Philosophiae Doctor - PhD / Transition metal oxides magneli phases present crystallographic shear structure which is of great interest in multiple applications because of their wide range of valence, which is exhibited by the transition metals. The latter affect chemical and physical properties of the oxides. Amongst them we have nanostructures VO2 system of V and O components which are studied including chemical and physical reactions based on non-equilibrium thermodynamics. Due to their structural classes of corundum, rocksalt, wurtzite, spinel, perovskite, rutile, and layer structure, these oxides are generally used as catalytic materials which are prepared by common methods under mild conditions presenting distortion or defects in the case of VO2. Existence of an intermediate phase is proved using an x-ray thermodiffraction experiment providing structural information as the nanoparticles are heated. Potential application as gas sensing device has been the first time obtained due to the high surface to volume ratio, and good crystallinity, purity of the material and presence of suitable nucleating defects sites due to its n-type semiconductor behavior. In addition, annealing effect on nanostructures VO2 nanobelts shows a preferential gas reductant of Ar comparing to the N2 gas. Also, the hysteresis loop shows that there is strong size dependence to annealing treatment on our samples. This is of great interest in the need of obtaining high stable and durable material for Mott insulator transistor and Gas sensor device at room temperature.

Under specific conditions short peptides modified with an N-terminal fluorenyl-9-methoxycarbonyl (Fmoc) group can self-assemble into hydrogel scaffolds similar in properties to the natural extracellular matrix. Fmoc-diphenylalanine (Fmoc-FF) for instance, has been shown to form hydrogels at physiological pH that have the ability to support 2D and 3D cell culture. The aim of this investigation is to provide further understanding of the self-assembly mechanism of such systems in order to progress towards the establishment of design rules for the preparation of scaffolds with tuneable properties.First, Fmoc-dipeptides composed of a combination of hydrophobic aromatic residues phenylalanine (F) and glycine (G) were studied with a particular emphasis on the effect of pH variations. The systems were investigated in order to assess what influence the position of such residues in the peptide sequence had on the physical properties of the molecules, and what impact the chemical structure had on the self-assembly behaviour and the gelation properties of the materials. Subsequently, phenylalanine was replaced by leucine (L), a non-aromatic amino acid that had the same relative hydrophobicity in order to determine whether the self-assembly of such molecules is driven by aromatic interactions or hydrophobic effects.Using potentiometry, the behaviour of the systems in solution has been investigated, revealing that they were all characterised by pKa shifts of up to six units above the theoretical values. Fmoc-FF exhibited two transitions whereas the other Fmoc-dipeptides only displayed one. These transitions were found to coincide with the formation of distinct self-assembled structures with differing molecular conformations and properties that were characterised using transmission electron microscopy, infrared and fluorescence spectroscopy, X-ray scattering and shear rheometry.π-stacking of the aromatic moieties was thought to be the driving force of the self-assembly mechanism, generating dimers that corresponded to the building blocks of the supramolecular structures formed. On the other hand, the peptide components were stabilised via hydrogen bonding and could form antiparallel β-sheets depending on the amino acid sequence and the associated influence on the rigidity of the molecules. Below their (first) apparent pKa transition, Fmoc-FF, Fmoc-LL, Fmoc-FG, Fmoc-LG and Fmoc-GG formed hydrogels, with the mechanical properties and stability varying depending on the amino acid sequence. Fmoc-FF and Fmoc-LL exhibited the lowest storage modulus values (G′ ~ 0.5–5 Pa) of the studied systems while Fmoc-LG displayed the highest (G′ ~ 1000–2100 Pa). Fmoc-FG and Fmoc-LG had the peculiarity of being obtained upon heating and where found to be particularly stable, as opposed to Fmoc-GG gels which showed a tendency to crystallise. On the microscopic scale, these gels were all associated with the presence of entangled fibrillar networks of different size and morphology, which in some cases could self-assemble further through a lamellar organisation. Again, Fmoc-FG and Fmoc-LG distinguished from the other systems as they were the only Fmoc-dipeptides to show a supramolecular chirality in the form of twisted ribbons under specific pH conditions. In contrast, Fmoc-GF and Fmoc-GL did not form hydrogels below their apparent pKa due to the formation of sheet-like and spherical structures respectively.

Nanoscale, conductive wires fabricated from organic molecules have attracted considerable attention in recent years due to their anticipated applications in the next generation of optical and electronic devices. Such highly ordered 1D nanostructures could be made from a number of routes. One route of particular interest is to self-assemble the wires from biomolecules due to the wide range of assembly methods that can be adapted from nature. For example, biomolecules with aromatic motifs can be self-assembled so that good π-π stacking is achieved in the resultant nanostructure. An additional advantage of using biomolecules is that it enables the interface of the electronic materials with biological systems, which is important for many applications, including nerve cell communication and artificial photosynthesis. In this study, nanowires were prepared by the molecular self-assembly of oligopeptides that were coupled to aromatic components. In order to achieve charge transport though the nanowires, it was imperative that the aromatic components were arranged so that there was π-π stacking with very few structural defects. Therefore, enzymes were used to control the formation of the hydogelators which subsequently self-assembled to produce nanowire networks. Two main systems were studied in this thesis.In the first system, hydrogelators were produced from aromatic peptide amphiphiles via the enzymatic hydrolysis of the methyl ester of fluorenylmethoxycarbonyl (Fmoc)-di/tripeptides. These hydrogelators formed nanostructures due to π-π stacking between the Fmoc groups and H-bonding between the peptides. The nanostructures in turn produced macroscale gel networks. The nanostructures were analyzed by wide angle X-ray diffraction and fluorescence spectroscopy. A combination of Fourier transform infra-red (FTIR), Transmission Electron Microscopy (TEM), Cryo-TEM, and Atomic Force Microscopy (AFM) was used to characterize the networks. The charge transport properties of the dried networks were studied using impedance spectroscopy. Fmoc-L₃ was found to assemble into nanotubes whose walls consisted of 3 self-assembled layers and possessed inner and outer diameters of ~ 9 nm and ~ 18 nm, respectively. The Fmoc-L₃ networks were structurally stabile and were electronically conductive under a vacuum. The sheet resistance of the peptide networks increased with relative humidity due to the increasing ionic conductivity. The resistance of the networks was 0.1 MΩ/sq in air and 500 MΩ/sq in vacuum (pressure: 1.03 mbar) at room temperature. The networks had a band gap of between 1 to 4 eV as measured by UV-Vis spectroscopy and the temperature-impedance studies. Possible routes for aligning the Fmoc-L3 networks were studied in an attempt to improve their conductivity in one direction. In particular, the peptides were assembled under an electric field (0 to 3.75 kV/cm). Random networks were produced at low field strengths, whereas a degree of alignment was obtained at a field strength of 3.75 kV/cm. The conductivity of the aligned networks in the direction of alignment was a factor of three times higher than that of the random networks.The second system studied was Fmoc-dipeptide-OMe hydrogels produced by the enzymatic condensation of an Fmoc-amino acid and an amino acid ester. Preliminary results found that Fmoc-SF-OMe assembled into nanosheets, nanoribbons and spherulites, depending on the temperature at which self-assembly occurred. The Fmoc-XY-OMe films possessed an extremely high resistance (1012 Ω).

This study presents a numerical technique that enables exact treatment of all boundary conditions including those that are given on the interface boundary of two distinct media. This interface boundary conditions for Poisson equation are formulated as equality of the physical field and fluxes across the interface boundary. In this work first, the range of physical and geometric parameters which allow the applicability of the meshfree method with distance fields are tested and compared with analytical solution. Second, it investigates how the solution error depends on the ratio of B-spline support and thickness of the interface layer. Further, this study also concentrates on developing improved computational tools like 1D integration and modification of distance fields for analysis of diffusion concentration in heterogeneous material with high contrast of physical and geometrical properties. These improved computational tools for meshfree method with distance fields improve the accuracy of solution and decreases the computational time. Finally, these improved tools are used to solve a 2D problem for analysis of diffusion concentration and the results are compared to FEM solution to show that the improved tools yield computationally better results.

Nanoscience dominates almost all areas of science and technology in the 21st century. Nanoparticles are of fundamental interest since they possess unique size dependent properties (optical, electrical, mechanical, chemical, magnetic etc.), which are quite different from the bulk and the atomic state. The research work presented in the thesis is on the preparation, characterization and studies on Ir, Os and graphene oxide-based systems. Interconnected Ir and Os nanochains are prepared under environmentally friendly conditions in aqueous media and subsequently used as substrates for surface enhanced Raman scaterring studies and also as electrocatalysts for oxygen reduction and formaldehyde oxidation. Ir and IrOx nanostructures are prepared using borohydride at different temperatures. The nature of interaction of heme proteins with IrOx is studied using spectroscopic techniques. Electrochemical studies on reduced graphene oxide include sensing of biomolecules with high sensitivity and oxygen reduction reaction (ORR) in aqueous alkaline medium. rGO is also used as support for anchoring Ir nanoparticles and the catalyst is used for the oxidation of benzyl amines to corresponding imines. The thesis is divided in to seven chapters and details are given below. Chapter 1 gives an introduction about the synthetic strategies and properties of metal nanostructures. This is followed by literature survey on Ir, Os and graphene oxide-based systems relevant to the present study. Aim and scope of the present investigation is given at the end. Chapter 2 discusses the experimental procedures and characterization techniques used in the present study. Chapter 3 involves the preparation, characterization and studies on interconnected Ir nanochains. Assemblies of small sized nanoparticles forming network-like structures have attracted enormous interest and different metal nanoassemblies have been reported using different procedures. Ir3+ reduction is kinetically not a very favourable process and hence there are not many attempts to synthesize Ir-based nanostructures. Assemblies of interconnected Ir nanoparticles have been synthesized in the present studies using borohydride as reducing agent and ascorbic acid as capping agent, at high temperatures. Polyfunctional capping molecules such as ascorbic acid and vitamin P play important role for the formation of network- like Ir nanostructures. Optical properties of the networks are probed using UV-Vis spectroscopy and evolution of coupled plasmon of Ir nanochains at 418 nm (figure 1) is observed. The nanochains are used as substrates for SERS studies while the catalytic activity is followed for the reduction of nitroaromatics. Electrocatalytic activity of Ir nanochains is exemplified using oxygen reduction and formaldehyde oxidation. Ir nanochains show better electrocatalytic activities than nanoparticles as shown in figure 2. Figure 1. Time dependent UV-Vis absorption spectra of Ir nanoparticles recorded at various time intervals of (a) 5; (b) 15; (c) 30 and (d) 60 minutes of reduction of Ir3+ using borohydride and the corresponding TEM images. Figure 2. Polarization curves for oxygen reduction on (i) Ir nanochains and (ii) Ir nanoparticles in (A) 0.5 M H2SO4 and (B) 0.1 M KOH at a scan rate of 0.005 V/s. Rotation speed used is 1000 rpm. Chapter 4 discusses the preparation of Ir and IrOx using borohydride. The reaction temperature determines the product. Various physicochemical, microscopic and spectroscopic techniques have been used to understand the evolution of nanostructures. Borohydride reduces Ir3+ at high temperatures to form high surface area foams, while at 25oC, it results in an alkaline environment that helps in the hydrolysis of the Ir precursor to form IrOx nanoparticles. Porous IrOx is formed when Ir foams are annealed at high temperatures. Water oxidation has been demonstrated using IrOx nanoparticles and foams. Biocompatibility of IrOx is used to study the nature of interaction of heme proteins and the formation of bioconjugates using spectroscopic techniques. IrOx forms bioconjugates with substantial changes observed in secondary and tertiary structures of proteins. Chapter 5 explores the synthesis of interconnected ultrafine Os nanoclusters and the nanostructured materials are used as SERS substrates. Os nanochains are prepared under environmentally friendly conditions using polyfunctional molecules like ascorbic acid and vitamin P as both reducing agent and capping agent in aqueous media. Small sized (1-1.5 nm) Os nanoparticles spontaneously self-assemble to form clusters of few tens of nm that in turn self-organize to form branched nanochains of several microns in size. The as-formed nanochains show surface plasmon absorption in the visible region 540 nm which make them active substrates for surface enhanced Raman scattering (SERS) studies. High SERS activity is observed for fluorescent analyte, rhodamine 6G and non-fluorescent analyte, mercaptopyridine, with different laser excitation sources. Efficient energy transfer from fluorescent R6G dye to Os nanochains is observed based on steady state and time resolved fluorescence measurements.Figure 3. (I) Time dependent UV-Vis absorption spectra of Os nanochains recorded at different time intervals of (a) 5; (b) 7; (c) 15; (d) 30 and (e) 60 minutes. Inset shows the TEM images of Os nanochains after 60 minutes of reduction. (II) SERS spectra of 4-MPy adsorbed on Os nanochains from (a) 1 mM; (b) 10 µM and (c) 1 µM solutions using 514 nm laser excitation. Chapter 6 discusses the studies based on reduced graphene oxide. Reduced graphene oxide (rGO) is explored as electrodes for simultaneous determination of dopamine (DA), ascorbic acid (AA) and uric acid (UA) at low concentrations useful in medical diagnostics (figure 4A). It is also used as metal-free electrocatalyst for ORR (figure 4B). The use of rGO as a support for anchoring Ir nanoparticles is probed and subsequently the Ir/rGO is used as catalyst for direct aerobic oxidation of benzyl amine derivatives to corresponding imines. Chapter 7 describes the summary of the work and scope for further studies. Appendix 1 discusses the preparation of different Ir nanostructures using simple galvanic displacement reaction on copper foil while appendix 2 describes the preparation of different sized Ir nanoparticles and their electrocatalytic activity towards oxygen reduction reaction

La nano-structuration de matériaux semiconducteurs à grand gap à base de GaN fait l'objet d'un très grand intérêt de par son potentiel pour l'élaboration de composants optoélectroniques innovants émettant dans la gamme spectrale de l’ultraviolet. Le contrôle de la croissance à l'échelle nanométrique doit être ainsi démontré. L'épitaxie sélective ou SAG (Selective Area Growth) étendue au domaine nanométrique (NSAG pour NanoSAG) est un excellent choix pour l'élaboration de nanostructures de semiconducteur. Cette technique consiste en la croissance localisée du matériau sur un substrat partiellement recouvert d'un masque en diélectrique. La NSAG permet l'élaboration d'hétéro-structures en fort désaccord de maille grâce aux mécanismes singuliers de relaxation des contraintes à l'intérieur des nanostructures qui réduisent considérablement la densité de dislocations créées. La première partie de la thèse porte sur la mise en œuvre de l'épitaxie sélective du GaN sur pseudo-substrat de GaN à l'échelle micrométrique puis nanométrique par la technique d'épitaxie en phase vapeur aux organométalliques. Dans un deuxième temps, la NSAG est utilisée pour l'épitaxie de nanostructures de GaN sur substrats de SiC-6H et pseudo-substrat d'AlN. L'influence des conditions de croissance et des motifs définis dans le masque sur la forme des nanostructures est étudiée par la microscopie électronique à balayage et la microscopie à force atomique. Finallement la microscopie électronique en transmission et la nano-diffraction des rayons X par rayonnement synchrotron sont utilisées pour l'analyse structurale approfondie des nanostructures / GaN based wide bandgap semiconductor materials nanostructures have a tremendous potential of applications for innovative optoelectronic devices emitting in the UV region (190-340nm). Thus, the feasibility of the nanoscale growth must be demonstrated. Selective Area Growth (SAG) extended to the nanoscale (NSAG for NanoSAG) is an excellent approach for growing semiconductor nanostructures. This technique is based on localized growth of the material on substrates partially covered by dielectric masks. NSAG technique allows the growth of highly mismatched materials because the density of dislocation is reduced thanks to singular stress relief mechanisms that occur at nanoscale. The first part of the work consists in the implementation of the GaN selective epitaxy on GaN template substrate at the micrometer and nanometer scales by Metal Organic Vapor Phase Epitaxy. In a second time, the NSAG technique is used for the growth of GaN nanostructures on SiC-6H substrate and AlN template substrate. The influence of the growth conditions and the mask pattern on the nanostructures shape is demonstrated using Scattering Electronic Microscopy and Atomic Force Microscopy. Fine structural analysis of the nanostructures is finally investigated using advanced characterization tools such as Transmission Electron Microscopy and X-rays nano-diffraction by synchrotron radiation

Ce travail de thèse porte sur la croissance et sur la caractérisation optique de nanostructures à base d’antimoine sur substrats InP, en vue d’applications dans le domaine des télécommunications optiques. La transition inter-sous-bande est un processus ultrarapide qui permet la modulation de la lumière dans les réseaux de télécommunication optique. Durant cette thèse, une absorption inter-sous-bande dans le proche-infrarouge provenant de puits quantiques Ga0.47In0.53As/AlAs0.56Sb0.44 a été observée pour la première fois au laboratoire. Les analyses par microscopie électronique à effet tunnel sur la face clivée montrent cependant de nombreux déviations à l’idéalité de nos structures : mélange à l’échelle atomique aux interfaces entre GaInAs et AlAsSb, inhomogénéité de l’alliage GaInAs, incorporation non-intentionnel d’antimoine dans le GaInAs. Les puits quantiques InAs/AlAs0.56Sb0.44 sont potentiellement des objets de choix pour la réalisation de composants intersous- bande travaillant à 1,55 μm. Des puits quantiques InAs/AlAs0.56Sb0.44 contraint, exempt de défauts ont été obtenus par croissance assistée par effet surfactant de Sb. En symétrisant la contrainte induite par le dépôt d’InAs par l’insertion de couches nanométriques de AlAs dans les barrières, des multi-puits InAs/AlAs0.56Sb0.44 sans contrainte macroscopique ont été réalisés. L’effet de l’antimoine en surface sur la croissance de structure InAs/GaAs0.51Sb0.49 a également été étudié. En présence d’antimoine sur substrats InP d’orientation (001), le dépôt d’InAs conduit à la formation de puits quantiques. Par contre sur ceux orientés suivant (113)B des boites quantiques sont formées suivant le mode de croissance Volmer-Weber. Ces résultats sont discutés en termes d’effets cinétiques ou énergétiques de l’antimoine en surface. La modification de l’anisotropie de l’énergie de surface induite par l’antimoine permet d’interpréter nos résultats sur substrats (100) et (113) B. / This PhD work presents molecular beam epitaxy growth and optical studies on several Sb-nanostructures on InP substrate, for their potential use in optical telecommunication. Inter-subband transition in Ga0.47In0.53As/AlAs0.56Sb0.44 quantum well is a useful physical process for implementing ultrafast fulloptical modulations. Near-infrared inter-subband transition in this material was achieved and microscopic studies on this structure has revealed that the intermixing at GaInAs/AlAsSb interface, unintentional Sb incorporation in GaInAs layer and the inhomogeneity within GaInAs layer could prevent Ga0.47In0.53As/ AlAs0.56Sb0.44 multiple quantum wells from achieving intersubband transition in 1.55 μm optical telecommunication band. The strained InAs/AlAs0.56Sb0.44 quantum well is another material that has potential use in 1.55 μm full-optical modulation. 2 nm-thick defect-free InAs/AlAs0.56Sb0.44 was obtained under Sb surfactant-mediated growth, and by using strain compensation techniques, InAs/AlAs0.56Sb0.44 multiple quantum wells with zero net-strain were realized. The study of Sb-mediated growth is also carried on to InAs/GaAs0.51Sb0.49 nanostructures. The growths of such structures on InP (001) substrate has led to the formation of flat InAs layer, while high-density InAs/GaAs0.51Sb0.49 quantum dots were obtained on InP (113)B substrates under Volmer-Weber growth mode. We attribute such phenomena to the surfaceorientation dependent surfactant effect of Sb. Emission wavelength close to 2 μm was achieved with only 5 ML of InAs deposition, which makes these quantum dots attractive to InPbased mid-wave applications.

La maîtrise des techniques de fabrication de matériaux nanostructurés a fait émerger ces dernières années de nouvelles problématiques relatives aux transferts thermiques à très courtes échelles d'espace et de temps. L'étude thermique s'effectue alors à partir de l'équation de transport de Boltzmann (ETB) pour les phonons qui sont les principaux porteurs de chaleur dans les semi-conducteurs. Ce travail résout l’ETB par une méthode statistique de type Monte Carlo en suivant le déplacement des phonons dans une nanostructure cristalline (de type nanofilm ou nanofil). On s’intéresse en particulier aux structures poreuses homogènes et avec gradient de porosité, ainsi qu’aux nanofils modulés en diamètre qui offrent des perspectives intéressantes en terme de réduction de conductivité / Since the past decades, progresses in nanomaterials engineering raise new questions about heat transport processes at very short time and space scales. Thermal properties of nanoscaled devices are determined from the resolution of the Boltzmann Transport Equation (BTE) for phonons, which are the main heat carriers in semiconductors. In this study, BTE is solved with a numerical tool based on a statistical method (Monte Carlo) which tracks phonons’ motion in two kinds of nanostructures: nanofilms and nanowires. We focus on the effect of homogeneous and heterogeneous porous materials as well as nanowires with varying diameters. All these devices present interesting prospects regarding thermal conductivity reduction

Zinc oxide and graphene nanostructures are important technological materials because of their unique properties and potential applications in future generation of electronic and sensing devices. This dissertation investigates a brief account of the strategies to grow zinc oxide nanostructures (thin film and nanowire) and graphene, and their applications as enhanced field effect transistors, chemical sensors and transparent flexible electrodes. Nanostructured zinc oxide (ZnO) and low-gallium doped zinc oxide (GZO) thin films were synthesized by a magnetron sputtering process. Zinc oxide nanowires (ZNWs) were grown by a chemical vapor deposition method. Field effect transistors (FETs) of ZnO and GZO thin films and ZNWs were fabricated by standard photo and electron beam lithography processes. Electrical characteristics of these devices were investigated by nondestructive surface cleaning, ultraviolet irradiation treatment at high temperature and under vacuum. GZO thin film transistors showed a mobility of ~5.7 cm 2/ V•s at low operation voltage of ~0.5 V with a sub threshold swing of ~85 mV/decade. Bottom gated FET fabricated from ZNWs exhibit a very high on-to-off ratio (~10 6) and mobility (∼28 cm 2 /V•s). A bottom gated FET showed large hysteresis of ~5.0 to 8.0 V which was significantly reduced to ~1.0 V by the surface treatment process. The results demonstrate charge transport in ZnO nanostructures strongly depends on its surface environmental conditions and can be explained by formation of depletion layer at the surface by various surface states. A nitric oxide (NO) gas sensor using single ZNW, functionalized with Cr nanoparticles was developed. The sensor exhibited average sensitivity of ~46% and a minimum detection limit of ~1.5 ppm for NO gas. The sensor also is selective towards NO gas as demonstrated by a cross sensitivity test with N2, CO and CO2 gases. Graphene film on copper foil was synthesized by chemical vapor deposition method. A hot press lamination process was developed for transferring graphene film to flexible polymer substrate. The graphene/polymer film exhibited a high quality, flexible transparent conductive structure with unique electrical-mechanical properties; ~88.80 % light transmittance and ~1.1742 kΩ/sq sheet resistance. The application of a graphene/polymer film as a flexible and transparent electrode for field emission displays was demonstrated.

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.