Le dioxyde de titane suscite un grand intérêt dans le domaine de la photocatalyse. Cependant, il n'utilise que la composante UV du flux solaire soit 4-5 % de l'énergie disponible. Un objectif de cette thèse est d'élaborer un matériau capable d'absorber dans le visible tout en restant actif sous lumière UV. Des nanoparticules de dioxyde de titane modifiées avec de l'or et/ou de l'azote ont été synthétisées par pyrolyse laser. Les poudres obtenues ont été caractérisées systématiquement par différentes techniques physico-chimiques (analyse ICP-AES), structurales (DRX), morphologiques et texturales (MET, MEB, BET), optiques (Spectroscopie UV-Visible) et électroniques (XPS, RPE et TRMC). Les particules présentent une structure cristalline majoritairement anatase, avec une taille moyenne de l'ordre de 7-10 nm. Leur efficacité photocatalytique a été évaluée par HPLC vis-à-vis de la dégradation d'acides carboxyliques (C1-C4) sous lumière UV et Visible. Les résultats photocatalytiques obtenus sur un polluant modèle (l'acide formique) ont révélé que sous UV le TiO2 préparé par pyrolyse laser est nettement plus actif que la référence commerciale. La modification à l'or améliore encore l'efficacité en facilitant le transfert de charge, alors que le dopage à l'azote introduit des sites de recombinaison provoquant donc un effet négatif. Ces résultats ont été corrélés à la dynamique des porteurs de charge étudiée par TRMC (Time Resolved Microwave Conductivity). La combinaison des deux élèments Au et N montre une efficacité proche de la référence commerciale, tout en introduisant une activité dans le visible. Dans le cas des acides à plus longue chaîne, la photoactivité des différents photocatalyseurs est proche de la référence commerciale sous lumière UV, mais reste très limitée dans le visible. La compréhension des mécanismes de dégradation a été abordée par la Résonance Paramagnétique Electronique (RPE). / Titanium dioxide is the most widely used photocatalyst due to its amazing properties. However, TiO2 is activated by UV radiation which represent about 4-5 % of solar light. One aim of this work is to shift the adsorption of TiO2 to the visible range while maintaining photoactivity under UV. Therefore N-doped and gold modified TiO2 nanoparticles have been synthesized in one step by laser pyrolysis. The materials have been characterized; their photocatalytic activity was evaluated by the degradation of carboxylic acids (C1-C4) under both UV and Visible irradiation. When dealing with the decomposition of formic acid under UV light, all samples exhibit a higher activity compared to commercial P25. Modification with Au increases the reaction rate by enhancing charge separation, while N-doped sample are less efficient due to recombination centers induced by Nitrogen. These results were correlated to the dynamic of electron/hole pairs studied by TRMC (Time Resolved Microwave Conductivity). Moreover, the combination of Au and N showed an efficiency similar to commercial P25 under UV irradiation associated to photoactivity in the visible range. In the case of C2-C4 acids, photocatalytic performances of all photocatalysts are similar to commercial P25 under UV, but very weak under visible light. Degradation mechanisms were investigated by ESR (Electron Spin Resonance).

abstract: This dissertation investigates the mechanisms that lead to fouling, as well as how an understanding of how these mechanisms can be leveraged to mitigate fouling. To limit fouling on feed spacers, various coatings were applied. The results showed silver-coated biocidal spacers outperformed other spacers by all measures. The control polypropylene spacers performed in-line with, or better than, the other coatings. Polypropylene’s relative anti-adhesiveness is due to its surface free energy (SFE; 30.0 +/- 2.8 mN/m), which, according to previously generated models, is near the ideal SFE for resisting adhesion of bacteria and organics (~25 mN/m). Previous research has indicated that electrochemical surfaces can be used to remove biofilms. To better elucidate the conditions and kinetics of biofilm removal, optical coherence tomography microscopy was used to visualize the biofouling and subsequent cleaning of the surface. The 50.0 mA cm-2 and 87.5 mA cm-2 current densities proved most effective in removing the biofilm. The 50.0 mA cm-2 condition offers the best balance between performance and energy use for anodic operation. To test the potential to incorporate electrochemical coatings into infrastructure, membranes were coated with carbon nanotubes (CNTs), rendering the membranes electrochemically active. These membranes were biofouled and subsequently cleaned via electrochemical reactions. P. aeruginosa was given 72h to develop a biofilm on the CNT-coated membranes in a synthetic medium simulating desalination brines. Cathodic reactions, which generate H2 gas, produce vigorous bubbling at a current density of 12.5 mA cm-2 and higher, leading to a rapid and complete displacement of the biofilm from the CNT-functionalized membrane surface. In comparison, anodic reactions were unable to disperse the biofilms from the surface at similar current densities. The scaling behavior of a nanophotonics-enabled solar membrane distillation (NESMD) system was investigated. The results showed the NESMD system to be resistant to scaling. The system operated without any decline in flux up to concentrations 6x higher than the initial salt concentration (8,439 mg/L), whereas in traditional membrane distillation (MD), flux essentially stopped at a salt concentration factor of 2x. Microscope and analytical analyses showed more fouling on the membranes from the MD system. / Dissertation/Thesis / Doctoral Dissertation Civil, Environmental and Sustainable Engineering 2019

Nowadays, there is an increasing risk of bacterial infections from bacteria strains resistant towards antibiotics. Thus, it is of utmost importance to research novel therapies which can overcome this difficulty. The presented thesis focuses on the preparation, characterization and antibacterial evaluation of polystyrene polymer nanomaterials (nanofiber membranes and nanoparticles) modified with compounds that can efficiently inhibit bacterial growth either by their nature (polyethyleneimine) or by photoactivation upon visible light excitation (NO- photodonors, photosensitizers) and consequent production of highly reactive inorganic bactericidal species, nitric oxide (NO) and singlet oxygen (O2(1 g)). All materials were fully characterized by several independent methods. The concentrations of NO and O2(1 g) were measured by amperometric and time-resolved spectroscopic techniques and by variety of chemical analytic procedures. Due to the presence of bactericidal species and the efficient photogeneration of NO and O2(1 g) at physiological conditions, all materials exhibit strong antibacterial action tested on a Gram-negative bacterial strain Escherichia coli. Hence, these functionalized polymer nanomaterials may be intriguing systems for medical-, biological-, or environmental- application where a...

Fuel Cells are important forms of sustainable power generation and Biofuel Cells utilize the use of bio-compatible/biodegradable molecules as fuels. Glucose is an ideal candidate to serve this purpose. In this project, a Glucose Fuel Cell (GFC) has been fabricated using the nanomaterials developed in the lab. The skeletal system of this GFC is a three-layered structure; a Membrane Electrode Assembly (MEA) composed of carbon electrodes (anode and cathode) and a Poly Vinyl Alcohol/Poly Acrylic Acid (PVA/PAA) polymer electrolyte. Gold and Silver (Au and Ag) nanoparticles are utilized as catalyst on the anode and cathode respectively, which are prepared by the use of green chemistry practice. One of the GFC has been compacted under hot press and the other non-hot pressed. ,which led to different surface areas. For the validation of the GFC stacks, the glucose concentration was selected around biologically available levels, i.e at 400 mg/dL in both the cases. One trial on hot pressed membrane with 200 mg/dL of glucose is also studied. Short Circuit Current (SCC) and Open Circuit Voltage (OCV) were measured following which the voltages and currents were measured across load resistances. The Thermal Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) studies were carried out on the membrane while the electrodes were characterized by Scanning Electron Microscopy (SEM). UV-Vis studies were carried out on the Au and Ag nanoparticle suspension before and after impregnation of carbon cloth electrodes. Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) has been utilized to estimate the concentration and thus the number of nanoparticles adsorbed on the surface of the carbon cloth. The variations of output current with the thickness of the membranes were studied. The assembly containing the catalytic particles showed power levels ranging between 128.7 nW-332.2 nW in the glucose concentration of 400 mg/dL. Rigorous efforts are under process to scale down the power consumption of electronics to extremely low levels. GFCs could be used as power generators in such devices. The inexpensiveness of the fuel is a remarkable factor.

Nanotechnology as a field has the potential to answer some of the major challenges that mankind faces in regards to environmental sustainability, energy generation and health care. Though, solutions to these concerns can not necessarily rely on our current knowhow. Instead, it is reasonable to expect that humanity must adapt and learn to develop new materials and methods to overcome the adversities that we are facing. This master thesis has involved developing novel materials, serving as a small step in the continuous march towards a bright future where this is possible. More specifically, this work sought to combine mesoporous magnesium carbonate with various metal-organic frameworks to utilize the beneficial aspects from each of these constituents. The ambition was that these could be joined to render combined micro-/mesoporous core-shell structures, with high surface areas and many active sites whilst maintaining a good permeability. Numerous different synthesis routes were developed and explored in the pursuit of viable routes to design novel materials with potential future applications within for instance drug delivery, water harvesting from air and gas adsorption. Coreshell structures of the hydrophilic mesoporous magnesium carbonate covered with the hydrophobic zeolitic imidazole framework ZIF-8 was successfully synthesized for the first time, and practical studies demonstrated a dramatically enhanced water stability, which is perceived to have an impact on further research on these materials. ZIF-67 was also combined with mesoporous magnesium carbonate in a similar manner. Further, Mg-MOF-74 was grown directly from mesoporous magnesium carbonate, where the latter acted as a partially self-sacrificing template, with the aim of rendering a porous hierarchical structure with contributions from the micro- and mesoporous ranges. The outcomes of all these syntheses were characterized using several analyzing methods such as scanning electron microscopy, X-ray diffraction, energy dispersive spectroscopy and nitrogen sorption analysis.

<p>Technological advancements in electronics industry are driven by innovations in device fabrication techniques and development of novel materials. Halide perovskites are one of the latest additions to the semiconductor family. The performance of solid-state devices based on halide perovskites is now competing with other well-established semiconductors like silicon and gallium arsenide. However, the intrinsic instability of three-dimensional (3D) perovskites poses a great challenge in their widespread commercialization. The soft crystal lattice of hybrid halide perovskites facilitates anionic diffusion which impacts material stability, optoelectronic properties, and solid-state device performance.</p> <p>Two-dimensional (2D) halide perovskites with organic capping layers have been used for improving the extrinsic stability as well as suppressing intrinsic anionic diffusion. Nevertheless, a fundamental understanding of the role of compositional tuning, especially the impact of organic cations, in inhibiting anionic diffusion across the perovskite-ligand interface is missing. In our research, we first developed a library of atomically sharp and flat 2D heterostructures between two arbitrarily determined phase-pure halide perovskite single crystals. This platform was then used to perform a systematic investigation of anionic diffusion mechanism and quantify the impact of structural components on anionic inter-diffusion in halide perovskites. </p> <p>Stark differences were observed in anionic diffusion across 2D halide perovskite lateral and vertical heterostructures. Halide inter-diffusion in lateral heterostructures was found to be similar to the classical Fickian diffusion featuring continuous concentration profile evolution. However, vertical heterostructures show a “quantized” layer-by-layer diffusion behavior governed by a local free energy minimum and ion-blocking effects of the organic cations. For both lateral and vertical migrations, halide diffusion was found to be faster in perovskites with larger inorganic layer thickness. The increment becomes less apparent as the inorganic layer thickness increases, akin to the quantum confinement effect observed for band gaps. Furthermore, we found that bulkier and more rigid π-conjugated organic cations inhibit halide inter-diffusion much more effectively compared to short chain aliphatic cations. These results offer significant insights into the mechanism of anionic diffusion in 2D perovskites and provide a new materials platform for heterostructure assembly and device integration.</p>

Ce manuscrit présente une étude expérimentale sur le processus de recouvrement de nanotubes de carbone mono parois en suspension micellaire par des molécules de colorants organiques. En raison des propriétés électroniques exceptionnelles et de la structure chimique carbonée de ces nanotubes, une modification de leur environnement physico-chimique a une grande influence sur leurs propriétés optoélectroniques. Les conséquences de cette fonctionnalisation de surface sont étudiées par des techniques de spectroscopie optique. Le procédé de fonctionnalisation non covalente de nanotubes par des molécules de porphyrines en milieu micellaire est détaillé selon trois axes de recherches complémentaires. Dans un premier temps, les aspects cinétiques de ce processus réactionnels seront discutés. En particulier, le rôle de l'organisation de l'environnement micellaire est mis en évidence. Cela permet de comprendre et de contrôler la durée de la réaction. Une étude thermodynamique de l'interaction nanotube/porphyrines sera ensuite détaillée. Le comportement associatif des porphyrines au cours de leur interaction avec le nanotube sera démontré. Dans un troisième chapitre, les caractéristiques spectrales de la porphyrine lorsqu'elle est adsorbée sur la surface de carbone seront discutées. Un modèle de couplage dipôle- dipôle est développé pour comprendre ces effets. Ce modèle permet de mettre en évidence / This manuscript presents an experimental study on the process of coverage of single-wall carbon nanotubes by organic dyes molecules. Due to the exceptional electronic properties and the monolayer carbon structures of such nanotubes, a modification of their physico-chemical environment has a great influence on their optoelectronic properties. The consequences of this surface functionalization are studied by means of optical spectroscopy. The process of non covalent functionalization of surfactant suspended nanotubes by porphyrin molecules is separated in three complementary studies. The first one details the kinetic aspects of this reaction process. In particular, the role of the organization of the surfactant environment will be highlighted. This allows to understand and control the reaction timescale. On the second hand, a comprehensive thermodynamic study of the nanotube/porphyrins interaction is performed. The associative behavior of the porphyrin during the interaction with the nanotube is evidenced. Then, the spectral characteristics of the porphyrin when it is adsorbed on a carbon surface is discussed. A dipole-dipole coupling model is developed to understand such effects. This model allows to highlight the geometry followed by the molecules when they are organized on the carbon template (nanotube or graphene).

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