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Reducing rare earth consumption in Nd₂Fe₁₄B magnets through controlled nanostructuresHopkinson, David Mark January 2015 (has links)
No description available.
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Cucurbit[n]uril-engineered nano-constructs for molecular sensingRen, Xiaohe January 2019 (has links)
Surface-enhanced Raman scattering (SERS) spectroscopy is a powerful analytical technique for ultrasensitive detection of chemicals and biomolecules. As the high sensitivity of SERS requires analytes to be in close contact with a plasmonic substrate, the detectionof analyte molecules with low chemical affinity towards the substrate is thus limited. Cucurbit[n]uril (CB[n]) exhibits strong and selective encapsulation of various guest molecules into its barrel-shaped cavity. In addition, it can function as a precise rigid spacer between metallic nanoparticles (NPs). The larger homologue CB[8] can simultaneously sequester two guest molecules to form ternary complexes, allowing for tailoring of the chemical environment of its cavity to trap specific analytes. CB[n] aggregated metallic NPs provide a powerful platform for the detection of a wide variety of molecules. However, the colloidal instability of this system requires the measurement to be finished within 60 min after the preparation of the substrate. In addition, in situ measurements may involve environments that affect such self-assembly processes. For example, the possible displacement of analytes in the nanogap by non-analyte moieties can give rise to fluctuating backgrounds. Therefore, a SERS substrate that can provide the same levels of detection and functionality but eliminates the need for aggregation is of great demand. This thesis mainly focuses on the preparation and characterisation of CB[n]-engineered nanostructures as SERS substrates with great colloidal stability, high SERS enhancements and sensitivities. Other applications of the prepared nanostructures such as peptide separation and high-performance catalysis are also discussed. In the first chapter, the historical development and the remaining challenges in the field of SERS are discussed. Three types of the most commonly used SERS substrates are introduced, followed by the introduction of rationally designed nanoplatforms for molecules with low chemical affinity towards metallic surfaces. In addition, CB[n] host guest complexation, examples of CB[n]-engineered nanostructures and the application of these nanostructures in SERS sensing are also discussed. The second chapter demonstrates the preparation of surface-bound CB[8] catenanes on silica NPs, where CB[8] is employed as a tethered supramolecular "receptor" to selectively capture target guest molecules. More specifically, CB[8] is threaded onto a methyl viologen (MV2+) axle and immobilised onto silica NPs with a surface density up to 0.56 nm$^{−2}$. Its use as an efficient and recyclable nanoplatform for peptide separation is demonstrated. The peptides captured by the catenanes can be released by reversible single-electron reduction of MV$^{2+}$. The entire process demonstrates high recoverability. Continued in the third chapter, a highly stable free-standing molecular sensor that exploits a catenane-engineered nanostructure is described. CB[8] is tethered onto spiky γ-Fe2O3@Au NPs in a similar approach, to collect target analytes from aqueous media. These target analytes can be detected with high sensitivities, on account of the high SERS enhancement (on the order of 10$^{8}$) of the spiky NPs. This CB[8] catenane-based molecular sensor provides a powerful SERS substrate that shows great promise in the detection of versatile chemicals, biomolecules, controlled substances and auxiliary diagnostics of various diseases. The fourth chapter introduces a facile preparation of monodispersed γ-Fe2O3@Au magnetic nanoraspberry NPs using a one-pot seeded growth method. The obtained nanoraspberry NPs show excellent colloidal stability and high SERS enhancement factors (on the order of 10$^{10}$). By immobilising a dense layer of CB[n]s onto the surface of nanoraspberry NPs, a new type of CB/Au NP SERS substrate is obtained. CB[n]s are located perpendicularly to the NP surface and their cavity maintain the capability to sequester guest molecules from aqueous media. More versatile molecules (both electron rich and electron deficient molecules) can thus be detected with high sensitivities. We envisage that this nanoraspberry-based molecular sensor will provide a powerful platform for SERS detection in various fields, such as chemical and biomolecule analysis, illegal drug detectionand pre-clinical/clinical diagnosis. The fifth chapter focuses on the preparation of CB[7]-based catalytic microreactors, where metallic NPs are immobilised onto microchannels via supramolecular interaction of methyl viologen@CB[7]. This microreactor exhibits remarkable catalytic activity on account of the high surface area to volume ratio of the microchannels and metallic NPs. Superior to most conventional heterogeneous catalytic reactions, separation post reaction and complicated recycling steps of the catalysts are not required. Moreover, CB[7] can complex a variety of metallic NPs onto its portal (e.g. gold, silver, palladium, quantum dot), providing a multifunctional in situ catalysis platform. In the end, a concluding chapter summarises the presented work, also giving a brief outlook of the potential future work.
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Electro-mechanically interfacing with biology using piezoelectric polymer nanostructuresSmith, Michael January 2019 (has links)
Biological cells are naturally exposed to a wealth of stimuli that influence their function and behaviour. In fields where the focus is on artificially growing biological material, such as tissue engineering and regenerative medicine, it is important to consider this array of senses to ensure correct cell signalling and tissue development. For decades, however, research has targeted only the chemical aspects of these stimuli. Mechanical and electrical signals are also fundamental in the development of our biology. Piezoelectric materials offer a promising solution to the electrical stimulation issue, and have drawn much attention recently as `active' cell culture scaffolds. However, little thought has been given to the mechanical properties of these materials and how they align with the requirements of cellular systems. Furthermore, the composition of many piezoelectric materials raises questions about biocompatibility. In this thesis, nanostructures of the piezoelectric bio-polymer poly-\textsc{l}-lactic acid (PLLA) have been fabricated, characterised and implemented in cell culture devices to investigate their potential for electromechanical stimulation of living tissue. Novel variations on the template-wetting method have been developed to create the nanostructures. PLLA nanowires were fabricated for the first time using temperature-controlled solution template-wetting. The nanowires were characterised using Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD) and Piezo-response Force Microscopy (PFM) combined with Finite Element Analysis (FEA). The results indicated that the nanowires were highly crystalline (up to 45 %) with a degree of molecular alignment, and that the nanowires displayed shear piezoelectricity with an estimated piezoelectric coefficient d₁₄ = 8 pC/N. This was the first observation and quantification of shear piezoelectricity in PLLA at the nanoscale. FEA was used to show that hollow nanotube structures would more closely align with the requirements for an active cell culture platform - namely, a greatly enhanced direct piezoelectric response compared to an equivalent wire. Therefore, melt template wetting was subsequently used to create PLLA nanotubes. Crystallisation induced by heat treatment was investigated using XRD, DSC and polarised light optical microscopy (POM). The results indicated that crystallisation in the confined nanotube environment leads to molecular alignment with the polymer chain parallel to the nanotube axis. No significant changes in crystal structure were observed between bulk PLLA and PLLA nanotubes. Various Scanning Probe Microscopy (SPM) modes were used to characterise the PLLA nanotubes at the nanoscale. PeakForce Quantitative Nanomechanical Mapping (PF-QNM) revealed the mechanical properties and lamellar structure of the polycrystalline polymer, although rigorous quantitative analysis proved challenging, as verified by FEA simulations. Kelvin Probe Force Microscopy (KPFM) highlighted the difference in surface potential between amorphous and crystalline nanotubes. PFM data also demonstrated the piezoelectric activity of both crystalline and amorphous nanotubes. The interaction between PLLA nanotubes and Human Dermal Fibroblast (HDF) cells was also investigated. Cell attachment was found to be significantly higher for nanotubes in comparison to bulk films, and a further increase in attachment was observed between amorphous and crystalline nanotubes. Electrodes embedded into the nanotube devices allowed for electrical stimulation to be applied during cell growth. Preliminary observations suggest that this stimulation improves cell attachment and/or proliferation, and the use of Aerosol Jet Printing (AJP) to pattern the electrodes can lead to directed cell growth.
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FDTD simulation on noble metal nanostructure. / Finite difference time domain simulation on noble metal nanostructure / 以時域有限差分法模擬貴金屬的納米結構 / FDTD simulation on noble metal nanostructure. / Yi shi yu you xian cha fen fa mo ni gui jin shu de na mi jie gouJanuary 2010 (has links)
Woo, Kat Choi = 以時域有限差分法模擬貴金屬的納米結構 / 胡吉才. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 84-86). / Abstracts in English and Chinese. / Woo, Kat Choi = Yi shi yu you xian cha fen fa mo ni gui jin shu de na mi jie gou / Hu Jicai. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- The Importance of Nanoscale Plasmonic Physics --- p.1 / Chapter 1.2 --- The Driving Forces behind Plasmon Physics --- p.2 / Chapter 1.3 --- Computation Method --- p.3 / Chapter 1.4 --- Conclusion and Interesting Topics --- p.5 / Chapter 2 --- The FDTD Mechanism --- p.6 / Chapter 2.1 --- Algorithm Method --- p.6 / Chapter 2.2 --- The Dielectric Function --- p.9 / Chapter 2.2.1 --- Drude Model Definition --- p.9 / Chapter 2.2.2 --- Drude Model Discretization --- p.10 / Chapter 2.2.3 --- Discussion on Models --- p.11 / Chapter 2.3 --- Accuracy and Stability --- p.12 / Chapter 2.3.1 --- Numerical Dispersion --- p.12 / Chapter 2.3.2 --- Courant Condition --- p.14 / Chapter 2.4 --- Time Dependence of the Methods --- p.15 / Chapter 2.5 --- Perfectly Matched Layer (PML) --- p.16 / Chapter 2.5.1 --- Boundaries Problem --- p.16 / Chapter 2.5.2 --- PML Main Theme --- p.17 / Chapter 2.5.3 --- Different Types of PMLs --- p.20 / Chapter 2.6 --- Conclusion: Simulation Laboratory --- p.20 / Chapter 3 --- Software Comparison and Scaling Usage --- p.22 / Chapter 3.1 --- Physical Quantity Interested --- p.22 / Chapter 3.1.1 --- Cross-sections and Relation to Surface Plasmon Excitation --- p.23 / Chapter 3.2 --- Mie Theory --- p.24 / Chapter 3.2.1 --- Spherical Harmonics --- p.24 / Chapter 3.2.2 --- Expressing the terms in Spherical Harmonics --- p.26 / Chapter 3.2.3 --- Matching Boundaries --- p.27 / Chapter 3.2.4 --- Scattering and Extinction Cross-sections --- p.28 / Chapter 3.3 --- Software Used --- p.29 / Chapter 3.3.1 --- Meep --- p.29 / Chapter 3.3.2 --- Lumerical FDTD Solution --- p.30 / Chapter 3.4 --- Machines Used for Comparison --- p.30 / Chapter 3.5 --- Ease of Usage --- p.30 / Chapter 3.5.1 --- Installation --- p.31 / Chapter 3.5.2 --- Support --- p.32 / Chapter 3.5.3 --- Parallel Computation --- p.33 / Chapter 3.6 --- The Check Case Building --- p.33 / Chapter 3.6.1 --- Monitor Measurement Related to Time for Simulation --- p.34 / Chapter 3.6.2 --- Meep's Implementation --- p.34 / Chapter 3.6.3 --- Total Field Scattering Field (TFSF) Source --- p.35 / Chapter 3.6.4 --- Lumerical FDTD Solutions' Implement at ion --- p.36 / Chapter 3.7 --- Comparison --- p.37 / Chapter 3.7.1 --- Accuracy of the Programs --- p.37 / Chapter 3.7.2 --- Time Needed for the Programs --- p.43 / Chapter 3.8 --- Conclusion: How to Build Reasonable Running Cases --- p.46 / Chapter 4 --- The Projects on Nanorods --- p.47 / Chapter 4.1 --- Basic Understanding of Nanorods --- p.47 / Chapter 4.1.1 --- Geometry Dependence on Localized Surface Plasmon Resonance in Au Nanorods --- p.48 / Chapter 4.1.2 --- Plasmonic Coupling in Au Nanorod Dimers --- p.49 / Chapter 4.2 --- Size-Dependent Scattering and Absorption Cross-sections for Au Nanocrystals --- p.51 / Chapter 4.2.1 --- Measurement of Data --- p.51 / Chapter 4.2.2 --- Setup of Simulation --- p.52 / Chapter 4.2.3 --- Results and Conclusion --- p.54 / Chapter 4.3 --- Angle-Dependent Plasmon Coupling in Au Nanorod Dimers --- p.56 / Chapter 4.3.1 --- Setup of Experiment --- p.56 / Chapter 4.3.2 --- Setup of Simulation --- p.57 / Chapter 4.3.3 --- Results of Simulation --- p.59 / Chapter 4.3.4 --- The Dipolar Model Discussion --- p.62 / Chapter 4.3.5 --- Conclusion --- p.65 / Chapter 4.4 --- Plasmon Coupling in Linear Au Nanorod Dimers --- p.65 / Chapter 4.4.1 --- Experimental Results --- p.66 / Chapter 4.4.2 --- Energy Dependent Plasmon Coupling of Au Nanorod Dimers --- p.67 / Chapter 4.4.3 --- Dependency of the Plasmon Coupling on the Inter-particle Distance --- p.70 / Chapter 4.4.4 --- Dependency of the Plasmon Coupling on the Head Shape of Au Nanocrystals --- p.74 / Chapter 4.4.5 --- Coupling-induced Fano-Resonance in Au Nanorod Het- erodimers --- p.74 / Chapter 4.4.6 --- Conclusion --- p.78 / Chapter 4.5 --- Conclusion --- p.80 / Chapter 5 --- Conclusion --- p.81 / Bibliography --- p.84
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Influência da concentração e tipo de funcionalização de nanoestruturas de TiO2 nas propriedades de resinas experimentais / Influence of the concentration and type of functionalization of TiO2 nanostructures on the properties of experimental resinsGuimarães, Genine Moreira de Freitas 27 February 2019 (has links)
O objetivo deste trabalho in vitro foi avaliar a influência de diferentes concentrações de nanoestruturas de TiO2 funcionalizadas e não-funcionalizados nas propriedades de uma resina experimental. Nanotubos e nanopartículas de TiO2 foram sintetizadas e funcionalizadas utilizando o silano 3-(aminopropil) trietoxisilano (APTMS) e o 3-(trimetoxisilil)propil metacrilato (TSMPM). As nanoestruturas de TiO2 foram caracterizadas através de difratometria de raios X, EDS, potencial Zeta, MEV e MET. Foi preparada uma resina experimental contendo BisGMA/TEGDMA e foram divididos de acordo com a nanoestrutura de TiO2 (nanotubo e nanopartícula), concentração (0,3% e 0,9%) e funcionalização (APTMS e TMSPM). Noventa e um discos de resina foram confeccionados (n=7) e fotoativados (1000 mW/cm2). O Grau de conversão (GC) foi avaliado imediatamante e após 24 horas e a microdureza Knoop (KHN) foi avaliada após 7 dias e após imersão em etanol 100% para análise de densidade de ligações cruzadas. Os testes foram submetidos à análise estatística através de ANOVA a um critério com medidas repetidas e Tukey (=0,05). Para o grau de conversão, houve diferença significante entre as resinas (p < 0.001) e o tempo (p < 0.001). Para a KHN, houve diferenças estatísticas entre as resinas (p < 0.001), após imersão no álcool (p < 0.001) e houve interação entre as variáveis (p < 0.001). Os maiores valores de GC foram encontrados no período de 24 horas para os grupos com nanotubos de TiO2 na concentração de 0,3% funcionalizados com TMSPM. Resultados satisfatórios também foram encontrados para nanopartículas de TiO2 na concentração de 0,9%. Os mesmos resultados também foram observados para a dureza após imersão em etanol. Pode-se concluir que as nanoestruturas de TiO2 possuem diferentes características e podem interferir diretamente nas propriedades da resina avaliada. / The aim of this in vitro study was to evaluate the influence of different concentrations of functionalized and non-functionalized TiO2 nanostructures on the properties of an experimental resin. TiO2 nanotubes and nanoparticles were synthesized and functionalized by 3- (aminopropyl)triethoxysilane (APTMS) and 3-(trimethoxysilyl)propyl methacrylate (TSMPM). TiO2 nanostructures were characterized by x-ray diffractometer, EDS, zeta potential, SEM, and TEM. Bis-GMA/TEGDMA resin mixtures were prepared and divided according to TiO2 nanostructure (nanotube and nanoparticle), concentration (0.3 and 0.9%), and functionalization (APTMS and TSMPM). Ninety-one resin discs were made (n = 7) and photoactivated (1000 mW/cm2). The degree of conversion (DC) was evaluated immediately and after 24 hours, and Knoop hardness (KHN) was evaluated after 7 days and after immersion in 100% ethanol for analysis of crosslink density. Data were analyzed with one-way repeated measures ANOVA and Tukey\'s HSD ( = 0.05). For DC, there was a significant difference between resins (p < 0.001) and times (p < 0.001). For KHN, significant differences were found between resins (p < 0.001) and between before and after immersion in alcohol (p < 0.001). The resin × hardness interaction was significant (p < 0.001). The highest values of DC were found at 24 hours for the groups with 0.3% TiO2 nanotubes functionalized with TSMPM. The same results were also observed for hardness after immersion in ethanol. We conclude that TiO2 nanostructures have different characteristics and can directly interfere with the properties of the resin.
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Etude expérimentale de la multifissuration et de la décohésion de films minces et nanostructures magnétiques sur substrats flexibles : effet sur l'anisotropie magnétique / Non communiquéMerabtine, Skander 15 December 2017 (has links)
Les systèmes magnétiques flexibles et étirables sont d’intérêt croissant pour le développement de dispositifs électromagnétiques conformables aux surfaces non planes. Dans ce contexte, l’objectif de cette thèse est d’identifier des relations entre phénomènes mécaniques irréversibles (fissuration et délamination) aux grandes déformations et propriétés magnétiques de films minces d’épaisseurs nanométriques (alliages de CoFeB et NiFe) élaborés sur substrat polymère (Kapton®) par pulvérisation magnétron. Dans un premier temps, des essais de traction couplés in situ à la microscopie à forces atomiques ou des mesures de résistance électrique ont permis d’étudier la multifissuration des films minces et les décollements localisés (cloques) subséquents. Ces mesures ont permis de mettre en évidence des domaines de déformations macroscopiques pour lesquels chaque mécanisme était prépondérant. De plus l’énergie d’adhésion a pu être discutée et estimée à partir du suivi des cloques sous déformation. Dans un second temps, des mesures par résonance ferromagnétique effectuées ex situ ont permis de relier les domaines des déformations identifiés précédemment aux évolutions de l’anisotropie magnétique des films minces. De plus, une corrélation entre hétérogénéités de déformations et coefficient d’amortissement de Gilbert a été trouvée. Enfin, les propriétés magnétomécaniques de réseaux de nanolignes de NiFe ont permis de mettre en évidence l’intérêt de la nanostructuration pour ces systèmes magnétiques déformables. / Flexible and stretchable magnetic systems are of increasing interest for the development of electromagnetic devices conformable to non-planar surfaces. In this context, the objective of this thesis is to identify the relationships between irreversible mechanical phenomena (cracking and delamination) at large strains and magnetic properties of thin films of nanometric thicknesses (CoFeB and NiFe alloys) deposited on polymer substrate (Kapton®) by magnetron sputtering. In a first time, tensile tests coupled in situ with atomic force microscopy or electrical resistance measurements were used to study thin film multifissuration and subsequent localized debonding (buckles). These measurements made it possible to highlight areas of macroscopic strains for which each mechanism was predominant. In addition, the adhesion energy could be discussed and estimated from the monitoring of the buckles under applied strain. In a second step, ferromagnetic resonance measurements carried out ex situ made it possible to link the previously identified areas of strains to the evolutions of the magnetic anisotropy of thin films. In addition, a correlation between strain heterogeneities and Gilbert damping coefficient was found. Finally, the magnetomechanical properties of NiFe nanowires arrays have made it possible to highlight the advantage of nanopatterning for these deformable magnetic systems.
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Nonlinear intersubband dynamics in semiconductor nanostructuresWijewardane, Harshani Ovamini, January 2007 (has links)
Thesis (Ph. D.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on December 17, 2007) Vita. Includes bibliographical references.
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Elaboration et caracterisation de nanostructures magnetiquesPopa, Adriana Paula 23 November 2004 (has links) (PDF)
Ce travail de thèse est consacré à l'étude des propriétés magnétiques et structurales de différents types de nanostructures magnétiques: fils électrodéposés, plots circulaires et carrés. Il ressort de cette étude que dans le cas des fils électrodéposés de petit diamètre (29nm), la variation des différents paramètres de préparation comme le pH de la solution électrolytique,le courant de dépôt, conduit à différentes orientations de l'axe c. Un deuxième aspect qui nous a intéressé pendant ce travail a été l'influencé des interactions dipolaires sur les propriétés magnétiques des plots circulaires et carrés. Dans le cas des plots circulaires nous avons montré la possibilité de contrôler le sens de circulation de l'aimantation à l'intérieur des plots en arrangeant les plots dans des différentes configurations. On a analysé trois types des réseaux formés: des chaînes de deux plots, chaînes des plots en zig- zag et des plots arrangés dans une structure hexagonale. Sur les réseaux des plots circulaires et carrés, on a mis en évidence l'existence d'une anisotropie du champ de nucléation et d'annihilation. Cette anisotropie se manifeste par la variation du champ de nucléation et d'annihilation avec l'angle fait par le champ magnétique extérieur avec l'axe de la chaîne.
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Nanostructured Materials for Energy Storage and ConversionJi, Xiulei January 2009 (has links)
Efficient, cost effective, and environmentally friendly energy storage and conversion systems are highly desirable to meet ever increasing demands. Nanostructured materials have attracted great interest due to their many superior characteristics in these energy applications. These materials, typically nanoporous or nanostructured, exhibit faster charge transports, better contact, and sometimes new electrochemical reactivity, which leads to their high energy density, high power and/or great catalytic performances. A series of functional nanostructured materials have been fabricated with new synthetic schemes. Nanoporous materials technology and solid state electrochemistry have been attempted to be integrated in this study.
New functional nanoporous materials have been sought for electrochemical purposes. By employing a simple dilution strategy, homogeneously sized, ordered mesoporous silica nanorods (SBA-15), spanning about 10 porous channels in width and ranging from 300 to 600 nm in length were prepared. By employing SBA-15 nanorods as a template, ordered mesoporous carbon (OMC) CMK-3 nanorods were prepared. These porous nanorods exhibit enhanced mass transfer kinetics in their applications owing to their short dimensions. To improve the electronic conductivity of OMC and exploit otherwise wasted copolymer surfactant cross-linked in the channels of as-synthesized SBA-15, direct graphitic mesoporous carbon (termed as DGMC) were synthesized from the copolymer surfactant by employing transition metals (Fe, Co, Ni) as a catalyst. DGMC exhibit three orders higher conductivity and better thermal stability than non-graphitic OMC materials.
A series of nanostructured composites were fabricated by employing OMC as structure backbones and/or electronic conduits. DGMC/MoO2 as a Li ion battery anode exhibits a reversible capacity more than twice the value that a graphite anode can provide. Due to the confined and nanosized dimensions of the MoO2, the composite exhibits a cycle life with no capacity fading. Polymer modified OMC/sulfur interwoven nanostructures were prepared and applied as a cathode in Li-S batteries. The nanostructure displays all of the benefits of confinement effects at a small length scale. The nanostructure provides not only high electronic conductivity but also great access to Li+ ingress/egress for reactivity with the sulfur. The tortuous pathways within the framework and the surface polymer strongly retard the diffusion of polysulfide anions out from the channels into the electrolyte and minimize the loss of active mass in the cathode, resulting in a stabilized cycle life at reasonable rates. The Li-S batteries can supply up to near 80% of the theoretical capacity of sulfur (1320 mA∙h/g). This represents more than five times the specific capacity of conventional intercalation Li ion batteries. The assembly process for OMC/S is simple and broadly applicable, conceptually providing new opportunities for materials scientists for tailored design that can be extended to many different electrode materials.
Size-controlled supported metal and intermetallic nanocrystallites are of substantial interest because of their wide range of electrocatalytic properties. These intermetallics are normally synthesized by high temperature techniques; however, rigorous size control at high temperature is very challenging. A simple and robust chemically controlled process was developed for synthesizing size controlled noble metal, or bimetallic nanocrystallites, embedded within the porous structure of OMC. The method is applicable to a wide range of catalysts, namely bimetallic PtBi but also including Pt, Ru, Rh and Pd. By using surface-modified OMC, nanocrystallites are formed with monodisperse sizes as low as 1.5 nm, that can be tuned up to 2 and 3.5 nm (equivalent to the channel size of OMC) by thermal treatment. The method is also tailored for the deposition of catalysts on conventional fuel-cell carbon supports. OMC-PtBi nanohybrids were investigated as catalysts for formic acid oxidation for the first time. OMC-PtBi catalysts show an absence of CO poisoning. The excellent catalytic properties can be attributed to the successful catalyst preparation and the faithful practice of the “ensemble effect” at the nanoscale level.
A new agitation-friction methodology was developed to prepare the nano-OMC/S composite. The method is completely different from any conventional impregnation which requires the voluntary molecular mobility of guest phases. The method relies on frictional forces, and the hydrophobic attraction of the mixing components. This is the first example of a nanoporous solid which can be infiltrated by another solid phase at room temperature. The C/S nanocomposite exhibits not only better Pt ion sorption kinetics than its bulk counterpart, but also a higher pseudo-second-order rate constant than chitosan sorbents.
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Nanostructured Materials for Energy Storage and ConversionJi, Xiulei January 2009 (has links)
Efficient, cost effective, and environmentally friendly energy storage and conversion systems are highly desirable to meet ever increasing demands. Nanostructured materials have attracted great interest due to their many superior characteristics in these energy applications. These materials, typically nanoporous or nanostructured, exhibit faster charge transports, better contact, and sometimes new electrochemical reactivity, which leads to their high energy density, high power and/or great catalytic performances. A series of functional nanostructured materials have been fabricated with new synthetic schemes. Nanoporous materials technology and solid state electrochemistry have been attempted to be integrated in this study.
New functional nanoporous materials have been sought for electrochemical purposes. By employing a simple dilution strategy, homogeneously sized, ordered mesoporous silica nanorods (SBA-15), spanning about 10 porous channels in width and ranging from 300 to 600 nm in length were prepared. By employing SBA-15 nanorods as a template, ordered mesoporous carbon (OMC) CMK-3 nanorods were prepared. These porous nanorods exhibit enhanced mass transfer kinetics in their applications owing to their short dimensions. To improve the electronic conductivity of OMC and exploit otherwise wasted copolymer surfactant cross-linked in the channels of as-synthesized SBA-15, direct graphitic mesoporous carbon (termed as DGMC) were synthesized from the copolymer surfactant by employing transition metals (Fe, Co, Ni) as a catalyst. DGMC exhibit three orders higher conductivity and better thermal stability than non-graphitic OMC materials.
A series of nanostructured composites were fabricated by employing OMC as structure backbones and/or electronic conduits. DGMC/MoO2 as a Li ion battery anode exhibits a reversible capacity more than twice the value that a graphite anode can provide. Due to the confined and nanosized dimensions of the MoO2, the composite exhibits a cycle life with no capacity fading. Polymer modified OMC/sulfur interwoven nanostructures were prepared and applied as a cathode in Li-S batteries. The nanostructure displays all of the benefits of confinement effects at a small length scale. The nanostructure provides not only high electronic conductivity but also great access to Li+ ingress/egress for reactivity with the sulfur. The tortuous pathways within the framework and the surface polymer strongly retard the diffusion of polysulfide anions out from the channels into the electrolyte and minimize the loss of active mass in the cathode, resulting in a stabilized cycle life at reasonable rates. The Li-S batteries can supply up to near 80% of the theoretical capacity of sulfur (1320 mA∙h/g). This represents more than five times the specific capacity of conventional intercalation Li ion batteries. The assembly process for OMC/S is simple and broadly applicable, conceptually providing new opportunities for materials scientists for tailored design that can be extended to many different electrode materials.
Size-controlled supported metal and intermetallic nanocrystallites are of substantial interest because of their wide range of electrocatalytic properties. These intermetallics are normally synthesized by high temperature techniques; however, rigorous size control at high temperature is very challenging. A simple and robust chemically controlled process was developed for synthesizing size controlled noble metal, or bimetallic nanocrystallites, embedded within the porous structure of OMC. The method is applicable to a wide range of catalysts, namely bimetallic PtBi but also including Pt, Ru, Rh and Pd. By using surface-modified OMC, nanocrystallites are formed with monodisperse sizes as low as 1.5 nm, that can be tuned up to 2 and 3.5 nm (equivalent to the channel size of OMC) by thermal treatment. The method is also tailored for the deposition of catalysts on conventional fuel-cell carbon supports. OMC-PtBi nanohybrids were investigated as catalysts for formic acid oxidation for the first time. OMC-PtBi catalysts show an absence of CO poisoning. The excellent catalytic properties can be attributed to the successful catalyst preparation and the faithful practice of the “ensemble effect” at the nanoscale level.
A new agitation-friction methodology was developed to prepare the nano-OMC/S composite. The method is completely different from any conventional impregnation which requires the voluntary molecular mobility of guest phases. The method relies on frictional forces, and the hydrophobic attraction of the mixing components. This is the first example of a nanoporous solid which can be infiltrated by another solid phase at room temperature. The C/S nanocomposite exhibits not only better Pt ion sorption kinetics than its bulk counterpart, but also a higher pseudo-second-order rate constant than chitosan sorbents.
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