<p>The understanding of the strengthening mechanisms is crucialboth in the development of new materials with improvedmechanical properties and in the development of better materialmodels in the simulation of industrial processes. The aim ofthis work has been to study different strengthening mechanismsfrom a fundamental point of view that enables the developmentof a general model for the flow stress. Two differentmechanisms namely, solid solution strengthening and grain sizestrengthening have been examined in detail. Analytical modelsproposed in the literature have been critically evaluated withrespect to experimental data from the literature. Two differentexperimental surface techniques, atomic force microscopy (AFM)and electron backscattered diffraction (EBSD) were used tocharacterize the evolving deformation structure at grainboundaries, in an ultra low-carbon (ULC) steel. A numericalmodel was also developed to describe experimental featuresobserved locally at grain boundaries.</p><p>For the case of solid solution strengthening, it is shownthat existing models for solid solution strengthening cannotexplain the observed experimental features in a satisfactoryway. In the case of grain size strengthening it is shown that asimple model seems to give a relatively good description of theexperimental data. Further, the strain hardening in materialsshowing a homogenous yielding, is controlled by grainboundaries at relatively small strains. The experimentalresults from AFM and EBSD, indicate more inhomogenousdeformation behaviour, when the grain size is larger. Bothtechniques, AFM and EBSD, correlate well with each other andcan be used to describe the deformation behaviour both on alocal and global scale. The results from the numerical modelshowed a good qualitative agreement with experimentalresults.</p><p>Another part of this project was directed towards thedevelopment of continuum models that include relevantmicrostructural features. One of the results was the inclusionof the pearlite lamellae spacing in a micromechanically basedFEM-model for the flow stress of ferriticperlitic steels.Moreover a good agreement was achieved between experimentalresults from AFM and FEM calculations using a non-local crystalplasticity theory that incorporates strain gradients in thehardening moduli.</p><p>The main philosophy behind this research has been to combinean evaluation of existing strengthening models, with newexperiments focused on studying the fundamental behaviour ofthe evolving dislocation structure. This combination can thenbe used to draw general conclusions on modelling thestrengthening mechanisms in metals.</p><p><b>Keywords:</b>strengthening mechanisms, flow stress, solidsolution strengthening, grain size strengthening,micromechanical modelling, AFM, EBSD</p>

According to IPCC reports, the greenhouse gas CO2 is responsible for global climate change. Studies show that CO2 concentration reached a level of 400 ppm in 2013, or 40 % above pre-industrial levels. The contribution of CO2 from industrial activity to increasing global CO2 concentrations is widely accepted and points to the need to reduce the emission of this greenhouse gas.One possible combustion technology that shows promise for reducing CO2 emissions is chemical looping combustion (CLC). It is an oxy-fuel technology, but has the advantages of in situ oxygen separation, low NOx emissions and low cost of CO2 emission abatement; it entails the use of an oxygen carrier (OC) to provide oxygen for combusting fuels. OC development is an important task in CLC. Iron based OCs have attracted most research attention in recent years, mainly due to their inexpensive and non-toxic nature. Bi-metal oxide OCs usually impart better CLC performance than mono-metal oxide OCs, one example of which is the introduction of CeO2 as a partially reducible material capable of generating oxygen vacancies that lead to oxygen storage and transfer. In this study, CeO2 was used as an additive to a Fe2O3-based OC and its effect on physical properties, such as morphology, surface area and mechanical strength, was analyzed in detail. The reactivity of OCs is studied using TGA-MS and a bench scale CLC setup. The results show that the reduction reaction at the surface is independent of whether CeO2 is present or not, but after the surface oxygen had been consumed, the OC with CeO2 provided faster oxygen transfer rates from the bulk to the surface to produce better average reaction rates. The OCs after reduction and oxidation were analyzed using XRD and Raman spectroscopy; based on these analytical data, a model for the promoting role of CeO2 is discussed. Furthermore, the reaction kinetics of the OCs were also studied using shrinking core model, the kinetics parameters were obtained and compared. Scale-up of laboratory-scale CLC reactors is another important task necessary to develop an understanding of the potential and efficiencies of CLC. In this study, scaling laws were used as a guide to design and then build two different-sized CLC reactors. Testing of the reactors involved a focus on chemical similarities. Comparisons of the performance of both reactors showed good consistency, thereby validating the scale modeling method and the scale laws for CLC reactors.

he extent of BiInO₃ substitution in the perovskite system xBiInO(₃)-(1 - x)PbTiO₃ and the corresponding raise in the transition temperature were investigated using thermal analysis, dielectric measurements, x-ray diffraction, and electron microscopy. Maximum tetragonal perovskite distortion (c/a = 1.082) was obtained for x = 0.20, with a corresponding Curie temperature of 582°C. Phase-pure tetragonal perovskite was obtained for x less than or equal to 0.25. Compound formation after calcining mixed oxide powders resulted in agglomerated cube-shaped tetragonal perovskite particles, which could be fired to 94.7% of theoretical density (TD). Niobium-modified BIPT ceramics with PT contents of 80% and 85% were found to possess significantly lower dielectric loss at elevated temperatures, making it possible to polarize the materials. Piezoelectric properties were measured for a 1.5 mol% Nb -0.15BI-0.85PT composition with a transition temperature of 542°C; the longitudinal piezoelectric coefficient and coercive field were found to be 60 pC/N and 125 kV/cm, respectively. Compositions of xBiLaO₃-(1 − x)PbTiO₃ over the range 0 < x < 0.225 were calcined and sintered. Dielectric constant with temperature and differential scanning calorimetry measurements were in excellent agreement with respect to a Curie-like tetragonal to cubic transformations starting at 495°C for pure PbTiO₃, shifting to lower temperatures with increasing x. For compositions of x > 0.05, a second higher-temperature (∼600°C) endotherm, and matching dielectric anomaly, were consistently observed, for which there were no structural changes indicated by hot-stage x-ray diffraction. This transformation was interpreted to be similar to a Curie transformation in relaxor ferroelectrics in which localized segregation of B-site cations (below the resolution limit of x-ray diffraction) facilitated ferroelectric behavior.

Made available in DSpace on 2016-06-02T20:36:56Z (GMT). No. of bitstreams: 1 6820.pdf: 31396624 bytes, checksum: baada275d7fcaaaca7447011730791b4 (MD5) Previous issue date: 2015-07-17 / Financiadora de Estudos e Projetos / The tungstates are important compounds and known for their optical properties. In this work, solid solutions with nickel silver tungstate, &#119860;&#119892;2&#8722;2&#119909;&#119873;&#119894;&#119909;&#119882;&#119874;4, compositions (0, 01 &#8804; &#119909; &#8804; 0, 08) were synthesized by the hydrothermal method of microwave to 140 ° C for 1 h, and to assess the influence of &#119873;&#119894;2+ ions in the structural, morphological and photoluminescent of the silver tungstate (&#119860;&#119892;2&#119882;&#119874;4). Materials &#119860;&#119892;2&#8722;2&#119909;&#119873;&#119894;&#119909;&#119882;&#119874;4 (0 &#8804; &#119909; &#8804; 0.08) were characterized by X-ray diffraction (XRD), spectroscopy micro-Raman (MR) and absorption in the Infrared (IR) region. The scanning electron microscopy (SEM) was used for image recording surface of these ceramic oxides, while the energy dispersive X-ray technique (EDS) with mapping of chemical elements, was used to qualitatively determine the chemical composition of the samples. The optical properties were studied by electron spectroscopy in the region of ultraviolet-visible (UV-vis) in which the values of energy band gap (&#119864;&#119892;&#119886;&#119901;) were estimated, and by means of photoemission spectroscopy was studied effect of &#119873;&#119894;2+ ions in photoluminescence (PL) of silver tungstate. The XRD patterns of the single-phase crystallization of all samples in the orthorhombic structure of the silver tungstate and they have indicated a long range structural order. Small changes in network parameters and atomic coordinates, indicate the existence of distortions on the cluster [&#119860;&#119892;&#119874;&#119899;] (&#119899; = 2, 4, 6 and 7) and [&#119882;&#119874;6] and inserting the &#119873;&#119894; atoms in the crystal lattice &#120572;-&#119860;&#119892;2&#119882;&#119874;4. Changes in MR spectra and peak detection regarding &#119873;&#119894; &#8722; &#119874; bond in IR spectra of solid solutions suggest the introduction of &#119873;&#119894; atoms in the &#119860;&#119892;2&#119882;&#119874;4 network.The SEM images showed that the ions &#119873;&#119894;2+ were able to modify the morphology of silver tungstate microcrystals, in the studied conditions. The EDS spectra and map images indicated that all materials are composed of the elements &#119860;&#119892;, &#119882; and &#119874;, as expected. They also noted the presence of &#119873;&#119894; element in the composition of solid solutions. The values of &#119864;&#119892;&#119886;&#119901; estimated by means of UV-vis spectra suggest the existence of intermediate states in the forbidden area, from structural defects. The changes in spectra of PL samples indicated that the &#119873;&#119894; atoms alter the effect of the order-disorder, and the average distance favored over energy emissions associated with shallow defects. / Os tungstatos são compostos importantes e conhecidos por suas propriedades ópticas. Neste trabalho, soluções sólidas de tungstato de prata com níquel, &#119860;&#119892;2&#8722;2&#119909;&#119873;&#119894;&#119909;&#119882;&#119874;4, nas composições de (0, 01 &#8804; &#119909; &#8804; 0, 08) foram sintetizados pelo método hidrotérmico de microondas a 140 °C por 1h, visando investigar a influência dos íons &#119873;&#119894;2+ nas propriedades estruturais, morfológicas e fotoluminescentes do tungstato de prata (&#119860;&#119892;2&#119882;&#119874;4). Os materiais (&#119860;&#119892;2&#8722;2&#119909;&#119873;&#119894;&#119909;&#119882;&#119874;4) (0 &#8804; &#119909; &#8804; 0, 08) foram caracterizados estruturalmente por difração de raios X (DRX), espectroscopias micro-Raman (MR) e de absorção na região do Infravermelho (IV). A microscopia eletrônica de varredura (MEV) foi empregada para registro de imagens de superfície desses óxidos cerâmicos, enquanto que a técnica de energia dispersiva de raios X (EDX), juntamente com o mapeamento dos elementos químicos, foi utilizada para determinar qualitativamente da composição química das amostras. As propriedades ópticas foram estudadas pela espectroscopia eletrônica na região do ultravioleta-visível (UV-vis), no qual os valores das energias de band gap (&#119864;&#119892;&#119886;&#119901;) foram estimados, e por meio de espectroscopia de fotoemissão estudou-se efeito dos íons &#119873;&#119894;2+ na fotoluminescência (FL) do tungstato de prata. Os padrões de DRX revelaram a cristalização monofásica de todas as amostras na estrutura ortorrômbica do tungstato de prata e indicaram que estas apresentam ordem estrutural a longa distância. As pequenas variações nos parâmetros de rede e nas coordenadas atômicas, indicam a existência de distorções sobre os clusters de [&#119860;&#119892;&#119874;&#119899;] (&#119899; = 2, 4, 6 e 7) e [&#119882;&#119874;6] e a inserção dos átomos de &#119873;&#119894; na rede cristalina &#120572; &#8722; &#119860;&#119892;2&#119882;&#119874;4. Os dados dos refinamentos de Rietveld também mostraram que os sítios da &#119860;&#119892;2 e &#119860;&#119892;4 referentes aos clusters [&#119860;&#119892;&#119874;7] e [&#119860;&#119892;&#119874;4], respectivamente, são os mais prováveis para a ocupação dos átomos de &#119873;&#119894;. Alterações nos espectros de MR e a detecção de picos referentes a ligação &#119873;&#119894; &#8722; &#119874; nos espectros de IV das soluções sólidas, sugerem a introdução de átomos de &#119873;&#119894; na rede do &#119860;&#119892;2&#119882;&#119874;4. As imagens de MEV revelaram que os íons &#119873;&#119894;2+ foram capazes de modificar a morfologia dos microcristais de tungstato de prata, nas condições estudadas. Os espectros de EDX e imagens de mapeamento indicaram que todos os materiais são compostos pelos elementos &#119860;&#119892;, &#119882; e &#119874;, como esperado. Estes também apontaram a presença do elemento &#119873;&#119894; na composição das soluções sólidas. Os valores da &#119864;&#119892;&#119886;&#119901; estimados por meio dos espectros de UV-vis, sugerem a existência de estados intermediários na região proibida, provenientes de defeitos estruturais. As mudanças nos espectros de FL das amostras indicaram que os átomos de &#119873;&#119894; alteraram o efeito de ordem-desordem a média distância e favoreceram emissões mais energéticas associadas aos defeitos rasos.

L’étude des matériaux multiferroiques est sans doute un des domaines de recherche actuelle les plus actifs et prolifiques de la matière condensée. Dans ces matériaux, coexistent polarisation, aimantation et élasticité. On comprend bien que cette coexistence permet une multifonctionnalité très attrayante pour un grand nombre d’applications mais aussi fournit un vivier extraordinaire pour étudier les interactions entre ces grandeurs ainsi que les mécanismes microscopiques sous-jacents. Cet attrait s’en trouve d’autant plus renforcé du fait des phénomènes de couplage entre ces grandeurs physiques autorisant des fonctionnalités nouvelles comme par exemple le renversement d’une aimantation avec un champ électrique au lieu d’un champ magnétique classiquement. Cependant, ces matériaux multiferroiques sont d’une part en petit nombre et d’autre part, exploitent pour beaucoup d’entre eux, la polarisation d’un ferroélectrique et l’aimantation d’un antiferromagnétique. Ceci étant, il existe d’autres types d’arrangements polaires et magnétiques encore non-exploités, c’est dans ce cadre que s’inscrit ce travail de thèse. L’objectif de la thèse était de synthétiser de nouveaux multiferroiques présentant des arrangements polaires et magnétiques originaux et d’en caractériser les propriétés. Nous nous sommes tout particulièrement intéressés aux oxydes PbFe2/3W1/3O3 (PFW) et PbZrO3 (PZO). PFW présente des ordres polaires et magnétiques à longue et à courte portée : ferroélectrique-relaxeur et antiferromagnétique-verre de spin (ou ferromagnétisme faible). PZO est quant à lui antiferroélectrique avec antiferrodistorsivité (rotation des octaèdres d’oxygène) et présence d’instabilité ferroélectrique. Nous avons d’une part combiné ces deux matériaux pour former une solution solide et d’autre part réalisé un dopage de PZO avec des ions magnétiques. Après avoir synthétisé ces matériaux, nous les avons caractérisés électriquement (constante diélectrique, phénomène de relaxation, polarisation, température de Curie), magnétiquement (susceptibilité magnétique, aimantation) et structuralement (transition de phase). Ainsi, nous avons montré qu’il était possible d’obtenir un matériau multiferroique (50%PFW-50%PZO) présentant l’ensemble des instabilités ferroiques et structurales. Ces nouveaux matériaux ouvrent ainsi de nouvelles perspectives d’étude dans ce riche domaine en particulier en utilisant des antiferroélectriques. / Multiferroics are currently intensely investigated because the coexistence and coupling of ferroic arrangements brings about new physical effects and, for the few room-temperature examples, interesting prospects for applications in various fields. This interest is illustrated by the recent publication of several articles on multiferroics in high impact reviews over the last five years. The main goal of the thesis was to look for new multiferroics by exploiting overlooked and original polar and magnetic arrangements. We more precisely investigated compounds based on lead iron tungsten PbFe2/3W1/3O3 (PFW) and lead zirconate PbZrO3 (PZO) oxides. PFW displays long- and short-range both polar and magnetic orders (ferroelectric-relaxor and antiferromagnetic-spin-glass) while PZO is antiferroelectric with antiferrodistorsivity (oxygen tilts) and existence of ferroelectric instabilities. Combining various techniques from synthesis to electric, magnetic and structural characterizations, we demonstrated that it is possible to get a multiferroic compound (50%PFW-50%PZO) with coexistence of multiple ferroic and structural arrangements with room temperature properties of practical interest. This work opens new prospects in this rich field of multiferroics in peculiar by using antiferroelectrics.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / In this work, innovative approaches of sorption data at solid/solution interfaces were shown. Firstly, sorption data of a yellow dye on sílica-aminopropyl were evaluated. The experimental data were well fitted to the sorption models in equilibrium of Langmuir, Langmuir-Freundlich e Sips. It was concluded that some values of the sorption equilibrium constants (Keq) of this sorption process were inadequate, since their numerical values were too low, which is not in agreement with high-performance chemically-stable sorption processes. Sorption data of a remazol blue dye on a silica/chitosan hybrid were evaluated using an innovative methodology proposed by Azizian. From this model, values of Keq can be calculated using sorption kinetic data of a given sorption system. The Azizian model was well fitted to the experimental data of this sorption system. In addition, it was observed that the values of Keq were all high in nature and decreased as temperature increases. The Azizian methodology was also tested in sorption data of the remazol dyes yellow, blue and red on Epichlorohydrin crosslinked chitosan spheres. However, the Azizian model was not fitted properly, due probably to changes of the value of Keq in relation to initial dye concentration in solution. An innovative methodology using the microcalorimetry technique was used to evaluate the sorption of the methylene blue dye on fish scales of Robalo fish. The kinetic data was well fitted to a three-parameter kinetic model. However, the Azizian model was also not fitted to this sorption system, due also to changes of the value of Keq in relation to initial dye concentration in solution. It was concluded that the choice of a given sorption model is important in order to calculate correct sorption parameters. In general, the Azizian methodology is promising to calculate the equilibrium constant values from kinetic data. It is believed that the contributions from this Dissertation are important in order to propose new ways to calculate and to understand sorption phenomena at solid/solution interfaces. / Nesse trabalho, realizaram-se abordagens inovadoras sobre a análise de dados de sorção em interfaces sólido/solução. Avaliaram-se dados de equilíbrio da sorção do corante amarelo remazol em sílica-aminopropil. Os melhores ajustes foram obtidos utilizando-se os modelos de equilíbrio químico de Langmuir, Langmuir-Freundlich e Sips. Muitas abordagens tradicionais para calcular as constantes de equilíbrio (Keq) de sorção desse processo mostraram-se inadequadas, obtendo-se valores numéricos extremamente baixos e inconsistentes com interações adsorvente/adsorbato de naturezas químicas intensas e estáveis. Dados de sorção do corante azul de remazol em híbrido sílica/quitosana foram avaliados utilizando-se a abordagem inovadora de Azizian, obtendo-se constantes de equilíbrio (Keq) utilizando-se dados cinéticos de sorção. Os valores das Keq foram levados e diminuiram com aumento da temperatura. Avaliaram-se também dados de sorção de corantes remazol amarelo, azul e vermelho em micropérolas de quitosana. Porém, a metodologia de Azizian não apresentou ajustes adequados, devido provavelmente às variações dos valores das Keq em função do aumento da concentração inicial do corante em solução. Uma nova metodologia de análise de dados de sorções sólido/solução também foi analisada, utilizando-se a técnica de microcalorimetria para estudar a sorção do corante azul de metileno em escamas do peixe Robalo. Os dados cinéticos mostraram bons ajustes ao modelo cinético de ordem fracionária. No entanto, o modelo de Azizian também apresentou falta de ajuste. A avaliação de dados de sorção em interfaces sólido/solução deve ser realizada criteriosamente, pois escolhas de metodologias inapropriadas levam a resultados errôneos. A metodologia de Azizian mostrou-se promissora para calcular constantes de equilíbrio de sorção a partir de dados cinéticos. Acredita-se que essa Dissertação tenha contribuído para introduzir novos aspectos relevantes, relacionados à obtenção e análise de parâmetros de sorção de processos em interfaces sólido/solução.

A reforma do metano é um processo de grande interesse industrial para a produção de hidrogênio e de gás de síntese. Entre as reações de reforma do metano, destacam-se as reações de reforma a vapor e a reação com dióxido de carbono. O catalisador comumente utilizado nos processos e Ni/Al2O3. Porém, durante este processo, ocorre uma indesejada formação de depósitos carbonáceos na superfície do catalisador, os quais levam a sua destruição mecânica e, consequentemente, sua desativação. Por isso, uma das propriedades mais importantes de um bom catalisador para as reações de reforma do metano é a sua resistência a desativação. Entre as propostas para melhorar o desempenho do catalisador encontra-se a incorporação do óxido de cério junto ao suporte alumina. Catalisadores Ni/Al2O3 incorporados em soluções sólidas formadas por CeO2-ZrO2, ZrO2-La2O3 e CeO2-La2O3 foram preparados, caracterizados e submetidos a ensaios catalíticos nas reações de reforma a vapor e com dióxido de carbono e oxidação parcial do metano com objetivo de avaliar o efeito da adição da solução sólida ao suporte. Os suportes foram preparados pelo método da co-precipitação e os catalisadores foram obtidos pelo método de impregnação e calcinados a 500&deg;C. Estes compostos foram caracterizados por Fisissorção de Nitrogênio, Difração de Raios X (DRX), Espectroscopia dispersiva de raios X (EDX), espectroscopia de na região do ultra violeta e do visível (UV-vis-NIR), Redução à Temperatura Programada (RTP), Espectrocopia RAMAN, Espectroscopia fotoeletrônica de Raios X (XPS), Espectroscopia de absorção de Raios X (XAS) e Análise termogravimétrica. Os ensaios catalíticos mostraram que a adição de solução sólida melhorou o desempenho do catalisador Ni/Al2O3 e, dentre todos os catalisadores avaliados, os melhores desempenhos obtidos foram com os catalisadores suportados em Ni/CeO2-La2O3-Al2O3. / Nowadays, the methane reforming is large interest industrial for the take advantage of these gas in production the hydrogen and synthesis gas (syngas). Among in the reactions of methane stand of the reactions steam reforming and carbon dioxide reforming of methane. The main catalysts uses in the methane reforming is Ni/Al2O3. However, the supported-nickel catalyst is susceptible to the deactivation or the destruction by coke deposition. The carbon dissolves in the nickel crystallite and its diffuses through the nickel, leading for formation of the carbon whiskers, which results in fragmentation of the catalyst. Modification of such catalysts, like incorporation of suitable promoters, is desirable to achieve reduction of the methane hydrogenolysis and/or promotion of the carbon gasification. Catalysts 5% Ni/Al2O3 supported on solid solutions formed by ZrO2-CeO2, La2O3 and CeO2-ZrO2-La2O3 were prepared, characterized and evalueted in reactions steam and carbon dioxide refoming and partial oxidation of methane with objetive the value effect loading solution solid in support. The supports were prepared by co-precipitation method and catalysts were prepared by impregnation method and calcined at 500&deg;C. The supports and catalysts were characterized by Nitrogen Adsorption, method -rays diffraction (XRD), X-rays dispersive spectroscopy (XDS), spectroscopy in the region of the ultraviolet and the visible (UV-vis NIR) to and temperature programmed reduction (TPR), RAMAN Spectrocopy, X-ray absorption spectroscopy and Termogravimetric Analysis. After all the catalytic reactions check which the addition of solid solution is beneficial for Ni/Al2O3 catalysts and the best catalysts are Ni/CeO2-La2O3-Al2O3.

Technologies based on alternative and sustainable energy sources present a vital solution in the present and for the future. These technologies are strongly driven by the increased global energy demand and need to reduce environmental issues created by fossil fuel. Solar energy is an abundant, clean and free-access resource, but it requires harvesting and storage for a sustainable future. Direct conversion and storage of solar energy using heterogeneous photocatalysts have been identified as parts of a promising paradigm for generating green fuels from sunlight and water. This thesis focused on developing semiconductor absorbers in a visible light region for photocatalytic hydrogen production reaction. In addition, theoretical studies are combined with experimental results for a deep understanding of the intrinsic optoelectronic properties of the obtained materials. The study presents a novel family of oxysulfide BiAgOS, produced by applying a full substitution strategy of Cu by Ag in BiCuOS. I was interested to address how the total substitution of Cu by Ag in a BiCuOS system affects its crystal structure, optical and electronic properties using experimental characterizations and theoretical calculations. Single-phase bismuth silver oxysulfide BiAgOS was prepared via a hydrothermal method. Rietveld refinement of the powder confirmed that BiAgOS is an isostructural BiCuOS. The diffraction peak positions of BiAgOS, relative to those of BiCuOS, were shifted toward lower angles, indicating an increase in the cell parameters. BiCuOS and BiAgOS were found to have indirect bandgaps of 1.1 and 1.5 eV, respectively. The difference in the bandgap results from the difference in the valence band compositions. The hybrid level of the S and Ag orbitals in BiAgOS is located at a more positive potential than that of S and Cu, leading to a widened bandgap. Both materials possess high dielectric constants and low electron and hole effective masses, making them interesting for photoconversion applications. BiAgOS has a potential for photocatalytic hydrogen evolution reaction in the presence of sacrificial reagents; however, it is inactive toward water oxidation. BiCuOS and BiAgOS can be considered interesting starting compositions for the development of new semiconductors for PV or Z-scheme photocatalytic applications. The second study investigates the synthesis and characterization of NaBiS2, this contains Bi3+, which belongs to the p-block electronic configuration Bi3+ 6s26p0, and NaLaS2, which contains La3+ with electronic configuration 6s05d0. Solid-state reactions from oxide precursor starting materials were applied for synthesis the materials. The sulfurization process was conducted by pressurizing a saturated vapor of CS2. The obtained black material of NaBiS2 has an indirect transition with high absorption coefficients in the visible region of the spectrum and the absorption edge is determined at 1.21 eV. However, NaBiS2 did not show photocatalytic activity toward hydrogen production. NaLaS2 is characterized by an indirect transition with a bandgap in the UV region at 3.15 eV and can drive the photocatalytic hydrogen evolution reaction in Na2S/Na2SO3 solution. Utilizing the solid solution NaLa1-xBixS2 strategy, the absorption properties and band edge position for photocatalytic hydrogen evolution reaction were optimized. The results indicated that the bismuth content is critical parameter for maintaining the photocatalytic activity. The incorporation of low Bi content up to 6% in NaLaS2 leads to extending the photon absorption from the UV to the visible region and enhancing the photocatalytic activity of hydrogen production. In contrast, all the solid solutions that have Bi content of more than 12% present absorption edges close to that of pure NaBiS2, and they are inactive for photocatalytic hydrogen production. Combining the experimental measurements with density functional theory calculations, such behavior can be explained by the degree of overlapping of Bi and La states on the conduction band minimum (CBM). Finally, self-assembly of Bi2S3 nanorods were grown on FG or FTO substrates. Bi2S3 thin films were prepared by sulfurization of Bi metal layer using the hydrothermal method. The results show that Bi2S3 has absorption up to 1.3 eV and has a moderate absorption coefficient in the visible region. The ultraviolet photoelectron spectroscopy and photoelectron spectroscopy in air results showed that the conduction band minimum of Bi2S3 is located slightly above the hydrogen redox potential. However, Pt/Bi2S3 did not evolve a detectable amount of hydrogen, suggesting the presence of surface states that can hinder the hydrogen reduction reaction.

No description available.

No description available.