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| Author |
Heyne, M.H. |
| Title |
Chemistry and plasma physics challenges for 2D materials technology |
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Doctoral thesis |
| Year |
2019 |
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167 p. |
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Doctoral thesis; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT) |
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Transition-metal dichalcogenides such as MoS2 or WS2 are semiconducting materials with a layered structure. One single layer consists of a plane of metal atoms terminated on the top and bottom by the chalcogen atoms sulfur, selenium, or tellurium. These layers show strong in-plane covalent bonding, whereas the Van-der-Waals bonds in between adjacent layers are weak. Those weak bonds allow the microcleavage and extraction of a monolayer. Transistors built on such monolayer nanosheets are promising due to high electrostatic controllability in comparison to a bulk semiconductor. This is important for fast switching speed and low-power consumption in the OFF-state. Nonetheless, prototypes of such nanosheet transistors show non-idealities due to the fabrication process. Closed films on a large area cannot be obtained by mechanical exfoliation from mm-sized crystals. For wafer-level processing, synthetic growth methods are needed. It is a challenge to obtain a few layer thick crystals with large lateral grains or even without grain boundaries with synthetic growth techniques. This requires pre-conditioned monocrystalline substrates, high-temperature deposition, and polymer-assisted transfer to other target substrates after the growth. Such transfer is a source of cracks in the film and degrades the layers' promising properties by residual polymer from the bond material. Apart from transfer, patterning of the stacked 2D layers is necessary to build devices. The patterning of a 2D material itself or another material on top of it is challenging. The integration of the nanosheets into miniaturized devices cannot be done by conventional continuous-wave dry etching techniques due to the absence of etch stop layers and the vulnerability of these thin layers. To eliminate these issues in growth and integration, we explored the deposition methods on wafer-level and low-damage integration schemes. To this end, we studied the growth of MoS2 by a hybrid physical-chemical vapor deposition for which metal layers were deposited and subsequently sulfurized in H2S to obtain large area 2D layers. The impact of sulfurization temperature, time, partial H2S pressure, and H2 addition on the stoichiometry, crystallinity, and roughness were explored. Furthermore, a selective low-temperature deposition and conversion process at 450 °C for WS2 by the precursors WF6, H2S, and Si was considered. Si was used as a reducing agent for WF6 to deposit thin W films and H2S sulfurized this film in situ. The impact of the reducing agent amount, its surface condition, the temperature window, and the necessary time for the conversion of Si into W and W into WS2 were studied. Further quality improvement strategies on the WS2 were implemented by using extra capping layers in combination with annealing. Capping layers such as Ni and Co for metal-induced crystallization were compared to dielectric capping layers. The impact of the metal capping layer and its thickness on the recrystallization was evaluated. The dielectric capping layer's property to suppress sulfur loss under high temperature was explored. The annealings, which were done by rapid thermal annealing and nanosecond laser annealing, were discussed. Eventually, the fabrication of a heterostack with a MoS2 base layer and selectively grown WS2 was studied. Atomic layer etching was identified as attractive technique to remove the solid precursor Si from MoS2 in a layer-by-layer fashion. The in-situ removal of native SiO2 and the impact towards MoS2 was determined. The created patterned Si on MoS2 was then converted into patterned WS2 on MoS2 by the selective WF6/H2S process developed earlier. This procedure offers an attractive, scalable way to enable the fabrication of 2D devices with CMOS-compatible processes and contributes essential progress in the field 2D materials technology. |
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UA @ admin @ c:irua:162027 |
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7662 |
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| Author |
Cui, Z. |
| Title |
Experimental and theoretical study on SF6 degradation by packed-bed DBD plasma |
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Doctoral thesis |
| Year |
2021 |
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Doctoral thesis; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT) |
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Sulfur hexafluoride (SF6), as a man-made gas, is widely used in power industry, semiconductor industry and metal-processing industry. However, SF6 is a greenhouse gas and its global warming potential is 23500 times that of CO2. Besides, SF6 is very stable, with a lifetime in the atmosphere for more than one thousand years. Under natural conditions, only the ultraviolet light can make it slowly decomposed. Thus, the emission of SF6 has a great threat to the environment. In recent years, with the development of our national economy, the use of SF6 increased dramatically. And 90% of the SF6 emissions come from the power industry. In the meantime, the emission of SF6 exists a ‘hysteresis effect’, as many of the SF6-gas insulation equipment will retire in next decades, the emission of SF6 may increase sharply, and this may put great pressure on the environment. Therefore, it’s necessary to make efforts in controlling and treating the SF6 emission. Among the SF6 abatement technologies, the non-thermal plasma(NTP) represented by the dielectric barrier discharge(DBD) can effectively degrade SF6 and is suitable for large-scale industry applications. However, its energy efficiency still gets room for improvement and this kind of method has a defect that it’s hard to regulate the degradation by-products. Therefore, this paper proposed the combination of the packed bed reactor and the DBD technology to form a packed DBD discharge system for SF6 degradation, so that to further improve the energy efficiency and regulate the selectivity of by-products. By experiment and simulation research, the following innovations have been achieved: (1) Based on the packed bed DBD platform, the power parameter and gas-phase parameters of SF6 degradation were studied. It was found that the discharge process was significantly enhanced with the addition of packing particles, and the discharge energy efficiency was improved. The increase of input voltage can obviously increase the degradation rate, but reduces the energy efficiency. The increase of SF6 initial concentration and gas flow rate can improve the energy efficiency, but reduce the degradation rate. Therefore, both degradation rate and energy efficiency should be considered in deciding basic experimental conditions. (2) Active gases, such as O2, H2O and NH3, could effectively promote the degradation rate of SF6, and changed the product selectivity. In our packed bed DBD system, O2 and H2O have the optimal concentration conditions, which are 2% and 1%, respectively. The addition of O2 can promote the generation of S-O-F products, and inhibit the selectivity of SO2, while the addition of H2O had the opposite effects. In addition, the synergistic degradation of NH3 and SF6 will produce solid products, such as NH3HF, NH4HF2 and elemental S. For gaseous products, the increase of NH3 will lead to the generation of SO2 in the final degradation products and inhibit the generation of S-O-F products. (3) Different kinds of packing materials have great impacts on the degradation system in the discharge parameters, degradation rate and energy efficiency, as well as the products distribution. In the experiment, we compared the degradation results in three systems: glass beads packing, γ-Al2O3 packing and no-packing system. The packing of glass beads effectively improved the discharge voltage amplitude and discharge power, while had a limited effect on the equivalent capacitance of the dielectric. Besides, γ-Al2O3 packing had little effect on voltage amplitude, but obviously increased the equivalent capacitance of the dielectric. Furthermore, the degradation rate and energy efficiency in γ-Al2O3 system was higher than that of glass bead system. For products selectivity, γ-Al2O3 system was more desirable, where S-O-F type of product selectivity was suppressed and the SO2 selectivity increased significantly. By contrast, the glass beads system hardly affected the product selectivity. This results are presumably due to the relatively high dielectric constant of γ-Al2O3 particles and γ-Al2O3 itself may act as a reactant or a catalyst participating in the degradation reactions. (4) The size and status of the packing particles also have significant effects on the degradation process. The systems packed with 1, 2 and 4mm γ-Al2O3 particles for SF6 degradation were compared, and the 2mm system had the best performance, which may because the 2mm system had a good balance between the active contact area and the gas residence time. In addition, the packing pellets suffered from a hydration process slightly reduced the discharge parameters in the γ-Al2O3 packing system and significantly reduced the degradation rate was, which may because the H2O molecules pre-occupied the active sites on the γ-Al2O3 surface and reduced the discharge process. (5) Based on density functional theory (DFT), the degradation process of SF6 in the packed bed DBD system was studied at atomic scale. It was found that the SF6 can occur a physical adsorption at AlⅢ active sites on γ-Al2O3 surface. The activation barrier for the first degradation step of SF6 on γ-Al2O3 surface is much lower than in gas phase, which proved that the SF6 molecule is activated on the γ-Al2O3 surface. In addition, the plasma may affect the γ-Al2O3 surface to generate excess electrons or external electric fields. This two effects can change the adsorbed SF6 molecules from physical adsorption to chemisorption, together with an obvious stretching of S-F bonds, indicating that the plasma surface effects prmote the activation and decomposition of SF6 molecules. Furthermore, the stepwise degradation process of SF6 on γ-Al2O3 surface were investigated. The influence of radicals produced by plasma on the degradation process was analyzed. It was found that via Eley–Rideal (ER) reactions, high-energy radicals could effectively reduce the activation barriers and promote the surface reactions. Finally, the degradation mechanism of SF6 molecules in the packed bed plasma system was summarized, which may provide a theoretical basis for the study of harmless degradation of SF6. Keywords: SF6; Packed Bed DBD; Discharge Parameters; Products Analysis; Degradation Mechanism |
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Most recent IF: NA |
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UA @ admin @ c:irua:180819 |
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7946 |
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| Author |
Belov, I. |
| Title |
Plasma-assisted conversion of carbon dioxide |
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Doctoral thesis |
| Year |
2017 |
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Doctoral thesis; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT) |
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UA @ admin @ c:irua:146275 |
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8387 |
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Ghasemitarei, M. |
| Title |
Study of the interaction of plasma radicals with malignant tumor cells by means of Molecular Dynamics simulation |
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Doctoral thesis |
| Year |
2019 |
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117 p. |
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Doctoral thesis; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT) |
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abstract not available |
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UA @ admin @ c:irua:164763 |
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8606 |
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Vervloessem, E. |
| Title |
The role of pulsing and humidity in plasma-based nitrogen fixation : a combined experimental and modeling study |
Type |
Doctoral thesis |
| Year |
2023 |
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358 p. |
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Doctoral thesis; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT) |
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Nitrogen (N) is an indispensable building block for all living organisms as well as for pharmaceutical and chemical industry. In a nutshell, N is needed for plants to grow and beings to live and nitrogen fixation (NF) is the process that makes N available for plants as food by converting N2 into a reactive form, such as ammonia (NH3) or nitrogen oxides (NOx), upon reacting with O2 and H2. The aim of this thesis is to elucidate (wet) plasma-based nitrogen fixation with a focus on (1) the role of pulsing in achieving low energy consumption, (2) the role of H2O as a hydrogen source in nitrogen fixation and (3) elucidation of nitrogen fixation pathways in humid air and humid N2 plasma in a combined experimental and computational study. Furthermore, this thesis aims to take into account the knowledge-gaps and challenges identified in the discussion of the state of the art. Specifically, (1) we put our focus on branching out to another way of introducing water into the plasma system, i.e. H2O vapor, (2) we de-couple the problem for pathway elucidation by starting with characterization of the chosen plasma, next a simpler gas mixture and building up from there, (3) we include modelling, though not under wet conditions and (4) we focus on also analyzing species and performance outside liquid H2O. Firstly, based on the reaction analysis of a validated quasi-1D model, we can conclude that pulsing is indeed the key factor for energy-efficient NOx- formation, due to the strong temperature drop it causes. Secondly, the thesis shows that added H2O vapor, and not liquid H2O, is the main source of H for NH3 generation. Related to this, we discuss how the selectivity of plasma-based NF in humid air and humid N2 can be controlled by changing the humidity in the feed gas. Interestingly, NH3 production can be achieved in both N2 and air plasmas using H2O as a H source. Lastly, we identified a significant loss mechanism for NH3 and HNO2 that occurs in systems where these species are synthesized simultaneously, i.e. downstream from the plasma, HNO2 reacts with NH3 to form NH4NO2, which decomposes into N2 and H2O. This reduces the effective NF when not properly addressed, and should therefore be considered in future works aimed at optimizing plasma-based NF. In conclusion, this thesis adds further to the current state of the art of plasma-based NF both in the presence of H2O and in dry systems. |
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Most recent IF: NA |
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UA @ admin @ c:irua:197038 |
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9088 |
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Biondo, O. |
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Towards a fundamental understanding of energy-efficient, plasma-based CO<sub>2</sub> conversion |
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Doctoral thesis |
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2023 |
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221 p. |
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Doctoral thesis; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT) |
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Plasma-based CO2 conversion is worldwide gaining increasing interest. The aim of this work is to find potential pathways to improve the energy efficiency of plasma-based CO2 conversion beyond what is feasible for thermal chemistry. To do so, we use a combination of modeling and experiments to better understand the underlying mechanisms of CO2 conversion, ranging from non-thermal to thermal equilibrium conditions. Zero-dimensional (0D) chemical kinetics modelling, describing the detailed plasma chemistry, is developed to explore the vibrational kinetics of CO2, as the latter is known to play a crucial role in the energy efficient CO2 conversion. The 0D model is successfully validated against pulsed CO2 glow discharge experiments, enabling the reconstruction of the complex dynamics underlying gas heating in a pure CO2 discharge, paving the way towards the study of gas heating in more complex gas mixtures, such as CO2 plasmas with high dissociation degrees. Energy-efficient, plasma-based CO2 conversion can also be obtained upon the addition of a reactive carbon bed in the post-discharge region. The reaction between solid carbon and O2 to form CO allows to both reduce the separation costs and increase the selectivity towards CO, thus, increasing the energy efficiency of the overall conversion process. In this regard, a novel 0D model to infer the mechanism underlying the performance of the carbon bed over time is developed. The model outcome indicates that gas temperature and oxygen complexes formed at the surface of solid carbon play a fundamental and interdependent role. These findings open the way towards further optimization of the coupling between plasma and carbon bed. Experimentally, it has been demonstrated that “warm” plasmas (e.g. microwave or gliding arc plasmas) can yield very high energy efficiency for CO2 conversion, but typically only at reduced pressure. For industrial application, it will be important to realize such good energy efficiency at atmospheric pressure as well. However, recent experiments illustrate that the microwave plasma at atmospheric pressure is too close to thermal conditions to achieve a high energy efficiency. Hence, we use a comprehensive set of advanced diagnostics to characterize the plasma and the reactor performance, focusing on CO2 and CO2/CH4 microwave discharges. The results lead to a deeper understanding of the mechanism of power concentration with increasing pressure, typical of plasmas in most gases, which is of great importance for model validation and understanding of reactor performance. |
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Most recent IF: NA |
| Call Number |
UA @ admin @ c:irua:197213 |
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9108 |
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Ahmadi Eshtehardi, H. |
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Combined computational-experimental study on plasma and plasma catalysis for N2 fixation |
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Doctoral thesis |
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2024 |
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160 p. |
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Doctoral thesis; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT) |
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Humanity feels the urge of shifting to a sustainable society more than at any other time in its history. Electrification of chemical industry plays a key role in this transition. The possibility of producing fertilizers from air using renewable electricity, and simultaneously, no greenhouse gas emission, resulted in an increasing interest toward plasma technology as a solution for electrification of a part of the chemical industry in the past few years. Additionally, the activation of nitrogen molecules by vibrational and electronic excitation reactions in plasma can lead to an energy-efficient process. Last but not least, the modularity (fast on/off characteristic) of plasma technology makes it capable of using intermittent renewable electricity on site for the production of fertilizers using air. All these advantages offered by plasma technology make it a potential solution for the on-site production of fertilizers in small and decentralized plants using air and renewable electricity, which leads to a considerable reduction in fertilizer production and transportation costs. However, industrialization of plasma-based NF suffers from several challenges, including challenges of plasma catalysis for the selective production of desired species, the high energy cost of plasma-based NF compared to current industrial processes, and the design and development of scaled up and energy-efficient plasma reactors for industrial purposes. In the framework of this thesis we have tried to add to the state-of-the-art (SOTA) in plasma-based NOx production and deal with its limitations using a combination of experimental and modelling work. |
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2024-06-14 |
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UA @ admin @ c:irua:205246 |
Serial |
9139 |
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De Luca, F.; Abate, S.; Bogaerts, A.; Centi, G. |
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Electrified CO2 conversion : integrating experimental, computational, and process simulation methods for sustainable chemical synthesis |
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2024 |
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xv, 152 p. |
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Doctoral thesis; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT) |
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Nowadays, the burning of fossil fuels, particularly petroleum, natural gas, and coal, meets the rising need for power and fuels for automobiles and industries. This has given rise to ecological and climate challenges. This thesis explores these issues from three distinct perspectives: (i) experimental, (ii) computational, and (iii) process simulation, with a focus on studying CO2 as an alternative and economically viable raw material. Firstly, the experimental study is focused on the synthesis, characterization, and testing of novel catalysts for electroreduction of CO2 and oxalic acid, an intermediate product of CO2. Electrocatalysts based on Cu supported by citrus (orange and lemon) peel biomass are prepared. These catalysts exhibit activity in the electrochemical reduction of CO2, emphasizing the effectiveness of biomasses, particularly orange peels, as environmentally friendly precursors for sustainable and efficient electrocatalysts. In addition, graphitic carbon nitrides/TiO2 nanotubes (g-C3N4/TiNT) composites are prepared for the electrocatalytic reduction of oxalic acid to glycolic acid, revealing superior electrocatalytic properties compared to pristine TiNT. Characterization by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electronic microscopy were performed for all the prepared electrocatalysts. Delving into the reduction of CO2 on Cu catalysts, a computational study about the synthesis of methanol on Cu(111) surface is performed by using the Vienna Ab initio Simulation Package. A systematic study is carried out to define the activation energies of the elementary reactions by using mGGA DF. Consequently, it is shown that the rate-controlling step is CH3O* hydrogenation and the formate pathway on Cu(111) proceeds through the HCOOH* intermediate. Finally, the process simulation, performed by using the software Aspen Plus 11 from AspenTech Inc., is based on the comparison of a catalytic (oxidation of ethylene glycol) and an electrocatalytic process (CO2 electroreduction chain) to synthesize glycolic acid. An economic analysis of the operational and investment costs reveals that the catalytic process is more cost-effective due to the current instability of electrocatalysts and proton exchange membranes, resulting in increased maintenance costs and, consequently, higher prices for the product. |
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UA @ admin @ c:irua:205262 |
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9147 |
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Manaigo, F. |
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Study of a gliding arc discharge for sustainable nitrogen fixation into NOx |
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Doctoral thesis |
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2024 |
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xxiv, 114 p. |
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Doctoral thesis; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT) |
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With the growth of the world population, the agricultural sector is required to meet an increasing demand for nutrients and currently relies on industrially produced fertilizers. Among them, nitrogen-based fertilizers are the most common choice and require N2 to be converted into more reactive molecules in a process called “nitrogen fixation”. This is mainly performed through the Haber-Bosch process, which, is not ideal since it requires large-scale facilities to be economical and is associated with a high energy cost and high CO2 emissions, resulting in an environmental impact that is pushing for the study of greener alternatives. Among these, plasma-based nitrogen fixation into NOx is promising, and gliding arc plasma, specifically, proved to be suitable for nitrogen fixation. This thesis aims to study plasma-based nitrogen fixation focusing on an atmospheric pressure gliding arc plasma on three different levels. On a fundamental level, an approach dealing with laser-based excitation of separate rotational lines was successfully developed. This method can be implemented on atmospheric discharges that produce rather high NOx densities and, thus, can impose essential restrictions for the use of “classical” laser-induced fluorescence methods. The approach is then implemented, providing a discussion on the two-dimensional distributions of both the gas temperature and the NO ground state density. A clear correlation between these quantities is found and the effects of both the gas temperature and the plasma power on NO and NO2 concentrations are discussed, revealing how the NO oxidation is already significant in the plasma afterglow region and how the gas flow rate is a crucial parameter affecting the temperature gradients. >From a technological level, the conventional approach of introducing external resistors to stabilize the arc is challenged by studying both its performance and its stability replacing the external resistor with an inductor. We conclude that similar stabilization results can be obtained while significantly lowering the overall energy cost, which decreased from up to a maximum of 7.9 MJ/mol N to 3 MJ/mol N. Finally, we study whether a small-scale fertilizer production facility based on a gliding arc plasma can be a local competitive alternative. This is done by proposing a comparative model to understand how capital, operative expenditures and transport costs affect the production costs. The model highlights how, with the current best available technology, plasma-based nitrogen fixation, while being an interesting alternative for NOx synthesis, still requires a more efficient use of H2 for direct NH3 production. |
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UA @ admin @ c:irua:205259 |
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9175 |
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Clavel, J. |
| Title |
Plant-mycorrhizal interactions and their role in plant invasions in mountains |
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Doctoral thesis |
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2024 |
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182 p. |
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Doctoral thesis; Plant and Ecosystems (PLECO) – Ecology in a time of change |
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Non-native species invasions are one of the most impactful drivers of biodiversity and ecosystem services loss worldwide. One aspect of plant species invasion, which is only recently starting to be recognized as a determinant of invasion success, is the symbiosis between plant and mycorrhizal fungi. Here, I focus on anthropogenic disturbance in mountain ecosystems and its impact on plant communities and mycorrhizal fungi to answer how these communities are impacted by disturbance and whether non-native plants can benefit to establish and spread. To this end I used a combination of different approaches: 1) repeated surveys of plants and arbuscular mycorrhizal fungi along disturbed roadsides in the mountains of Norway, 2) combining a global dataset of native and non-native plants along mountain roads with a database associating plants with their mycorrhizal types, and 3) an in-situ experiment measuring non-native plant success and changes in fungal community following different types of disturbances. Through these methods, I could assess the effects of anthropogenic disturbance on mycorrhizal symbiosis and non-native plant species at multiple scales and resolutions. We found that road disturbance has a globally consistent effect on mycorrhizal types in mountain systems, as plants associated with arbuscular mycorrhizal (AM) fungi were more abundant following disturbance. Conversely, vegetation associated with either ectomycorrhizal (EcM) or ericoid mycorrhizal (ErM) fungi was less abundant in disturbed sites. In the regional study, AM fungi were most abundant and diverse in the roots of plant communities affected by road disturbance. Non-native plants were also restricted to these disturbed sites. The experimental results showed that physical disturbance and nutrient addition have negative effects on EcM fungi and positive effects on fungal pathogens, and facilitate non-native plant success. Our results show that anthropogenic disturbance does have an effect on mycorrhizal fungi that in turn impacts the distribution of plant species in disturbed mountain systems. The resulting shift in mycorrhizal fungi benefiting AM fungi and AM plant species could have implications for non-native plant invasions. Indeed, we know that non-native plants predominantly form associations with AM fungi. Therefore, anthropogenic disturbance can facilitate non-native plant success through disruption of the native fungal communities, and especially so in high elevation and cold climate regions which are naturally less dominated by AM plants. I believe this highlights the importance of mycorrhizal symbiosis in understanding plant invasions and emphasizes the importance of monitoring sources of anthropogenic disturbance in mountains to prevent future establishment of non-native plants. |
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UA @ admin @ c:irua:204154 |
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9219 |
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Ramirez-Rojas, I. |
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Underground connections : the interplay between tropical rainforest trees and soil microbial communities |
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Doctoral thesis |
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2024 |
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205 p. |
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Doctoral thesis; Plant and Ecosystems (PLECO) – Ecology in a time of change |
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Tropical rainforests host an exceptional biodiversity and play a fundamental role in the regulation of global climatic cycles. Soil fungi and bacteria are key players in the transformation and processing of nutrients in terrestrial ecosystems while having an essential role as tree mutualists or antagonists. Still, there are gaps in our understanding of the main variables driving soil microbes on these forests and it is unclear how future climate change scenarios may impact soil microbes and further affect the ecosystem. In this thesis, we first explored the drivers of the microbial community composition in two pristine forests in French Guiana by using amplicon DNA sequencing. The neighboring tree species were found to be a crucial factor influencing the fungal and bacterial community composition at our sites regardless of the season. Additionally, within the environmental factors explored, soil moisture, phosphorus (P) and nitrogen (N) availability were consistently the main soil properties controlling the composition of soil microbial communities. Secondly, as increased nutrient deposition due to anthropogenic activities are expected to affect tropical forests ecosystems N and P availability, a factorial N and P nutrient addition experiment in the same sites was used to assess the effects of changes in the soil nutrient stoichiometry on the soil microbial communities. These results showed that after 3 years of nutrient additions, the bacterial and fungal community composition was affected by both the N and P additions. Besides, the fungal community composition had a stronger response to the nutrient addition, especially when P was added. Moreover, when the nutrient addition effect was assessed in bacteria and fungi with different life strategies, we found different nutrient optima between them. Furthermore, to study the effect of the connection to an existing mycorrhizal mycelium on tree seedlings, I established a mycelium exclusion experiment. Interestingly, we could not detect an effect of the mycorrhizal mycelium exclusion on the seedling N uptake, performance, or fungal community composition in roots after one year. All together this work provides a deeper understanding of the factors influencing the soil microbial communities on these lowland tropical forests, demonstrating that the tree community composition exerts a higher influence on the soil microbial community composition than previously expected. Moreover, our results show that the fungal and bacterial community composition and its relationship with trees in the vicinity is highly dependent on the ecosystem nutrient availability. |
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UA @ admin @ c:irua:204907 |
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9237 |
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Cong, S. |
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Numerical study on low-pressure hollow cathode argon arc plasma |
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Doctoral thesis |
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2021 |
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XIX, 126 p. |
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Doctoral thesis; Philosophy; Educational sciences; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT) |
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The low-pressure hollow cathode discharge made of a hollow circular tube and an anode is a type of simple structure discharge system. In particular, under the arc discharge mode, hollow cathodes have high plasma density and energy density with a wide range of adaptability of pressure and current. Low-pressure hollow cathode arc (HCA) discharges have been widely used as plasma sources in various fields such as manufacturing, vacuum welding, and aerospace since the 1960s. Despite the early experimental and applied researches on low-pressure HCA discharges, the basic theoretical study was relatively lagged much behind, resulting in many unanswered questions, such as the optimal discharge operating parameters, the power deposition inside the cathode, the causes of plasma instability, and how to effectively reduce cathode erosion and so on. Due to the special discharge structure of the hollow cathode, it is difficult to make an accurate experimental diagnosis, so a reasonable numerical simulation is an effective study method. However, up to now, there is still a lack of complete and effective numerical models which can evaluate various physical fields in the low-pressure hollow cathode discharges. To address the above problems and difficulties, a comprehensive and self-consistent 2D multi-physical coupling numerical model based on a commercial program of finite element method, the COMSOL Multiphysics, was provided in this paper. The model involves plasma transport, arc flow and heat transfer, and cathode thermal equilibrium, and can consider the effect of an applied magnetic field. The processes of secondary electron emission, thermal-field electron emission, ions and backflow high-energy electrons bombardment, and thermal radiation from the cathode surface are considered in the cathode thermal equilibrium process. Based on the above background, this paper works from the following aspects： In Chapter 1, the basic concepts of low-pressure HCA discharge including the hollow cathode effect, the basic characteristics, and operation modes were introduced firstly; Secondly, the application fields, development history, and overseas and domestic research status of hollow cathode discharge were reviewed; finally, the problems were presented and the research background was explained, and the research purpose of this paper was clarified. In Chapter 2, a complete and self-consistent numerical model of low-pressure hollow cathode discharge was proposed based on the fundamental theory and assumptions, and the set of control equations and boundary conditions in the model were elaborated. In addition, the electron energy distribution function, the collision processes, the solving tools of this model, and calculation schemes were introduced in detail. Finally, a validation example was given to test the rationality and applicability of the numerical model. In Chapter 3, the fundamental plasma properties of low-pressure hollow cathode arcs were investigated. Firstly, the ion Joule heating effect was studied. The results showed that the temperature distributions of the arc and cathode are only able to approach the experimental measurements after considering the ion Joule heating, which shows that the Joule heating of ions is crucial for the heating of the arc plasma. Secondly, by comparing the radial distribution of electron and ion density inside the cathode, the structure of the cathode sheath could be simulated well using this model. Finally, it was shown that the thermal radiation from the cathode surface is an important cooling mechanism of the cathode and only under higher surface emissivity can balance the larger heat flow given by the plasma to the cathode, and the temperature distribution of the cathode shows a non-monotonic increasing trend and is consistent with the profile of experimental measurement so that the so-called active zone is formed. In Chapter 4, the power deposition in the low-pressure HCA was studied in simulation. Two main aspects were considered: the power deposition into particles (both electrons and heavy particles) and the power deposition onto the cathode. It was found that the deposited power into particles increases with the rise of discharge current, but there is no effect on the total power deposition onto the cathode. In high-density plasmas, Coulomb collisions between electrons and ions also become very important, especially since a portion of the deposition energy on heavy particles comes mainly from the energy transfer from electrons to ions. It was also found that regardless of external parameters, half of the power deposition onto the cathode always comes from the particle contribution, while the other half is the net contribution of heat transfer and cathode radiation. The HCA model also allows the simulation of multiple discharge modes for low-pressure HCA discharges over a wide range of gas flow rates. It was also shown that the discharge operating conditions and the external magnetic field can change the distribution of the particle flow on the cathode wall. In Chapter 5, the ion sputtering erosion process on the cathode was simulated by coupling the HCA numerical model with the moving grid technique. The results showed that the ion sputtering erosion on the cathode depends on the ion flux and the plasma potential near the cathode wall and that their distribution and magnitude jointly determine the erosion morphology of the cathode. It was also found that the location of the most severe erosion on the cathode is located in the region of the densest ion flux on the cathode wall, rather than in the longitudinal correspondence with the central region of the internal positive column (IPC). The external magnetic fields can mitigate the cathode erosion and reduce the erosion depth, but stronger magnetic fields lead to a concentration of current density at the cathode tip, which can enhance erosion slightly at the cathode outlet end. Finally, the conclusions and innovation highlights were summarized, and prospects for future work were discussed. |
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Most recent IF: NA |
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UA @ admin @ c:irua:178725 |
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8323 |
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De Backer, J. |
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The versatile nature of cytoglobin, the Swiss army knife among globins, with a preference for oxidative stress |
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Doctoral thesis |
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2023 |
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XVIII, 232 p. |
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Doctoral thesis; Pharmacology. Therapy; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT); Proteinscience, proteomics and epigenetic signaling (PPES) |
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Since its discovery 20 years ago, many studies have been performed to gain insight into the functional role of cytoglobin (Cygb). However, Cygb has been proven to be a promiscuous protein. Yet, there is a consensus that Cygb is a cytoprotective protein involved in redox homeostasis. CYGB is a ubiquitously expressed hexacoordinated globin that is highly expressed in melanocytes and is often found to be downregulated during melanocyte-to-melanoma transition. In Chapter III, we investigated the molecular mechanism through which CYGB could be involved in redox regulation. Here, we showed that CYGB contains two redox-sensitive cysteine residues and that the formation of an intramolecular disulfide bridge resulted in the heme group becoming more accessible to external ligands. This supports the hypothesis that Cys38 and Cys83 serve as sensitive redox sensors. In Chapter IV we showed that CYGB mRNA and protein levels were elevated upon exposure to hypoxia. Interestingly, this upregulation was most likely HIF-2α-dependent. We propose that in melanoma, HIF-2α, rather than HIF-1α, positively regulates CYGB under hypoxic conditions in a cell type specific way. In Chapter V, the cytotoxic effect of indirect NTP treatment in two melanoma cell lines with divergent endogenous CYGB expression levels was investigated. We confirmed that NTP endows cytotoxicity that induces cell death through apoptosis and that this was mediated through the production of ROS. Moreover, we showed that CYGB protects melanoma cells from ROS-induced apoptosis by the scavenging of ROS. Interestingly, CYGB expression influenced the expression of NRF2 and HO-1. We identified the lncRNA MEG3 as a possible mechanism through which NRF2 expression and its downstream target HO-1 can be regulated by CYGB. In chapter VI, increased basal ROS levels and higher degree of lipid peroxidation upon RSL3 treatment contributed to the increased sensitivity of CYGB knockdown G361 cells to ferroptosis. Furthermore, transcriptome analysis demonstrates the enrichment of multiple cancer malignancy pathways upon CYGB knockdown, supporting a tumor-suppressive role for CYGB. Remarkably, CYGB expression regulation was identified as a critical determinant of the ferroptosis–pyroptosis therapy response. This suggests that CYGB is involved in the regulation of multiple modes of programmed cell death. FInally, we sought to delineate the RONS that are responsible for plasma-induced ICD. Our results highlight the importance of the short-lived species. Furthermore, we are first to demonstrate that NTP-created vaccine is safely prepared and offers complete protection. Moreover, we provide conclusive evidence that direct application of NTP induces ICD in melanoma. |
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UA @ admin @ c:irua:193568 |
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7277 |
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Drăgan, A.-M. |
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Investigation of the electrochemical behaviour of illicit substances and their redox pathways in the development of nanomaterial-modified platforms for decentralized analysis |
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Doctoral thesis |
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2023 |
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169 p. |
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Doctoral thesis; Pharmacology. Therapy; Engineering sciences. Technology; Antwerp Electrochemical and Analytical Sciences Lab (A-Sense Lab) |
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UA @ admin @ c:irua:199086 |
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8892 |
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Schram, J. |
| Title |
Electrochemical sensing strategies for multiple illicit drugs |
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Doctoral thesis |
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2024 |
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290 p. |
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Doctoral thesis; Pharmacology. Therapy; Engineering sciences. Technology; Antwerp Electrochemical and Analytical Sciences Lab (A-Sense Lab) |
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Today, illicit drugs are omnipresent in society. Clandestine markets are growing faster than ever before, record amounts of cocaine are seized in seaports and airports, while the associated violence is spiralling out of control. In addition, drug monitoring centres worldwide are warning for the increasing complexity of the drug markets, as the traditionally popular drugs are joined by countless new synthetic variants, while medical drugs are also increasingly being abused. In order to provide services confronted with illicit drug samples (police, customs, forensic scientists, first responders, …) with important information on the identity of an unknown sample, suitable analytical tests are required. While these exist for laboratory environments, on-site applicable tests are important to accelerate the decision-making process. Electrochemical sensors have all the advantages required for such on-site tests: they are fast, portable, easy-to-use and reliable. Furthermore, they are not influenced by colours, which are frequently added to drug samples to deceive the existing tests. Previous work has mainly focussed on the detection of a single drug per analysis. However, many drugs could be encountered due to the diversity of the drug markets. Therefore, this project developed electrochemical strategies for the detection of multiple drugs simultaneously. First, the electrochemical behaviour of the individual drugs was studied in different measuring conditions (assessing the influence of pH, concentration and temperature). Then, all findings and strategies were combined to detect multiple targets simultaneously. An electrochemical sensor was developed for the four most popular drugs at music festivals: cocaine, MDMA, amphetamine and ketamine. This sensor generates a so-called ‘superfingerprint’ of the sample, which is then automatically interpreted by a developed algorithm in order to produce a straightforward output. Finally, a pill analysis sensor was developed in the context of drug checking services, where a consumer can anonymously have a sample chemically analysed to obtain information on the composition, dose and potentially harmful additives. The sensor achieved an outstanding accuracy in identifying the main component and provided the option to quantify, as well as an indication on the presence of other substances in the sample. The project’s findings demonstrate the potential for electrochemistry in illicit drug detection and provide a basis for the development of new sensors, targeting other drug combinations. |
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UA @ admin @ c:irua:203199 |
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9029 |
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Van Echelpoel, R. |
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Making an impact with voltammetric illicit drug sensors : bridging the gap between fundamental lab research and on-site application |
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Doctoral thesis |
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2023 |
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xxviii, 194 p. |
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Doctoral thesis; Pharmacology. Therapy; Engineering sciences. Technology; Antwerp Electrochemical and Analytical Sciences Lab (A-Sense Lab) |
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Illicit drugs are harmful substances, posing a threat to the health and safety of society. Policies, such as supply reduction and harm reduction, are in place to combat the illicit drug problem. Science can play a substantial role in this fight, by providing tools that enable these policies to be successfully enforced. One example are on-site detection tools, i.e. sensors that allow the on-site identification of an illicit drug in a sample of interest. Several technologies, such as color tests and portable spectroscopic techniques, are currently employed for this goal. Although these are valuable techniques, there is an opportunity for voltammetry, an electrochemical technique, to make an impactful addition to this repertoire of on-site detection tools. Despite its attractive features (low-cost, portable, short analysis time, indifference to color,...), voltammetric illicit drug sensor have failed to make an impact in real scenarios. The work outlined in this PhD thesis aims to change this by bringing the technology from the lab to the field. Strategic choices, fueled by feedback from end-users, were made to further develop those specific aspects of the technology that previously haltered the technology to fulfill its potential. A detection algorithm was introduced that converts the voltammetric output into a clear-cut interpretation thereof, opening up the technology to end-users without prior knowledge of the technology. A sensor that allows qualitative and quantitative detection of the psychoactive drug MDMA was introduced, and importantly, validated on a large set of 212 confiscated samples. A state-of-the art mobile application and adequate sampling methodology were developed, alongside other, often more practical studies and product developments, to evolve the technology into a product that truly creates value for end-users. Important steps towards multidrug detection were made with a festival sensor and a flowchart based on visual appearance that ties together a variety of voltammetric single sensors into a single multidrug sensing approach. Last but not least, multiple valorization aspects were researched, including a market study and an analysis to determine the optimal commercialization strategy. Overall, this PhD thesis has facilitated the transition of the voltammetric illicit drug sensing technology from lab to on-site application. The final application creates value for end-users, and is ready to make an impact in real on-site scenarios. |
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987-90-5728-534-7 |
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UA @ admin @ c:irua:200601 |
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9055 |
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Montiel, F.N. |
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Voltage against illicit drug trafficking : capabilities of electrochemical fingerprinting to detect illicit drugs |
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Doctoral thesis |
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2024 |
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256 p. |
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Doctoral thesis; Pharmacology. Therapy; Engineering sciences. Technology; Antwerp Electrochemical and Analytical Sciences Lab (A-Sense Lab) |
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UA @ admin @ c:irua:204707 |
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9243 |
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Blidar, A.-M. |
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The development of sensitive and selective electrochemical methods for the detection of antibiotics |
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Doctoral thesis |
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2021 |
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139 p. |
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Doctoral thesis; Pharmacology. Therapy; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation); Antwerp Electrochemical and Analytical Sciences Lab (A-Sense Lab) |
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The discovery of antibiotics represented one of the greatest breakthroughs in medicine. Their success combined with an increasing intensive use is apparently bound to be also their undoing. This is due to the development of acquired antibiotic resistance, leading to inefficient antibiotherapy and even to the impossibility of treatment and death. The development and spread of antibiotic resistance are fueled by the widespread presence of trace levels of antibiotics residue, in various media, from environment to aliments. One of the solutions is the rigorous monitoring of the levels of antibiotics, which in term requires an almost constant development of new, more accessible analytical methods, especially screening methods, capable of decentralized analysis. In this direction, the electrochemical detection of antibiotics represents a very viable alternative. In this context, the aim of this thesis was to develop new electrochemical methods for the detection of antibiotics by employing and expanding on several strategies, like biomimetic sensors and electrochemical fingerprinting. Five studies were described in this thesis, that can be roughly divided in three categories, based on the analytical strategy employed. The first group is represented by direct electrochemical methods. The second group focuses on the use of biomimetic elements, molecularly imprinted polymers and aptamers. The hyphenation of electrochemical methods with other analytical methods was explored in the last group. In the last study, included in this group, the singlet oxygen-based photoelectrochemical approach was used for the detection of a phenolic antibiotic, rifampicin. The originality of the thesis consists in the testing and development of new approaches to various strategies used in electrochemical detection, revealing new insights in the field of electrochemical detection of antibiotics. The complex electrochemical fingerprint and the mechanism of the electrochemical oxidation were created and investigated, respectively, for the antibiotic vancomycin. New sensitive nanoplatforms were prepared by employing and combining new protocols. Additionally, important contributions were brought through the study involving the singlet oxygen-based detection of rifampicin. We demonstrated how a photocatalyst can exhibit analyte selectivity by strongly interacting with a complex phenolic compound, rifampicin. Summing up, the studies presented in this thesis will have an important impact in the field of electrochemical detection of antibiotics. |
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UA @ admin @ c:irua:182955 |
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7804 |
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Bjørnåvold, A. |
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Unlocking lock-in : accelerating socio-technical transitions to sustainability |
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Doctoral thesis |
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2021 |
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189 p. |
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Doctoral thesis; Linguistics; Engineering Management (ENM) |
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Achieving global sustainability goals will require cleaner and cheaper technologies. Public policy is central to achieving these goals and, in turn, ensuring a quicker pace of change. A major obstacle lies in the fact that technologies cannot be considered isolated entities: they are embedded in a powerful social context of cultural, organisational and institutional systems. This intertwining of different elements is referred to as a socio-technical system. This thesis discusses how socio-technical systems have, over time, allowed locked-in configurations to emerge, referring to a combination of systematic forces that perpetuate unsustainable infrastructures embedded in society. Such lock-ins can inhibit innovation and competitiveness of low-carbon and sustainable technologies, and this thesis looks to concrete solutions for unlocking them. Vital to this objective lies better understanding preferences, intentions, and behaviour of actors involved at each stage of technological development to improve public policy design. A discrete choice experiment – a quantitative non-market valuation method – was, therefore, a core method used to model preferences of key target groups. Target groups considered in the four components of the thesis include i) industry players, ii) policymakers, iii) farmers, and iv) the general public in Belgium, France, Germany, Italy and Spain. The thesis seeks to establish how both economic and regulatory instruments can be leveraged to overcome lock-in. One conclusion sees that implementing an efficient environmental tax regime – an economic instrument – requires balancing political feasibility and public acceptance considerations in line with tax and environmental policy. Results indicate that public acceptance for environmental taxation increases with earmarking. Another conclusion highlights the importance of taking behavioural and habitual considerations into account – both when considering policymakers’ investment decisions, and farmers’ decisions to adopting agro-ecological practices when responding to regulatory instruments. Overall, policy design should emphasise a more continuous and systemic approach to innovation and technology policy on the road to accelerating socio-technical transitions to sustainability. |
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978-90-5728-692-6 |
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Most recent IF: NA |
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UA @ admin @ c:irua:179247 |
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6949 |
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| Author |
Eliaerts, J. |
| Title |
Qualitative and quantitative determination of cocaine using mid-infrared spectroscopy and chemometrics |
Type |
Doctoral thesis |
| Year |
2020 |
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184 p. |
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Doctoral thesis; Law; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation) |
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Most recent IF: NA |
| Call Number |
UA @ admin @ c:irua:169398 |
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6589 |
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| Author |
Michielsen, I. |
| Title |
Plasma catalysis : study of packing materials on CO2 reforming in a DBD reactor |
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Doctoral thesis |
| Year |
2019 |
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215 p. |
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Doctoral thesis; Laboratory of adsorption and catalysis (LADCA); Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT) |
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Most recent IF: NA |
| Call Number |
UA @ admin @ c:irua:160087 |
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5278 |
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| Author |
Xu, W. |
| Title |
Plasma-catalytic DRM : study of LDH derived catalyst for DRM in a GAP plasma system |
Type |
Doctoral thesis |
| Year |
2023 |
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Pages |
350 p. |
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Doctoral thesis; Laboratory of adsorption and catalysis (LADCA); Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT) |
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Plasma is considered one of the promising technologies to solve greenhouse gas problems, as it can activate CO2 and CH4 at relatively low temperatures. Among the various types of plasmas, the gliding arc plasmatron (GAP) is promising, as it has a high level of non-equilibrium and high electron density. Nevertheless, the conversion of CO2 and CH4 in the GAP reactor is limited. Therefore, combining the GAP reactor with catalysts and making use of the heat produced by the plasma to provide thermal energy to the catalyst, forming a post-plasma catalytic (PPC) system, is hypothesized to improve its performance. Therefore, in this PhD research, we investigate important aspects of the PPC concept towards the use of the heat produced by GAP plasma to heat the plasma bed, without additional energy input. Aiming at this, based on a literature study (chapter 1), Ni-loaded layered double hydroxide (LDH) derived catalyst with good thermal catalytic DRM performance were chosen as the catalyst material. Before applying the LDH as a support material, the rehydration property of calcined LDH in moist and liquid environment was studied as part of chapter 2. The data indicated that after high temperatures calcination (600-900 C), the obtained layered double oxides (LDOs) can rehydrate into LDH, although, the rehydrated LDH were different from the original LDH. In chapter 3, different operating conditions, such as gas flow rate, gas compositions (e.g. CH4/CO2 ratio and nitrogen dilution), and addition of H2O were studied to investigate optimal conditions for PPC DRM, identifying possible differences in temperature profiles and exhaust gas compositions that might influence the catalytic performance. Subsequently, the impact of different PPC configurations, making use of the heat and exhaust gas composition produced by the GAP plasma, is shown in Chapter 4. Experiments studying the impact of adjusting the catalyst bed distance to the post-plasma, the catalyst amount, the influence of external heating (below 250 C) and the addition of H2O are discussed. As only limited improvement in the performance was achieved, a new type of catalyst bed was designed and utilized, as described in chapter 5. This improved configuration can realize better heat and mass transfer by directly connecting to the GAP device. The performance was improved and became comparable to the traditional thermal catalytic DRM results obtained at 800 C, although obtained by a fully electrically driven plasma. |
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| Call Number |
UA @ admin @ c:irua:201534 |
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9074 |
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| Author |
Zhang, K. |
| Title |
Revealing the correlation between titania support properties and propylphosphonic acid modification by in-depth characterization |
Type |
Doctoral thesis |
| Year |
2023 |
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Pages |
XVI, 262 p. |
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Doctoral thesis; Laboratory of adsorption and catalysis (LADCA) |
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Grafting organophosphonic acids modification (PAs) on metal oxides has shown to be a flexible technology to tune the surface properties of metal oxides for various applications. Nevertheless, there are still puzzles that need to be addressed, such as the correlations between metal oxides properties (types of surface reactive sites) and the modification (modification degree), the correlations between metal oxides properties and the properties of modified surfaces. Moreover, the currently used liquid-phase method for the grafting has associated impeding effects of solvent on tailoring the modification degrees, and also causes the formation of metal phosphonate side products. The solid-phase method can induce the unwanted changes in crystal phase of supports. Based on these questions, the three titania supports with divergent surface properties were selected as the metal oxides supports investigated, propylphosphonic acid (3PA) modification was carried out under the same synthesis conditions: four different concentrations, two solvents (water or toluene), and one reaction time (4 h) and temperature (90 ). MeOH chemisorption was introduced to probe the surface (un)reactive sites for 3PA modification. On the other hand, MeOH chemisorption and inverse gas chromatography (IGC) were combined to characterize the changes in surface polarity and acidic properties induced by the modification. Next, a solid-phase method, manual grinding, was proposed to graft 3PA on titania, avoiding the impeding effects of solvent on improving modification degree and the formation of the titania phosphonate side products, as well as preserving the crystal phase. The results indicate that methanol chemisorption can qualitatively analyze the surface active sites that are consumed by 3PA modification, its chemisorption capacity shows the consistent trend with the maximum modification degree, hereby revealing the kinds of interactions that are important in controlling surface coverage. Titania supports is found to play an important role in changes in surface polarity and acidic properties by charactering the three modified titania samples at a similar modification degree using the methanol chemisorption coupled with in-situ infrared and thermogravimetric-mass spectrometer, and the IGC. Moreover, IGC provides additional information about the changes in binding modes. Furthermore, grafting 3PA modification on titania was achieved by manual grinding. Compared to the liquid-phase method, the maximum modification degree obtained by the manual grinding is 25 % higher while using 83.3 % or 75.0% lower amounts of expensive 3PA and limiting the formation of titania phosphonate side products. Compared to the reactive milling method, the proposed manual grinding method preserves the crystal phase(s) of titania. |
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Most recent IF: NA |
| Call Number |
UA @ admin @ c:irua:198726 |
Serial |
8924 |
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| Author |
Li, L. |
| Title |
Untangling microbial community assembly in rainforest and grassland soils under increasing precipitation persistence |
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Doctoral thesis |
| Year |
2023 |
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179 p. |
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Doctoral thesis; Integrated Molecular Plant Physiology Research (IMPRES); Plant and Ecosystems (PLECO) – Ecology in a time of change |
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Climate change is causing alterations in precipitation patterns, leading to adverse ecological consequences in many ecosystems. Recently, an increasingly persistent weather pattern has emerged, characterized by lengthening the duration of alternating dry and wet periods, which is more complex than exclusively drought or increasing precipitation. It is currently unclear how soil microbial communities respond to these new regimes in relation to their interactions with plants, especially in precipitation-sensitive ecosystems, such as tropical rainforests and grasslands. In this thesis, we explored responses of soil bacterial and fungal communities to increasing weather persistence in rainforests and grasslands, using high throughput sequencing technology. We firstly investigated the resistance and resilience of microbial communities to prolonged drought in a mature seasonal tropical rainforest which experiences unusually intensive dry seasons in the current century. Through excluding rainfall during and after the dry season, a simulated prolongation of the dry season by five months was compared to the control. Our results indicate that as rain exclusion progressed, the microbial communities increasingly diverged from the control, indicating a moderate resistance to prolonged drought. However, when the drought ceased, the composition and co-occurrence patterns of soil microbial communities immediately recovered to that in the control, implying a high resilience. To further investigate the ecological roles of soil microbial communities in response to increasing weather persistence, we set up grassland mesocosm experiments. In these experiments, precipitation frequency was adjusted along a series, ranging from 1 to 60 consecutive days alternating of dry and wet periods, while keeping the total precipitation constant. Our results show that microbial community assembly tended to be more stochastic processes at intermediate persistence of dry and wet alternations while more deterministic processes dominated at low and high persistence within 120 days regime exposure. Moreover, more persistent precipitation reduced the fungal diversity and network connectivity but barely impacted that of bacterial communities. The prior experiences of persistent weather events for one year caused legacy effects. The soil microbial legacy induced by soil microbial communities subjected to prior persistent weather events was more enduring in subsequent fungal communities than bacterial communities, likely due to slower growth of fungi compared to bacteria. However, a minor effect of soil microbial legacy was observed on plant performance. In addition, we kept the grassland mesocosm experiment for two growing seasons. The effects of precipitation persistence on soil microbial communities increased in the second year. The dissimilarities of microbial communities between the first and second year were less with more persistent precipitation, potentially resulting in more vulnerable microbial communities, due to some taxa disappearing and a reduction in functional redundancy under more persistent weather. To conclude, our findings provide a comprehensive theoretical understanding of soil microbial communities in response to the current and future climate change, drawing from both natural and experimental systems. It helps in predicting and managing the impacts of future climate change on ecosystems mediated by microbial communities. Additionally, the findings of microbe-mediated legacy effects on grassland ecosystems can provide practical guidance for their application in agriculture, specifically for using an inoculum to mitigate the impacts of climate change. |
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UA @ admin @ c:irua:198498 |
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9240 |
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Voordeckers, D. |
| Title |
Design to breathe : understanding and altering wind patterns in street canyons to reduce human exposure to air pollution |
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Doctoral thesis |
| Year |
2023 |
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xxii, 303 p. |
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Doctoral thesis; Engineering sciences. Technology; Sustainable Energy, Air and Water Technology (DuEL); Research Group for Urban Development; Intelligence in PRocesses, Advanced Catalysts and Solvents (iPRACS) |
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Air pollution is proclaimed by the World Health Organiaation (WHO) as the biggest environmental threat to human health. Street canyons, or urban roads flanked by a continuous row of high buildings on both sides, are perceived as typical bottleneck areas for air quality due to their lack of natural ventilation. This doctoral thesis aims to integrate expert knowledge on in-canyon flow fields and pollution dispersion in street canyons from the specialized field of (bio)engineering into the field of urban planning and vice versa. In Chapter 1, a Geospatial Information System (GIS) method was developed to detect exposure zones and hotspot street canyons. A critical combination between aspect ratio (AR > 0.65) and traffic volume (TVmax > 300) was detected and subsequently used to detect hotspot street canyons in three major European cities (Antwerp, London and Paris). Chapter 2 focusses on acquiring in-depth knowledge on flow and concentration fields in street canyons by conducting an extensive literature review on over 200 studies and translates this knowledge into nineteen guidelines and eleven spatial tools, comprised in a toolbox for urban planning. Subsequently, computational fluid dynamics (CFD) was used into a research trough design process (Chapter 4) to illustrate how the design tools can be applied to a specific case study (Belgiëlei, Antwerp). Alternations to traffic lanes (traffic lane reduction and lateral displacement) combined with low boundary walls (LBWs), were found to reduce NO2 levels in the entire pedestrian area up to – 3.6 % and peak pollutions were reduced by -8 %. A maximum NO2 reduction was reached by combining a traffic lane displacement with hedges, adjustments to the tree planting pattern and an increased ground-level permeability, leading to reductions up to – 4.5 % in the pedestrian areas. In conclusion, urban design was found to be a valuable tool to enhance the effect of emission reduction strategies and draw in-canyon concentrations closer to the value of the background concentration. However, the background concentration seemed to dominate the efficiency of the urban design interventions and therefore, additional measures should be taken to reduce background pollution levels. This dissertation aims to contribute to the awareness of air pollution in street canyons, as well as support local governments in taking action by delivering spatial tools and guidelines applicable for urban planning and represents a framework for the dissemination of expert information on air quality in street canyons to the field of urban planning. |
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Most recent IF: NA |
| Call Number |
UA @ admin @ c:irua:196399 |
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7767 |
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Sóti, V. |
| Title |
Catalytic detoxification of lignocellulose hydrolyzate |
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Doctoral thesis |
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2019 |
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XXVII, 243 p. |
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Doctoral thesis; Engineering sciences. Technology; Sustainable Energy, Air and Water Technology (DuEL); Biochemical Wastewater Valorization & Engineering (BioWaVE) |
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The present PhD research investigated the possibility of catalytic detoxification of poplar wood based and steam exploded lignocellulosic hydrolyzate with different types of laccase enzymes, with special focus on ethanol and lactic acid products at industrially relevant parameters: high final product concentration, high initial substrate loading and integrated processes. The simultaneous saccharification and fermentation (SSF) process was taken as a base case and five types of laccases were thoroughly investigated on their utilization potential. Phenolic removal from the liquid xylose rich fraction (XRF) was higher with fungal laccases (65-90 %) compared to approximately 30 % removal with bacterial laccase. Moreover, the optimal pH of fungal laccases was close to pH 4.5, the optimum for cellulase, while the bacterial laccase worked at basic pH. Integrating laccase treatment and hydrolysis together showed that fungal laccases have negative impact on final sugar concentration, while bacterial laccase had a strong positive effect. Although bacterial laccase removed less phenol and although its optimal conditions are difficult to integrate with hydrolysis, its enhancing effect on cellulase activity makes it a better candidate for application. The presence of the solid fraction (SF) alters the phenolic concentration evolution significantly, thus screening experiments with the liquid fraction alone do not provide sufficient information for the combined process. Magnetic Cross-Linked Enzyme Aggregates (m-CLEAs) immobilization was assessed for bacterial laccase. m-CLEAs decreased phenolic concentration faster at every pH compared to free bacterial laccase; however, the removal was caused by adsorption rather than by enzyme activity. Although the size of m-CLEAs particles are in the µm range, around 90 % of the initial catalyst mass was recycled from a dense (15 % substrate loading) mixture via magnetic separation. The high recycling rate is promising; m-CLEAs immobilization method can have industrial utilization potential. Minimum sugar revenue (MSR) estimations show that currently hardwood based MSR is 70 % more expensive than corn grain based MSR. About 7-10 fold cellulase activity increase will be needed until MSR will be competitive with corn grain MSR. However, m-CLEAs cellulase can already be competitive if the corn prices are in the higher regime of last year’s prices. |
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UA @ admin @ c:irua:180125 |
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7584 |
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Wittner, N. |
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Improving and characterising solid-state fungal pretreatment by Phanerochaete chrysosporium for sugar production from poplar wood |
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Doctoral thesis |
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2023 |
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206 p. |
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Doctoral thesis; Engineering sciences. Technology; Sustainable Energy, Air and Water Technology (DuEL); Biochemical Wastewater Valorization & Engineering (BioWaVE) |
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Pretreatment is a critical step in the conversion of lignocellulose into biofuels and biochemicals. During pretreatment, the recalcitrance of lignocellulose is reduced, e.g. by removing lignin, thereby making the carbohydrates more accessible for enzymatic saccharification. Fungal delignification by white-rot fungi is a biotechnological alternative to chemical/physicochemical methods, which is carried out in solid-state fermentation with mild reaction conditions and without the formation of microbial inhibitors. However, fungal pretreatment presents some challenges, such as long pretreatment time, non-selective and low delignification, low enzymatic digestibility and feedstock sterilisation requirement, making its commercial implementation challenging compared to conventional methods. This study investigates the possibility of improving and characterising the solid-state fungal pretreatment of poplar wood by Phanerochaete chrysosporium. The individual and combined effects of MnSO4 and CuSO4 supplements on the delignification of sterilised wood are investigated using response surface methodology to improve the degree and selectivity of fungal delignification. Spore-inoculated solid-state fermentations are carried out for 4 weeks in sterile vented bottles. The mechanism of the concerted action of the metal ions on lignin degradation is then elucidated by relating fungal growth and ligninolytic enzyme activities to lignocellulose degradation as a function of pretreatment time. The optimised metal-supplemented system is then applied to the pretreatment of non-sterilised wood using different inoculation techniques (spores and pre-colonised substrate), nutrients (metal ions with or without glucose and sodium nitrate) and cultivation environments (sterile aerated bottles and open trays). The fermentations are then characterised using infrared spectroscopy, in particular NIR and ATR-FTIR spectroscopy, with the aim of developing rapid lignin quantification methods as an alternative to conventional wet chemical methods. Finally, the feasibility of producing fermentable sugars from sterilised and non-sterilised poplar wood using fungal pretreatment is evaluated through a techno-economic analysis. Supplementing the pretreatment system with 2.01 µmol CuSO4 and 0.77 µmol MnSO4 g-1 wood resulted in 1.9-fold higher lignin degradation, 2.3-fold higher delignification selectivity value and 2.9-fold higher glucose yield. The improved delignification could be explained by the concerted action of Mn2+ and Cu2+ ions, with Mn2+ ions inducing and Cu2+ prolonging manganese peroxidase production responsible for delignification. Fungal pretreatment at non-sterile conditions was obtained using trays in a simple solid-state fermentation set-up without sterile aeration. A 1:3 ratio of pre-colonised and untreated wood was applied for inoculation and only Cu2+, Mn2+ and sodium nitrate as supplements. Remarkably, this technology resulted in a comparably high glucose yield (28.51 ± 0.28%) to the traditional method using sterilised wood, sterile aeration and spores as inoculum, while reducing the amount of wood to be sterilised by 71.2%. Infrared spectroscopy-based methods with high coefficients of determination (R_CV |
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Most recent IF: NA |
| Call Number |
UA @ admin @ c:irua:197185 |
Serial |
8883 |
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Verbruggen, S. |
| Title |
TiO2 gas phase photocatalysis from morphological design to plasmonic enhancement |
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Doctoral thesis |
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2014 |
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173 p. |
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Doctoral thesis; Engineering sciences. Technology; Sustainable Energy, Air and Water Technology (DuEL) |
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978-90-5728-441-0 |
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Most recent IF: NA |
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UA @ admin @ c:irua:116937 |
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5998 |
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Borah, R. |
| Title |
Photoactive nanostructures : from single plasmonic nanoparticles to self-assembled films |
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Doctoral thesis |
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2022 |
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xxxiv, 220 p. |
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Doctoral thesis; Engineering sciences. Technology; Sustainable Energy, Air and Water Technology (DuEL) |
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Photoactive nanoparticles and their light-driven applications have gained tremendous scientific attention towards remediation of the global environmental problems, meeting alternative energy demands, and other new technological discoveries. The research work presented in this dissertation includes a fundamental investigation of such nanoparticles to gain deeper insights that will ultimately benefit their application. In particular, the study of plasmonic metal nanoparticles and metal oxide nanoparticles for light driven applications is the major theme of this work. The investigation begins with isolated plasmonic Au and Ag nanoparticles, followed by a natural extension to nanoparticle clusters, and then further to nanoparticle films. Next, the application of such plasmonic nanoparticle films for gaseous phase sensing of volatile organic compounds is explored. Finally, the film formation of metal-oxide nanoparticles by self-assembly is investigated for the fabrication of photoactive functional interfaces. The fundamental theoretical investigation of the isolated plasmonic nanoparticles encompasses alloy and core-shell nanostructures of Au-Ag bimetallic compositions. First, the optical properties of bimetallic alloy and core-shell nanoparticles are compared for different structures such as nanospheres, nanotriangles and nanorods. Based on the optical properties, the photothermal properties of these nanostructures are also evaluated for relevant light-driven applications. Further, to bridge the gap between the theoretical and experimental optical properties of colloidal plasmonic nanoparticles, the effect of different statistical parameters pertaining to the particle size distribution is studied. Going from isolated nanoparticles to nanoparticle clusters, the changes in the optical properties of plasmonic nanoparticles when they form finite clusters is investigated. A strong effect of clustering on the absorption intensities of the nanoparticles and hence, on the photothermal properties is found. Next, for the study of plasmonic nanoparticle infinite arrays, Au and Ag nanoparticles films are experimentally obtained by the self-assembly at the air-ethylene glycol interface. Upon further validation of the computational models with the experimental optical properties of these films, the near-field and far-field optical response of the plasmonic nanoparticle arrays is investigated. An application of the self-assembled Au nanoparticle film is then demonstrated in the sensing of volatile organic compounds (VOCs). Finally, the focus is shifted from plasmonic nanoparticles to metal oxide nanoparticles for their self-assembly at the air-water interface to obtain self-assembled films. For this, the hydrophobic functionalization of four metal oxides nanoparticles namely, TiO2, ZnO, WO3 and CuO is investigated. The insights from this work is useful for the design and fabrication of functional nanoparticles and interfaces for light driven applications. |
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Most recent IF: NA |
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UA @ admin @ c:irua:189155 |
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7188 |
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Spanoghe, J. |
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Purple bacteria cultivation on light, carbon dioxide and hydrogen gas : exploring and tuning the potential for microbial food production |
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Doctoral thesis |
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2022 |
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vi, 207 p. |
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Doctoral thesis; Engineering sciences. Technology; Sustainable Energy, Air and Water Technology (DuEL) |
| Abstract |
The human population is projected to grow to 9.7 billion by 2050, resulting in an estimated increase in protein demand of 50%. From an environmental perspective, the current and future demand of protein cannot be sustainably met as the conventional food production chain is severely altering biogeochemical cycles of nitrogen and phosphorus, biodiversity and land-use, with flows towards the biosphere and oceans that are exceeding the planetary boundaries. Microbial protein (protein derived from microorganisms) has been suggested as an excellent sustainable protein source, a fortiori when produced in a land- and fossil free manner. The photoautohydrogenotrophic cultivation (i.e. with light, CO2 and H2) of purple bacteria links up perfectly with the upcoming green electrification of industry (green H2) and the need for carbon capture and utilization. However, this metabolism represented a gap in literature, and thus this thesis aimed to establish a basic knowledge platform on its kinetic, stoichiometric and nutritional performance. At first, three originally photoheterotrophically enriched purple bacteria were studied of which Rhodobacter capsulatus reached the highest protein productivity of 0.16 g protein/L/d, which aligned well with the commonly-known photoautotrophic microalgae. Moreover, a full dietary essential amino acid match was found for human food, while the fatty acid content was dominated by the health-stimulating vaccenic acid (82-86%). Lastly, the achieved protein yield in photoautohydrogenotrophic purple bacteria was 2.3 times higher compared to hydrogen oxidizing bacteria, indicating a resource-efficient use of H2. Next, a photoautohydrogenotrophic enrichment of wastewater treatment microbiomes was performed in search for specialist species. While the isolates of this enrichment showed improvements in their performance during acclimation, the kinetic and nutritional performance of Rhodobacter capsulatus still excelled. Subsequently, the influence of nutrient limitations (C or N) and nitrogen gas fixation was studied on the nutritional tuning potential. Both the limitations as well as the N2 fixation resulted in the shift of the essential amino acid profiles. Additionally, the limitations significantly decreased the pigment content, while an increase in the storage of poly-P was seen in case of carbon limitations. The next major challenge was the production intensification in a photobioreactor of which the design was linked to minimizing both H2 and light limitations. The chosen bubble-column photobioreactor already resulted in a doubled biomass productivity. Finally, the remaining technological and non-technological challenges ahead for the production of a high-value, cost-efficient, environment-friendly microbial protein that complies with legislative requirements and appeals to future consumers were discussed. |
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978-90-5728-741-1 |
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UA library record |
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Most recent IF: NA |
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UA @ admin @ c:irua:188233 |
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7198 |
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