Rozprawy doktorskie na temat „MoS2 Nanoparticles”

Thesis (M.S.)--University of Maryland, College Park, 2003.
Thesis research directed by: Dept. of Chemistry and Biochemistry. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

Nanoparticles of MoS2 and WS2 were synthesized by decomposing the appropriate metal hexacarbonyl in the presence of sulfur dissolved in decalin at 140°C. A significant fraction of the nanoparticles was ≤ 15 nm in diameter as verified by Transmission Electron Microscopy. The process was repeated in the presence of silica and then titania to produce supported metal sulfides. The unsupported nanoparticles were found to exhibit a size-dependent shift in their threshold UV-visible absorption due to quantum confinement. Photocatalytic properties of each sulfide from synthesis in decalin were explored by using each as a catalyst in the photodegradation of methylene blue by visible light. These sulfides were also used to catalyze the photodegradation of acetone. Unsupported MoS2 and WS2 nanoparticles catalyzed the photodegradation of acetone under visible light of ≥ 400 nm wavelength. This is the first study reporting the photocatalytic properties of the unsupported WS2 nanoparticles. Photodegradation of methylene blue under ≥ 435 nm irradiation was detected using unsupported WS2 but not unsupported MoS2, likely because activity was masked by the likely photobleaching of the dye. When deposited on silica or titania, the nanosized MoS2 and WS2 could be uniformly distributed in aqueous solutions to maximize the photocatalytic efficiency. Correcting the absorbance measurements for light scattering by solids proved to be beneficial for extracting kinetic information. Both silica deposited sulfides were found to significantly increase the rate of methylene blue photodegradation, and deposited WS2 increased this rate significantly more than deposited MoS2. Similarly, both titania deposited sulfides significantly increased the rate of methylene blue photodegradation, and the deposited WS2 increased this rate significantly more than the deposited MoS2
Synthesis of the sulfide photocatalysts -- Characterization of synthesized nanoparticles -- Photocatalytic degradation tests : setup and protocols -- Photocatalytic degradation tests : results.
Department of Chemistry

De nos jours, afin de réduire le frottement et l'usure dans les moteurs thermiques et par voie de conséquence les émissions polluantes ainsi que la consommation énergétique, des revêtements APS (Atmospheric Plasma Spray) sont appliqués sur les chemises des cylindres. Le MoDTC (Di-ThioCarbamate de Molybdène), est un additif organométallique largement utilisé dans la lubrification automobile pour réduire le frottement grâce à la formation sur les surfaces frottantes de feuillets de MoS2. Ce travail de thèse porte sur l’étude de la réaction tribochimique du MoDTC avec le revêtement TiO2 APS dans des conditions de lubrification mixte / limite. Des poudres de TiO2 de taille micrométrique ont été utilisées pour obtenir un revêtement APS de TiO2 de 70 µm d'épaisseur. Différents tribomètres ont été utilisés pour effectuer des essais de frottement en présence d’une huile de base contenant du MoDTC. Les résultats obtenus pour un contact acier / TiO2 APS lubrifié avec du MoDTC présente une réduction significative du frottement par rapport au contact acier / acier (contact de référence). Les analyses de surface montrent que le tribofilm formé sur le plan de TiO2 APS est composé de MoS2 et de MoO3 tandis qu’il est constitué d’oxysulfure de molybdène, de MoS2 et de MoO3 sur le plan de référence en acier. De plus, les résultats indiquent que des phases Magneli résistantes à l'usure sont formées sur la surface du plan de TiO2 réduisant ainsi l'usure du contact lorsque celui-ci est uniquement lubrifié avec l'huile de base. L'impact de divers paramètres tels que la rugosité, la température d'essai, la pression de contact, la concentration en MoDTC et le remplacement des billes en acier par des billes en céramique sur le comportement tribologique du TiO2 APS a également été étudié. Les résultats ont été comparés avec ceux obtenus dans les mêmes conditions avec un contact acier / acier de référence et révèlent que le coefficient de frottement est toujours plus faible dans le cas des contacts impliquant un revêtement de TiO2 APS. Des résultats similaires à ceux obtenus avec le TiO2 APS (en termes de comportement tribologique et de composition chimique du tribofilm) ont été obtenus avec des nanoparticules de TiO2 mélangées dans l’huile de base avec du MoDTC dans le cas d'un contact acier / acier de référence. Dans les deux cas, une décomposition complète de MoDTC conduisant à la formation de MoS2 a été observée. Un phénomène de tribocatalyse a été suggéré comme pouvant être le mécanisme responsable de la décomposition du MoDTC en présence de matériaux à base de TiO2 comme le revêtement TiO2 APS et les nanoparticules de TiO2
Nowadays to reduce friction and wear as well as gas emission and oil consumption of the passenger car engines, Atmospheric Plasma Spray (APS) coatings are used on cylinder liner. MoDTC (Molybdenum Di-Thiocarbamate), organometallic friction modifier has been previously used to reduce friction by formation of layered molybdenum disulphide flakes. This study focuses on tribochemical interaction of MoDTC with TiO2 APS coating under mixed / boundary lubrication conditions. Fused and crushed micron sized powders were used to obtain a 70 µm thick TiO2 coating. Various tribometers were used to carry out tribotests in presence of lubricant containing MoDTC. Steel / TiO2 APS contact showed significant friction reduction than steel / reference steel contact. It was shown that the tribofilm is composed of MoS2 and MoO3 on TiO2 APS flats while it is composed of Mo-oxysulphide, MoS2 and MoO3 on reference steel flats. It was shown that wear resistant Magneli phases are formed on the surface of TiO2 APS disc, decreasing wear when the contact was lubricated only with base oil. Impact of various parameters like roughness, test temperature, contact pressure, concentration of MoDTC and change of counterpart materials from steel balls to ceramic balls, on the tribological behavior of TiO2 APS was also studied. Results obtained were compared with contacts involving reference steel and it was confirmed that friction coefficient was always lower in case of contacts involving TiO2 APS coating. Similar tribological results and chemistry were obtained for TiO2 nanoparticles blended with MoDTC in case of steel / reference steel contact. Both the cases, TiO2 APS and TiO2 nanoparticles showed complete decomposition of MoDTC to form MoS2. Tribocatalysis was suggested as the mechanism responsible for complete decomposition of MoDTC in case of TiO2 based materials like TiO2 APS coating and TiO2 nanoparticles

Afin de réduire la teneur en soufre des essences, l’hydrodésulfuration transforme les molécules soufrées en hydrocarbures en présence d’un catalyseur supporté (métaux de transition sulfurés : MoS2) et dopé (Co, Ni). Cette phase active, déposée sur des nanoparticules, présente un nombre plus important de défauts, sites actifs essentiels à la catalyse. Les nanoparticules ont un ratio S/V élevé, une grande réactivité de surface avec une juste utilisation des quantités de métaux. L’objectif de ce projet de thèse est de synthétiser des catalyseurs nanométriques de type coeur@coquille possédant une meilleure activité catalytique qu’un simple mélange mécanique de deux métaux sulfurés. Le coeur est composé de Fe3O4 ou de nanodiamants et la coquille de MoS2, NiMoS, CoMoS ou NiCoMoS, supporté sur du TiO2 ou de la γ-Al2O3. Une réaction modèle (HDS du thiophène) a été utilisée afin d’évaluer l’activité catalytique et d’optimiser la structure du catalyseur. L’étude portera sur les paramètres de synthèse et l’effet de la taille du coeur, la synthèse utilisée, les interactions entre le coeur et la coquille, le support, la (co)– promotion (Ni/Co) et l’activation par la température
In hydrodesulfurization of fossil fuels, the sulfur levels are reduced by sulfur extraction from hydrocarbons by using supported catalysts (MoS2), doped (Co, Ni). Ultra-deep hydrodesulfurization will be achieved by improving new catalysts. Nanoparticles are a promising candidate with their high S/V ratio and permit to use the precise amount of metallic sulphide. The aim of this thesis is the synthesis of core@shell nanometric catalyst with improved activities. Core composed of Fe3O4 or nanodiamonds will be surrounded by a shell formed of MoS2, NiMoS, CoMoS or NiCoMoS, supported on TiO2, γ-Al2O3. Model reaction (thiophene) has allowed to compare conversion rates between each catalyst. Additionally, characterizations have provided a better understanding of the HDS catalyst structure and performances. Some factors have been investigated such as the size of the core, theinteractions between the core and the shell, the type of synthesis, the support chosen, the synergetic effect with doping ions and also the activation of the catalyst at low temperature

IV Resumo Título: Nanoestruturas de Dissulfeto de Molibdênio: Síntese e caracterização para produção de Hidrogênio Mestrando: André Luís Silveira Fraga Orientador: Prof. Marcos José Leite Santos Palavras Chave: nanoestruturas de MoS2, nanopartículas de ouro, semicondutores, produção de hidrogênio. Neste trabalho é apresentada a síntese e caracterização de nanoestruturas de MoS2 e nanoestruturas de MoS2 decoradas com nanopartículas de ouro. O MoS2 foi obtido através de rota hidrotermal a 200 °C durante períodos de síntese de 2, 6, 12 e 24 horas. Como precursores foram utilizados molibdato de sódio, ácido 3-mercaptopropiônico, cisteamina e L-cisteína. Para avaliar o efeito da presença dos ligantes nas estruturas, as amostras de MoS2 foram tratadas térmicamente a temperaturas de 250, 550 e 750 °C, em atmosfera de argônio. Com o objetivo de avaliar o efeito da presença de nanopartículas de ouro nas propriedades fotocatalíticas do material, foi realizada a síntese in situ de nanopartículas de ouro aderidas às estruturas de MoS2. Os materiais foram caracterizados através das técnicas de difração de raios X (DRX), microscopia eletrônica de transmissão (MET), microscopia eletrônica de varredura (MEV) e espectroscopia do ultravioleta e visível (UV-Vis). As áreas superficiais e quantidade de poros foram avaliadas através das técnicas de BET (Brunauer, Emmett and Teller) e DFT (density functional theory). O precursor ácido 3-mercaptopropiônico resultou na formação de aglomerados de nanofolhas com cerca de 500 nm de diâmetro na sua maior dimensão. Ao usar cisteamina e L-cisteína foram obtidas nanoestruturas com formato de nanoflores com cerca de 300 nm de diâmetro formadas por pétalas com cerca de 30 nm. Um resultado interessante foi a rápida formação das nanoflores na presença de L-cisteína. As estruturas de nanoflores apresentaram produção de hidrogênio de até 9,6 mmol/gh.
In this work the synthesis and characterization of MoS2 nanostructures and MoS2 nanostructures decorated with gold nanoparticles is presented. The materials were obtained by hydrothermal route at 200 °C during synthesis periods of 2, 6, 12 and 24 hours. Sodium molybdate was used as Molybdenium precursor and 3-mercaptopropionic acid, cysteamine and L-cysteine as sulfur precursors. To evaluate the effect of ligands on the structures, the MoS2 samples were thermally treated at 250, 550 and 750 °C under argon atmosphere. The effect of gold nanoparticles on the photocatalytic properties of the material was evaluated by obtaining and materials with gold nanoparticle adhered to the MoS2 structures. The materials were characterized by X-ray diffraction (XRD) techniques, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and ultraviolet and visible spectroscopy (UV-Vis). The surface areas and amount of pores were evaluated using BET (Brunauer, Emmett and Teller) and DFT (density functional theory) techniques. The precursor 3-mercaptopropionic acid resulted in the formation of nano-foil agglomerates of about 500 nm in diameter. On the other hand, when using cysteamine and L-cysteine, flower-shaped nanostructures of about 300 nm in diameter formed by petals of about 30 nm were obtained. An interesting result was the rapid formation of nanoflores in the presence of L-cysteine. Nanoflower structures showed hydrogen production up to 9.6 mmol / gh.

The ability to convert photons into mechanical motion is of significant importance for many energy conversion and reconfigurable technologies. Establishing an optical-mechanical interface has been attempted since 1881; nevertheless, only few materials exist that can convert photons of different wavelengths into mechanical motion that is large enough for practical import. Recently, various nanomaterials including nanoparticles, nanowires, carbon nanotubes, and graphene have been used as photo-thermal agents in different polymer systems and triggered using near infrared (NIR) light for photo-thermal actuation. In general, most photomechanical actuators based on sp bonded carbon namely nanotube and graphene are triggered mainly using near infra-red light and they do not exhibit wavelength selectivity. Layered transition metal dichalcogenides (TMDs) provide intriguing opportunities to develop low cost, light and wavelength tunable stimuli responsive systems that are not possible with their conventional macroscopic counterparts. Compared to graphene, which is just a layer of carbon atoms and has no bandgap, TMDs are stacks of triple layers with transition metal layer between two chalcogen layers and they also possess an intrinsic bandgap. While the atoms within the layers are chemically bonded using covalent bonds, the triple layers can be mechanically/chemically exfoliated due to weak van der Waals bonding between the layers. Due to the large optical absorption in these materials, they are already being exploited for photocatalytic, photoluminescence, photo-transistors, and solar cell applications. The large breaking strength together with large band gap and strong light- matter interaction in these materials have resulted in plethora of investigation on electronic, optical and magnetic properties of such layered ultra-thin semiconductors. This dissertation will go in depth in the synthesis, characterization, development, and application of two- dimensional (2D) nanomaterials, with an emphasis on TMDs and molybdenum disulfide (MoS2), when used as photo-thermal agents in photoactuation technologies. It will present a new class of photo-thermal actuators based on TMDs and hyperelastic elastomers with large opto-mechanical energy conversion, and investigate the layer-dependent optoelectronics and light-matter interaction in these nanomaterials and nanocomposites. Different attributes of semiconductive nanoparticles will be studied through different applications, and the possibility of globally/locally engineering the bandgap of such nanomaterials, along with its consequent effect on optomechanical properties of photo thermal actuators will be investigated. Using liquid phase exfoliation in deionized water, inks based on 2D- materials will be developed, and inkjet printing of 2D materials will be utilized as an efficient method for fast fabrication of functional devices based on nanomaterials, such as paper-graphene-based photo actuators. The scalability, simplicity, biocompatibility, and fast fabrication characteristics of the inkjet printing of 2D materials along with its applicability to a variety of substrates such as plastics and papers can potentially be implemented to fabricate high-performance devices with countless applications in soft robotics, wearable technologies, flexible electronics and optoelectronics, bio- sensing, photovoltaics, artificial skins/muscles, transparent displays and photo-detectors.

La possibilité de créer des monocouches de dichalcogenures à métaux de transition (MoS2, WSe2,MoSe2 pour ceux étudiés dans ce manuscrit) a été démontrée récemment (2005) et a ouvert la voie à l’étude de ces matériaux sous leur forme 2D. Il apparaît depuis que les propriétés de ces semi-conducteurs sous leur forme monocouche offrent des perspectives intéressantes à la fois du point de vue de la physique fondamentale et des potentielles applications qui peuvent en découler ; en plus de bénéficier d’un fort couplage avec la lumière, l’existence d’un gap important (situé dans le visible, 1.7-1.8 eV) permet entre autres de réaliser des transistors d’épaisseur mono-atomique. Par ailleurs, la physique de ces matériaux est prometteuse pour les applications dans le domaine de l’optoélectronique. En effet, lorsque le matériau est affiné jusqu’à la monocouche atomique, son gap optique devient direct et la brisure de symétrie d’inversion associée au fort couplage spin-orbite provoque l’apparition de règles de sélection optique originales qui relient directement la polarisation de la lumière émise ou absorbée à une des deux vallées non-équivalentes de l’espace réciproque. Cela ouvre la possibilité d’explorer une nouvelle physique, basée sur l’indice de vallée et intitulée en conséquence vallée-tronique, avec comme perspectives futures la manipulation de l’indice de vallée et l’exploitation d’effetsliés à cette relation originale entre propriétés optiques et électroniques (effet vallée-Hall par exemple). Cemanuscrit de thèse regroupe une série d’expériences réalisées dans le but de comprendre et caractériser les propriétés optoélectroniques de ces matériaux. Un premier chapitre introductif présente le contexte scientifique de ces travaux de recherche et démontre l’origine des propriétés électroniques et optiques de ces matériaux via un modèle théorique simple. Le second chapitre présente en détails les échantillons étudiés ainsi que le dispositif expérimental utilisé lors des mesures. Enfin les chapitres 3 à 6 détaillent les expériences menées et les résultats obtenus ; le lecteur y trouvera des mesures de photoluminescence apportant la démonstration expérimentale des règles de sélection optique, l’identification des différents raies spectrales d’émission pour les différentstypes d’échantillons mentionnés plus haut ainsi que des mesures de photoluminescence résolues en temps permettant d’extraire la dynamique des propriétés des porteurs photo-générés. Une part importante de ce manuscrit est consacrée à l’étude expérimentale des propriétés excitoniques de ces matériaux dont la structure de bande électronique est finalement sondée via des études de magnéto-spectroscopie
The possibility of isolating transition metal dichalcogenide monolayers by simple experimental means has been demonstrated in 2005, by the same technique used for graphene. This has sparked extremely diverse and active research by material scientists, physicists and chemists on these perfectly two-dimensional (2D) materials. Their physical properties inmonolayer formare appealing both fromthe point of view of fundamental science and for potential applications. Transition metal dichalcogenidemonolayers such asMoS2 have a direct optical bandgap in the visible and show strong absorption of the order of 10% per monolayer. For transistors based on single atomic layers, the presence of a gap allows to obtain high on/off ratios.In addition to potential applications in electronics and opto-electronics these 2D materials allow manipulating a new degree of freedom of electrons, in addition to the spin and the charge : Inversion symmetry breaking in addition to the strong spin-orbit coupling result in very original optical selection rules. The direct bandgap is situated at two non-equivalent valleys in k-space, K+ and K−. Using a specific laser polarization, carriers can be initialized either in the K+ or K− valley, allowing manipulating the valley index of the electronic states. This opens up an emerging research field termed "valleytronics". The present manuscript contains a set of experiments allowing understanding and characterizing the optoelectronic properties of these new materials. The first chapter is dedicated to the presentation of the scientific context. The original optical and electronic properties of monolayer transition metal dichalcogenides are demonstrated using a simple theoreticalmodel. The second chapter presents details of the samples and the experimental setup. Chapters 3 to 6 present details of the experiments carried out and the results obtained. We verify experimentally the optical selection rules. We identify the different emission peaks in the monolayer materials MoS2, WSe2 and MoSe2. In time resolved photoluminescence measurements we study the dynamics of photo-generated carriersand their polarization. An important part of this study is dedicated to experimental investigations of the properties of excitons, Coulomb bound electron-hole pairs. In the final experimental chapter, magneto-Photoluminescence allows us to probe the electronic band structure and to lift the valley degeneracy

Dans cette thèse, des matériaux 2D ont été étudiés principalement par méthodes ab initio de type DFT, ainsi que par des techniques expérimentales. Le manuscrit se focalise sur le polymorphisme, les bords et la fonctionnalisation du matériau 2D MoS2. Nous montrons que la fonctionnalisation avec des espèces similaires peut être étendue à d’autres matériaux 2D en incluant des études sur le graphène. Nous étudions par des calculs DFT la stabilité relative des polymorphes et des reconstructions des bords de monocouches de MoS2, et nous proposons des modèles qualitatifs pour comprendre la stabilité. La fonctionnalisation du MoS2 par des stratégies covalentes et non covalentes a également été étudiée en lien avec des expérimentateurs. En particulier, nos calculs indiquent que le MoS2 peut être fonctionnalisé de manière covalente avec des dérivés de 1,2- dithiolane. Cette fonctionnalisation se fait préférentiellement sur les bords, produisant un hybride stable. Ceci peut être utilisé pour produire un système avec un groupe pyrène photoactif qui interagit de manière significative avec MoS2. Les résultats expérimentaux obtenus par nos collaborateurs sont conformes à nos résultats théoriques et une interaction entre le fragment pyrène photoexcité et MoS2 a été mise en évidence. La fonctionnalisation directe non covalente de la surface de MoS2 avec du pyrène a également été étudiée théoriquement et expérimentalement, en trouvant une interaction similaire à celle du cas précédent. Finalement, nous montrons que des dérivés de pyrène peuvent être utilisés pour la fonctionnalisation de matériaux liés au graphène, système d’intérêt pour le stockage de l'énergie
In this thesis, ab initio DFT methods and complementary experimental techniques are used to study 2D materials. The manuscript focuses on our studies on the polymorphism, edges and functionalization of the 2D-material MoS2. Additionally, we show that functionalization with similar species can be extended to other 2D materials by including studies on the functionalization of graphene. We have studied using DFT calculations the relative stability of different MoS2 polymorphs and associated edge reconstructions, and have proposed qualitative models for understanding the stability trends. Functionalization of MoS2 by covalent and non-covalent strategies is also explored in collaboration with experimental partners. In particular, our calculations indicate that MoS2 can be covalently functionalized, preferentially at edges, leading to a final stable hybrid. This strategy is used to functionalize MoS2 with a photoactive pyrene group that shows significant interaction with MoS2. Experimental results obtained by our collaborators are consistent with our theoretical findings, and an interaction between the photoexcited pyrene moiety and MoS2 is found. A similar interaction is found for direct noncovalent functionalization of the basal plane of MoS2 both theoretically and experimentally. Finally, we show that pyrene derivatives can also be used for functionalizing graphenerelated materials for energy storage applications

In this communication, we present solution-based coating procedure of MoSI nanowires (NW) with platinum nanoparticles. The average particle diameter was found to be around 2.82 nm, showing a narrow size distribution. This single-step in situ reduction method at room temperature in water solution can easily be applied for large-scale applications. We also prepared two-dimensional networks of MoSI NW bundles by deposition via spraying from a purified stable dispersion in acetonitrile onto NaCl crystals and nonconductive silicon wafer with pre-assembled molybdenum electrodes. The formation of a conductive molybdenum network was achieved by annealing in hydrogen due to coalescence of the templates MoSI bundles during transformation. Stable water dispersion of molybdenum NW network was prepared by simply dissolving the NaCl substrate with molybdenum network on the surface. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35168

La preparation de mos 2 par suspension-precipitation constitue une nouvelle voie de synthese de mos 2 par la chimie douce. Elle permet, par precipitation en solution aqueuse a basse temperature, d'obtenir directement mos 2 cristallise a partir d'un precurseur oxyde de mo v i. Selon les reactifs et les protocoles employes, des solides mos x de divers degres de cristallinite peuvent etre obtenus : mos x avec x = 3 amorphe, et mos 2 + x cristallise ou en voie de cristallisation. Le mos 2 obtenu presente une structure turbostratique avec des feuillets empiles et enchevetres. L'application d'un post-traitement thermique a tous les solides synthetises, quels que soient leur degre de cristallinite et leur preparation, permet d'obtenir mos 2 cristallin. La caracterisation des solides obtenus par xps montre que trois etats de valence du mo sont presents dans les echantillons synthetises : mo i v en environnement sulfure, mo v et mo v i en environnement sulfure ou oxysulfure. Deux types de ligands sulfures sont detectes : s 2 et s 2 2 , ainsi que du soufre elementaire. Les solides amorphes de type mos x avec x = 3 seraient composes de mos 3 et/ou d'oxysulfures de mo v et mo v i. Les solides de type mos 2 + x seraient composes de mos 2, de mos 3 et d'oxysulfures de mo v et et mo v i. Le suivi de syntheses par spectroscopies raman et uv-vis a permis de montrer que le mo v i n'est pas reduit sous forme oxyde et que l'anion mos 4 2 est un intermediaire reactionnel dans la formation de mos 2. Un modele de formation de mos 2 passant par un processus de condensation-reduction des anions mos 4 2 est propose : les especes mo 2s 7 2 pourraient tout d'abord etre formees puis des chaines de mo i v-s avec intervention de reactions d'oxydation-reduction internes. Le degre de condensation et l'organisation de ces chaines en solution determineraient les caracteristiques structurales et morphologiques des solides obtenus, particulierement interessants pour une application en catalyse d'hydrotraitement.

A logical progression from the maturing field of colloidal semiconductor quantum dots to the emerging subclass of impurity-doped colloidal semiconductor nanoparticles is underway. To this end, the present work describes the formation and analysis of a new form of Tin-doped Indium Oxide (ITO). The form is that of a colloidal dispersion comprised of pure-phase, 4-6 nanometer ITO particles possessing an essentially single crystalline character. This system forms a non-agglomerated, optically clear solution in a variety of non-polar solvents and can remain in this state, at room temperature, for months and potentially, years. ITO is the most widely used member of the exotic materials family known as Transparent Conductive Oxides (TCOs) and is the primary enabling material behind a wide variety of opto-electronic device technologies. Material synthesis was achieved by initiating a series of interrelated nucleophilic substitution reactions that provided sufficient intensity to promote doping efficiencies greater than 90% for a wide range of tin concentrations. The optical clarity of this colloidal system allowed the intrinsic properties of single crystalline ITO particles to be evaluated prior to their use in thin-films or composite structures. Monitoring the temporal progression of n-type degeneracy by its effects on the optical properties of colloidal dispersions shed light on the fundamental issues of particle formation, band filling (Burstein-Moss) dynamics, and the very origin of n-type degeneracy in ITO. Central to these studies was the issue of excess electron character. The two limiting cases of entirely free and entirely confined electron motion were evaluated by application of bulk-like band dispersion analysis and the effective mass approximation, respectively. This provided a means to estimate the number of excess conduction band electrons present within an individual particle boundary. The ability to control and optimize the level of n-type degeneracy within the colloidal ITO nanoparticle form by compositional variation was also demonstrated. A key to the widespread adoption of a new material by industry is an ability to produce multi-gram and perhaps, kilogram quantities with no significant sacrifice in quality. Accordingly, a modified synthesis process was developed to allow for the mass production of high-quality colloidal ITO nanocrystals.

Les enjeux environnementaux actuels, ainsi que la hausse continue du prix du pétrole, ont incité les constructeurs automobiles du monde entier à améliorer le rendement de leurs véhicules. Les propriétés tribologiques des lubrifiants des moteurs et boîtes de vitesses ont une influence considérable sur le rendement global des véhicules. Ils réduisent en effet le frottement généré par un grand nombre de contacts, et permettent parfois la réduction de la taille de différents composants en leur conférant une meilleure résistance à l’usure. Les avancées récentes en termes de synthèse de nanoparticules ont ouvert de nouvelles perspectives en termes d’additivation de lubrifiants avec, par exemple, la découverte des excellentes propriétés tribologiques des nanoparticules inorganiques de type fullerène comme le disulfure de molybdène ou de tungstène. L’objectif de ce manuscrit est d’évaluer le potentiel tribologique des nanoparticules IF-MoS2 dans l’optique d’une application automobile. L’influence de la taille et de la structure des nanoparticules a d’abord été étudiée. Les nanoparticules peu cristallines se sont révélées être plus aptes à maintenir un tribofilm performant sur des surfaces en acier dans des conditions de lubrification limite, indépendamment de leur taille. Toutes les nanoparticules testées ont cependant atteint des performances équivalentes lorsqu’une recirculation de l’huile était imposée, permettant de maintenir une alimentation continue du contact en nanoparticules. Une fois incorporées dans une formulation d’huile complète, les nanoparticules IF-MoS2 perdent leurs propriétés tribologiques. Les dispersants contenus dans l’huile, bien que permettant une bonne dispersion des IF-MoS2, semblent responsables de leur inefficacité en empêchant la formation de tribofilms sur les surfaces antagonistes. Une fois correctement dispersées, les nanoparticules pénètrent toujours le contact et se retrouvent bien exfoliées. Une adsorption excessive des dispersants sur les feuillets de MoS2 ainsi libérés et/ou sur les surfaces en acier semble nuire à l’adhésion du tribofilm. Un équilibre entre dispersion des nanoparticules et performance tribologique a ensuite été trouvé, en utilisant de très faibles concentrations de dispersants. Le comportement des huiles dopées en nanoparticules dans des conditions plus proches d’une application automobile a finalement été exploré. Les IF-MoS2 ont permis une réduction significative du frottement et de l’usure à température ambiante et en roulement/glissement, à la fois pour des surfaces lisses et rugueuses. Les risques associés à la présence de nanoparticules dans l’huile dans les régimes de lubrification en film complet ont été partiellement levés. Aucun impact significatif n’a en effet été constaté sur le coefficient de frottement pour l’ensemble des conditions d’essais retenues. Le potentiel des nanoparticules IF-MoS2 pour la protection des surfaces soumises à la fatigue de contact a enfin été démontré
The growing environmental concerns, along with the continuous increase in the price of fossil fuels, have highly motivated car manufacturers worldwide to improve the efficiency of their vehicles. The tribological properties of engine and gearbox lubricants have a significant impact on the global efficiency of vehicles, as they contribute to reducing friction in many contacts and allow the downsizing of various components by providing their surfaces with anti-wear protection. The recent breakthroughs in nanoparticle synthesis have opened new prospects in terms of lubricant additivation, with the discovery of the excellent friction and wear reducing properties of nanoparticles such as Inorganic Fullerene-like (IF-) molybdenum or tungsten disulfides. The tribological potential of IF-MoS2 for automobile applications was investigated in this work. The respective influences of nanoparticle size and structure were first of all studied, revealing that poorly crystalline nanoparticles were more efficient in maintaining low-friction tribofilms on steel substrates in severe boundary lubrication regimes regardless of size (for the range studied). All the nanoparticles tested however showed similar performances when proper oil recirculation was ensured, providing a continuous feeding of the contact in nanoparticles. The IF-MoS2 nanoparticles lost their lubricating abilities when added to fully-formulated lubricants. This behavior was attributed to the presence of dispersants in the oil, which dispersed the nanoparticles effectively but prevented them from forming tribofilms on the rubbing surfaces. The well-dispersed IF-MoS2 were shown to enter the contact and exfoliate, but an excessive adsorption of the dispersants on the released MoS2 platelets and/or the steel surfaces is thought to prevent tribofilm adhesion. A balance between nanoparticle dispersion and tribological performance was then found, by using very low concentrations of dispersants. The behavior of nanoparticle-doped oils in various scenarios related to automobile applications was finally explored. The IF-MoS2 provided significant friction and wear reduction at ambient temperature and in milder rolling/sliding test conditions, for smooth and rough surfaces. The risks related to the presence of nanoparticles in the oil in full-film lubrication regimes were partially lifted, with no significant influence on friction witnessed for all the test conditions considered. The ability of IF-MoS2 nanoparticles to protect steel surfaces from surface-initiated Rolling Contact Fatigue was finally shown

Le sujet principal de cette thèse est l'utilisation de la Théorie Fonctionnelle de la Densité dans sa variante à liaisons fortes (DFTB) pour l'étude de l'effet de la pression sur des nanotubes de carbone. Nous commençons par étudier l'effondrement radial sous l'effet de la pression de nanotubes de carbone (CNTs) individualisés, soit dans leur forme originale (vides), soit remplis avec des molécules d'eau ou de dioxyde de carbone. Nous étudions à continuation le processus d'effondrement radial de fagots de nanotubes de carbone a faible nombre de parois (double ou triple-parois) en fonction de la pression combinant modélisations et études expérimentales. Finalement nous présentons une étude sur les propriétés électroniques et magnétiques d'une monocouche de MoS2 déposée sur une surface de Ni(111) dans le cadre de laThéorie Fonctionnelle de la Densité incluant des interactions de van der Waals. Le manuscrit est structuré en 7 chapitres. Le chapitre 1 est notre introduction à cette thèse, incluant les motivations, les connaissances préalables sur nos sujets que nous intéressent ici, ainsi que notre contribution et principaux résultats. Le chapitre 2 présente les principaux éléments et définitions sur les CNTs. Nous décrivons ensuite les propriétés électroniques des CNTs et celles du graphène qui constitue un système de référence. Le chapitre 3 contient les éléments théoriques de notre étude. D'abord nous faisons une courte introduction à la Théorie Fonctionnelle de la Densité (DFT). Ensuite nous présentons deux des fonctions d'échange-corrélation les plus utilisées, suivi d'une revue sur les fonctions de van der Waals dont la DFT ordinaire ne peut rendre compte. Finalement, nous faisons une brève introduction à la méthode DFTB que nous utilisons dans nos modélisations des CNTs. Dans le chapitre 4 nous présentons nos modélisations sur l'effondrement radial sous pression hydrostatique de nanotubes de carbone contenant soit de l'eau doit du dioxyde de carbone. Nous montrons que la présence de ces molécules à l'intérieur des tubes modifie la dynamique du processus d'effondrement radial, donnant lieu soit à un support mécanique et repoussant la pression d'effondrement radial soitréduisant leur stabilité mécanique. Pour les CNTs vides, l'effondrement radial est très peu affecté par la nature du milieu transmetteur de pression, mais déterminé par le diamètre des nanotubes de carbone. Nos modélisations avec la méthode DFTB sont en excellent accord avec les modèles de milieux continues surla dépendance de la pression d'effondrement radial avec le diamètre du tube, d, mais montrent égalementune déviation de ce modèle pour les petites valeurs de d, ce qui est dû au moins en partie à la nature atomistique des nanotubes de carbone. Dans le chapitre 5, nous présentons une étude théorique de l'effondrement radial en fonction de la pression pour des nanotubes de carbone à parois simple, double et triple. Nos modélisations sont réalisées par DFTB pour des diamètres internes allant de 0.6 à 3.3 nm. Quand les parois sont séparées par la distance graphitique, nous montrons que la pression d'effondrement radial, Pc, est déterminé par le diamètre du tube interne, din, mais avec un important écart par rapport à une loi à la Lévy-Carrier, Pcdin-3. Nous proposons une expression modifiée, Pcdin3= (1- 2/din2) où  et  sont des paramètres numériques. Dans le chapitre 6 nous étudions par DFT les propriétés électroniques et magnétiques d'une monocouche de MoS2 déposée sur une surface de Ni(111). La prise en compte des interactions de van der Waals s'est avérée essentielle afin de stabiliser la monocouche de MoS2. L'interface est métallique en raisonde la présence sur le niveau de Fermi d'états d du Mo. Elle présente une barrière Schottky de 0.3 eV et une probabilité tunnel pour les électrons élevée. Enfin le dernier chapitre constitue une synthèse des derniers résultats et la présentation de quelques perspectives
In this thesis we mainly use the density functional tight-binding method (DFTB) to investigate the effect of high pressure on carbon nanotubes (CNTs). We start by investigating the collapse behavior of individualized CNTs, either empty or filled with water and carbon dioxide molecules. Then we study the collapse process of bundled few-wall (double, triple wall) carbon nanotubes as the function of pressure combining theoretical and experimental studies. Afterwards, we investigate the electronic and magnetic properties of a monolayer MoS2 on the Ni(111) surface with accounting for van der Waals interactions by the density functional theory (DFT). The manuscript is structured in 7 chapters and the following paragraphs summarize the content by chapter of this document.Chapter 1 is our introduction of this thesis, including the motivation and background of our topic as well as our important findings and results. Chapter 2 introduces the main concepts and definitions of CNTs. Then we describe the electronic properties of CNTs as well graphene as a comparison. Chapter 3 consists of the theoretical framework used for our study. Firstly, a short introduction of Density Functional Theory (DFT) is presented. Next we list two mainly used exchange-correlation functions in DFT, then followed by an overview of van der Waals functions which normal DFT cannot account for. Finally, we briefly introduces the Density Functional Tight-Binding method (DFTB) which we use for our CNTs modeling simulation.In chapter 4, we present simulations of the collapse under hydrostatic pressure of carbon nanotubes containing either water or carbon dioxide. We show that the molecules inside the tube alter the dynamics of the collapse process, providing either mechanical support and increasing the collapse pressure, or reducing mechanical stability. At the same time the nanotube acts as a nanoanvil, and the confinement leads to the nanostructuring of the molecules inside the collapsed tube. In this way, depending on the pressure and on the concentration of water or carbon dioxide inside the nanotube, we observe the formation of 1D molecular chains, 2D nanoribbons, and even molecular single and multi-wall nanotubes. For the perfect empty CNTs, collapse behavior theoretically is barely affected by the PTM environment under high pressure but only mainly is determined by the CNTs diameter. Our simulation using DFTB method gives good agreement both for the d dependence predicted by continuum mechanics models and for the deviation at small d which is at least partly due to the atomistic nature of the carbon nanotubes. In chapter 5, we present a theoretical study of the collapse process of single-, double and triple-wall CNTs as a function of pressure. Our theoretical simulations were performed using DFTB for inner tube diameters ranging from 0.6 nm to 3.3 nm. When the walls are separated by the graphitic distance, we show that the radial collapse pressure, Pc, is mainly determined by the diameter of the innermost tube, din and its value significantly deviates from the usual Pcdin-3 Lévy-Carrier law. A modified expression, Pcdin3= (1- 2/din2) with  and  numerical parameters is proposed. In chapter 6 we investigate the electronic and magnetic properties of a monolayer of MoS2 deposited on a Ni(111) surface using DFT method. Accounting for van der Waals interactions is found to be essential to stabilize the chemisorbed MoS2 monolayer. The interface is metallic due to Mo d states positioned at the Fermi energy, with a Schottky barrier of 0.3 eV and a high tunneling probability for electrons. Small magnetic moments are induced on Mo and S atoms, while we measure a significant demagnetization of the Ni layer at the interface. Finally the last chapter synthesizes the main results of this work presenting also some perspectives

Solar energy is by far the most abundant renewable resource available to mankind. However, it is diffused and intermittent, and often geographically separated from that of the production results in underwhelming utilization of this resource. Inspired by photosynthesis, various efforts were made to store solar energy in form of chemical bonds than can be used when the sun is not shining. A promising approach is to produce hydrogen, a carbon-neutral energy carrier is via water splitting which requires electrocatalysts to accelerate the two half-cell reactions, hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The state-of-art catalysts used for HER is Pt and for OER is IrO2/RuO2 that are prohibitively expensive. We have developed new synthesis methodologies for various earth-abundant electrocatalysts supported heteroatom-doped carbon nanostructures and exploited for water splitting. An in-situ solid state route was developed to integrate ruthenium nanoparticles with N-doped graphene sheets which exhibited an HER activity rivalling state-of-art Pt/C over a wide pH range. In order to find further cost-effective materials, we sought inspiration from NiFe-hydrogenase (the most efficient catalyst for HER) to develop a general solid state method for bimetallic MFe@ N-doped carbon core-shell nanostructures (M = Ni, Cu, Co, Zn, Mn) as efficient total water splitting catalyst. Thereafter, a new, phosphine-free, solid state method to hybridize Co2P with N, P co-doped CNTs was developed which could also be extended to synthesize Fe2P, Ni2P and Cu3P. Moreover, glucose oxidation was attempted as a possible replacement for the kinetically sluggish OER half-cell reaction, wherein Co2P/N, P-CNTs were demonstrated to be an efficient non-enzymatic glucose sensor for the first time. Thereafter, Co-imidazolate frameworks (ZIF-67) were transformed into hierarchal Co-N-Se nanosheets via a simple selenization method. Investigations were carried out to establish a structure-property correlation between the nanostructures evolved over various interval of time along with their OER activity. Finally, an in-situ strategy was developed to hybridize N-doped graphitic carbon seets with Ni and MoxC (Mo2C and MoC) nanoparticles which exhibited resilient HER activity besides effectively accelerating OER, thereby resulting in overall water splitting that can be attributed to favorable electronic modulation between various strongly coupled components.

Layered metal sulfides MoS2 and WS2 exhibit highly anisotropic surface chemistry. Adsorption of molecules is stronger on the atomic layer edges than on atomic planes. The edges are catalytically active in the petroleum hydrodesulfurization, while the layer planes are inert. Dispersing MoS2 and WS2 on the nanometer scale can also lead to the onset of photocatalytic properties due to the bandgap tuning by quantum confinement. In this work, we aim at determining how the adsorption on surface sites is altered for the nanoparticles compared to the bulk sulfides (micron-sized particles). A comparative study of the MoS2 and WS2 nanoparticles and bulk materials is done by attempting the adsorption of small molecules (N2, CO, acetone, and acetonitrile) to probe the surface sites. MoS2 and WS2 nanoparticles were synthesized by thermal decomposition of the metal hexacarbonyls in presence of sulfur in high-boiling solvents. The size range is 5-30 nm from Transmission Electron Microscopy. Transmission Infrared Spectroscopy was used to monitor the spectra of the probe molecules. A dedicated experimental setup has been constructed that consists of a high-vacuum chamber with a base pressure of 5×10-7 Torr. At the lowest achievable temperature of the sample (-145°C), N2, CO, and acetone were found to not adsorb strongly enough to be retained in vacuum on these materials. Acetonitrile was found to adsorb on these materials at -145°C and to desorb between -90°C and -50°C. The nanomaterial samples adsorbed significantly more acetonitrile than the corresponding bulk sulfides, as judged by the infrared signals intensity. Qualitatively, adsorbed acetonitrile species on nanodispersed and bulk sulfides are the same. It is likely that most of the adsorbed acetonitrile observed is physisorbed as ice or adsorbed on the sulfur-terminated terraces. At the final stages of desorprtion, distinctly different adsorbed species are seen whose CN stretching IR bands are shifted to higher frequencies. It is likely that these minority species are at monolayer or submonolayer coverages. The exact nature of the species requires further studies.
Department of Chemistry

碩士
國立中央大學
化學學系
106
Transition metal oxides and Transition-metal dichalcogenides as anode materials in lithium ion batteries have attracted tremendous attention because of their high theoretical capacities compared with commercial graphite. However, the large volume expansion during the charge-discharge process leads to low electrical conductivities. In first part, we design a tubular nanocomposite of CoO@CMK-9 to overcome this problem. A three-dimensional (3-D) hollow-type ordered mesoporous carbon (CMK-9) could not only provide enough space during the Li+ insertion-extraction process, but also increase the electrical conductivity. CoO is regarded as one of the most promising anode material for lithium ion batteries (LIBs), due to its high theoretical capacity (715 mAh/g), natural abundance, and low cost. CoO@CMK-9 delivers a reversible capacity of 828 mAh/g after 200 cycles at a current density of 100 mAh/g with an outstanding rate performance. The CoO@CMK-9 nanocomposite is expected to have high specific capacity and good cycling performance. In second part, we design a novel structured SnO2/MoS2@CMK-9, MoS2 is a graphene-like layered structure, Mo is sandwiched between two S layers. The atoms in the layers are bound strongly by covalent bonds, while the adjacent layers interact by weak van der Waals forces. MoS2 nanosheets can be easily restacked together during charge–discharge processes. To solve this problem, we add SnO2 nanoparticles which can avoid to restack of MoS2 nanosheets. SnO2/MoS2@CMK-9 demonstrate an excellent Li-storage performance as an anode of LIBs, deliver a high reversible charge capacity of 782 mAh/g after 50 cycles at a current density of 100 mAh/g.

No
Here we report a hierarchical composite structure composed of few-layers molybdenum disulfide nanosheets supported by vertical graphene on conductive carbon cloth (MDNS/VG/CC) for high-performance electrochemical hydrogen evolution reaction (HER). In the fabrication, 3D vertical graphene is first prepared on carbon cloth by a micro-wave plasma enhanced chemical vapor deposition (MPCVD) and then few-layers MoS2 nanosheets are in-situ synthesized on the surface of the vertical graphene through a simple hydrothermal reaction. This integrated catalyst exhibits an excellent HER electrocatalytic activity including an onset potential of 50 mV, an overpotential at 10 mA cm(-2) (eta(10)) of 78 mV, a Tafel slop of 53 mV dec(-1), and an excellent cycling stability in acid solution. The excellent catalytic performance can be ascribed to the abundant active edges provided by the vertical MoS2 nanosheets, as well as the effective electron transport route provided by the graphene arrays on the conductive substrate. Moreover, the vertical graphene offers robust anchor sites for MoS2 nanosheets and appropriate intervals for electrolyte infiltration. This not only benefits hydrogen convection and release but also avoids the damaging or restacking of catalyst in electrochemical processes.
This work was financially supported by the National Natural Science Foundation of China (Grant nos. 61176007, 51372213, and 51402343).

In conventional tribological experiments that study friction and wear behavior of materials, the contact interface is hidden by the contacting bodies. The physical or chemical phenomena taking place at the interface must then be examined through intermittent tests. These kinds of postmortem studies have remained speculative and model based. The inadequacy of such analysis has long been recognized. For a fundamental understanding of interfacial phenomena, it is important to study interactions in real-time. The present work attempts to overcome this hidden-interface problem by developing a tribometer using optically transparent surfaces which can carry out real-time tribological experiments under a microscope equipped with a Raman spectrometer. Such a micro-Raman system enables combined optical imaging capability with chemical mapping and is consequently a promising tool for in situ studies in tribology. Chapter 2 describes the development of a novel in situ total internal reflection (TIR) Raman tribometery, a technique based on TIR Raman spectroscopy combined with tribological experiments. The in situ TIR-Raman tribometer test rig is based on a ball-on-flat geometry. The rotating ball is immersed in an oil bath and carries a film of lubricant while rotating as it rubs against a flat (transparent) surface. Raman spectra of the lubricant are recorded from the contact region through the transparent window as a function of load, time, and velocity. A unique advantage of the TIR technique is that the sample can be analyzed from a known depth beneath the interface using evanescent waves. The capabilities of this TIR Raman tribometer have been demonstrated by carrying out experiments with known solid lubricant material molybdenum disulfide (MoS2). MoS2 is known for its solid lubricant properties. Nanoparticles of MoS2 are used as an anti- wear additive in engine oil. The commissioning of the tribometer rig was carried out using MoS2 nanoparticles to lubricate a steel-steel contact. Before carrying out in situ Raman tribometry on MoS2 nanoparticles, a set of characteristic friction and wear data was obtained from MoS2 nanoparticle-lubricated steel- steel contact (chapter 3) and compared with the data obtained from a commercial tribometer. In addition, friction characteristics of dry MoS2 and MoS2- hexadecane lubricated steel-steel contact were studied as a function of temperature. The friction in the dry particle lubrication was found to increase with temperature while the friction in wet condition was found to decrease with increasing temperature. Micro-Raman and FTIR spectroscopy are used to explore the roles of environmental moisture and chemical degradation of oil on the formation of antifriction films on the steel substrate. Ex situ optical and Raman analysis revealed the formation of an anti-friction film on the steel substrate. To understand the underlying mechanism of nanoparticle lubrication, in situ Raman tribometry was performed and results are presented in Chapter 4. By combining in situ optical imaging and Raman spectroscopy, the sliding history in friction-induced material transfer of dry 2H-MoS2 particles in a sheared contact was studied. Video images in contact showed the fragmentation of lubricant particles and build-up of a transfer film. Contact imaging was used to measure the speed of fragmented particles in the contact region. Total internal reflection (TIR) Raman spectroscopy was used to follow the build-up of the MoS2 transfer film. The combination of in situ and ex-situ analysis of the mating bodies was used to understand the mechanism of transfer film formation in the early stages of sliding contact. Application of in situ TIR Raman tribometry for the study of liquid lubricants was demonstrated by using PAO to lubricate SF10 glass – silica contact and results are discussed in Chapter 5. It is well established that under high shear rates, synthetic base oils undergo shear thinning. Earlier studies of shear thinning relied mainly on viscosity measurements from which it is not possible to obtain information on molecular alignments or ordering. In the present study, TIR Raman spectra were used to estimate the thickness of the lubricant film under sliding conditions and polarized Raman data was used to study the alignment of molecules during shear thinning. The experimentally obtained film thickness data was superposed with theoretical calculations and a transition from Newtonian to non-Newtonian behavior was observed at high shear rates. Also, the effect of additive molecules on the shear thinning behavior of poly alpha olefin lubricant was studied. The in situ TIR Raman tribometer is a powerful tool to detect the physiochemical changes lubricants undergo at the hidden interface under sliding conditions. The capability of this technique in enabling tribological processes to be observed dynamically in real time with concomitant chemical changes at the interface has the potential to make it an indispensable tool in fundamental studies of tribological interactions. The application of total internal reflection resulted in significant signal enhancement which makes the technique developed in this study an important addition to the already available ones for future tribological studies. The information and insight generated in a range of tribological phenomena taking place at the hidden interface of contact will be useful in developing new lubricant materials.

This thesis deals with the research work carried out on the properties and applications such as GaN nanoparticles, Graphene etc. Chapter 1 of the thesis gives introduction to nanomaterials and various aspects of the thesis. Chapter 2 of the thesis describes the synthesis of GaN nanocrystals and their use as white light sources and as room temperature gas sensors. It also discusses negative differential resistance above room temperature exhibited by GaN. Electroluminescence from GaN-polymer heterojunction forms the last section of this chapter. Chapter 3 demonstrates the role of defect concentration on the photodetecting properties of ZnO nanorods with different defects prepared at different temperatures. Chapter 4 presents remarkable infrared and ultraviolet photodetector properties of reduced graphene oxide and graphene nanoribbons. Chapter 5 presents the infrared detecting properties of graphene-like few-layer MoS2. The summary of the thesis is given at the end of the thesis.

This thesis deals with the research work carried out on the properties and applications such as GaN nanoparticles, Graphene etc. Chapter 1 of the thesis gives introduction to nanomaterials and various aspects of the thesis. Chapter 2 of the thesis describes the synthesis of GaN nanocrystals and their use as white light sources and as room temperature gas sensors. It also discusses negative differential resistance above room temperature exhibited by GaN. Electroluminescence from GaN-polymer heterojunction forms the last section of this chapter. Chapter 3 demonstrates the role of defect concentration on the photodetecting properties of ZnO nanorods with different defects prepared at different temperatures. Chapter 4 presents remarkable infrared and ultraviolet photodetector properties of reduced graphene oxide and graphene nanoribbons. Chapter 5 presents the infrared detecting properties of graphene-like few-layer MoS2. The summary of the thesis is given at the end of the thesis.

Lightweight, flexible, and easy-to-integrate solutions are in great demand in electronic devices. The present work deals with the preparation of Poly dimethyl siloxane (PDMS) based nanocomposite for suppressing electromagnetic interference (EMI). This work is broadly divided into five chapters. The first chapter discusses the state-of-the-art literature on polymeric nanocomposites in general and PDMS-based composites in particular for EMI shielding applications. The second chapter discusses the materials and methods used for the preparation of nanocomposite in this study. The third chapter discusses the synthesis and characterization of MoO3-MWCNTs conjugates and their composites with PDMS. The bulk electrical conductivity and the EMI shielding performance of the nanocomposites are discussed in this chapter. The challenges associated with the curing of PDMS are also discussed in this chapter. This filler system exhibited shielding effectiveness of SET ca. 25 dB for a 1 mm thick sample. The fourth chapter highlights the synthesis and preparation of hybrid fillers consisting of carbonaceous fillers such as rGO and MWCNT and MoS2 using a hydrothermal technique. When incorporated in PDMS and cured using condensation curing, the composites showed SE of ca. 25 dB for a 1 mm thick sample. In the last chapter, the EMI shielding performance of multi-layered stacking of previously prepared sheets was evaluated. The composite with the best configuration showed SET up to 40 dB for a 3 mm thick sample. In summary, two different filler systems were explored in this thesis for the efficient absorption of EM waves. In this thesis, two different crosslinking mechanisms (addition and condensation curing) were explored based on the chemistry of the filler system. The composite was further characterized for AC conductivity, EMI shielding and UV blocking characteristics.
Momentive Performance Materials PVT. LTD. and CII

碩士
東海大學
化學系
106
Hydrogen is considered a kind of energy fuels of cleanliness and usefulness. Hydrogen burning is the process of water transformation after releasing energy without pollution.Zero carbon emission can be acieved. However, Pt is too scarce and expensive to utilize widely. Therefore, this study is developing low cost and highly efficient catalyst for hydrogen evolution application in photocatalytic decomposition of water. In this project, we successfully synthesized core-shell structure Au@Ag nanoparticles and loaded it with the MoS3/rGO. To form a photocatalytic composite, we chose the ErY as a photosensor which SPR is similar to the core-shell Au@Ag nanoparticles.Because of Surface Plasmon Resonance, photon effects greatly on the surface that improves quantum conversion efficiency and photocatalytic activity. Besides, as the concentration of ammonium tetrathiomolybdate ((NH4)2MoS4 ) increased, the amount of hydrogen production by the MoS3/rGO composite also increased.However, there is non the same phenomenon the amount of the hydrogen production by MoS3/Au@Ag/rGO composite.We might predict that the coverage of gold and silver core-shell nanoparticles reduce the absorption of visible light because of the excessive load concentration of (NH4)2MoS4. When the concentration of (NH4)2MoS4 is 3mM, the amount of hydrogen producs most highly by the MoS3/Au@Ag/rGO , and the MoS3/rGO with the same loading concentration increases 290% of the hydrogen production. We also do a lot of control experiments to verify the role of each material in the composite. To support the consequence, fluorescence spectrometer, single wavelength test and photocurrent experiments are used. We also do the composite long term stability test. Based on the above results, we discussed the photocatalytic hydrogen production mechanism of MoS3/Au@Ag/rGO.