[pt] A hidroxiapatita está entre os biomateriais cerâmicos de maior interesse na área médica, pois, além da sua semelhança com a fase inorgânica dos ossos e dentes, apresenta exelente biocompatibilidade e bioatividade. Devido a sua ampla aplicação e aos gastos inerentes a utilização de implantes em processos cirúrgicos, torna-se necessário o desenvolvimento de processos mais viáveis encomonicamente e de materiais com melhores propriedades, com isso, este trabalho teve como objetivo a síntese de hidroxiapatita (HAp) pelo método de precipitação utilizando cascas de ovos de galinha como fonte de cálcio na presença de diferentes concentrações de sacarose, para avaliar sua influência nas características dos materiais sintetizados. A utilização da casca de ovo surge como um insumo atrativo, uma vez que é composta majoritariamente por carbonato de cálcio, um material abundante e barato. A casca de ovo foi calcinada à 1000 graus Celsius para obtenção do CaO que foi hidrolisado para a obtenção do Ca(OH)2.Os materiais foram obtidos pela reação de precipitação entre o Ca(OH)2 e H3PO4 a temperatura ambiente e com controle de pH, utilizando diferentes quantidades de sacarose. Os materiais obtidos foram caracterizados pelos métodos de Difração de Raios X (DRX), Microscopia Eletrônica de Varredura com emissão de campo (MEV-FEG), adsorção de N2 a 77K (BET), Microscopia Eletrônica de Transmissão (MET), espectroscopia de infravermelho com transformada de Fourier (FTIR), análise termogravimétrica (TG) e Fluorescência de Raios X (FRX). Os resultados de DRX confirmaram a formação da HAp. O FTIR apresentou as bandas correspondentes a HAp, corroborando os resultados de DRX, identificando também bandas de carbonato. Os resultados de EDXS confirmaram a composição química das amostras, sendo esta de P, O e Ca. A caracterização por MEV permitiu a avaliação da mudança da morfologia com o para as diferentes da quantidade de sacarose utilizada, sendo observada uma tendência a formação de partículas esferoidais. Os resultados de BET evidenciaram um aumento de superfície específica com o aumento da quantidade de sacarose, passando de 36 para 93 m2/g, decorrente do aumento de porosidade e diminuição do tamanho de partícula, resultado confirmado pelo MET, com tamanho de partícula passando 50 nm para valores em torno de 10-20 nm. Para avaliação da citotoxicidade foi realizado o ensaio da redução da resazurina para o período de 24h. Os resultados obtidos indicaram que as amostras são não citotóxicas. O ensaio de bioatividade foi realizado em meio McCoy para o período de 3 e 7 dias, apresentando resultados de dissolução das amostras compatíveis com caracteríticas de superfícies bioativas, porém, para o período de da análise, não foi observada a formação da camada bone like apatite. Os materiais sintetizados apresentaram propriedades semelhantes aos obtidos a partir de fontes de cálcio comerciais, apresentando promissor potencial em aplicações da engenharia de tecido ósseo, além de contribuir para a reciclagem desses bio-resíduos que é a casca de ovo. Os resultados obtidos indicam que a sacarose pode alterar as características do material, sendo um promissor aditivo/template de fácil obtenção e baixo custo, proporcionando materiais com elevada superfície específica e redução do tamanho de partícula. / [en] Hydroxyapatite is among the ceramic biomaterials of greatest interest in the medical field, because, in addition to its similarity with the inorganic phase of bones and teeth, it presents excellent biocompatibility and bioactivity. Due to its wide application and the expensive surgical processes, it is necessary to develop more viable processes and materials with better properties, therefore, the work aimed the hydroxyapatite synthesis (HAp) by precipitation method using hen’s eggshells as a calcium source in the presence of different sucrose concentrations, to evaluate its effect on the characteristics of the synthesized materials. A comparative study was also carried out with HAp samples obtained without sucrose and with commercial Ca(OH)2. The use of eggshells appears as an attractive raw material since it is mainly composed of calcium carbonate and because it is an abundant and cheap material. The eggshell was calcined at 1000 Celsius to obtain CaO, which was hydrolyzed to obtain Ca(OH)2. The materials were obtained by the precipitation reaction between Ca(OH)2 and H3PO4 at room temperature with pH control, using different amounts of sucrose. The obtained materials were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy with field emission (SEM-FEG), N2 to 77K adsorption (BET), Transmission Electron Microscopy (TEM), infrared spectroscopy with Fourier transform (FTIR), thermogravimetric analysis (TG) and X-Ray Fluorescence (XRF). The XRD results confirmed the formation of HAp. The FTIR showed the bands corresponding to HAp, corroborating the results of DRX, in addition to the presence of carbonate bands. The results of EDXS confirmed the composition of the samples, being of P, O and Ca. The SEM characterization allowed the evaluation of the morphology changes for the different amounts of the sucrose used, forming spheroidal particles. The BET results showed an increase in specific surface area with the rise in the sucrose amount, from 36 to 93 m2/g, due to the rise in porosity and decrease in particle size, a result confirmed by TEM, with particle size changing from 50 nm to values around 10-20 nm. The resazurin reduction assay was performed for the 24h period to evaluate of cytotoxicity. The results obtained indicate that the samples were non-cytotoxic. The bioactivity assay was carried out in McCoy medium for 3 and 7 days, showing dissolution results of the samples compatible with characteristics of bioactive surfaces. The formation of the bone-like apatite layer was not observed for the analysis period. The synthesized materials showed properties similar to those obtained from synthetic calcium sources. Therefore, it presents promising potential in bone tissue engineering applications, besides contributing to the recycling of this bio-residue, the eggshell. The high specific surface area and small particle size results obtained indicate that sucrose can be a promising additive/template that is easy to obtain at low cost.

Metal oxide semiconductor (MOS) gas sensors have proven to be useful in many applications, ranging from detection of hazardous gases to monitoring of air quality. The demand for power efficient and high performance gas sensors has seen an increase in situations facing contemporary society. Currently it is common for sensors to employ an energy inefficient heater to provide for the optimal working temperature of the sensor. Light activation has been proposed as an alternative that could possibly improve modern gas sensors by decreasing energy utilization as well as increasing sensitivity and selectivity. The purpose of the following project is to explore the mechanisms and characteristics of light activated gas sensing using cuprous oxide (Cu2O), such that the findings may contribute to the development of power efficient gas sensors able to distinguish between gases at low concentrations. Several Cu2O-sensors with thicknesses of 300, 500 and 700 nm were examined, many of which also were doped with materials such as silver, graphene and titanium. Multiple types of measurements were performed where the sensors were exposed to nitrogen and carbon dioxide gas under illumination from one of three distinct light sources. The results show that conditions such as low light intensities, doping the sensors and air as the operating environment (compared to nitrogen gas) are beneficial for the carbon dioxide response under light activation. However, these findings are only indications and would need confirmation by additional measurements, both in terms of variation and repetition, under improved conditions.

Nanotechnology has reached the status of the 21st century's leading science and technology based on fundamental and applied research during the last two decades. An important feature of nanotechnology is to bridge the crucial dimensional gap between the atomic and molecular fundamental sciences and microstructural scale of engineering. Accordingly, it is very important to have an in-depth understanding of the synthesis of nanomaterials for the use of state-of-the-art high technological devices with enhanced properties. Recently, the 'bottom-up' approach for the fabrication of nanomaterials has received a great deal of attention for its simplicity and cost effectiveness. Tailoring the various parameters during synthesis of selected nanoparticles can be used to fabricate technologically important components. During the last decade, carbon nanotubes (CNTs) have been envisioned for a host of different new applications. Although carbon nanotubes can be synthesized using a variety of techniques, large-scale synthesis is still a great challenge to the researchers. Three methods are commonly used for commercial and bulk productions of carbon nanotubes: arc-discharge, chemical vapor deposition and laser ablation. However, low-cost, large-scale production of high-quality carbon nanotubes is yet to be reported. One of the objectives of the present research is to develop a simplified synthesis method for the production of large-scale, low-cost carbon nanotubes with functionality. Herein, a unique, simple, inexpensive and one-step synthesis route of CNTs and CNTs decorated with nanoparticles is reported. The method is simple arc-discharge in solution (ADS). For this new method, a full-fledged optoelectronically controlled instrumen is reported here to achieve high efficiency and continuous bulk production of CNTs. In this system, a constant gap between the two electrodes is maintained using a photosensor which allows a continuous synthesis of the carbon nanostructures. The system operates in a feedback loop consisting of an electrode-gap detector and an analogue electronic unit, as controller. This computerized feed system was also used in single process step to produce in situ-decorated CNTs with a variety of industrially important nanoparticles. To name a few, we have successfully synthesized CNTs decorated with 3-4 nm ceria, silica and palladium nanoparticles for many industrially relevant applications. This process can be extended to synthesize decorated CNTs with other oxide and metallic nanoparticles. Sixty experimental runs were carried out for parametric analysis varying process parameters including voltage, current and precursors. The amount of yield with time, rate of erosion of the anode, and rate of deposition of carbonaceous materials on the cathode electrode were investigated. Normalized kinetic parameters were evaluated for different amperes from the sets of runs. The production rate of pristine CNT at 75 A is as high as 5.89 ± 0.28 g.min-1. In this study, major emphasis was given on the characterizations of CNTs with and without nanoparticles using various techniques for surface and bulk analysis of the nanostructures. The nanostructures were characterized using transmission electron microscopy, high resolution transmission electron microscopy, scanning transmission electron microscopy, energy dispersive spectroscopy and scanning electron microscopy, x-ray photo electron spectroscopy, x-ray diffraction studies, and surface area analysis. Electron microscopy investigations show that the CNTs, collected from the water and solutions, are highly pure except the presence of some amorphous carbon. Thermogravimetric analysis and chemical oxidation data of CNTs show the good agreement with electron microscopy analysis. The surface area analysis depicts very high surface area. For pristine multi-walled carbon nanotubes, the BET surface area is approximately 80 m2.g-1. X-ray diffraction studies on carbon nanotubes shows that the products are clean. Nano-sized palladium decorated carbon nanotubes are supposed to be very efficient for hydrogen storage. The synthesis for in-situ decoration of palladium nanoparticles on carbon nanotubes using the arc discharge in solution process has been extensively carried out for possible hydrogen storage applications and electronic device fabrication. Palladium nanoparticles were found to form during the reduction of palladium tetra-chloro-square planar complex. The formation of such a complex was investigated using ultraviolet-visible spectroscopic method. Pd-nanoparticles were simultaneously decorated on carbon nanotubes during the rolling of graphene sheets in the arc-discharge process. Zero-loss energy filtered transmission electron microscopy and scanning transmission electron microscopy confirm the presence of 3 nm palladium nanoparticles. The deconvoluted X-ray photoelectron spectroscopy envelope shows the presence of palladium. Surface area measurements using BET method show a surface area of 28 m2.g-1. The discrepancy with pristine CNTs can be explained considering the density of palladium (12023 kg.m-3). Energy dispersive spectroscopy suggests no functionalization of chlorine to the sidewall of carbon nanotubes. The presence of dislodged graphene sheets with wavy morphology as observed with high-resolution transmission electron microscopy supports the formation of CNTs through the 'scroll mechanism'.

This study evaluates soil properties that impact the effectiveness of soil aquifer treatment (SAT) as a polishing step to the remove two classes of ECs from wastewater effluent: pharmaceuticals and personal care products (PPCPs), and engineering nanomaterials (ENMs). In recent years, it has been determined that elevated levels of emerging contaminants (ECs) are being released into the environment with wastewater effluent. ECs are proven to cause adverse environmental and health effects as a result of long-term exposure. It is important to evaluate sustainable solutions to improve the current methods of wastewater treatment to address these ECs. Soil aquifer treatment (SAT) is a sustainable, cost effect treatment alternative to advanced treatment at a wastewater treatment plant. SAT replenishes local groundwater supplies while allowing for indirect potable reuse, if contaminants of concern such as ECs can be effectively removed from the water. Since wastewater effluent can contain a variety of contaminants with myriad physical and chemical properties, understanding the potential of the aquifer itself to provide EC removal is a key step in establishing SAT as a viable treatment alternative. Peer-reviewed research studies were analyzed to determine the soil properties that affect the fate and transport of ECs in the aquifer environment. The data was complied to produce recommendations for an effective SAT site. Physical and chemical properties of the soil facilitate contaminant removal as the groundwater flows through the aquifer. This study determined that removal of ECs from effluent had a correlation with (1) high clay content, (2) small Darcy Velocity, (3) high soil organic matter content, and (4) low sand content. Based on the 6 peer-reviewed research studies reviewed, the removal of nanomaterials is affected by clay content and sand content, but not soil organic matter content. Conversely, the removal of PPCPs is affected by clay content and soil organic mater content, but not sand content. It can be concluded that two different removal mechanisms facilitate the removal of nanomaterials versus PPCPs; physical removal for nanomaterials and chemical removal (sorption) for PPCPs. Clay facilitates the removal of both contaminants. The small soil diameter of clay forms smaller pores in the soil media. This causes increased pore straining, while also restricting the flow through the soil, which increases the contact time between the soil particle and the ECs. Additionally, clay has a large surface area, which increases surface interactions, such as sorption, of the EC to the surface of the clay particle.

京都大学 / 新制・課程博士 / 博士(エネルギー科学) / 甲第24302号 / エネ博第453号 / 新制||エネ||85(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 佐川 尚, 教授 萩原 理加, 教授 野平 俊之 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DGAM

Supercapacitors have emerged as a promising energy storage technology with unique characteristics that set them apart from conventional batteries and capacitors. Supercapacitors bridge the gap between these two technologies by combining the high power density of capacitors with the high energy storage capacity of batteries, offering a compelling solution for various applications. In the pursuit of enhancing supercapacitor performance, magnetite (Fe3O4) has been researched as a potential anode material. Fe3O4 offers several desirable properties, including high theoretical capacitance, low cost, and environmental friendliness. Compositing Fe3O4 with conductive additives has served to address the issue of limited conductivity in Fe3O4 anodes for practical uses, however, a focus must be shifted to enhancing the capacitive performance of such anodes to unlock their full potential. Achieving the full potential of Fe3O4 for supercapacitor applications requires addressing challenges in the colloidal fabrication of high-active mass electrodes. This is done by exploring the exceptional adsorption properties of two dispersing and capping agents: 3,4-dihydroxybenzoic acid and murexide. Exceptional adsorption properties of catecholate-type 3,4-dihydroxybenzoic acid molecules were explored for surface modification of Fe3O4 nanoparticles to enhance their colloidal dispersion as verified by sedimentation test results and Fourier-transform infrared spectroscopy measurements. Electrodes prepared in the presence of 3,4-dihydroxybenzoic acid exhibited nearly double the capacitance at slow charging rates as compared to the control samples without the dispersant or with benzoic acid as a non-catecholate dispersant. Density functional theory analysis of adsorption behavior of 3,4-dihydroxybenzoic acid and benzoic acid at the (001) surface of Fe3O4 corroborated these experimental results by providing an understanding of the basic mechanism of 3,4-dihydroxybenzoic acid adsorption on the surface of nanoparticles. Furthermore, murexide for surface modification of Fe3O4 nanoparticles effectively enhanced the performance of multi-walled carbon nanotube-Fe3O4 supercapacitor anodes. Our experimental results demonstrate significant improvements in electrode performance when murexide is used as a capping or dispersing agent compared to the case with no additives. From impedance measurements, we revealed a substantial decrease in the real part of impedance for samples prepared with murexide, indicating easier charge transfer at more negative electrode potentials, and reinforcing the role of murexide as a capping agent and charge transfer mediator. The theoretical investigation allowed us to identify the nature of chemical bonds between murexide and the surface, with significant charge transfer taking place between the Fe3O4 surface and murexide adsorbate. / Thesis / Master of Applied Science (MASc)

<p>  </p> <p>From applications in nanoscale electronics to regenerative medicine, there is a strong need for control assembly processes at nanometer length scales.1,2 In this work, we investigate the application of microscale droplet delivery as a rapid and scalable approach to pattern the molecular assembly of nanoscale chemical patterns on highly oriented pyrolytic graphite (HOPG). Furthermore, it was also observed that variations in the blend of alkyl impurities present in technical-grade OLAm reagents influenced the temperature-dependent assembly behavior.13 This suggests a likely role of alkyl chain phase transitions in the ligand shell, particularly in more complex mixtures and for anisotropic nanocrystals.</p> <p>Oleylamine (OLAm) is a common technical-grade reagent used in nanocrystal synthesis. Most nanocrystal synthesis is done using technical grade Oleylamine (70% purity). Higher purity reagents are not readily available because in certain instances, technical grades are obtained from natural substances, resulting in differing impurities compared to those generated during preparative reactions using pure raw materials.3 Technical grade reagents of OLAm contain 70% of the cis chain OLAm and 30% of an unspecified mixture of Elaidylamine (ELAm) , Octadecylamine (ODAm) and segments of various lengths and saturated alkyl chains.4,5 Here, we use Differential Scanning Calorimetry thermograms to investigate the miscibility of binary mixtures of OLAm/ELAm, OLAm/ODAm, and ELAm/ODAm. Ternary mixtures of the lipids showed clear peaks for the trans and saturated impurities.</p> <p>We patterned graphite surfaces with amphiphiles via inkjet printing to quickly generate 1-nm-wide functional patterns. Inkjet printing allowed for long-scale hierarchical patterning. We investigated various ink formulations and the resulting printing quality of functional monolayers on 2D crystalline materials. </p>

<p>Obtaining full-field \emph{dynamic} material state awareness would have profound and wide-ranging implications across many fields and disciplines. For example, achieving dynamic state awareness in soft tissues could lead to the early detection of pathophysiological conditions. Applications in geology and seismology could enhance the accuracy of locating mineral and hydrocarbon resources for extraction or unstable subsurface formations. Ensuring safe interaction at the human-machine interfaces in soft robotic applications is another example. And as a final representative example, knowing real-time material dynamics in safety-critical structures and infrastructure can mitigate catastrophic failures. Because many materials (e.g., carbon fiber-reinforced polymers composites, ceramic matrix composites, biological tissues, cementitious and geological materials, and nanocomposites) exhibit coupling between their mechanical state and electrical transport characteristics, self-sensing via the piezoresistive effect is a potential gateway to these capabilities. While piezoresistivity has been mostly explored in static and quasi-static conditions, using piezoresistivity to achieve dynamic material state awareness is comparatively unstudied. Herein lies the significant gap in the state of the art: the piezoresistive effect has yet to be studied for in-situ dynamic sensing.</p> <p><br></p> <p>In this thesis, the gap in the state of the art is addressed by studying the piezoresistive effect of carbon nanocomposites subject to high-rate and transient elastic loading. Nanocomposites were chosen merely as a representative self-sensing material in this study because of their ease of manufacturability and our good understanding of their electro-mechanical coupling. Slender rods were manufactured using epoxy, modified with a small weight fraction of nanofillers such as carbon black (CB), carbon nanofibers (CNFs), and multi-walled carbon nanotubes (MWCNTs), and subject to loading states such as steady-state vibration at structural frequencies ($10^2-10^4$ Hz), controlled wave packet excitation, and high-strain rate impact loading in a split-Hopkinson pressure bar. This work discovers foundational principles for dynamic material state awareness through piezoresistivity. </p> <p><br></p> <p>Three major scholarly contributions are made in this dissertation. First, an investigation was pursued to establish dynamic, high-strain rate sensing. This investigation clearly demonstrated the ability of piezoresistivity to accurately track rapid and spatially-varying deformation for strain rates up to $10^2$ s$^{-1}$. Second, piezoresistivity was used to detect steady-state vibrations common at structural frequencies. Utilizing simple signal processing techniques, it was possible to extract the excitation frequency embedded into the collected electrical measurements. The third contribution examined the dynamic piezoresistive effect through an array of surface-mounted electrodes on CNF/epoxy rods subject to highly-controlled wave packet excitation. Electrode-spacing adjustments were found to induce artificial signal filtering by containing larger portions of the injected wave packets. The strain state in the rod was found after employing an inverse conductivity-to-mechanics model, thereby demonstrating the possibility of deducing actual in-situ strains via this technique. A digital twin in ABAQUS was constructed, and an elastodynamic simulation was conducted using identical dynamic loading, the results of which showed very good agreement with the piezo-inverted strains. </p> <p><br></p> <p>This work creates the first intellectual pathway to full-field dynamic embedded sensing. This work has far-reaching potential applications in many fields, as numerous materials exhibit self-sensing characteristics through deformation-dependent changes to electrical properties. Therefore, \emph{piezoresistive elastodynamics} has the incredible potential to be applied not just in structural applications but in other potentially innovated applications where measuring dynamic behavior through self-sensing materials is possible.  </p>

With the rapid development of concrete 3D printing for construction projects, it is crucial to produce sustainable 3D-printed cementitious composites that meet the required fresh and hardened properties. This study investigates the application of cellulose-based nanomaterials (CN) (i.e., abundant natural polymers) that can improve the mechanical properties of cement-based materials – in 3D-printed cementitious composites of ordinary portland cement (OPC) and alkali-activated materials (AAMs). A combination of low calcium fly ash and ground granulated blast-furnace slag was used as the precursor in AAM systems. This work examines the 3D-printed mixtures with varying binders and mixture proportions and with different dosages of cellulose-based nanomaterial known as cellulose nanocrystals (CNC) to optimize the formulation for the production of sustainable high-performance 3D-printed elements. A suite of experimental techniques was applied to study the impact of CNC on the fresh and hardened properties of the 3D-printed samples. The buildability of the alkali-activated mixtures was improved by increasing the CNC content, suggesting that the CNC performs as a viscosity-modifying agent in AAMs. The inclusion of CNCs up to 1.00% (by volume of the binder) improves the overall mechanical performance and reduces the porosity of 3D-printed OPC and heat-cured AAM samples. Further, the addition of CNC (up to 0.30%) in sealed-cured AAM samples improves their flexural strength due to the crack-bridging mechanism of CNCs. The addition of CNC densifies the microstructure of OPC samples by increasing the degree of hydration, however, no significant impact on the microstructure of AAMs is noticed. The OPC sample with CNC has approximately 25% increase in the degree of hydration at inner depths which can be attributed to the internal curing potential of CNC materials. The initial water absorption rate of heat-cured AAM samples is lower than the sealed-cured AAM samples and comparable to the OPC system. The developed printable “alkali-activated-CNC” composites can provide an overall reduction in the environmental impacts of the 3D-printed cementitious composites by eliminating/reducing the need for different chemical admixtures to improve 3D-printed material consistency and stability, and replacing 100% of portland cement with fly ash and slag. / Civil Engineering

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