No / Successful joining of dissimilar metals such as Al and Mg can provide significant advantages to the automotive industry in the fabrication of vehicle bodies and other important components. This study explores dissimilar joining of Al–Mg using a resistance spot welding process to produce microstructurally sound lap joints and evaluates the impact of interlayer composition on microstructural evolution and the formation of intermetallic compounds within the weld nugget. The results indicated that mechanically sound joints can be produced, with fine equiaxed and columnar dendrites within the weld nugget. The presence of intermetallic compounds was also confirmed by the variation in the microhardness values recorded across the weld zone.

The textile industry’s linear model of production and reliance upon nonrenewable resources to manufacture synthetic fibers, dyes, and finishing agents make it one of the most polluting industries globally, responsible for 1.2 billion tons of CO₂ emissions per year, 20% of wastewater, and 35% of marine microplastic pollution. Similarly, medical textiles fabricated as wound dressing or replacement grafts utilize petroleum-derived polymers processed with harsh solvents, not only limiting their biocompatibility and scalability, but also creating environmental concern at industrial volumes. To mitigate these negative environmental and health impacts, new biofabrication strategies are required to design functional biomaterials that not only meet performance criteria for medical or non-medical application, but also support a sustainable circular economy. Inspired by the complex bottom-up assembly and regenerative potential of nature, the objective of this thesis is to harness biofabrication and in particular, microbial biosynthesis of nanofibril cellulose for the development of non-medical and medical textiles. Specifically, this thesis aims to improve our understanding of the microbial cellulose fabrication process and establish a controlled microbial cellulose modular engineering platform. By controlling biosynthesis and applying sustainability considerations to polymer processing strategies, we can regulate bacterial response and control resultant material properties for the engineered nanocellulose, targeting performance goals relevant for the textile industry. For medical applications, a controlled purification strategy will be explored for the development of a functional and biocompatible matrix. To this end, both biofabrication and post-processing strategies were assessed for the synthesis of microbial cellulose biotextiles that meet low toxicity and environmental impact criteria. The biofabrication of microbial cellulose with Gluconacetobacter xylinus was first evaluated by determining the effects of carbon source and concentration on bacterial response and emergent biomaterial properties. While glucose, fructose, sucrose, mannitol, and xylitol all supported microbial growth, differences observed in cellulose production rate, and mechanical properties revealed unique opportunities to regulate material properties through biosynthesis. Post-synthesis processing offers another level of control in achieving desired material properties. Both green chemistry and bioinspired processes were developed using plant-derived lecithin, green plasticizers (sorbitol and glycerol), and tannin-iron complexation to control elastic and viscoelastic properties of the microbial cellulose. It was demonstrated that these methods altered chemical crosslinking and stabilized mechanical properties, in which lecithin and tannin-iron complex imbued biomaterials with flame retardant and anti-bacterial properties, respectively. Life cycle analyses were performed to ensure transparency in considerations of climate and health impact of carbon source for biofabrication, crosslinkers and plasticizers for scaled up functionality. After developing and optimizing the purification protocol, the biocompatibility of microbial cellulose scaffolds was evaluated through in vitro culture with human monocyte-like cells (THP-1) and also with human ligament fibroblasts. It was observed that microbial cellulose did not stimulate a pro-inflammatory response from naïve macrophages, and the matrix supported fibroblast viability and growth over two weeks of culture. In comparison to biocompatible synthetic PLGA:PCL unaligned microfiber scaffolds, microbial cellulose stimulated comparable macrophage cytokine secretion, albeit the matrix maintained lower cell attachment. Collectively, this thesis has elucidated critical synthesis and biofabrication criteria that dictate the performance properties of microbial cellulose for: 1) regenerative, multi-functional biotextiles; and 2) biocompatible scaffold supporting in-vitro eukaryotic cell viability and basal-inflammatory response. These approaches are innovative as this work represents the first attempt to systematically understand how to leverage biofabrication to engineer multifunctional microbial cellulose with tailorable nano-, micro-, and macro- scale properties. Beyond biotextile development, this material platform and optimized green processing strategies demonstrate the potential of engineering regenerative materials for a circular material economy across various industries.

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In Chapter 1, I give a basic introduction to the scientific background necessary for understanding the rest of the dissertation. I describe semiconductor nanocrystals and quantum confinement, how nanocrystals grow and a brief description of the various characterization methods. Finally, I provide some of the general considerations and chemical sources for the experiments performed in the thesis as a whole. In Chapter 2, I summarize the journey towards working with molecular precursors and show the advances and challenges in modeling and understanding conversion made a step into nanoplatelets more feasible. The chalcogenourea syntheses are not included and the modeling of the spherical nanocrystals is in a fairly summarized form here. This chapter is intended to give a brief overview of the highlights, key conclusions, and resulting questions upon which I designed my own experiments. In Chapter 3, I discuss applying precursor conversion method to nanoplatelets and focus on 3ML CdE growth. I briefly introduce nanoplatelets, explain the new conditions necessary to adapt the chalcogenourea library, demonstrate my efforts in characterizing the kinetics and growth mechanisms, and finally show the relationship of precursor reactivity and final nanoplatelet size. The “kobs catalogue” which summarizes the kinetics and sizing from STEM is an appendix at the end of the chapter. In this chapter, we put to the test the idea that we can control nanocrystal synthesis through precursor reactivity. The synthesis of nanocrystal heterostructures controlled by precursor conversion was discussed in Chapter 2. In Chapter 4, the same theory is applied to nanoplatelet synthetic conditions, but because nanoplatelet nucleation is fast compared to the total reaction time, the precursors should result in something closer to what is modeled without extraneous products. At the end of the chapter, a nanoplatelet alloy catalogue records many of the modeling and alloy experiments. Chapter 5 attempts to gather the various side projects that working with nanoplatelets has brought about. All these projects come together when thinking about how the solute supply and surface ligands might determine nanoplatelet formation, which I hope to shed some insight on. In the end, I hope to have gathered enough information to provide thoughtful answers for why nanoplatelets form, how they are ideal for studying compositional growth, and how nanocrystal alloying changes the structural and optical properties of these materials.

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Esta tesis presenta un conjunto original de procedimientos para la síntesis de nanoestructuras de TiO2 y ZnO por biomimetización de membranas de cáscara de huevo obteniendo materiales valiosos para fotovoltaica como se muestra en su evaluación de rendimiento como ánodo en células solares sensibilizadas por colorante. "El manuscrito está dividido en 7 capítulos. En el primer capítulo, titulado Introducción, se presentan las bases teóricas para la comprensión de los procesos de biomimetización, membranas de cáscara de huevo, síntesis de ZnO y TiO2, y células solares sensibilizadas por colorantes (DSSC). Después del capítulo introductorio, el Capítulo 2 revela los objetivos generales y específicos de esta investigación. Posteriormente, el Capítulo 3 describe el procedimiento experimental utilizado para las síntesis y caracterizaciones de ZnO y TiO2, así como el procedimiento utilizado en el ensamblaje y la caracterización de las células fotovoltaicas. En el capítulo 4 se presentan y discuten los resultados obtenidos con las síntesis y la aplicación de los polvos como fotodoles en DSSC. En este capítulo, hemos decidido subdividirlo en secciones específicas para explicar cuestiones científicas específicas sobre el tema. En el capítulo 5 se presentan las conclusiones del estudio en vista de los diferentes aspectos: obtención de TiO2 biomimético y ZnO, diferencias entre los polvos sintetizados por biomimetización de las membranas de cáscara de huevo, y la caracterización de las células construidas con los polvos biomiméticos. / Esta tesi presenta un conjunt original de procediments per a la síntesi de nanoestructuras de TiO2 i ZnO per biomimetización de membranes de corfa d'ou obtenint materials valuosos per a fotovoltaica com es mostra en la seua avaluació de rendiment com a ànode en cèl·lules solars sensibilitzades per colorant. "El manuscrit està dividit en 7 capítols. En el primer capítol, titulat Introducció, es presenten les bases teòriques per a la comprensió dels processos de biomimetización, membranes de corfa d'ou, síntesi de ZnO i TiO2, i cèl·lules solars sensibilitzades per colorants (DSSC) . Després del capítol introductori, el Capítol 2 revela els objectius generals i específics d'esta investigació. Posteriorment, el Capítol 3 descriu el procediment experimental utilitzat per a les síntesis i caracteritzacions de ZnO i TiO2, així com el procediment utilitzat en l'acoblament i la caracterització de les cèl·lules fotovoltaiques. En el capítol 4 es presenten i discutixen els resultats obtinguts amb les síntesis i l'aplicació de les pols com fotodoles en DSSC. En este capítol, hem decidit subdividir-ho en seccions específiques per a explicar qüestions científiques específiques sobre el tema. En el capítol 5 es presenten les conclusions de l'estudi en vista dels diferents aspectes: obtenció de TiO2 biomimético i ZnO, diferències entre les pols sintetitzats per biomimetización de les membranes de corfa d'ou, i la caracterització de les cèl·lules construïdes amb les pols biomiméticos. / This thesis introduces an original set of procedures for the Synthesis of ZnO and TiO2 nanostructures by biomimetization of eggshell membranes obtaining valuable materiales for photovoltaic as shown on their performance evaluation as anode in Dye-Sensitized Solar Cells". The manuscript is divided into 7 chapters. In the first chapter, entitled Introduction, it is presented the theoretical bases for the understanding of the biomimetization processes, eggshell membranes, ZnO and TiO2 syntheses, and dye-sensitized solar cells (DSSC). After the introductory chapter, Chapter 2 reveals the general and specific objectives of this research. Subsequently, Chapter 3 describes the experimental procedure used for the syntheses and characterizations of ZnO and TiO2 as well as the procedure used in the assembly and characterization of the photovoltaic cells. In chapter 4 are presented and discussed the results obtained with the syntheses and application of the powders as photoanodes in DSSC. In this chapter, we have chosen to subdivide it into specific sections to explain specific scientific issues on the subject. In chapter 5 the conclusions of the study are presented in view of the different aspects: obtaining ZnO and biomimetic TiO2, differences between the powders synthesized by biomimetization of eggshell membranes, and the characterization of the cells constructed with the biomimetic powders. / Camaratta, R. (2018). Synthesis Of ZnO and TiO2 By Biomimetization Of Eggshell Membranes And Its Evaluation As Anode In Dye-Sensitized Solar Cells [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/113416

Affinity biosensors are crucial in clinical settings for their ability to provide rapid, accurate and sensitive detection of analytes, enabling early diagnosis and monitoring of diseases. These biosensors operate on the principle of high-affinity binding between recognition receptors and the target analyte to cause a physicochemical change which is converted by a transducer into a measured signals to obtain the analyte concentration. Current commercial affinity biosensors, utilizing optical, electrochemical and mass-based transduction methods, offer high sensitivity and specificity of analyte measurements for clinical applications, but face limitations such as high costs and bulkiness for optical biosensors, difficulty in detecting small molecules for mass-based biosensors, and complexity and label degradation issues for electrochemical biosensors. 2D nanomaterial-based aptameric nanosensors, which utilize 2D nanomaterials as transduction materials and aptamers as receptors to specifically recognize target analytes, hold the potential to address these limitations of traditional commercial biosensors. However, the nanosenors still face challenges for practical applications in clinical settings, such as nonspecific binding in physiological media, the necessity for individual sensor calibration, and limitations in current 2D nanomaterial properties and performance degradation over time. This thesis focuses on developing 2D-nanomaterial based aptameric FET nanosensors to enhance their adaptability toward practical clinical applications. We first present the optimization of surface modification of aptameric graphene nanosensors for measurement of biomarkers in undiluted physiological media. In these sensors, graphene surfaces are coated with a polyethylene glycol (PEG) nanolayer to minimize nonspecific adsorption of matrix molecules. We perform a systematic study of the aptamer and PEG attachment schemes and parameters, including the impact of the serial versus parallel PEG and aptamer attachment scheme, PEG molecular weight and surface density, and aptamer surface density on the sensor behavior, and then use the understanding from this parametric study to identify optimal surface modification of the nanosensor to enable sensitive and specific biomarker measurements in undiluted physiological media. We then present a calibration-free method that exploits kinetic measurements to enable the calibration-free operation of aptameric graphene nanosensors. In our kinetically based calibration-free method, a time constant estimated based on the aptamer-analyte kinetic binding process is used to determine the analyte concentration. The time constant depends on the to-be-measured analyte concentration and reaction rate constants 𝑘_on and 𝑘_off, respectively, which is unaffected by variations in measurement conditions and sensor properties, thereby allowing devices functionalized with the same aptamer to be used without individual calibration once one particular device is calibrated, and enabling accurate analyte concentration determination independent of variations in parameters. Next, we present an affinity nanosensor that uses Ni₃(HITP)₂ metal-organic framework (MOF) as the conducting channel which is functionalized with an aptamer for specific biomarker recognition. Binding between the aptamer and the target biomarker induces a change in the carrier density in the MOF and resulting in measurable changes in FET characteristics for determination of the biomarker concentration. 𝘐𝘯-𝘴𝘪𝘵𝘶 synthesis of the MOF enhances the adhesion between the MOF film and electrodes to reduce noise during sensor operations, while also allowing devices to be potentially mass-produceable at reduced cost. Thanks to the porous structure of the MOF, the aptamer surface density on the MOF is optimized to enhance sensitivity for biomarker measurements. We finally present the preliminary development of aptameric graphene nanosensors for accurate and stable extended-time measurement of analyte. We perform a systematic study of the stability of the nanosensor including the graphene, aptamers and aptamer attachment, to identify the cause of performance degradation, and use the understanding to develop a differential nanosensor functionalized the aptamer through covalent reaction and implement graphene compensation method to achieve the accurate and stable extended-time analyte measurement.

Electrochemical energy storage has been widely used in various areas, including new energy sources, auto industry, and information technology. However, the performance of current electrochemical energy storage devices does not meet the requirements of these areas that include both high energy and power density, fast recharge time, and long lifetime. One solution to meet consumer demands is to discover new materials that can substantially enhance the performance of electrochemical energy storage devices. In this dissertation we report four transition metal materials systems with potential applications in electrochemical energy storage. Nanoscale and nanostructured materials are expected to play important roles in energy storage devices because of their enhanced and sometimes unique physical and chemical properties. Studied here is the comparative electrochemical cation insertion into a nanostructured vanadium oxide, a promising electrode material candidate, for the alkali metal ions Li+, Na+ and K+ and the organic ammonium ion, in aqueous electrolyte solutions. Observed are the distinctive insertion processes of the different ions, which yield a correlation between physical degradation of the material and a reduction of the calculated specific charge. The results reveal the potential of this nanostructured vanadium oxide material for energy storage. Vanadium based electrochemical systems are of general interest, and as models for vanadium based solid-state electrochemical processes, the solution state and the solid-state electrochemical properties of two cryolite-type compounds, (NH4)3VxGa1-xF6, and Na3VF6, are studied. The electrochemical behavior of (NH4)3VxGa1-xF6 explored the possibility of using this material as an electrolyte for solid state energy storage systems. Zeolite-like materials have large surface to volume ratios, with ions and neutral species located in the nanometer sized pores of the 3-dimensional framework, potentially yielding high energy density storage capabilities. Yet the insulating nature of known zeolite-like materials has limited their use for electrical energy storage. Studied here are two vanadium based zeolite-like structures, the oxo-vanadium arsenate [(As6V15O51)-9]∞, and the oxo-vanadium phosphate [(P6V15O51)-9]∞, where the former shows electronic conduction in the 3-dimensional framework. Mixed electronic and ionic conductivity, from the framework and from the cations located within the framework, respectively, is measured in the oxo-vanadium arsenate, and allows the use of this material in electrochemical double-layer capacitor configuration for energy storage. By contrast, the oxo-vanadium phosphate shows ionic conduction only. Lastly, a new strontium manganese vanadate with a layered structure exhibiting mixed protonic and electronic conductivity is studied. The various transition metal compounds and materials systems experimentally studied in this thesis showcase the importance of novel materials in future energy storage schemes. / Ph. D.

Nanostructured ferritic alloy and silicon carbide composite materials (NFA-SiC) were sintered with spark plasma sintering (SPS) method and systematically investigated through X-ray diffraction (XRD), scanning electron microscopy (SEM), as well as density and Vickers hardness tests. Pure NFA, pure SiC, and their composites NFA-SiC with different compositions (2.5 vol% NFA-97.5 vol% SiC, 5 vol% NFA-95 vol% SiC, 97.5 vol% NFA-2.5 vol% SiC, and 95 vol% NFA-5 vol% SiC) were successfully sintered through SPS. In the high-NFA samples, pure NFA and NFA-SiC, minor gamma-Fe phase formation from the main alfa-Fe matrix occurred in pure NFA 950 degree C and 1000 degree C. The densities of the pure NFA and NFA-SiC composites increased with sintering temperature but decreased with SiC content. The Vickers hardness of the pure NFA and NFA-SiC composites was related to density and phase composition. In the high-SiC samples, NFA addition of 2.5 vol% can achieve full densification for the NFA-SiC samples at relative low temperatures. With the increase in sintering temperature, the Vickers hardness of the pure SiC and NFA-SiC composite samples were enhanced. However, the NFA-SiC composites had relative lower hardness than the pure SiC samples. A carbon layer was introduced in the NFA particles to prevent the reaction between NFA and SiC. Results indicated that the carbon layer was effective up to 1050 degree C sintering temperature. Green samples of gradient-structured NFA-SiC composites were successfully fabricated through slip casting of an NFA-SiC co-suspension. / Master of Science