This thesis reports the study of single photon sources that emit one infrared wavelength photon at a time, creating cavity quantum electrodynamical effects for applications such as quantum information processing. This work considers two major single photon sources: a) InAs single quantum dots and b) single carbon nanotubes, which both emit in the infrared range. Photonic crystal slabs and photonic crystal waveguides are served as distinctive passive devices with manipulated photonic band-gaps to control the propagating light. A simulation of leaky modes of two-dimensional photonic crystal slabs is introduced to constrain model parameters in the device design. Fullerenes are used as fluorescent material to achieve resonance of a leaky mode with excitation 1492 nm and emission at 1519 nm and to see enhancement of the PL. We include novel characterization techniques and PL measurements to show sharp emission peaks from single quantum dots and successfully couple them to micro-cavities. The strong coupling effect is observed and is amongst the best examples of cavity-dot structures achieved to date. Single-walled carbon nanotubes have shown anti-bunched light emission, thus we systematically study them as another possible candidate of single photon sources. PLE spectra show clear evidence of the existence of excited states, and time evolution measurements reveal the disorder induced diffusion, which separate the tubes into a series of quantum dots. These strongly confined states are concluded as the origin of the possibility that single-walled carbon nanotubes are single photon sources.

This thesis explores how the carrier dynamics within semiconductor nanocrystals can be directly engineered through specific core-shell design. Emphasis is placed on how material characteristics, such as strain or alloying at a core-shell interface, can influence the exciton energies and the recombination dynamics within semiconductor nanocrystals. This study synthesises type-II heterojunction ZnTe/ZnSe core-shell nanocrystals via a diethyl zinc-free synthesis method, producing small size distributions and quantum yields as high as 12%. It was found that the 7% lattice mismatch between the core and shell materials places limitations on the range of structures in which coherent growth is achieved. By developing compositional and strained atomistic core-shell models a variety of physical and optical properties could be simulated and has led to a clear picture of the core-shell architecture to be built. This characterisation provides evidence that the low bulk modulus ZnTe cores are compressed by the higher bulk modulus smaller lattice constant ZnSe shells. Further studies show how strain is manifested in structures with 'sharp' core-shell interfaces and how intentional alloying the interface can influence the growth and exciton energies. A (2-6)-band effective mass model was able to distinguish between the as-grown 'sharp' and 'alloyed' interfaces which indicated that strain accentuates the redshift of the excitonic state whilst reduced strain within an alloyed interface sees a reduced redshift. Single nanocrystal spectroscopy investigations of brightly emitting single graded alloyed nanocrystals and of a size series of commercially available CdSe/ZnS nanocrystals showed almost no fluorescence intermittency (nearly 'non-blinking'). These investigations also identified trion recombination as the main mechanism within the blinking 'off' state. Ultimately this thesis adds to the growing understanding of how specific core-shell architectures manipulate the electronic structure and develops techniques to identify specific material characteristics and how these characteristics influence the physical and optical properties within semiconductor nanocrystals.

The uniquely predictable and controllable binding mechanism of DNA strands has been exploited to construct a vast range of synthetic nanodevices, capable of autonomous motion and computation. This thesis proposes novel ideas for the control and observation of such devices. The first of these proposals hinges on introducing mismatched base pairs into toehold-mediated strand displacement – a fundamental primitive in most dynamic DNA devices and reaction networks. Previous findings that such mismatches can impede strand displacement are extended insofar as it is shown that this impediment is highly dependent on mismatch position. This discovery is examined in detail, both experimentally and through simulations created with a coarse-grained model of DNA. It is shown that this effect allows for kinetic control of strand displacement decoupled from reaction thermodynamics. The second proposal improves upon a previously presented strand displacement scheme, in which two strands perform displacement cooperatively. This scheme is extended to be cascadable, so that the output of one such reaction serves as input to the next. This scheme is implemented in reaction networks capable of performing fundamental calculations on directed graphs. The third proposal is exclusively concerned with a novel observation methodology. This method is based on single-molecule fluorescence microscopy, and uses quantum dots, a fluorescent type of semiconductor nanocrystal, as a label. These quantum dots display a set of characteristics particularly promising for single-molecule studies on the time- and length scales most commonly encountered in DNA nanotechnology. This method is shown to allow for highly precise measurements on static DNA devices. Preliminary data for the observation of a complex dynamic device is also presented.

Quantum mechanics has a long history of helping computer science. For a long time, it provided help only at the hardware level by giving a better understanding of the properties of matter and thus allowing the design of ever smaller and ever more efficient components. For the last few decades, much research has been dedicated to finding whether one can change computer science even more radically by using the principles of quantum mechanics at both the hardware and algorithm levels. This field of research called Quantum Information Processing (QIP) has rapidly seen interesting theoretical developments: it was in particular shown that using superposition of states leads to computers that could outperform classical ones. The experimental side of QIP however lags far behind as it requires an unprecedented amount of control and understanding of quantum systems. Much effort is spent on finding which particular systems would provide the best physical implementation of QIP concepts. Because of their nearly endless versatility and the high degree of control over their synthesis, organic materials deserve to be assessed as a possible route to quantum computers. This thesis studies the QIP potential of spin degrees of freedom in several such organic compounds. Firstly, a study on low-spin antiferromagnetic rings is presented. It is shown that in this class of molecular nanomagnets the relaxation times are much longer than previously expected and are in particular long enough for up to a few hundred quantum operations to be performed. A detailed study of the relaxation mechanisms is presented and, with it, routes to increasing the phase coherence time further by choosing the suitable temperature, isotopic and chemical substitution or solvent. A study of higher-spin systems is also presented and it is shown that the relaxation mechanisms are essentially the same as in low-spin compounds. The route to multi-qubit system is also investigated: the magnetic properties of several supermolecular assemblies, in particular dimers, are investigated. Coupling between neighbouring nanomagnets is demonstrated and experimental issues are raised concerning the study of the coherent dynamics of dimers. Finally a study of the purely organic compound phenanthrene is reported. In this molecule the magnetic moment does not result from the interactions between several transition metal ions as in molecular nanomagnets but from the photoexcitation of an otherwise diamagnetic molecule. The interest of such a system in terms of QIP is presented and relaxation times and coupling to relevant nuclei are identified.

Tandem solar cells are potentially much more efficient than the silicon solar cells that currently dominate the market but require materials with different bandgaps. This thesis presents work on silicon nanocrystals (Si-NC) embedded in silicon carbide (SiC), which are expected to have a higher bandgap than bulk Si due to quantum confinement, with a view to using them in the top cell of a tandem cell. The strong photoluminescence (PL) of precursor films used to prepare Si-NC in SiC (Si-NC/SiC) was markedly reduced upon Si-NC formation due to simultaneous out-diffusion of hydrogen that passivated dangling bonds. This cannot be reversed by hydrogenation and leads to weak PL that is due to, and limited by, non-paramagnetic defects, with an estimated quantum yield of ≤5×10^-7. Optical interference was identified as a substantial artefact and a method proposed to account for this. Majority carrier transport was found to be Ohmic at all temperatures for a wide range of samples. Hydrogenation decreases dangling bond density and increases conductivity up to 1000 times. The temperature-dependence of conductivity is best described by a combination of extended-state and variable-range hopping transport where the former takes place in the Si nanoclusters. Furthermore, n-type background doping by nitrogen and/or oxygen was identified. In the course of developing processing steps for Si-NC-based tandem cells, a capping layer was developed to prevent oxidation of Si-NC/SiC, and diffusion of boron and phosphorus in nanocrystalline SiC was found to occur via grain boundaries with an activation energy of 5.3±0.4 eV and 4.4±0.7 eV, respectively. Tandem cells with a Si-NC/SiC top cell and bulk Si bottom cell were prepared that exhibited open-circuit voltages V_oc of 900 mV and short-circuit current densities of 0.85 mAcm^-2. Performance was limited by photocurrent collection in the top cell; however, the V_oc obtained demonstrates tandem cell functionality.

The ability to encapsulate linear nanoparticle (NP) chains in scrolled nanosheets is an important advance in the formation of nanocomposites.These nanopeapods (NPPs) exhibit interesting properties that may not be achieved by individual entities. Consequently, to fully exploit the potential of NPPs, the fabrication of NPPs must focus on producing composites with unique combinations of morphologically uniform nanomaterials. Various methods can produce NPPs, but expanding these methods to a wide variety of material combinations can be difficult. Recent work in our group has resulted in the in situ formation of peapod-like structures based on chains of cobalt NPs. Building on this initial success, a more versatile approach has been developed that allows for the capture of a series of preformed NPs in NPP composites. In the following chapters, various synthetic approaches for NPPs of various material combinations will be presented and the key roles of various reaction parameters will be discussed. Also, uniform hexaniobate nanoscrolls were fabricated via a solvothermal method induced by heating up a mixture of TBAOH, hexaniobate crystallites, and oleylamine in toluene. The interlayer spacing of the nanoscrolls was easily tuned by varying the relative amount and chain lengths of the primary alkylamines. To fabricate NPPs, as-synthesized NPs were treated with hexaniobate crystallite in organic mixtures via solvothermal method. During solvothermal treatment, exfoliated hexaniobate nanosheets scroll around highly ordered chains of NPs to produce the target NPP structures in high yield. Reaction mixtures were held at an aging temperature for a few hours to fabricate various new NPPs (Fe3O4@hexaniobate, Ag@hexaniobate, Au@hexaniobate, Au-Fe3O4@hexaniobate, TiO2@hexaniobate, CdS@hexaniobate, CdSe@hexaniobate, and ZnS@hexaniobate). This versatile method was first developed for the fabrication of magnetic peapod nanocomposites with preformed nanoparticles (NPs). This approach is effectively demonstrated on a series of ferrite NPs (≤ 14 nm) where Fe3O4@hexaniobate NPPs are rapidly (~ 6 h) generated in high yield. When NP samples with different sizes are reacted, clear evidence for size selectivity is seen. Magnetic dipolar interactions between ferrite NPs within the Fe3O4@hexaniobate samples leads to a significant rise in coercivity, increasing almost four-fold relative to free particles. Other magnetic ferrites NPPs, MFe2O4@hexaniobate (M = Mn, Co, Ni), can also be prepared. This synthetic approach to nanopeapods is quite versatile and should be readily extendable to other, non-ferrite NPs or NP combinations so that cooperative properties can be exploited while the integrity of the NP assemblies is maintained. Further, this approach demonstrated selectivity by encapsulating NPs according to their size. The use of polydispersed NP systems is also possible and in this case, evidence for size and shape selectivity was observed. This behavior is significant in that it could be exploited in the purification of inhomogeneous NP samples. Other composite materials containing silver and gold NPs are accessible. Partially filled Fe3O4@hexaniobate NPPs were used as templates for the in situ growth of gold to produce the bi-functional Au- Fe3O4@hexaniobate NPPs. Encapsulation of Ag and Au NP chains with a hexaniobate nanoscroll was shifted the surface plasmon resonance to higher wavelengths. In these composites NPs can be incorporated to form NPP structures, decorated on nanosheets before scrolling, or attached to the surfaces of the nanoscrolls. The importance of this advancement is the promise it holds for the design and assembly of active nanocomposites. One can create important combinations of nanomaterials for potential applications in a variety of areas including catalysis, solar conversion, thermoelectrics, and multiferroics.

Estudamos propriedades magnéticas de ligas nano cristalinas de Sm-F e-Co. As ligas foram preparadas por mecano-síntese e posterior tratamento térmico. Como resultado, obtivemos ímãs nanocristalinos de Sm18 (Fe,Co)82 , com Sm(Fe,Co)7 como fase principal. As ligas apresentaram excelentes propriedades magnéticas: remanências relativas Mn/ Ms ~ 0.6 e coercividades na faixa 5-20 kOe, dependendo do teor de Fe nos materiais. Interações magnéticas nas ligas foram estudadas com base nos gráficos ele Henkel. Interpretamos, nestes gráficos, de maneira consistente a influência elas interações e dos estados desmagnetizados. / We studied the magnetic properties of nanocrystalline Sm-Fe-Co alloys. These alloys were prepared by mechanical alloying and subsequent annealing. We obtained nanocrystalline rnagnets of composition Sm18 (Fe, Co )82 , for which the main hard magnetic phase is Sm(Fe, Co)82. The alloys showed excellent magnetic properties: relative remanence Mn/ Ms :2; 0.6 and coercive fields ranging from 5 to 20 k0e, depending upon the amount of Fe present. Henkel plots were used in order to study magnetic interactions in these alloys. The influence of the interactions and the demagnetized state on the Henkel plots was also studied.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O nitreto de boro hexagonal (h-BN) tem uma estrutura cristalina similar ao grafite e é conhecido como um importante material cerâmico com propriedades interessantes, tais como a excelente estabilidade química, boa resistência à corrosão, baixa densidade, alto ponto de fusão e boa condutividade térmica. Estas características fazem do h-BN um candidato atraente para uma ampla gama de aplicações técnicas. Recentemente, muitos estudos têm relatado a preparação de estruturas de nitreto de boro (BN) com morfologias especiais, tais como nanofolhas, nanofios e nanotubos. Este trabalho apresenta uma rota de síntese de nanoestruturas de BN produzidas a partir de boro elementar, nitrato de amônio e hematita como catalisador, em forno tubular pelo método CVD (chemical vapor deposition). O objetivo do trabalho é sintetizar nanoestruturas de nitreto de boro buscando aprimorar suas propriedades magnéticas oriundas do catalisador utilizado na reação. Para isso foram realizadas diferentes sínteses variando-se a concentração de catalisador no material de partida e a duração dos tratamentos térmicos. O estudo das propriedades magnéticas do material tem o intuito de verificar o potencial de aplicação dessas nanoestruturas, principalmente em tratamentos biomédicos como a hipertermia magnética. Estas amostras foram tratadas termicamente em diferentes etapas. A caracterização das amostras foi feita através de espectroscopia de infravermelho (FTIR), espectroscopia Mössbauer, difração de raios X (XRD), magnetômetro de amostra vibrante (VSM), microscopia eletrônica de varredura (MEV) e microscopia eletrônica de transmissão (MET). Através da análise dos resultados obtidos foi possível confirmar a formação do h-BN, e elucidar as propriedades físico-químicas, estruturais e magnéticas das amostras. A partir das imagens de microscopia foi possível comprovar a formação de nanoestruturas de BN com morfologias variadas. Entre as nanoestruturas encontradas estão: nanofolhas, nanofibras, nanofios e nanotubos. Medidas de magnetização e espectroscopia Mössbauer mostraram que amostras com uma maior concentração do catalisador ou submetidas a um tratamento térmico prolongado apresentaram melhor magnetização. Testes de hipertermia magnética mostraram que as amostras que tiverem suas propriedades magnéticas aprimoradas apresentaram um maior potencial para geração de calor. / Hexagonal boron nitride (h-BN) has a crystal structure similar to graphite and it is well known as one important ceramic material with interesting properties, such as excellent chemical stability, good resistance to corrosion, low density, high melting point, and outstanding thermal and electrical properties. These characteristics make h-BN an attractive candidate for a wide range of technical applications. Recently, many studies have been reporting the preparation of nanostructures of boron nitride (BN) with special morphologies, such as nanosheets and nanotubes. This work reports a synthesis of boron nitride nanotubes produced from elemental boron powder, ammonium nitrate and hematite in tubular furnace by CVD (chemical vapor deposition) method. The aim of this work is to synthesize nanostructures of boron nitride seeking to improve their magnetic properties originating from the catalyst used in the reaction. For this different synthesis were carried out varying the catalyst concentration in the starting material and the duration of heat treatment. The magnetic properties of the materials were evaluated to verify the potential application of these nanostructures, especially in biomedical applications such as magnetic hyperthermia. These samples were thermally treated at different stages. The characterization of the samples was carried out by infrared spectroscopy (FTIR), Mössbauer spectroscopy, X-ray diffraction (XRD), vibrating sample magnetometer (VSM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). By analyzing the results it was possible to confirm the formation of h-BN, and to elucidate the physico-chemical, structural and magnetic properties of the samples. From the microscope images it was possible to prove the formation of BN nanostructures with different morphologies, like nanosheets, nanofibers, nanowires and nanotubes. Magnetization measurements and Mössbauer spectroscopy showed that samples with a higher concentration of the catalyst or subjected to prolonged treatment showed better magnetization. Tests have shown that hyperthermia magnetic samples which have enhanced magnetic properties had a greater potential for heat generation.

Titanatos nanoestruturados (TNS) obtidos pelo tratamento hidrotérmico de TiO2 são semicondutores muito estudados por suas propriedades de alta área superficial e capacidade de troca iônica. No entanto, sua estrutura cristalina e a influência das condições de síntese e pós-tratamento ainda são motivos de controvérsia. Neste estudo, TNSs foram produzidos em diversas condições e submetidos a diferentes tipos de tratamento ácido e térmico. Os materiais foram caracterizados por difratometria de raios X (DRX), espectroscopias vibracionais (Raman e FTIR), espectroscopia de refletância difusa (DRS), análise térmica (TG, DTG e DSC), análise textural por adsorção de N2 a 77 K, análise química por ICP-OES, e microscopia eletrônica de transmissão. Acompanhando a transformação hidrotérmica de TiO2 (anatase) nanocristalino obtido em laboratório com o tempo, observou-se que os nanocristais de TiO2 se transformam em estruturas lamelares com formato de folhas entre 3h e 12h. As nanofolhas se enrolam parcial ou totalmente formando nanotubos. A transformação da morfologia é acompanhada por uma transformação de fase de anatase para uma fase titanato lamelar, que se completa entre 12h e 24h. Utilizando TiO2 P25 como precursor, observou-se que as amostras obtidas apresentam alto teor de Na+, que é progressivamente eliminado por lavagens do sólido com H2O ou solução ácida. Quanto menor o pH de equilíbrio da suspensão, menor foi o teor de Na+ até o limite de pH 2, em que esse cátion foi praticamente eliminado. A diminuição do teor de sódio foi acompanhada de aumento da área superficial (BET, 155 e 205 m2.g-1 para pH 9 e 2, respectivamente); aumento do espaço interlamelar; diminuição da cristalinidade; e diminuição do bandgap (3,60 e 3,45 para pH 9 e 2, respectivamente). Em pH 1,5, ocorreu ainda maior aumento do espaço interlamelar e da área superficial (368 m2.g-1) indicando que a troca iônica de Na+ por H3O+ não é unicamente responsável pelas transformações estruturais que ocorrem durante a neutralização de TNSs. A desidratação em baixa temperatura (até 150 °C) sofrida por TNSs acidificados é irreversível, levando à diminuição do espaço interlamelar, e formação de vacâncias de oxigênio responsáveis pela absorção de radiação acima de 420 nm (visível). A transformação de fase de titanato para anatase ocorreu à temperatura ambiente quando a neutralização foi feita com HF; entre 300 e 400 °C quando feita com HCl, HNO3, H2SO4 ou ácido acético; e acima de 600 °C quando usado H3PO4. Foi possível inserir diferentes quantidades de prata em TNS através da suspensão dos sólidos em solução de AgNO3. A reação levou à formação de nanopartículas cristalinas de 3 a 5 nm, contendo prata, na superfície das partículas de TNS. Ag+ foi reduzido a Ag0 pelo tratamento térmico das amostras a 250 °C em presença de H2(g). Essas amostras apresentaram absorção de radiação em todo o espectro visível e menor bandgap (3,06 em amostra contendo 3% de Ag, em massa). Em amostras com pouca quantidade de prata (menos de 0,05% em massa), foram observadas bandas largas de absorção (DRS) de ressonância de plasmon de superfície quando calcinadas a 250 °C em H2(g). / Titanate nanostructures (TNS) obtained by the hydrothermal treatment of TiO2 are extensively studied due to their high surface area and ion-exchange ability. However, their crystal structure and influence of synthesis and post-treatment conditions are still under debate. In this study, TNSs were produced under different synthetic conditions and underwent different types of acid and thermal treatments. The materials were characterized by means of X-ray diffractometry (XRD), vibrational spectroscopy (Raman and FTIR), diffuse reflectance spectroscopy (DRS), thermal analysis (TG, DTG and DSC), textural analysis by N2 adsorption at 77 K, chemical analysis by ICP-OES, and transmission electron microscopy (TEM). Following the hydrothermal transformation of homemade crystalline TiO2 (anatase) with time, we observed that TiO2 nanocrystals change into lamellar sheet-like structures between 3h and 12h. The nanosheets roll up partial or totally, thus forming nanotubes. The morphological transformation is accompanied by a phase transformation from anatase to lamellar titanate, which is completed between 12h and 24h. Using TiO2 P25 as precursor, we observed that as-obtained samples have a high Na+ content, which is progressively removed by washing the solids with H2O or acidic solution. The smaller the suspensions equilibrium pH, the smaller the Na+ content to the limit of pH 2, when the removal of this cation was complete. The decrease in sodium content was followed by an increase in the surface area (BET, 155 and 205 m2.g-1 at pH 9 and 2, respectively); an increase in the interlamellar distance; a decrease in crystallinity; and a decrease in bandgap energy (from 3.60 eV at pH 9 to 3.45 eV at pH 7). After treating at pH 1.5, the interlamellar distance and the surface area (368 m2.g-1) increased further, suggesting that the Na+ to H3O+ ion-exchange is not the only factor in the structural transformations that take place during the acid treatment of TNSs. Acidic TNSs undergo an irreversible dehydration process at low temperature (150 °C). It leads to the decrease of the interlamellar distance and to the formation of oxygen vacancies responsible for the absorption of radiation in the visible range (> 420 nm). The phase transformation of the titanate phase to TiO2 anatase took place at room temperature when the TNS was treated with HF; between 300 and 400 °C for samples neutralized with HCl, HNO3, H2SO4 or acetic acid; and over 600 °C when H3PO4 was used. It was possible to insert different amounts of silver by the immersion of the solids in AgNO3 solution, leading to the formation of nanocrystalline-silver-containing nanoparticles (3 to 5 nm) on the surface of the TNS particles. Ag+ was reduced to Ag0 by heat treating the samples at 250 °C in presence of H2(g). These materials showed absorption of radiation in entire visible spectrum and narrowed bandgap energy (3,06 eV for sample with 3wt% of Ag). Samples containing low amounts of Ag (less than 0,05 wt%) showed a wide surface plasmon resonance band (DRS) when calcined at 250 °C under H2(g).

Titanatos nanoestruturados (TNS) obtidos pelo tratamento hidrotérmico de TiO2 são semicondutores muito estudados por suas propriedades de alta área superficial e capacidade de troca iônica. No entanto, sua estrutura cristalina e a influência das condições de síntese e pós-tratamento ainda são motivos de controvérsia. Neste estudo, TNSs foram produzidos em diversas condições e submetidos a diferentes tipos de tratamento ácido e térmico. Os materiais foram caracterizados por difratometria de raios X (DRX), espectroscopias vibracionais (Raman e FTIR), espectroscopia de refletância difusa (DRS), análise térmica (TG, DTG e DSC), análise textural por adsorção de N2 a 77 K, análise química por ICP-OES, e microscopia eletrônica de transmissão. Acompanhando a transformação hidrotérmica de TiO2 (anatase) nanocristalino obtido em laboratório com o tempo, observou-se que os nanocristais de TiO2 se transformam em estruturas lamelares com formato de folhas entre 3h e 12h. As nanofolhas se enrolam parcial ou totalmente formando nanotubos. A transformação da morfologia é acompanhada por uma transformação de fase de anatase para uma fase titanato lamelar, que se completa entre 12h e 24h. Utilizando TiO2 P25 como precursor, observou-se que as amostras obtidas apresentam alto teor de Na+, que é progressivamente eliminado por lavagens do sólido com H2O ou solução ácida. Quanto menor o pH de equilíbrio da suspensão, menor foi o teor de Na+ até o limite de pH 2, em que esse cátion foi praticamente eliminado. A diminuição do teor de sódio foi acompanhada de aumento da área superficial (BET, 155 e 205 m2.g-1 para pH 9 e 2, respectivamente); aumento do espaço interlamelar; diminuição da cristalinidade; e diminuição do bandgap (3,60 e 3,45 para pH 9 e 2, respectivamente). Em pH 1,5, ocorreu ainda maior aumento do espaço interlamelar e da área superficial (368 m2.g-1) indicando que a troca iônica de Na+ por H3O+ não é unicamente responsável pelas transformações estruturais que ocorrem durante a neutralização de TNSs. A desidratação em baixa temperatura (até 150 °C) sofrida por TNSs acidificados é irreversível, levando à diminuição do espaço interlamelar, e formação de vacâncias de oxigênio responsáveis pela absorção de radiação acima de 420 nm (visível). A transformação de fase de titanato para anatase ocorreu à temperatura ambiente quando a neutralização foi feita com HF; entre 300 e 400 °C quando feita com HCl, HNO3, H2SO4 ou ácido acético; e acima de 600 °C quando usado H3PO4. Foi possível inserir diferentes quantidades de prata em TNS através da suspensão dos sólidos em solução de AgNO3. A reação levou à formação de nanopartículas cristalinas de 3 a 5 nm, contendo prata, na superfície das partículas de TNS. Ag+ foi reduzido a Ag0 pelo tratamento térmico das amostras a 250 °C em presença de H2(g). Essas amostras apresentaram absorção de radiação em todo o espectro visível e menor bandgap (3,06 em amostra contendo 3% de Ag, em massa). Em amostras com pouca quantidade de prata (menos de 0,05% em massa), foram observadas bandas largas de absorção (DRS) de ressonância de plasmon de superfície quando calcinadas a 250 °C em H2(g). / Titanate nanostructures (TNS) obtained by the hydrothermal treatment of TiO2 are extensively studied due to their high surface area and ion-exchange ability. However, their crystal structure and influence of synthesis and post-treatment conditions are still under debate. In this study, TNSs were produced under different synthetic conditions and underwent different types of acid and thermal treatments. The materials were characterized by means of X-ray diffractometry (XRD), vibrational spectroscopy (Raman and FTIR), diffuse reflectance spectroscopy (DRS), thermal analysis (TG, DTG and DSC), textural analysis by N2 adsorption at 77 K, chemical analysis by ICP-OES, and transmission electron microscopy (TEM). Following the hydrothermal transformation of homemade crystalline TiO2 (anatase) with time, we observed that TiO2 nanocrystals change into lamellar sheet-like structures between 3h and 12h. The nanosheets roll up partial or totally, thus forming nanotubes. The morphological transformation is accompanied by a phase transformation from anatase to lamellar titanate, which is completed between 12h and 24h. Using TiO2 P25 as precursor, we observed that as-obtained samples have a high Na+ content, which is progressively removed by washing the solids with H2O or acidic solution. The smaller the suspensions equilibrium pH, the smaller the Na+ content to the limit of pH 2, when the removal of this cation was complete. The decrease in sodium content was followed by an increase in the surface area (BET, 155 and 205 m2.g-1 at pH 9 and 2, respectively); an increase in the interlamellar distance; a decrease in crystallinity; and a decrease in bandgap energy (from 3.60 eV at pH 9 to 3.45 eV at pH 7). After treating at pH 1.5, the interlamellar distance and the surface area (368 m2.g-1) increased further, suggesting that the Na+ to H3O+ ion-exchange is not the only factor in the structural transformations that take place during the acid treatment of TNSs. Acidic TNSs undergo an irreversible dehydration process at low temperature (150 °C). It leads to the decrease of the interlamellar distance and to the formation of oxygen vacancies responsible for the absorption of radiation in the visible range (> 420 nm). The phase transformation of the titanate phase to TiO2 anatase took place at room temperature when the TNS was treated with HF; between 300 and 400 °C for samples neutralized with HCl, HNO3, H2SO4 or acetic acid; and over 600 °C when H3PO4 was used. It was possible to insert different amounts of silver by the immersion of the solids in AgNO3 solution, leading to the formation of nanocrystalline-silver-containing nanoparticles (3 to 5 nm) on the surface of the TNS particles. Ag+ was reduced to Ag0 by heat treating the samples at 250 °C in presence of H2(g). These materials showed absorption of radiation in entire visible spectrum and narrowed bandgap energy (3,06 eV for sample with 3wt% of Ag). Samples containing low amounts of Ag (less than 0,05 wt%) showed a wide surface plasmon resonance band (DRS) when calcined at 250 °C under H2(g).