Academic literature on the topic 'Silicon dioxide nanoparticles'

Increasing use of engineered nanomaterials presents concerns as some nanoparticles appear to be harmful to both human health and the environment. Effective treatment methods are required to remove problematic nanoparticles from (waste)water streams. Porous media filtration, commonly used for the removal of particulate matter, shows promise for nanoparticle treatment. The goal of this work is to investigate the potential of porous media filtration for the abatement of nanoparticles from aqueous waste streams. To this end, an automated method was developed that allows real-time and in-situ monitoring of nanoparticle transport and retention in porous media using online measurement of UV-visible absorbance or fluorescence. Development of fluorescent-core nano-silica (n-SiO₂) in controllable sizes provided an excellent tracer for nanoparticle transport in porous media. Measurement of n-SiO₂ by destructive techniques is complicated by high natural Si background levels. Fluorescence monitoring enables real-time measurement, facilitating rapid evaluation of n-SiO₂ transport. Synthesized n-SiO₂ remain in their primary sizes making an evaluation of the behavioral change of particles due to transition into the "nano" range possible. A comparison of the role of particle size on transport in porous media displayed the importance of particle number concentration as the dominance of site-specific adsorption may be obscured by simple mass concentration evaluation.T he effectiveness of different bed materials, namely, sand, activated carbon (AC), and diatomaceous earth (DE), for the removal of TiO₂ nanoparticles (n-TiO₂) from aqueous streams was investigated. DE proved promising for n-TiO₂ capture shown by its high bed capacity (33.8 mg TiO₂ g⁻¹(medium)) compared to AC (0.23 mg TiO₂ g⁻¹(medium)) or sand (0.004 mg TiO₂ g⁻¹(medium)). The presence of organic and synthetic contaminants produced varying effects on n-TiO₂ retention, mostly due to either enhanced electrostatic or steric interactions. Application of a process simulator combining physical straining with site-specific interactions, delineating physisorption from chemisorption and diffusion limited interactions, enabled the accurate fit of n-TiO₂ transport in sand, AC and DE. The fitting process revealed the advantage of DE due to increased physisorption and physical straining of n-TiO₂. Modeling of this system afforded the elucidation of controlling retention mechanisms and provides a basis for future scaling and system design.

Metal oxide and metal oxide-supported metal nanoparticles can adsorb and decompose chemical warfare agents (CWAs) and their simulants. Nanoparticle activity depends on several factors including chemical composition, particle size, and support, resulting in a vast number of materials with potential applications in CWA decontamination. Current instrumentation in our laboratory used to investigate fundamental gas-surface interactions require extensive time and effort to achieve operating conditions. This thesis describes the design and construction of a high-throughput, high vacuum surface analysis instrument capable of studying interactions between CWA simulants and nanoparticulate surfaces. The new instrument is small, relatively inexpensive, and easy to use, allowing for expeditious investigations of fundamental interactions between gasses and nanoparticulate samples. The instrument maintains the sample under high vacuum (10?⁷-10?⁹ torr) and can reach operating pressures in less than one hour. Thermal control of the sample from 150-800 K enables sample cleaning and thermal desorption experiments. Infrared spectroscopic and mass spectrometric methods are used concurrently to study gas-surface interactions. Temperature programmed desorption is used to estimate binding strength of adsorbed species. Initial studies were conducted to assess the performance of the instrument and to investigate interactions between the CWA simulant dimethyl methylphosphonate (DMMP) and nanoparticulate silicon dioxide.<br>Master of Science

Master of Science<br>Mechanical and Nuclear Engineering<br>Kevin B. Lease<br>Gurpreet Singh<br>Energy has always been one of the most important factors in any type of human or industrial endeavor. Clean energy and alternative energy sources are slowly but steadily replacing fossil fuels, the over-dependence on which have led to many environmental and economic troubles over the past century. The main challenge that needs to be addressed in switching to clean energy is storing it for use in the electrical grid and transportation systems. Lithium ion batteries are currently one of the most promising energy storage devices and tremendous amount of research is being done in high capacity anode and cathode materials, and better electrolytes and battery packs as well, leading to overall high efficiency and capacity energy storage systems. Polymer derived ceramics (PDCs) are a special class of ceramics, usually used in high temperature applications, but some silicon based PDCs have demonstrated good electrochemical properties in lithium ion batteries. The goal of this research is to explore a special hybrid ceramic of titanium dioxide (TiO₂) and silicon oxy carbide (SiOC) ceramic derived from 1,3,5,7 -- tetravinyl -- 1,3,5,7 -- tetramethylcyclotetrasiloxane (TTCS) polymer for use in lithium ion batteries and investigate the source of its properties which might make the ceramic particularly useful in some highly specialized energy storage applications.

Die breite Anwendung von Modellsystemen, um heterogene katalytische Prozesse zu verstehen, basiert darauf, die Lücke der strukturellen Komplexität zu überbrücken zwischen heutigen technischen Katalysatoren, bestehend aus einem Metalloxid sowie einem darauf geträgerten Metall, sowie kristallinen Metallen und planaren Metall/Oxid-Systemen, welche dazu benutzt werden, Struktur-Reaktivitäts-Beziehungen mittels einer Fülle von Surface Science-Methoden zu untersuchen. In der vorliegenden Arbeit liegt das Hauptaugenmerk auf so genannten Vanadiumoxid-‚Monolagen’-Katalysatoren, die insbesondere für Oxidationsreaktionen von Methanol eingeführt wurden. Mittels eines ‚bottom-up’-Ansatzes wurden Silica-geträgerte Vanadiumoxid-Modellkatalysatoren untersucht. Durch Kombination einer Reihe experimenteller Techniken wurde die Oberfläche von Mo(112), die als Substrat für den Silica-Film diente, im Detail untersucht und die atomare Struktur des Silica-Films wurde ermittelt. Adsorption von Wasser und das Wachstum von Vanadiumoxid-Nanopartikeln auf dem Silica-Film und schließlich die Reaktivität von Vanadiumoxid/Silica-Systemen gegenüber Methanol wurden untersucht. Im Gegensatz zu früher vorgeschlagenen Modellen sollte eine Sauerstoff-induzierte p(2×3)-Überstruktur, die sich auf einer Mo(112)-Oberfläche ausbilded, angenommen werden als ein eindimensionales Oberflächenoxid, bei dem sich Mo=O-Gruppen bevorzugt entlang der [-1-11]-Richtung der Mo(112)-Oberfläche ausbilden. Monolagen-Silica-Filme, die auf Mo(112) gewachsen wurden, bestehen aus einem zweidimensionalen Netz von SiO4-Tetraedern. In Abhängigkeit der Bedingungen, unter denen der Film präpariert wurde, kann die Struktur durch zusätzlich auf dem Mo-Substrat adsorbierte Sauerstoff-Atome verändert werden. Die Defekt-Struktur schließt Antiphasen-Domänengrenzen ein, die durch eine Verschiebung um die halbe Gitterkonstante entlang der [-110]-Richtung gebildet werden, und eine geringe Dichte von Punkt-Defekten, die höchstwahrscheinlich Silizium-Fehlstellen darstellen. Wasser dissoziiert nicht auf dem Monolagen-Silica-Film. Eine Wasser-Struktur, die geordnet bezüglich des Silica-Films ist, wurde bei 140 K beobachtet, was der guten Übereinstimmung der Gitterkonstanten von Silica-Film und hexagonalem Eis geschuldet ist. Amorphe Lagen festen Wassers, die die Oberfläche bei 100 K homogen bedecken, wurden als reaktive Lagen für Vanadiumoxid-Partikel benutzt, um die ‚Nasschemie’ nachzubilden, wie sie in der Präparation technischer Katalysatoren zum Einsatz kommt. Die Ergebnisse verdeutlichen, dass die Eis-Lagen die Bildung von hydratisierten Vanadiumoxid-Nanopartikeln, welche teilweise von V=O und V-OH-Gruppen terminiert werden, begünstigen. Die Dehydratisierung geschieht oberhalb 500 K, wobei eine V-terminierte Oberfläche entsteht. Methanol dissoziiert auf dehydratisierten Vanadiumoxid-Partikeln, und Methoxy-Spezies sind auf der Oberfläche stabil bis 500 K, allerdings nur in der Gegenwart von V-Plätzen. Die Produktion von Formaldehyd, die bei etwa 550 K stattfindet, ist stark abhängig von der Struktur der Oberfläche der Vanadiumoxid-Partikel und weist ein Maximum bei einem spezifischen Verhältnis zwischen V- und V=O-Oberflächenplätzen auf. Die hier vorgestellten Ergebnisse könnten unser Verständnis von katalytischen Reaktionen auf molekularer Ebene bedeutend vorantreiben.<br>The widespread use of model systems for understanding the heterogeneous catalytic processes is based on bridging the structural complexity gap between present generation of supported metal and metal oxide technical catalysts and crystalline metal and planar metal/oxide systems, which are utilized to investigate structure-reactivity relationships by a large variety of surface science techniques. In this thesis, we focused on a concept of so-called ''monolayer'' vanadium oxide catalysts, which have been introduced particularly for methanol oxidation reactions. Following a bottom-up approach, silica supported vanadium oxide model catalysts were investigated. Combining a number of experimental techniques, the surface of Mo(112) used as a substrate for the silica films was characterized in detail and the atomic structure of the silica film was determined. Adsorption of water and growth of vanadium oxide nanoparticles on the silica films, and finally the reactivity of vanadium oxide/silica systems towards methanol were studied. In contrast to the previously suggested models, an oxygen induced p(2×3) superstructure formed on a Mo(112) surface should be considered as one dimensional surface oxide where Mo=O groups are formed preferentially along the [-1-11] direction of the Mo(112) surface. Monolayer silica films grown on Mo(112) surfaces are composed of two-dimensional network of SiO4 tetrahedra. Depending on the film preparation conditions, the structure can be altered by additional oxygen atoms adsorbed on the Mo substrate. The defect structure includes antiphase domain boundaries which form by a half-lattice shift along the [-110] direction and a low density of point defects, most probably silicon vacancies. Water does not dissociate on the monolayer silica film. An ordered structure of water with respect to silica film was observed at 140 K owing to good lattice matching between the silica film and hexagonal ice. Amorphous solid water layers homogenously covering the surface at 100 K were used as reactive layers for vanadium oxide particles in order to mimic ''wet chemistry'' used in preparation of technical catalysts. The results revealed that ice layer assisted the formation of hydrated vanadium oxide nanoparticles partially terminated by V=O and V-OH groups. The dehydration takes place above 500 K, thus exposing V-terminated surface. Methanol dissociates on dehydrated vanadium oxide particles and methoxy species are stable on the surface up to 500 K only in the presence of vanadium terminated surface sites. Formaldehyde production which takes place at ~550 K is strongly affected by the surface structure of the vanadium oxide particles and exhibits a maximum at specific ratio between V- and V=O sites on the surface. The results presented may have a strong impact on our understanding of the catalytic reactions at the molecular level.

This work presents membrane development applicable in nanofluidic devices. These membranes can also be termed suspended thin films, supported on two or more edges. I first discuss motivation and background for developing these structures. Then I derive the formative principles for nanofluidic systems. Following the derivation of the Navier-Stokes and Washburn equations, I discuss applying these theories to planar nanofluidic capillaries and finish the derivation by discussing the forces that drive liquid flow in nanochannels. I next discuss the membrane development process, starting with my work in static height traps, and develop the concept of analyzing nanoparticles using suspended membranes. After reviewing the lessons learned from the double-nanopore project I discuss developing an oxide layer tuned to the needs of a membrane and present the design of an adjustable membrane structure. Afterward, I discuss modeling and simulating the structure, and present a procedure for fabricating robust membranes. I then explain applying the membrane structure to form a nanofluidic pump and document the process for recording and analyzing the pumping characteristics for nanodevices. As part of the pump section I propose a theory and model for predicting the behavior of the pumps. I next present applying active membranes as nanoparticle traps. I document a quick-turn optical profilometry method for charicterizing the devices, then present experimental data involving trapping. Early results show that the device functions as a nanoparticle concentrator and may work well as a size-based trap for nanoparticles. I conclude by summarizing the main contributions made during my course of study and by providing supplemental material to guide future research.

Orientador: Carlos Kenichi Suzuki<br>Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica<br>Made available in DSpace on 2018-08-17T18:43:06Z (GMT). No. of bitstreams: 1 Manfrim_TarcioPelissoni_M.pdf: 2213852 bytes, checksum: 20f8b76513e6d5acf1ec8af66bed9951 (MD5) Previous issue date: 2011<br>Resumo: Este trabalho visou estabelecer um novo método para síntese de vidros fotônicos através da sinergia das técnicas "Vapor-phase Axial Deposition" (VAD) e "Atomic Layer Deposition" (ALD), tendo como intuito obter um material completamente transparente, contendo uma distribuição uniforme do elemento dopante tanto na posição radial como axial. Na primeira etapa deste trabalho foi projetado, construído e testado um reator ALD de nível laboratorial adaptado à dopagem de preformas porosas VAD. A etapa subseqüente contou com a fabricação de preformas porosas de sílica pura através da técnica VAD, dopagem com titânia via técnica ALD e consolidação em forno elétrico para obtenção do material vítreo final. Foi estudado o efeito da variação dos parâmetros dos processos VAD e ALD sobre as propriedades estruturais e ópticas do material. As propriedades estruturais foram caracterizadas através das técnicas de espectrometria de fluorescência de raios-X, difração de raios-X e espectroscopia Raman. As propriedades ópticas foram determinadas pela técnica de espectrofotometria de absorção óptica. Maiores uniformidades do dopante (TiO2) foram alcançadas através das dopagens realizadas sob altas temperatura, uma vez que era possível evitar o efeito de condensação dos precursores. Além disso, preformas porosas de maior densidade média apresentaram uma maior tendência a formação de um perfil mais constante de dopagem. Para as amostras dopadas a 90°C, a taxa de dopagem estimada foi de aproximadamente 0,75 % em massa de TiO2/ciclo para os 4 primeiros ciclos. As amostras de SiO2-TiO2 apresentaram uma transmitância óptica máxima na região do infravermelho e visível muito semelhante a da sílica pura, sofrendo um absorção abrupta próximo a faixa do ultravioleta devido a formação de átomos de titânio com valência 4+<br>Abstract: This study aimed to establish a new method for synthesis of photonic glasses through the synergy of Vapor-phase Axial Deposition (VAD) and Atomic Layer Deposition (ALD) techniques. Having the intention to obtain a completely transparent material containing a uniform distribution of dopant element both radial and axial position. In the first stage of this study it was designed, built and tested an ALD reactor of laboratory scale appropriate for doping of VAD porous preforms. The subsequent stage included the manufacture of pure silica porous preform by VAD technique, doping with titania by ALD technique and consolidation in an electric furnace to obtain the final material in glassy state. The effect of variation of parameters of VAD and ALD processes on structural and optical properties of the material was studied. The structural properties were characterized by X-ray fluorescence spectrometry, X-ray diffraction and Raman spectroscopy. The optical properties were determined using optical absorption spectroscopy. Greater uniformity of the dopant (TiO2) have been achieved through doping carried out under high temperature, since it was possible to avoid the effect of condensation of the precursors. Furthermore, porous preforms with higher average density showed a greater tendency to form a more constant doping profile. For samples doped at 90 °C, the doping rate was approximately 0.75 wt% of TiO2/cycle for the first 4 ALD cycles. Samples of SiO2-TiO2 showed a maximum optical transmittance in the infrared and visible very similar to that of pure silica, suffering an abrupt absorption near the UV range due to formation of titanium atoms with valence 4+<br>Mestrado<br>Materiais e Processos de Fabricação<br>Mestre em Engenharia Mecânica

Nanoparticles have been used in industry and in medicine due to their properties which give them beneficial uses. This usage of the nanoparticles has risen the question about how harmful they are to the human body, the connection between the exposure to nanoparticles, and many diseases that occur in the body. Methods This study focused on the effect of nanoparticles in a whole human blood loop model. The blood was incubated with Silica, Titanium dioxide and Palladium particles in heparinized loops without any anticoagulants added. The blood’s cell count was analyzed with a cell counter and then complement, and contact system’s markers were analyzed with ELISA to detect a presence of activations in the systems. Experiments one to five were an optimization of test settings. Results An activation of the contact system was initiated in the loops containing the aggregated titanium dioxide nanoparticles. A high platelets consumption up to 73.8 % was observed as well as two visible clots. On top of that, blood smears showed micro-clots in the blood incubated with the aggregated nanoparticles. Conclusion Nanoparticles initiated an activation in the contact system in the aggregated form in comparison with the dispersed form. Further and deeper studies should be executed to observe the importance of the single or the aggregated form in the actual effect on the immune system.