was found that NM decomposition (CH₃NO₂ + M -> CH₃ + NO₂ + M, where M = N₂ /Ar) corresponds well to a law of first order. Arrhenius expressions corresponding to NM diluted either in N₂ or in Ar were found as k_N2 = 1017.011×exp(-182.6 kJ/mole / R×T 3/mole×s> and k_Ar = 1017.574×exp(-207 kJ/mole / R×T )/mole×s>, respectively. A new reaction mechanism was then proposed, based on new experimental data for NM decomposition both in Ar and N₂ and on three previously developed mechanisms. The new mechanism predicts well the decomposition of NM diluted in both N₂ and Ar within the pressure and temperature range covered by the experiments.

In parallel to, and following the decomposition experiments, oxidative experiments on the ignition delay times of NM/O₂/Ar mixtures were investigated over high temperature and low to high pressure ranges. These experiments were carried out with eight different mixtures of gaseous NM and oxygen diluted in argon, with pressures ranging between 44.3-600 kPa, and temperatures ranging between 842-1378 K.

The oxidation experiments were divided into different categories according to the type of decomposition signals achieved. For signals with and without emission, the apparent quasi-constant activation energy was found from the correlations, to be 64.574 kJ/mol and 113.544 kJ/mol, respectively. The correlations for the ignition delay for time signals with and without emission were deduced as τemission = 0.3669×10^-2×[NM]^-1.02[O₂]^-1.08×[Ar]^1.42×exp(7767/T) and τno emission = 0.3005×10^-2×[NM]^-0.28[O₂]^0.12×[Ar]^-0.59×exp(13657/T), respectively.

The second approach to molecular decomposition concerned the application of non-thermal plasma to initiate reactions and decompose/oxidize selected hydrocarbons, methane and propane, in air. Experiments with a gliding arc discharge device were performed at the university of Orléans on the decomposition/reforming of low-to stoichiometric concentration air/CH₄ mixtures. The presented results show that complete reduction of methane could be obtained if the residence time in the reactor was sufficiently long. The products of the methane decomposition were mainly CO₂, CO and H₂O. The CH₄ conversion rate showed to increase with increasing residence time, temperature of the operating gas, and initial concentration of methane. To achieve complete decomposition of CH₄ in 1 m³ of a 2 vol% mixture, the energy cost was about 1.5 kWh. However, the formation of both CO and NOx in the present gliding discharge system was found to be significant. The produced amount of both CO (0.4-1 vol%) and NO_x (2000-3500 ppm) were in such high quantities that they would constitute an important pollution threat if this process as of today was to be used in large scale CH₄ decomposition. Further experimental investigations were performed on self-built laboratory scale, single- and double dielectric-barrier discharge devices as a means of removing CH₄ and C₃H_{8 f}rom simulated reactive inlet mixtures. The different discharge reactors were all powered by an arrangement of commercially available Tesla coil units capable of high-voltage high-frequency output. The results from each of the different experiments are limited and sometimes only qualitative, but show a tendency that the both CH₄ and C₃H₈ are reduced in a matter of a 3-6 min. retention time. The most plausible mechanism for explaining the current achievements is the decomposition by direct electron impact.

Actuellement et en raison de la diminution des ressources pétrolières pour les années à venir, l'hydrogène ou le gaz de synthèse (H2 + CO) sont considérés comme des vecteurs énergétiques qui pourraient permettre de répondre aux enjeux environnementaux et besoins énergétiques. L'exploitation de la biomasse constitue une réserve de carbone et d'hydrogène pouvant être transformée en carburant utilisable. Le travail de cette thèse s'inscrit dans le cadre des recherches concernant la thématique de la conversion de biomasse par plasma non thermique. L'objectif de ce travail a été d'évaluer l'efficacité d'un réacteur plasma spécifique appelé "Statarc" pour la production de gaz de synthèse à partir de composés issus de la biomasse. Afin de caractériser le comportement du réacteur "Statarc", une étude physique de la décharge dans la vapeur d'eau a d'abord été effectuée. Ce travail préliminaire a été considéré comme une base de référence pour l'interprétation des différents résultats obtenus avec des molécules issues de la biomasse : méthanol, éthanol et phénol. Dans tous les cas étudiés, la concentration en Hydrogène obtenue dans les gaz secs ne dépasse pas 66 %. Des bilans énergétiques et chimiques ont été établis afin d'évaluer les différentes pertes dans notre système. Des essais sur le traitement de l'ammoniaque, représentatif d'autres sources hydrogénées, ont montré l'efficacité de notre réacteur plasma pour la production de gaz de synthèse. Un traitement direct du bois nous a permis de déduire que le traitement plasma génère un mélange gazeux libérant plus d'énergie que celle fournie par la combustion du bois consommé. Afin d'obtenir une meilleure compréhension des phénomènes qui se produisent dans le réacteur plasma, un modèle chimique a été élaboré dans le cas des mélanges méthanol - eau. Les résultats expérimentaux obtenus au cours de ce travail ouvrent des perspectives pour de futures modélisations.

L'objectif de ces travaux était d'étudier l'interaction entre des plasmas froids à pression atmosphérique et des milieux biologiques en vue d'application de ce type de technologie au secteur biomédical.Dans un premier temps, des sources plasma ont été conçues, réalisées et caractérisées. Il s'agissait de réacteurs mettant en œuvre des décharges sur barrière diélectrique dans différents gaz en flux (air synthétique, argon, avec ou sans apport de vapeur d'eau). L'utilisation de l'argon a permis de sélectionner des conditions dans lesquelles le plasma demeurait confiné dans la zone inter-électrodes (humidité relative supérieure à 95% à température ambiante) ou au contraire se propageait soit en atmosphère libre, soit guidé dans un tube isolant dans lequel circulait le gaz (argon sec). Dans ce dernier cas, le phénomène de propagation a été examiné par des mesures électriques résolues dans le temps et les résultats ont été discutés à l'aide des travaux antérieurs disponibles dans la littérature. Le choix de l'air comme gaz plasmagène a également été considéré en raison des contraintes d'application ne permettant pas systématiquement l'utilisation d'un autre gaz.Deux études spécifiques ont été conduites, l'une susceptible de trouver des applications dans le domaine de la « plasma médecine », l'autre dans le domaine de la lutte contre les épidémies virales.Dans ce dernier cas, les travaux ont porté sur l'inactivation de virus bactériens, ou bactériophages, infectant Escherichia coli. Il s'agissait du phage T4, phage à ADN double brin, et du phage MS2, phage à ARN simple brin. Les suspensions de phages ont été diluées dans différentes solutions tampons et déposées sur un substrat de papier hydrosoluble pour être exposées aux différents traitements par plasma froid. L'utilisation originale de ce substrat a permis de résoudre le problème difficile de la récupération des particules de phage après traitement. Ce substrat correspond également à une situation d'application défavorable à ce type de traitement (surface complexe avec diffusion en volume de la suspension, au contraire d'une surface lisse non-adsorbante telle qu'une lamelle de verre), conduisant à obtenir des résultats plus réalistes et transposables à une application réelle. L'inactivation des phages a été quantifiée par comptage de plages de lyse sur culture de E. coli. Ainsi, des taux d'inactivation compris entre 0,66 log/min et 2 log/min ont été mesurés suivant le type de phage, la nature de la solution tampon et le type de traitement. L'influence de la température imposée au substrat a également été examinée.Dans le cadre de l'application en plasma médecine, des cellules d'adénocarcinome humain (cancer du poumon) provenant de cinq patients ont été traitées in-vitro à l'aide du réacteur à barrière diélectrique dans deux conditions de fonctionnement déterminées par la composition du gaz d'alimentation : jet de plasma avec de l'argon sec et source d'espèces oxydantes avec de l'argon saturé en vapeur d'eau à température ambiante. A l'issue d'une exposition de 5 minutes au traitement par décharge d'argon humide, 65% des cellules étaient dans un état apoptotique/nécrotique. Pour le traitement par plasma d'argon sec, les tests globaux de prolifération et d'apoptose n'ont pas montré une grande efficacité. Toutefois, le jet de plasma d'argon sec a présenté un effet rapide et localisé sur les cellules cancéreuses, induisant une inhibition de la capacité des cellules à proliférer et à migrer. Ces deux conditions de fonctionnement sont d'intérêt pour l'application clinique, permettant d'avoir un seul dispositif plasma capable de délivrer un traitement très localisé des cellules (jet plasma) ou de transférer des espèces oxydantes sur une plus grande surface conduisant à des mécanismes d'apoptose (décharge d'argon humide)
The objective of this work was to study the interaction between non-thermal plasmas at atmospheric pressure and biological media in perspective of the application of this type of technology to the biomedical sector.In a first step, plasma sources were designed, realized, and characterized. These reactors implement dielectric barrier discharges in various gases in flow (synthetic air, argon, with or without water vapor admixture). The use of argon allowed the selection of conditions in which the plasma remained confined in the inter-electrode zone (relative humidity higher than 95% at room temperature) or on the contrary propagated either in free atmosphere or guided in an insulating tube in which the gas was flowing (dry argon). In the latter case, the propagation phenomenon was examined by time-resolved electrical measurements and the results were discussed with the help of previous works available in the literature. The choice of air as reactor feed-gas was also considered because of the application constraints that do not systematically allow the use of another gas.Two specific studies were conducted, one likely to find applications in the field of "plasma medicine", the other in the field of control of viral epidemics.In the latter case, the work focused on the inactivation of bacterial viruses, bacteriophages, infecting Escherichia coli. These were phage T4, a double-stranded DNA phage, and phage MS2, a single-stranded RNA phage. The phage suspensions were diluted in different buffer solutions and deposited on a water-soluble paper substrate to be exposed to different non-thermal plasma treatments. The original use of this substrate solved the difficult problem of phage particle recovery after treatment. This substrate also corresponds to an unfavorable application situation for this type of treatment (complex surface with volume diffusion of the suspension, as opposed to a smooth non-adsorbent surface such as a glass slide), leading to more realistic results that can be transposed to a real application. Phage inactivation was quantified by counting lysis plaques on E. coli culture. Thus, inactivation rates ranging from 0.66 log/min to 2 log/min were measured depending on the type of phage, the nature of the buffer solution and the type of treatment. The influence of the temperature imposed on the substrate was also examined.For the plasma medicine application, human adenocarcinoma cells (lung cancer) from five patients were treated in-vitro using the dielectric barrier reactor under two operating conditions determined by the composition of the feed-gas: plasma jet with dry argon and reactive oxidizing species (ROS) source with argon saturated with water vapor at room temperature. After a 5-minute exposure to the humid argon discharge treatment, 65% of the cells were in an apoptotic/necrotic state. For the dry argon plasma treatment, the overall proliferation and apoptosis assays did not show much efficacy. However, the dry argon plasma jet exhibited a rapid and localized effect on the cancer cells, inducing inhibition of the cells' ability to proliferate and migrate. These two operating conditions are of interest for clinical application, allowing to have a single plasma device able to deliver a very localized treatment of cells (plasma jet) or to transfer ROS on a larger surface leading to apoptosis mechanisms (humid argon discharge)

Compounds labelled with 11C (β+, t1/2 = 20.4 min) are used in positron emission tomography (PET), which is a quantitative non-invasive molecular imaging technique. It utilizes computerized reconstruction methods to produce time-resolved images of the radioactivity distribution in living subjects. The feasibility of preparing [11C]methyl iodide from [11C]methane and iodine via a single pass through a non-thermal plasma reactor was explored. [11C]Methyl iodide with a specific radioactivity of 412 ± 32 GBq/µmol was obtained in 13 ± 3% decay-corrected radiochemical yield within 6 min via catalytic hydrogenation of [11C]carbon dioxide (24 GBq) and subsequent iodination, induced by electron impact. Labelled ethyl-, propyl- and butyl iodide was synthesized, within 15 min, via palladium-mediated carbonylation using [11C]carbon monoxide. The carbonylation products, labelled carboxylic acids, esters and aldehydes, were reduced to their corresponding alcohols and converted to alkyl iodides. [1-11C]Ethyl iodide was obtained via palladium-mediated carbonylation of methyl iodide with a decay-corrected radiochemical yield of 55 ± 5%. [1-11C]Propyl iodide and [1-11C]butyl iodide were synthesized via the hydroformylation of ethene and propene with decay-corrected radiochemical yields of 58 ± 4% and 34 ± 2%, respectively. [1-11C]Ethyl iodide was obtained with a specific radioactivity of 84 GBq/mmol from 10 GBq of [11C]carbon monoxide. [1-11C]Propyl iodide was synthesized with a specific radioactivity of 270 GBq/mmol from 12 GBq and [1-11C]butyl iodide with 146 GBq/mmol from 8 GBq. Palladium-mediated hydroxycarbonylation of acetylene was used in the synthesis of [1-11C]acrylic acid. The labelled carboxylic acid was converted to its acid chloride and subsequently treated with amine to yield N-[carbonyl-11C]benzylacrylamide. In an alternative method, [carbonyl-11C]acrylamides were synthesized in decay-corrected radiochemical yields up to 81% via palladium-mediated carbonylative cross-coupling of vinyl halides and amines. Starting from 10 ± 0.5 GBq of [11C]carbon monoxide, N-[carbonyl-11C]benzylacrylamide was obtained in 4 min with a specific radioactivity of 330 ± 4 GBq/µmol.

L'étude des interactions entre les espèces actives générées par un plasma non thermique et diverses surfaces de matériaux font l'objet de ce travail.Dans un premier temps, des polymères provenant de la biomasse ont été le sujet de nos recherches. Ils représentent une source importante de molécules plateforme telle que le glucose à partir desquelles peuvent être générés des produits de haute valeur ajoutée. Plus précisément, les effets d'un plasma à décharge à barrière diélectrique sur la structure et la dépolymérisation de l'inuline, de la cellulose et de l'amidon ont été étudiés. Une variation des paramètres électriques et chimiques de la décharge plasma a été effectuée et leurs effets sur les biopolymères évalués afin de comprendre les mécanismes de réaction. Nos résultats ont montré qu'un traitement initial par le plasma permettait d'augmenter considérablement le rendement final en sucre monomère (fructose ou glucose) par rapport au même produit de départ non traité par le plasma (84 et 54% de glucose à partir réciproquement de l'amidon et de la cellulose traités par plasma, au lieu de 65 et 1 % pour les mêmes produits non traités). Cet effet pourrait être du en partie à une dépolymérisation par attaque acide induite au sein du plasma sur les zones amorphes des biopolymères.Dans un second temps, l'étude a porté sur l'élimination des COV par couplage plasma non-thermique et catalyseur. Pour cette étude, nous avons conçu et mis en oeuvre un appareillage original formé par un réacteur plasma-catalyseur permettant une analyse sous atmosphère contrôlée de la surface du catalyseur par spectroscopie IR (DRIFT). Cet appareillage a permis d'étudier la décomposition de quatre COV (isopropanol, acétone, éthanol et toluène) adsorbé sur différents oxydes métalliques (g-Al2O3, CeO2 et TiO2) placés dans la zone de décharge en temps réel (in-situ). Les premiers résultats ont permis d'élucider certaines voies de décomposition de ces différents COV
The interactions between the active species generated by a non thermal plasma and various material surfaces have been studied in this work. In a first part, biopolymers coming from biomass have been the subject of our investigations as they offer a great reservoir for a platform molecule, glucose, from which valuable chemicals can be generated. More specifically, the effects of a dielectric barrier discharge plasma on the structure and depolymerization of inulin, cellulose and starch were evaluated. For that purpose, the electrical and chemical characteristics of the plasma discharge were varied and their effects on the biopolymers evaluated in order to understand the reaction mechanisms. Our results showed that a plasma pre-treatment increased considerably the final monomer yield (in glucose and fructose) compared to the untreated starting material (84 and 54 % yield in glucose from plasma treated starch and cellulose, instead of 65 and 1 % for the same untreated samples). This effect could be partly explained by the depolymerization of the amorphous areas of the polymers by and acid attack within the plasma discharge.In a second part, the study focused on the removal of VOCs by coupling non-thermal plasma and inorganic materials. For this purpose, we designed and implemented an innovative apparatus. It consists of a plasma-catalyst reactor with controlled atmosphere that allows the analysis of the catalyst surface by IR spectroscopy (DRIFT). The decomposition of four VOCs (isopropanol, acetone, ethanol and toluene) adsorbed on different metallic oxides (y-Al2O3, CeO2 and TiO2) placed within the discharge area have been studied in situ using this method. The first results have enlightened the decomposition pathways of the different VOCs

Objectives: Non-thermal plasma (NTP) has been used to modify enamel and dentin surfaces and improve the interfacial bonding of dental composite restorations. NTP is shown to cause super hydrophilic surface by decreasing the contact angle measurements and improve the quality of the adhesive - enamel and adhesive - dentin interface. We sought to determine the effects of NTP treatment on the bond strength of brackets to enamel. We investigated the application of NTP alone and in combination with phosphoric acid (PA) etching and assessed the outcomes after 24 hours and 1 month. Methods: 84 extracted pre-molars washed and disinfected were divided into 2 broad groups: No-treatment and Treatment group. No - treatment group consisted of 12 premolars on which orthodontic bracket bonding was performed without any surface - treatment except for polishing with pumice. Treatment group consisted of 72 premolars which were divided randomly into 3 main groups of 24 premolars each. These groups were Group 1: PA Etch (30s), Group 2: PA Etch (30s) + NTP (30s) and Group 3 NTP (30s). The bonded teeth were stored in water at 37° C and tested in shear mode after 24 hours and 1 month (n= 12). The fracture mode and adhesive remnant index were determined on de-bonded surfaces. SEM pictures were taken from enamel surfaces after each treatment. Results: During the first 24 hours of testing, SBS was maximum with Etch+ NTP and Etch treated group followed by NTP group ( P < 0.05). After 1 month of ageing the SBS was maximum with the Etch group followed by Etch+ NTP and NTP group ( P < 0.05). ARI scoring was higher with Etch and Etch+ NTP group. SEM pictures showed Type 1 acid etch pattern with Etch and Etch+ NTP group whereas NTP treated group showed no surface changes. Conclusions: NTP application by itself has a potential to bond orthodontic brackets however a longer ageing time will explain more about this feasibility.
Dentistry, Faculty of
Graduate

Every day numerous sources contribute to contaminate water resources with different types of pollutants among which organic compounds represent a major fraction. Conventional remediation processes are not able to remove completely all these contaminants, especially when the compounds are persistent and resistant to oxidation or when they are present in small concentrations, with the consequent increase of probability of find them even in drinking water. The most innovative techniques recently applied to water purification are based on advanced oxidation processes that use highly reactive species and oxidants such as O3, and OH radicals. Examples are ozonation, the Fenton process and all techniques that combine UV radiation, H2O2, O3, with also the possible presence of a catalyst. A more recent approach, still under study and development, applies electrical discharges in the water or in the air above the water. Electrical discharges are the manifestation of the passage of current in a gas and are generated by applying a high voltage between an active electrode and a grounded electrode. The electrical discharge generates a plasma, a highly reactive environment which contains electrons, ions, excited molecules and radicals and as a whole is electrically neutral. When an electric non-thermalizing discharge is applied in a gas at atmospheric pressure and ambient temperature a non-thermal plasma is produced, which is a system thermodynamically not at equilibrium, with high energy electrons in a gas which remains at room temperature. If the gas is air, the generated plasma is rich in active oxygen species such as O3, •OH, O, O•-, O2•-, etc. It is therefore a strongly oxidizing environment that can be employed for the oxidation of any organic pollutant dissolved in the water. Electrical discharges can be applied directly in the water or above the water. From the point of view of energy discharges in the water are more costly. This is one reason that led the research group in which this thesis was carried out to develop a plasma reactor based on discharge above the water. Non-thermal plasma processing is a strongly interdisciplinary field covering engineering, physics and chemistry. It is evident from the literature that our present understanding of the chemical processes occurring in the plasma, and especially the mechanisms of pollutants degradation in water, is still rather incomplete. The aim of my thesis was to study the degradation products and mechanisms of non-thermal plasma induced advanced oxidation of some organic pollutants under well characterized experimental conditions. Phenol was chosen as a model pollutant, to study the role of the main oxidizing species of non-thermal plasma in air, the OH radical and ozone. The research was then extended to a few important emerging organic contaminants. The experiments were carried out with two prototype reactors built in the Department of Chemical Sciences in collaboration with the Department of Electrical Engineering of University of Padova. In this reactors plasma is generated by dielectric barrier discharges in air above the aqueous solution to be treated. In both reactors, the liquid phase is stationary while the air flows above the solution. They differ in size and in the number of wires that constitute the active electrode. In the first part of my project I tested and compared the performance of the two reactors and found that the larger one has an efficiency similar to that of the smaller but allows to treat larger quantities of solution (200 mL instead of 70 mL). This is a good result in view of possible scaling up of the process. Moreover larger samples of treated solution were available for the analyses. I first performed experiments at different pH and with different salts which showed that the oxidation of phenol is much favored in a basic environment. There appears to be no correlation between the reaction rate and the nature and concentration of the salts used (carbonate and phosphate). By means of ionic chromatography I identified and quantified some reaction intermediates. These results integrated with data obtained previously by our group by HPLC and ionic chromatography, TOC analysis and with data on CO2 quantified by FT-IR spectroscopy, allowed me to determine the carbon balance. From these analyses it appeares that the rate of formation of CO2 is much less than that of disappearance of phenol and that an important fraction of the organic carbon present in solution at the end of the treatment of phenol is yet to be identified. I measured the release of CO2 as a function of the treatment time not only for phenol but also for numerous of its reaction intermediates treated individually under the same experimental conditions (formic acid, acetic acid, oxalic acid, glyoxylic acid, malonic acid and glyoxal). Formic acid, the most advanced intermediate of phenol oxidation to CO2, is the only one among those tested which is completely mineralized to CO2 under the conditions investigated. The mechanism of phenol mineralization proceeds through several consecutive reaction steps and possibly involves also some competitive reactions. The slow determining step or steps in the oxidation are before formic acid degradation. I studied also the effect of the pollutant initial concentration on the process efficiency and found that efficiency increases as the pollutant concentration is reduced. Notably at the low pollutant concentrations present in the environment, the DBD discharge induced oxidation leads to complete mineralization of phenol. To determine the role of the main reactive species, O3 and OH, I conducted a series of experiments of treatment of aqueous solutions containing phenol with ozone produced by ex situ discharge, i.e. ozonation, and in situ discharge, i.e. discharge applied directly above the aqueous solution. These experiments have shown that at the same concentration of ozone, the treatment of phenol with in situ discharge is more efficient. So I studied the phenol oxidation with DBD in the presence of tert-butanol, a compound that reacts very slowly with ozone and is used as an efficient OH radicals scavenger. I verified that in the presence of a large excess of tert-butanol the oxidation of phenol is significantly slowed down. The tert-butanol, treated individually, has proved very useful as a mechanistic probe because it reacts only with the OH radical and not with ozone. Therefore it allowed me to estimate the concentration of OH radicals present in solution under the different types of treatment and pH conditions investigated. Finally, the use of argon instead of air allowed me to generate a plasma without ozone and to study the oxidation process of phenol and of tert-butanol, treated individually and together, by the OH radical. The results of all these experiments allowed me to conclude that the greater efficiency of non-thermal plasma applied directly above the solution to be treated with respect to ozonation, is to be attributed to OH radicals produced directly from the in situ discharge. My attention finally turned to so-called emerging organic contaminants. Among them there are several drugs, whose presence in surface waters is documented since a couple of decades in many European countries. They are continuously released into waters from various sources especially from livestock and patients treated pharmacologically and, thanks to the increased sensitivity of today's detection techniques, they have been also detected in trace amounts in drinking water. I chose three drugs detected in Italian waters, especially in the Po Basin: carbamazepine, an antiepileptic, hydrochlorothiazide, a diuretic, and atenolol, a beta-blocker. I determined the rate of degradation in mQ water and in phosphate buffer at pH 7 and I found that the reactivity of the three compounds follows the order: carbamazepine > hydrochlorothiazide > atenolol. I determined the mineralization yields and I found that they considerably increase with decreasing concentration. This is a very encouraging result considering that the low concentrations used in my experiments are still ten thousand times greater than those found in natural waters. Finally, through HPLC analysis coupled with mass spectrometry (LC-ESI) I have identified numerous oxidation intermediates of these drugs and found that in turn they undergo oxidative degradation in the course of the treatment. This thesis provides evidence that plasma treatment of aqueous solutions contaminated by organic compounds is a promising approach to develop novel techniques for water purification that can help the traditional remediation techniques, especially in the complete removal of persistent pollutants in low concentrations.
Innumerevoli sorgenti di inquinamento immettono ogni giorno nelle acque del nostro pianeta inquinanti dei tipi più svariati di cui i composti organici costituiscono una frazione molto consistente. Le tradizionali tecniche di depurazione delle acque non sono in grado di rimuovere completamente tutti questi contaminanti, soprattutto quelli più persistenti e resistenti all’ossidazione, che possono essere presenti, seppur in concentrazioni molto basse, addirittura nelle acque potabili. Le tecniche più innovative recentemente applicate per la depurazione delle acque si basano su processi di ossidazione avanzata che utilizzano specie altamente reattive e ossidanti quali l’O3, e i radicali OH. Esempi ne sono l’ozonizzazione, il processo Fenton e tutte le tecniche che combinano radiazione UV, H2O2, O3 con l’eventuale presenza di catalizzatori. Più recente e ancora in fase di studio l’applicazione di scariche elettriche nell’acqua e sopra l’acqua. La scarica elettrica è la manifestazione del passaggio di corrente in un gas e viene generata applicando una tensione elevata tra un elettrodo detto attivo e un contro elettrodo posto a potenziale di terra. La scarica elettrica genera un plasma, un ambiente altamente reattivo contenente elettroni, ioni, molecole eccitate, radicali, specie neutre, che nell’insieme risulta elettricamente neutro. Quando viene applicata una scarica elettrica non termalizzante in un gas a pressione atmosferica e temperatura ambiente si genera un plasma non-termico, in non-equilibrio termodinamico, in cui gli elettroni acquistano elevata energia e temperatura mentre tutti gli altri costituenti permangono a temperatura ambiente. Se il gas è aria, il plasma generato è ricco di specie attive dell’ossigeno quali O3, •OH, O, O2•-, etc. ed è un quindi un ambiente fortemente ossidante che può essere impiegato per l’ossidazione di inquinanti organici disciolti nelle acque. La scarica elettrica può essere innescata direttamente nell’acqua oppure nell’aria sopra l’acqua da trattare: nel primo caso la scarica è energeticamente più dispendiosa. Questo è uno dei motivi che hanno condotto il gruppo di ricerca presso cui è stata svolta questa tesi ad impiegare scariche elettriche sopra l’acqua da trattare. Inoltre ad oggi, nonostante la complessità del sistema plasma necessiti ancora di molto studio sotto tutti gli aspetti, quello ingegneristico, fisico e chimico, gli sviluppi di tipo applicativo sono piuttosto avanzati mentre ancora pochi sono gli studi di carattere fondamentale sui processi chimici che avvengono nel plasma e soprattutto sui meccanismi di degradazione degli inquinanti in acqua. Lo scopo della mia Tesi è stato proprio quello di studiare il processo di degradazione di alcuni inquinanti organici modello, tra cui principalmente il fenolo, ed il ruolo delle principali specie ossidanti del plasma non-termico in aria. Gli esperimenti sono stati condotti utilizzando due prototipi di reattore al plasma costruiti nel Dipartimento di Scienze Chimiche in collaborazione con il Dipartimento di Ingegneria Elettrica dell’Università di Padova. Essi generano scariche a barriera di dielettrico nell’aria sovrastante la soluzione acquosa da trattare. In entrambi i reattori la fase liquida è stazionaria mentre l’aria fluisce sopra la soluzione, mentre differiscono per le dimensioni e per il numero di fili (7 oppure 2) che costituiscono l’elettrodo attivo. Essendo il reattore grande di più recente costruzione, mi sono innanzitutto occupata del suo collaudo e della caratterizzazione. Presenta efficienza pressoché simile al primo ma permette di trattare quantitativi maggiori di soluzione (200 mL anziché 70 mL) con conseguente facilitazione anche per le analisi degli intermedi di ossidazione. La selettività del processo a dare CO2 è infatti un aspetto molto importante, in quanto alcuni intermedi di ossidazione possono essere inquinanti più pericolosi del composto di partenza. Ho quindi perfezionato il metodo di quantificazione dell’anidride carbonica, prodotto finale del processo d’ossidazione indotto da scarica elettrica, estendendo la calibrazione a concentrazioni molto piccole di CO2 per ridurre gli errori sulla misura del grado di mineralizzazione degli inquinanti trattati. Utilizzando fenolo come inquinante modello ho effettuato esperimenti a diversi valori di pH e con diversi sali presenti in soluzione da cui è risultato che l’ossidazione del fenolo è molto favorita in ambiente basico. Non è stata invece osservata alcuna correlazione evidente fra la velocità di reazione e la natura e concentrazione del sale utilizzato (carbonato e fosfato). Mediante cromatografia ionica ho individuato e quantificato alcuni intermedi di reazione completando così uno studio svolto in precedenza tramite analisi di cromatografia HPLC, analisi TOC e analisi della CO2 tramite spettroscopia FT-IR e determinando il bilancio del carbonio. Da queste analisi è risultato che la velocità di formazione della CO2 è molto minore della velocità di scomparsa del fenolo e che una frazione importante del carbonio organico presente in soluzione alla fine del trattamento del fenolo è ancora da identificare. Ho misurato il rilascio di CO2 in funzione del tempo di trattamento effettuando esperimenti nel reattore al plasma con numerosi intermedi di reazione del fenolo (l’acido formico, l’acido acetico, l’acido ossalico, l’acido gliossilico, l’acido malonico ed il gliossale). L’unico intermedio che mineralizza completamente a CO2 nelle condizioni investigate è l’acido formico, l’intermedio più avanzato della ossidazione a CO2 del fenolo. Il meccanismo di mineralizzazione del fenolo quindi procede attraverso più stadi consecutivi di reazione, con la complicazione anche di possibili reazioni competitive e lo stadio o gli stadi lenti dell’ossidazione sono a monte di questo intermedio. Infine lo studio dell’effetto della concentrazione iniziale mi consente di concludere che alle basse concentrazioni presenti nell’ambiente, l’ossidazione indotta da scarica DBD porta alla completa mineralizzazione del fenolo. Per determinare il ruolo delle principali specie reattive, O3 e OH, ho effettuato una serie di esperimenti di trattamento di soluzioni acquose contenenti fenolo con scarica in situ, cioè applicata direttamente sopra la soluzione acquosa, e con ozono prodotto tramite scarica applicata ex situ in un ozonizzatore commerciale posto a monte del reattore, utilizzato in questo caso come semplice recipiente di reazione. Questi esperimenti hanno indicato che a parità di concentrazione di ozono il trattamento del fenolo con scarica DBD in situ è più efficiente. Quindi ho studiato l’ossidazione del fenolo con scarica DBD in presenza di ter-butanolo, un composto che reagisce molto lentamente con l’ozono ed è noto dalla letteratura essere un efficace sequestratore di radicali OH. Questi esperimenti hanno dimostrato che in presenza di un forte eccesso di ter-butanolo l’ossidazione del fenolo viene fortemente rallentata. Il ter-butanolo, trattato singolarmente, si è rivelato una sonda meccanicistica utilissima in quanto reagisce solo con il radicale OH e non con l’ozono: ha consentito quindi di determinare la concentrazione di radicali OH presenti in soluzione nei diversi tipi di trattamento e ai diversi pH sperimentati. Infine l’impiego di argon anzichè d’aria mi ha permesso di generare un plasma privo di ozono e studiare il processo di degradazione del fenolo e del ter-butanolo trattati singolarmente e assieme, ad opera del radicale OH. I risultati di tutti questi esperimenti mi hanno permesso di verificare che l’applicazione della scarica in situ induce un processo di degradazione più efficiente rispetto a quello osservato, a parità di condizioni sperimentali, in esperimenti di ozonizzazione, ovvero con scarica ex situ. Questo risultato è attribuito alla presenza di una maggiore quantità di radicali OH, noti per la loro estrema reattività con tutte le strutture molecolari organiche, prodotti direttamente dalla scarica in situ a contatto con la soluzione da trattare. La mia attenzione infine si è rivolta ad alcuni contaminanti organici emergenti, in particolare a tre farmaci, la cui presenza nelle acque superficiali è documentata da un paio di decenni in molti paesi europei, e, grazie alle odierne tecniche di analisi molto sensibili, è stata rilevata addirittura nelle acque di falda e potabili. Ho scelto quindi tre farmaci tra quelli maggiormente rilevati nelle acque italiane, in particolare nel bacino del Po: la carbamazepina, un antiepilettico, l’idroclorotiazide, un diuretico, e l’atenololo, un beta-bloccante. Ho determinato la velocità di degradazione nel reattore al plasma in acqua mQ e in tampone fosfato a pH 7, riscontrando che la reattività dei tre composti segue l’ordine: carbamazepina > idroclorotiazide > atenololo. Ho determinato le rese di mineralizzazione e verificato che aumentano notevolmente al diminuire della concentrazione, risultato molto incoraggiante se si considera che le concentrazioni più basse utilizzate nei miei esperimenti sono ancora diecimila volte maggiori di quelle riscontrate nelle acque naturali. Infine attraverso analisi di cromatografia liquida accoppiata alla spettrometria di massa (LC-ESI) ho potuto identificare numerosi intermedi di ossidazione che nel corso del trattamento subiscono a loro volta degradazione ossidativa fino al prodotto ultimo, l’anidride carbonica. Questa tesi conferma ed estende risultati che dimostrano come il trattamento al plasma di soluzioni acquose inquinate da composti organici sia una tecnica promettente di depurazione delle acque che può essere efficacemente affiancata a quelle più tradizionali, soprattutto per la rimozione completa di composti persistenti presenti in basse concentrazioni. La Tesi fornisce inoltre un contributo alla comprensione dei meccanismi di ossidazione indotti da plasma non termico prodotto a contatto con soluzioni acquose.

Biofilms are colonies of bacteria attached to the surface at a solid-fluid interface. Bacteria in biofilm produce exopolysaccharides (EPS) that form a gel-like matrix in which the bacteria are embedded. Biofilms have numerous consequences in industrial and medical settings, both positive (bioreactors, digestion) and negative (blocking, as corrosive damage of materials/devices, food contamination, clinical infection). The use of antibiotics or mechanical clearing can be effective at removing biofilms, but such treatments are not always effective or appropriate in all situations. Recently, non-thermal atmospheric plasma treatments have been proposed as an alternative (or complementary) form of treatment, that can target sites of infection with minimal damage to the surroundings (e.g. host cells in a clinical setting). These plasmas generate a multitude of chemical species, most of which are very short lived, that can infiltrate and diffuse into the biofilm killing the bacteria within. The aim of this thesis is to develop a multi-dimensional mathematical model to investigate the effect of a non- thermal plasma on biofilms in time and space and to identify key factors that determine effectiveness of the treatment. Most of the chemical products of cold plasmas are too short lived, or too reactive, to be effective in killing the biofilms, it is the longer live species, e.g. ozone, hydrogen peroxide, acid species, that penetrated the biofilm and do the most damage. However, the EPS in biofilms is an effective barrier against ozone and hydrogen peroxide. No published biofilm model combines multi-dimensional growth with a detailed description of EPS production, hence a new mathematical model is developed and applied to simulating plasma treatment. The thesis is split broadly into two parts. The first part presents a new biofilm model framework that simulates growth in response to any number of substrates (e.g. nutrient, oxygen). The model combines an Individual based model (IbM) description of bacteria (individuals or clusters) and substrates are described as a continuum. Novel features of the framework are the assumption that EPS forms a continuum over the domain and the explicit consideration of cellular energy (ATP). Simulations of this model demonstrate the contrast between biofilm grown with topical nutrient sources (forming irregular, bumpy biofilm) and basal nutrient source with topical oxygen such as biofilm grown on agar (forming regular spatially uniform biofilms). The former is in broad agreement with experiments whilst the latter, to our knowledge, has been the subject of very little experimental study. The second part extends the modelling framework to consider the effect of the plasma species. The simulations demonstrate that penetration is a key factor in their effectiveness, for which EPS plays a key role in preventing spread within and beyond the plasma treated zone. The simulations provide estimates of the timescale of equilibration of the main plasma species, predict the effect of combining these species and demonstrate how the constituents of the biofilm can change following treatment. A number of recommended suggestions for future theoretical and experimental study are discussed in the conclusions.

Combiné à une demande en énergie croissante, les ressources limitées de pétrole et de gaz naturel nous obligent à rechercher des alternatives plus propres et de plus en plus efficaces pour la production d'énergie. L'hydrogène (H2) est considéré comme un vecteur énergétique prometteur. Cependant, il existe plusieurs problèmes liés à l'utilisation de H2, depuis son transport jusqu'à sa distribution. La transformation de la molécule de H2 peut s’effectuer par la synthèse d’un composé contenant du carbone, à savoir du méthane (CH4), offrant ainsi la possibilité d'utiliser le réseau de transport existante. En effet, la réaction de Sabatier, qui est fortement exothermique, implique la réaction du dioxyde de carbone (CO2) et du dihydrogène afin de produire du méthane et de l’eau. Ce procédé, appelé méthanation, représente une approche réalisable contribuant à la réduction des émissions de CO2 dans l'atmosphère, à travers un cycle fermé du carbone impliquant la valorisation du CO2. Cependant, en dessous d’une température de 200 °C, la conversion devient proche de zéro, tandis qu’à des températures plus élevés (>300 °C), des réactions secondaires favorisant la formation du CO et d’H2 apparaissent. C’est une des raisons pour laquelle de nouveaux types de catalyseurs doivent être étudiés dans le but de maximiser la sélectivité du méthane à des basses températures et à pression atmosphérique. Par conséquent, en utilisant des catalyseurs associés aux plasmas DBD, l’activation de la réaction de méthanation peut ainsi être améliorée. Plusieurs catalyseurs contenant du Ni ont donc été synthétisés en utilisant différents oxydes de Ce-Zr en tant que supports, avec un ratio Ce-Zr variable. Les résultats obtenus dans des conditions adiabatiques à basses températures (comprises entre 120 et 150 °C), en présence de catalyseurs activés par plasma, sont prometteurs. La conversion du CO2 en CH4 est d’environ 85 % avec une sélectivité proche de 100 %. En l’absence de catalyseurs activés par plasma, cette même conversion est observée à 350 °C, tandis qu’à basses températures et sans plasma, celle-ci est presque nulle. Ce système à basse consommation d’énergie permet donc de diminuer le coût de production du méthane synthétique avec une durée de vie du catalyseur prolongée
The limited resources of oil and natural gas, together with an increasing energy demand, forces us to seek more and more efficient and cleaner energy production alternatives. Hydrogen has been recently considered as a promising energy carrier. However, there are several inherent problems to the utilization of H2, from its transportation to its distribution. Transformation of the H2 molecule by fixing into a carbon-containing compound, i.e. CH4, will offer the possibility of using the conventional transportation network. Indeed, the Sabatier reaction, which is highly exothermic, involves the reaction of carbon dioxide and hydrogen gas in order to produce methane and water. This process, called methanation, represents a feasible approach contributing to the reduction of the CO2 emissions in our atmosphere, through a closed carbon cycle involving the valorization of CO2, i.e. from capture. However, below a temperature of 250 °C, the conversion becomes practically close to 0 %, whereas at higher temperatures, i.e., (>300 ºC), the co-existence of secondary reactions favours the formation of CO and H2. This is the reason why new catalysts and process conditions are continuously being investigated in order to maximize the methane selectivity at low reaction temperatures at atmospheric pressure. Therefore, by using catalysts combined to Dielectric Barrier Discharge plasmas (DBD), the activation of the methanation reaction can be enhanced and overcome the drawbacks of existing conventional processes. Several Ni-containing catalysts were prepared using various ceria-zirconia oxides as supports, with different Ce/Zr ratios. The results obtained in the adiabatic conditions at low temperatures (ranging between 100-150 °C), in the presence of catalysts activated by plasma, are promising. Indeed, the conversion of CO2 to CH4 is about 85 % with a selectivity close to 100 %. The same conversion in the absence of the plasma activation of the catalyst is observed at 350 °C. At low temperatures (120-150 °C) and without plasma, conversion is almost close to zero. This low consumption energy system helps reduce the cost of production of synthetic methane together with an extended life of the catalyst

Diesel Particulate Filter (DPF) is believed to be one of the most effective methods and provides an efficient system that traps more than 90% of PM. However, the soot accumulated within the filter requires a regeneration process to recover its performance. Thus, the high oxidation ability of NO-NO₂ increases the interest of applying it in the low temperature regeneration process. The intention of this thesis is to investigate several possibilities of on-board NO-NO₂ oxidation methods for increasing the NO₂/NO_x ratio in the exhaust gas. These possible oxidation routes incorporate the in-cylinder to the exhaust gas treatment processes. A wide range of operated temperatures are managed by the application of the non-thermal plasma oxidation (NTP) for low temperatures, catalytic oxidation for moderated temperatures and thermal oxidation for high temperatures studied. The in-cylinder NO oxidation was significantly improved by adding H₂ or the reformed EGR (REGR) to the combustion. The remaining H₂ after the combustion also contributes to the downstream HC-SCR which in turn promotes the NO oxidation. The thermal and NTP methods in the exhaust treatment cannot adequately achieve a satisfactory NO oxidation result under a single occupied condition. The propane (C₃H₈) addition may potentially create useful radicals (HO₂, RO₂) within the system and convert a large portion of NO into NO₂.

Le dioxyde de carbone et le méthane représentent les deux principaux gaz à effet de serre produits par l’Homme. Dans le contexte environnemental actuel, leur valorisation constitue un enjeu scientifique majeur. Cette thèse s’inscrit ainsi dans cet objectif de valorisation du CO2 et du CH4. Pour cela, la réaction de reformage sec du méthane a été réalisée par couplage plasma non-thermique et catalyse. De façon générale, des catalyseurs à base de métaux, comme Ni/Al2O3, sont utilisés lors du couplage plasma-catalyse. Toutefois, les résultats obtenus en termes de conversions et de sélectivités sont très hétérogènes, voire contradictoires. Afin de mieux comprendre les origines de cette disparité, l’influence de la nature du solide présent dans la zone plasma a été étudiée. Pour ce faire, divers oxydes métalliques, tels que γ-Al2O3, α-Al2O3, MgO, CaO, La2O3, ZnO, CeO2, SiO2, BaO, TiO2 ou encore une zéolithe, ont été sélectionnés pour leurs propriétés physico-chimiques distinctes (permittivité, acidité, basicité, surface spécifique). Ces oxydes ont été testés dans des conditions opératoires identiques en utilisant un réacteur plasma à barrière diélectrique (DBD), une puissance de 8W (fréquence 800 Hz, tension de 13 et 16 kV), et un débit total de 40 mL.min-1, l’hélium étant le constituant majoritaire : 75% volumique.L’étude des caractéristiques physiques des catalyseurs a par exemple permis de souligner l’impact de la permittivité ou de la taille des grains des différents matériaux sur la décharge. Une constante diélectrique élevée n’est pas favorable à la réaction. La présence de TiO2 (εr=2903) dans la décharge entraîne une chute des conversions du CH4 et du CO2, qui passent respectivement de 20 et 9 % à vide, à 5 et 2% avec TiO2. Par ailleurs, il a été montré que la présence de grains trop volumineux réduit la surface accessible au plasma, ce qui entraîne une diminution des conversions des réactifs. Ces dernières passent de 30 et 15% respectivement pour CH4 et CO2 pour des grains de petite taille (250-355µm), à 24 et 11% pour les plus gros grains (800-1000µm). De plus, l’étude des propriétés chimiques des catalyseurs a mis en avant l’influence de la basicité sur les conversions du dioxyde de carbone. Il semble que plus le solide possède de sites basiques, plus l’adsorption du CO2 est favorisée. En outre, une étude plus détaillée a été réalisée en couplant plasma et oxyde de calcium, car ce dernier possède non seulement une faible permittivité (εr=2,1), mais également un nombre important de sites basiques. L’influence du ratio CH4/CO2 et de la température sur CaO a permis de mettre en évidence l’apparition de modifications structurales et texturales après décharge plasma. Il a été montré que pour un ratio CH4/CO2 = 2, et à 300°C, la formation d’eau (réaction inverse de gaz à l’eau) favorise la formation de Ca(OH)2 et CaCO3. L’ajout d’eau (0,1g.h-1) au mélange réactionnel a permis de mettre en avant l’hydroxylation de CaO et la carbonatation de Ca(OH)2. Par ailleurs, la carbonatation de l’hydroxyde de calcium hydraté (Ca(OH)2+ 18% H2O) est favorisée sous plasma. L’analyse des gaz en sortie par spectromètre de masse fait ressortir un phénomène d'oscillation lié à l’adsorption du CO2. Un mécanisme réactionnel, au cours duquel l’élimination et l’adsorption de CO2 et H2O s’effectuent successivement, a été proposé. Un plasma peu énergétique (4W) favorise la carbonatation du solide puisque sa composition est initialement : 0,9Ca(OH)2, 0,9 H2O, 0,1 CaCO3 et devient 0,1Ca(OH)2, 0,9CaCO3 après plasma. Par conséquent, il semble que l’application d’un plasma non-thermique favorise la diffusion du CO2 au cœur de Ca(OH)2+ 18% H2O. En outre, la carbonatation de solides, qui constitue une méthode de stockage du CO2, est un procédé lent et le plus souvent limité par la diffusion du dioxyde de carbone. Dans cette étude, il a été montré que le plasma pourrait présenter un grand intérêt, à condition d’augmenter l’efficacité du procédé
The two main greenhouse gases emitted by human activities are carbon dioxide and methane. Within the context of the current environmental crisis, it has become vital to find a method to valorise these gases. Therefore, this thesis has been conducted to be a part of this process: CO2 and CH4 valorisation. To this end, dry reforming of methane was carried out by coupling non-thermal plasma and catalysts. Metal-based catalysts, such as Ni/Al2O3, are usually used for plasma-catalyst. However, the results are often dissimilar, and even contradictory, as far as conversions and selectivities are concerned. In order to better understand the reasons behind this heterogeneity, the influence of the nature of the solid was studied. For this purpose, metal oxides, such as γ-Al2O3, α-Al2O3, MgO, CaO, La2O3, ZnO, CeO2, SiO2, BaO, TiO2, and a zeolite, were selected because of their respective physicochemical properties (permittivity, acidity, basicity, specific surface). These oxides were submitted to identical tests with identical operational conditions, e.g. a dielectric barrier discharge reactor (DBD), 8W power (800 Hz frequency, 13 and 16 kV tension), a total output of 40 mL.min-1 and a CH4/CO2=0,5 ratio.The study of the physical characteristics of catalysts highlighted the impact of the material’s permittivity or of the size of its grains on the discharge. A high dielectric constant hindered the reaction. When TiO2 (εr=2903) was found in the discharge, it led to a decline in CH4 and CO2 conversions, as they decreased from respectively 20 and 9% without catalyst, to 5 and 2% with TiO2. Furthermore, when grains were too large, there was less surface accessible to plasma, which led to a fall in the reagents’ conversions. Indeed, they dropped from respectively 30 and 15% for CH4 and CO2 for small-sized grains (250-355µm), to 24 and 11% for the largest grains (800-1000µm). In addition to this, the study of the catalysts’ chemical properties showed how basicity influenced the conversions of carbon dioxide. It seemed that when there was a great number of basic sites in a solid, CO2 adsorption was likely to be better. Furthermore, a more detailed study was carried out by coupling calcium oxide with non-thermal plasma. Indeed, the former does not only have a low permittivity, but also a high number of basic sites. Structural and textural modifications appeared after plasma. This was shown by examining the influence of the CH4/CO2 ratio and of the temperature on CaO. When there was a CH4/CO2 = 2 ratio, for a temperature of 300°C, the production of water (reverse water-gas shift reaction) tended to result in the formation of Ca(OH)2 and CaCO3.When water (0,1g.h-1) was added to the reaction mixture, CaO hydroxylation and Ca(OH)2 carbonatation were observed. Furthermore, hydrated calcium hydroxide (Ca(OH)2+ 18% H2O) carbonatation is more likely to occur under plasma. The analysis of gases at the outlet by a mass spectrometer revealed an oscillatory phenomenon associated with CO2 adsorption. A reaction pathway, during which CO2 and H2O adsorption and elimination occur successively, was therefore put forward. A low-energy plasma (4W) is likely to cause carbonatation, as the solid is originally composed of 0,9Ca(OH)2, 0,9 H2O, 0,1 CaCO3, and is made of 0,1Ca(OH)2, 0,9CaCO3 after plasma. Thus, applying a non-thermal plasma seems to encourage CO2 diffusion at the core of Ca(OH)2+ 18% H2O. Carbonatation is a method to store CO2 but it is a slow process, which is often hindered by CO2 diffusion. In this study, plasma was proved to be a highly interesting process, provided that its efficiency could be increased

In recent years, there has been growing interest in developing non-thermal atmospheric pressure plasma (NAPP) devices for biomedical applications. Many of these applications are dependent on the production of nitric oxide (NO) and reactive oxygen species (ROS) by NAPP devices. These reactive species are bioactive molecules which have important and diverse roles in many types of cells and tissues. A potential application of NAPP devices that has yet to be explored is the topical treatment of cutaneous leishmaniasis (CL). Leishmaniasis is a neglected yet widespread disease in tropical and subtropical countries caused by the parasites of genus Leishmania. Inside human skin, Leishmania species infiltrate macrophages, cells which normally kill parasites and other pathogens by producing cytotoxic quantities of NO and ROS. Leishmania parasites are able to survive inside these cells by subverting their normal cell functions, including preventing NO and ROS generation. Hence, NAPPs could be used to treat CL by providing NO and ROS to the site of infection. The goal of this thesis is to investigate this possibility.To that end, the atmospheric pressure glow discharge jet (APGD-j) was developed and used in both in vitro and in vivo experiments. Reactive species generation by the APGD-j was characterized using optical emission spectroscopy, demonstrating production of NO and ROS. A preliminary characterization of plasma treated cell culture media confirmed that NO transfers into the extracellular environment in an in vitro setting. The bone-marrow derived murine macrophage cell line B10R was used to assess the effects of the plasma on macrophage cell signalling and function. Treatments of the cells directly with the plasma and indirectly with plasma-treated media were shown to induce phosphorylation of p38, and the direct treatment also induced phosphorylation of JNK. These two proteins are part of the mitogen activated protein kinase (MAPK) family of signalling proteins involved in the immune response of macrophages which are down regulated by Leishmania infections. The translocation of the transcription factor downstream of these MAPK, activator protein 1 (AP-1), into the nucleus of the macrophage also increases following APGD-j treatment. Gene expression related to the macrophage immune response assessed 8 hours after indirect treatment. Out of 89 genes tested, 23 genes were modulated by the plasma treatment. The most notable change in gene expression was a 27-fold upregulation of interleukin-1B (IL-1B), suggesting that the treatment has a pro-inflammatory effect on macrophages. Treating the Lm-LUC strain of L. major with the APGD-j resulted in cell membrane disruption and loss of metabolic activity in part of the population, demonstrating the toxic effects of the plasma treatment. Finally, APGD-j treatments of non-curing CL wounds of BALB/c mice significantly reduced the level of ulceration without affecting the parasite load in the skin. Together, these results suggest that although there is still work to be done regarding the optimization of the APGD-j for CL treatments, future generations of the device could potentially be used to minimize scarring and reduce recovery time of CL wounds.
Au cours des dernières années, le domaine des applications biomédicales des plasmas non-thermiques a connu une croissance exponentielle. Plusieurs de ces applications dépendent de la production du monoxyde d'azote (NO) et des espèces réactives à base d'oxygène (ROS) à l'intérieur des plasmas. Ces espèces réactives ont une activité biologique, et elles ont des rôles importants et diversifiés dans de nombreux types de cellules et tissues humains. Une application potentielle des plasmas non-thermiques qui à date n'a pas encore été exploré en profondeur est le traitement de la leishmaniose cutané. La leishmaniose est une maladie négligée bien que très rependue mondialement dans les régions tropicales et subtropicales. Elle est causée par un parasite appartenant au genre Leishmania. A l'intérieur de la peau humaine, les espèces de Leishmania infiltrent les macrophages, des cellules qui normalement tuent les parasites et d'autres agents infectieux en produisant des quantités cytotoxiques de NO et des ROS. Leur survie dans ce milieu est possible grâce à leur capacité d'inhiber le fonctionnement normal des macrophages, y compris d'empêcher la production du NO et des ROS. Par conséquent, l'application d'un plasma non-thermique au site de l'infection pourrait aider à traiter la leishmaniose cutanée. L'objectif de cette thèse est d'étudier cette possibilité.À cette fin, une source à jet de plasma non-thermique miniature opérant à atmosphérique, l'APGD-j, a été fabriquée et utilisée pour effectuer des expériences in vitro et in vivo. La production du NO et des ROS par l'APGD-j a été confirmée avec le spectre d'émission de la décharge électrique. Une caractérisation préliminaire des milieux in vitro a aussi confirmé le transfert du NO à l'intérieur du milieu extracellulaire. Une lignée de macrophages dérivés de la moelle osseuse murine nommé B10R a été utilisée pour effectuer des études sur l'effet des traitements de plasma sur la signalisation et le fonctionnement cellulaire des macrophages. Le traitement direct ainsi que le traitement indirect des cellules avec une solution de milieu cellulaire traité par l'APGD-j induit la phosphorylation du p38, et le traitement direct induit aussi la phosphorylation du JNK. Ces deux molécules sont des protéines kinases activées pas les mitogènes (MAPK), des protéines de signalisation qui sont désactivés suivant une infection à la leishmaniose. De plus, le traitement indirect des B10R induit la translocation de la protéine activatrice 1 (AP-1), un facteur de transcription en aval des MAPKs, vers l'intérieur du noyau. Ceci confirme l'activation de la cascade de signalisation associé au MAPK. L'expression des gènes associés aux fonctions immunitaires du macrophage a été évaluée. Des 89 gènes testés, 23 gènes ont été modulé par l'APGD-j. Le changement le plus important a été l'expression de Interleukine-1B (IL-1B), dont l'expression a augmenté 27 fois. Ce dernier résultat suggère que le traitement APGD-j a un effet pro-inflammatoire sur les macrophages. Le traitement de la lignée de promastigote Lm-LUC provenant de l'espèce L. major a entraîné une rupture de la membrane cellulaire ainsi qu'une perte de l'activité métabolique pour une fraction de la population, ce qui démontre les effets toxiques du traitement. Enfin, des lésions cutanées sur les peaux des souris BALB/c causées par l'administration des parasites de la lignée Lm-LUC ont été traitées avec l'APGD-j. Malgré que le nombre de parasites à l'intérieur du tissue n'a pas été affecté, le niveau d'ulcération des lésions a été réduit de façon significative. Ensemble, ces résultats suggèrent que même s'il y a encore du travail à faire en ce qui concerne l'optimisation de l'APGD-j pour cette application, les générations futures de l'appareil pourraient être utilisées pour minimiser les cicatrices et réduire le temps de récupération des lésions.

Bacterial spores have remarkable resistance to a variety of harsh conditions, causing spoilage in food industry and becoming the primary bacterial agent in biowarfare and bioterrorism. In this study, inactivation mechanisms of Bacillus amyloliquefaciens (BA) spores by non-thermal plasma (NTP) were investigated by using Fourier-transform infrared spectroscopy (FTIR) as a major tool to exam spores after NTP treatment. Chemometric techniques, such as multivariate classification models based on soft independent modeling of Class Analogy (SIMCA) and Principal Component Analysis (PCA), were employed to identify functional group changes in FTIR spectra. The IR absorbance bands correlated to dipicolinic acid (DPA) decreased after NTP treatment indicating that DPA released and then reacted with reactive species generated by NTP and it was confirmed by nuclear magnetic resonance (NMR). Also IR absorbance bands corresponding to protein structure changed. FTIR combined with UV-Vis spectroscopy was used to monitor spore germination. Large amount of DPA released in a short time when spores germinated at 50°C, showing that DPA released in response to heating. NTP treated spores could germinate with little DPA release due to sub-lethal effects induced by plasma. Also an empirical model based on Weibull distribution was established to describe the spore germination process showing that NTP treated spores exhibited abnormal germination pattern. Inactivation mechanisms of NTP with air as feed gas was compared with high-pressure, wet heat, chemical treatment using chlorine dioxide (CD) and NTP with argon as feed gas. The results showed that few chemical changes in spores after autoclave and high pressure treatments, though protein structure changed. CD and NTP with air as feed gas inactivated spores by oxidation. DPA released after NTP with argon as feed gas treatment and it is possible that UV and charged particles accounts for the inactivation. This study provides in depth insight into the inactivation mechanism of NTP and information for optimizing NTP process.

Today we face the formidable challenge of meeting the fuel needs of a growing population while minimizing the adverse impacts on our environment. Thus, we search for technologies that can provide us with renewable fuels while mitigating the emission of global pollutants. To this end, use of non-thermal plasma processes can offer novel methods for efficiently and effectively converting carbon dioxide and water vapor into synthesis gas for the production of renewable fuels. Particularly, non-thermal plasma technologies offer distinct advantages over conventional methods including lower operating temperatures, reduced need for catalysts and potentially lower manufacturing and operation costs. The non-thermal plasma reactors have been studied for ozone generation, material synthesis, decontamination, thruster for microsatellites, and biomedical applications. This dissertation focuses on producing synthesis gas using a non-thermal, microhollow cathode discharge (MHCD) plasma reactor. The prototype MHCD reactor consisted of a mica plate as a dielectric layer that was in between two aluminum electrodes with a through hole. First, electrical characterization of the reactor was performed in the self-pulsing regime, and the reactor was modeled with an equivalent circuit which consisted of a constant capacitance and a variable, negative differential resistance. The values of the resistor and capacitors were recovered from experimental data, and the introduced circuit model was validated with independent experiments. Experimental data showed that increasing the applied voltage increased the current, self-pulsing frequency and average power consumption of the reactor, while it decreased the peak voltage. Subsequently, carbon dioxide and water vapor balanced with argon as the carrier gas were fed through the hole, and parametric experiments were conducted to investigate the effects of applied voltage (from 2.5 to 4.5 kV), flow rate (from 10 to 800 mL/min), CO₂ mole fraction in influent (from 9.95% to 99.5%), dielectric thickness (from 150 to 450 [mu]m) and discharge hole diameter (from 200 to 515 [mu]m) on the composition of the products, electrical-to-chemical energy conversion efficiency, and CO₂-to-CO conversion yield. Within the investigated parameter ranges, the maximum H2/CO ratio was about 0.14 when H2O and CO₂ were dissociated in different reactors. Additionally, at an applied voltage of 4.5 kV, the maximum yields were about 28.4% for H2 at a residence time of 128 [mu]s and 17.3% for CO at a residence time of 354 [mu]s. Increasing residence time increased the conversion yield, but decreased the energy conversion efficiency. The maximum energy conversion efficiency of about 18.5% was achieved for 99.5% pure CO₂ at a residence time of 6 [mu]s and an applied voltage of 4.5 kV. At the same applied voltage, the maximum efficiency was about 14.8% for saturated CO₂ at a residence time of 12.8 [mu]s. The future work should focus on optimizing the conversion yield and efficiency as well as analyzing the temporal and spatial changes in the gas composition in the plasma reactor.
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碩士
嘉南藥理科技大學
環境工程與科學系暨研究所
96
It has been known that lots of air pollutants exist in the indoor environment. It also has been reported that these pollutants, particularly bioaerosols, can cause a serious illness on human respiratory system. Therefore, an innovative non-thermal dielectric barrier discharges (DBD) plasma system was used to test its feasibility of removing bioaerosols in the study. The sterilization efficacy of bioaerosols by DBD plasma system was evaluated based on different pivotal parameters including types of bioaerosols, plasma power inputs and frequencies, relative humidity (RH), and retention times. 　　 　　The results showed that the sterilization efficacy of bioaerosols was following the order: Yeast > S. aurcus > P. citrinum > B. subtilis. It found that the sterilization efficacy of fungi with either non spore-form or spore-form was greater than that of bacteria. With regard to the effect of power inputs and frequencies, the results concluded that high voltage and low frequency could achieve better sterilization efficiency in comparison with low voltage and high frequency. In addition, the results indicated that the higher efficacy was appeared at longer retention time. Finally, it also found that high RH significantly improved the sterilization efficacy of S. aurcus, Yeast, and P. citrinum. However, increasing RH has limited effect on B. subtilis. 　　The electricial particles charged in non-thermal DBD plasma system was the main mechanism of sterilizing bioaerosols. With the deposition of the electricial particles on outer cell membrane, it generated the electrostatic tension to break down the cell. Another mechanism of sterilization was the production of the reactive species, such as O3 and OH∙. These reactive species could desconstruct cell membrane, and oxidize amino acids and DNA inside the cells. 　　The optimal operating conditions of non-thermal DBD plasma system were controlled at retention time of 1.5 sec, input power with 10W, and power frequency of 60Hz in this study. For the four different bioaerosols, the sterilization efficacy were all greater than 90% regardless the effect of RH. This research demonstrated the potential of non-thermal DBD plasma system to break down bioaerosols, and this system could be applied to improve indoor air quality.