Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第15393号 / 工博第3272号 / 新制||工||1493(附属図書館) / 27871 / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 井上 正志, 教授 江口 浩一, 教授 大江 浩一 / 学位規則第4条第1項該当

The work is focused on the investigation of synthesis and structure of crystalline coordination networks by combining first a row transition metal ion with one anionic and one neutral bridging ligand. In the field of crystalline coordination networks, the goal is to synthesize porous 3D crystalline coordination networks with molecular sized cavities. The materials are characterized by XRD and TGA. It is important to understand the structural topologies to develop practical applications, such as gas storage, gas separation, and catalysis. The bi- and tetra-dentate flexible imidazole ligands, 9,10-bis(imidazol-1-ylmethyl)anthracene (Chapter 2) and 1, 2, 4, 5-tetrakis(imidazol-1ylmethyl)benzene (Chapter 3), are synthesized and used as linkers to construct 1D, 2D, and 3D crystalline coordination networks with cobalt(II) or zinc(II) cations and H3BTC anions under solvothermal conditions. Two 1D chain networks, [M(HBTC²⁻)(C₂₂H₁₈N₄)(H₂O)₂]•H₂O, are constructed from M(Zn(II) or Co(II)), H₃BTC, and 9,10-bis(imidazol-1-ylmethyl)anthracene (Compound 2.1 and 2.2). These two 1D zigzag chains are linked into infinite 2D sheets by inter-chain π•••π stacking and hydrogen bonding. ⁺ Two 2D and one 3D cobalt(II) coordination networks are constructed from the tetradentate imidazole ligand and H3BTC. Compound 3.1 has a 2D corrugated sheet structure that is linked by inter-layer π•••π stacking and hydrogen bonding. Compound 3.2 has a 2D sheet structure. These sheets are interconnected by hydrogen bonds at the free acid group of the HBTC²⁻ ligand. Compound 3.3 forms a two fold interpenetrated 3D network structure. Void spaces in the structure are filled with six water molecules. Six 3D cobalt (II) coordination networks are constructed with bidentate rigid imidazole containing neutral ligands, 1,4-bis(imidazol-1-yl)benzene(L1), 1,4-bis(imidazol-1-yl)naphthalene(L2), and 9,10-bis(imidazol-1-yl)anthracene(L3), and H₂BDC or H₃BTC anion (Chapter 4). In 4.1-4.3, L1-L3 affects on degree of interpenetrations constructed with H₂BDC ligand. In 4.1 and 4.2 are interpenetrating 3D networks with no accessible void space. In 4.3, void spaces of 3D networks are filled with 2D sheets. Compounds 4.4-4.6 are prepared by different concentrations of starting materials and different solvents. In 4.4-4.6, L3 serves as a pillar building block to construct 3D networks by applying with H₃BTC ligand. The solvent exchange experiment for 4.4 is further discussed. / Ph. D.

Les matériaux de type graphène suscitent depuis une dizaine d’années un grand engouement de la part de la communauté scientifique en raison de leurs propriétés remarquables. Les mousses de graphène, notamment, offrent la restitution d’une partie des propriétés du graphène combinée à une surface accessible élevée, et sont particulièrement intéressantes dans certains domaines d’application tels que l’énergie. Ce travail de thèse s’attache à l’étude de l’élaboration de mousses graphéniques par voie solvothermale, une méthode originale qui consiste en une réaction solvothermale entre un alcool et du sodium métallique, suivie par un traitement thermique. L’étude des produits issus de la réaction solvothermale ainsi que de la pyrolyse sous azote a été menée à l’aide de techniques de caractérisation complémentaires et multi-échelles : des mécanismes de formation du composé solvothermal ainsi que des mousses graphéniques ont pu être proposés. Les conditions optimales de pyrolyse ont également été déterminées, et permettent l’obtention d’une mousse de graphène possédant une grande qualité structurale et une surface accessible élevée. Par ailleurs, plusieurs traitements post-élaboration ont été mis en place : un recuit sous vide, en particulier, améliore sensiblement la qualité structurale et la pureté des échantillons. Enfin, l’étude de la modification des propriétés physico-chimiques des mousses à travers la chimie de l’intercalation des matériaux carbonés a été effectuée. Des films de graphène ont pu être préparés à partir des mousses intercalées et leurs propriétés électriques ont été évaluées / Graphene-based materials have attracted a great interest these last years, due to their outstanding properties. In particular, graphene foams offer a part of the properties of graphene, combined with a high surface area: they show great potentiality in some application domains such as energy. This thesis work is focused on the elaboration of graphene foams by a solvothermal-based process, an original method involving a solvothermal reaction between an alcohol and sodium, followed by a thermal treatment. The study of the compounds produced by the solvothermal reaction and the pyrolysis under a nitrogen flow was lead through multi-scale and complementary characterization techniques: mechanisms of formation of the solvothermal compound and graphenic foams have been proposed. The optimal conditions of pyrolysis were also determined, and provide the obtaining of graphene foams with a high structural quality and a large specific surface area. Furthermore, some types of post-elaboration treatments were carried out: notably, a vacuum annealing significantly improves the structural quality and the purity of the samples. Lastly, the modification of the physico-chemical properties of the foams through the chemistry of carbon materials intercalation has been studied. Graphene films were prepared from the intercalated foams and their electrical properties were evaluated

In this thesis, 60 crystal structures which have been synthesised by the solvothermal method are reported, with 57 of them representing novel materials. The remaining three materials have previously been reported but have been made by a new and milder method of synthesis. Ti, Zr, Hf, V, Nb, Ta and Mo have all been used to make fluoride or oxyfluoride materials at temperatures ranging from 60C to 200C. Both inorganic and organic moieties ("templates") have been used to direct the formation of the (oxy)fluoride materials, usually as an anionic species. These materials have then been studied for their magnetic properties, where relevant. Initially, 10 vanadium-based compounds were made at 100C using a range of templates. Through variations in water content, temperature and cation ratio, a further 19 compounds were synthesised. The inorganic species in these structures ranged from monomers, to dimers, tetramers and chains, to infinite 2D sheets. A family of vanadium compounds has been synthesised, with piperazine as a template, which shows an increase in covalent connectivity through the increase of the reaction temperature, with a decrease in oxidation state as a result. These materials are also interrelated through the use of a "Y" shaped motif in their structural composition. Through a change in cation content a novel trigonal chain compound (related to the structure of CsCrF₄) has been synthesised with piperazine which possibly shows strong geometric frustration. Vanadium oxyfluoride analogues of (VO)₂P₂O₇ have been made, which show interesting magnetic properties with a range of different templates, ranging from alkali metal cations to the bulky protonated template trans 1,2 bis (4-pyridyl) ethene. The best fits to the magnetic susceptibility data are obtained with an antiferromagnetic Heisenberg chain model. Nine molybdenum-based structures have also been synthesised, with five of the structures being made through changes in the temperature and cation ratio of the reactions. An example of this is the formation of tetrameric units with ammonium, through the condensation of monomers as a result of an increase in the reaction temperature. A further 22 structures have also been made with metals, M = Ti, Zr, Hf, Nb and Ta. These structures have a tendency to form isolated polyhedral units under the conditions studied in this work. Several examples of isolated [MF₆][superscript n-] and [MF₇][superscript n-] monomers are reported and also one example of a trans-connected [TiOF₄]²⁻ infinite chain structure.

A busca pelo aprimoramento de materiais nanocristalinos baseia-se na variação do processo de síntese e na alteração de sua estrutura através da inserção de defeitos na estrutura cristalina. O processo de dopagem tem sido considerado de fundamental importância para estabilizar determinadas fases ou faces cristalinas. Por outro lado, o uso de uma metodologia de síntese versátil como a síntese hidrotérmica e solvotérmica mostra-se como uma proposta interessante para obter materiais já produzidos por técnicas convencionais, mas que apresentam propriedades diferenciadas. Nesse trabalho, verificou-se o efeito do método de síntese utilizado e da adição de íons dopantes como Mg+2 e Ni+2 nas propriedades morfológicas e estruturais do composto titanato de cálcio (CaTiO3) que foi preparado através dos métodos hidrotérmico e solvotérmico. Através das técnicas de difração de raios X e microscopia eletrônica de varredura, foi verificado o efeito dos parâmetros de síntese (tempo e temperatura) e dos materiais precursores nas propriedades estruturais e microestruturais das amostras. Na avaliação de fotoatividade realizada (fotodegradação do corante rodamina B) foi observado que os compostos sintetizados pelo método hidrotérmico com os precursores oxisulfato de titânio e cloreto de cálcio apresentaram melhor atividade fotocatalítica que os compostos sintetizados pelo método solvotérmico (solvente PEG-200). / The search for the improvement of nanocrystalline materials is based on the variation of the synthesis process and the modification of its structure through the insertion of defects in its crystalline structure. The doping process has been considered of fundamental importance to stabilize certain crystalline phases or faces of nanomaterials. On the other hand, the use of a versatile synthesis methodology such as hydrothermal and solvothermal methods is an interesting proposal to obtain materials already produced by conventional techniques, but with different properties. In this work, the effect of the synthesis method and the addition of dopant ions such as Mg+2 and Ni+2 on the morphological and structural properties of the calcium titanate (CaTiO3) compound was verified, which was prepared by hydrothermal and solvothermal methods. The effect of the synthesis parameters (time and temperature) and the precursor materials on the structural and microstructural properties of the samples were verified by means of the X-ray diffraction and scanning electron microscopy techniques. It was observed that the compounds synthesized by the hydrothermal method with the titanium oxysulfate and calcium chloride precursors presented better photocatalytic activity than the compounds synthesized by the solvothermal method (solvent PEG-200).

Transparent ceramics are used in a variety of applications such as protective visors, thermo-graphic lens, night vision devices and windowpane of an armed vehicle, missile domes and in aircrafts. Yttrium Aluminium Garnet (YAG, Y3Al5O12) exhibits uniform index of refraction without birefringence owing to its cubic crystal structure and offers a range of optical and mechanical properties that makes it suitable for transparent applications.

Dióxido de titânio com alta área superficial específica na fase anatase é considerado um material promissor para aplicações ambientais. Neste trabalho, TiO2 com boa aplicabilidade em processos fotocatalíticos e na produção de hidrogênio foi obtido pelo método com baixo consumo de energia baseado na rota dos peróxidos oxidantes combinado com tratamento solvotermal assistido por microondas. Para preparar o material, propóxido de titânio, peróxido de hidrogênio e álcool isopropílico foram utilizados. A influência do tempo, do pH e da temperatura durante a etapa solvotermal nas propriedades como morfologia, cristalinidade, composição de fase, área superficial específica e comportamento fotocatalítico foram investigados. As amostras foram caracterizadas por difração de raios X (DRX), microscopia eletrônica de varredura (MEV), microscopia eletrônica de transmissão (MET), análise termogravimétrica (ATG), teoria Brunauer-Emmett-Teller (BET), reflectância difusa e espectroscopia por emissão fluorescente. A fotoatividade foi determinada usando o método de decomposição do corante alaranjado de metila em luz UV-A e a produção de hidrogênio foi realizada em água usando etanol como agente de sacrifício. Com o aumento da temperatura durante a etapa solvotermal, as propriedades fotocatalíticas foram melhoradas. As nanoestruturas de TiO2 sintetizadas a 200°C e 30 min a partir deste método mostraram atividade fotocatalítica comparável ao do TiO2 P25 comercial Aeroxide©. Isso pode ser atribuído ao fato de que a energia associada a esta temperatura tenha sido suficiente para converter a maioria dos precursores em produtos cristalinos e pouca fase amorfa está presente. Foi possível produzir, com sucesso, nanoestruturas de TiO2, via método dos peróxidos oxidantes e tratamento solvotermal assistido por microondas em diferentes pHs. O material tratado em pH 1 exibiu melhor comportamento fotocatalítico na degradação da solução contendo alaranjado de metila. Aparentemente, o pH do meio não afetou significativamente a microestrutura das amostras. Foi observado uma diminuição na intensidade fotoluminescente da amostra preparada em pH ácido. Isso ocorre provavelmente porque as modificações ácidas em TiO2 favorecem eficientemente a separação das cargas, que está também relacionada com o comportamento dessa amostra durante o processo de degradação. Em relação à produção de hidrogênio, foi possível observar que a razão aumentou com o aumento do pH da solução. Isso pode ser atribuído ao aumento da concentração de OH- fisisorvidos, os quais podem participar dos processos de trapeamento das lacunas e nas reações de transferência de cargas. Por último, esses resultados foram notáveis porque foi utilizado um método de preparação com baixo consumo de energia onde apenas precursores orgânicos e baixas temperaturas foram empregados. Além disso, calcinação ou dopagem não foram necessários para alcançar tal desempenho, uma vez que, os catalisadores assim preparados exibiram boa atividade fotocatalítica na remoção de poluentes da água como o alaranjado de metila e na produção de hidrogênio. / Titanium dioxide with high specific surface area in the crystalline anatase phase is a promising material for environmental applications. In this work, TiO2 with good applicability for photocatalytic processes and hydrogen production has been obtained using the low energy consumption synthesis based on oxidant peroxide method combined with microwave-assisted low temperature solvothermal treatment. To prepare the material, titanium propoxide, hydrogen peroxide, and isopropyl alcohol were used. The influence of time, pH and temperature during the solvothermal step on properties like, morphology, crystallinity, phase composition, specific surface area, and photocatalytic behavior were investigated. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), scanning electron transmission (TEM), thermal gravimetric analysis (TGA), Brunauer- Emmett-Teller theory (BET), UV–Vis diffuse reflectance and fluorescence emission spectroscopy. Photoactivity was determined using the methyl orange decomposition method in UV-A light and hydrogen production was performed in water using ethanol as sacrificial agent. Increasing temperature during solvothermal step, photocatalytic properties could be improved. The nanostructured TiO2 particles synthesized at 200ºC and 30 min with this method showed photocatalytic activity comparable to commercial Aeroxide® TiO2 P25. This can be attributed to the fact that the energy associated with this temperature has been sufficient to convert most of precursors into crystalline products and small amount of amorphous phase is present. We successfully produced nanostructured TiO2 via the oxidant peroxide method and microwave-assisted solvothermal treatment at different pHs. The material that we treated at pH 1 exhibited better photocatalytic performance on the degradation of methyl orange solutions. It appears that the pH of the medium does not significantly affect the microstructure of the samples. It was observed a decrease in the photoluminescence intensity of the sample prepared at acidic pH. This finding likely occurred because the acidic modification of TiO2 favors efficiently separating the charge carriers, which is also related to the behavior of this sample during the degradation process. Related to hydrogen production, it was possible to observe that the rate increases with increasing solution pH. This has been attributed to the increased concentrations of physisorbed OH− groups at basic solutions, which participate in hole trapping processes and charge transfer reactions. Lastly, these results are remarkable because of the low energy consumption preparation method: only organic-metalic compounds and low temperatures were employed. Furthermore, calcination or doping was not necessary to achieve such performance, since the asprepared catalysts exhibited good photocatalytic activity on removal of pollutants from water as the methyl orange and on hydrogen production.

A busca pelo aprimoramento de materiais nanocristalinos baseia-se na variação do processo de síntese e na alteração de sua estrutura através da inserção de defeitos na estrutura cristalina. O processo de dopagem tem sido considerado de fundamental importância para estabilizar determinadas fases ou faces cristalinas. Por outro lado, o uso de uma metodologia de síntese versátil como a síntese hidrotérmica e solvotérmica mostra-se como uma proposta interessante para obter materiais já produzidos por técnicas convencionais, mas que apresentam propriedades diferenciadas. Nesse trabalho, verificou-se o efeito do método de síntese utilizado e da adição de íons dopantes como Mg+2 e Ni+2 nas propriedades morfológicas e estruturais do composto titanato de cálcio (CaTiO3) que foi preparado através dos métodos hidrotérmico e solvotérmico. Através das técnicas de difração de raios X e microscopia eletrônica de varredura, foi verificado o efeito dos parâmetros de síntese (tempo e temperatura) e dos materiais precursores nas propriedades estruturais e microestruturais das amostras. Na avaliação de fotoatividade realizada (fotodegradação do corante rodamina B) foi observado que os compostos sintetizados pelo método hidrotérmico com os precursores oxisulfato de titânio e cloreto de cálcio apresentaram melhor atividade fotocatalítica que os compostos sintetizados pelo método solvotérmico (solvente PEG-200). / The search for the improvement of nanocrystalline materials is based on the variation of the synthesis process and the modification of its structure through the insertion of defects in its crystalline structure. The doping process has been considered of fundamental importance to stabilize certain crystalline phases or faces of nanomaterials. On the other hand, the use of a versatile synthesis methodology such as hydrothermal and solvothermal methods is an interesting proposal to obtain materials already produced by conventional techniques, but with different properties. In this work, the effect of the synthesis method and the addition of dopant ions such as Mg+2 and Ni+2 on the morphological and structural properties of the calcium titanate (CaTiO3) compound was verified, which was prepared by hydrothermal and solvothermal methods. The effect of the synthesis parameters (time and temperature) and the precursor materials on the structural and microstructural properties of the samples were verified by means of the X-ray diffraction and scanning electron microscopy techniques. It was observed that the compounds synthesized by the hydrothermal method with the titanium oxysulfate and calcium chloride precursors presented better photocatalytic activity than the compounds synthesized by the solvothermal method (solvent PEG-200).

Le nitrure de gallium, GaN, semi-conducteur à large gap (3.4 eV), est un composé qui présente des propriétés très attractives pour des applications en opto- et micro-électronique. L'amélioration des performances des dispositifs passe par l'amélioration des propriétés des films de GaN. C'est pourquoi l'obtention de monocristaux massifs de GaN, susceptibles de servir de substrats pour l'homoépitaxie de films de GaN, représente un enjeu considérable. L'objectif de ce travail de thèse était de transposer le procédé de croissance hydrothermale du quartz-α au composé GaN afin de faire croître des monocristaux de GaN. Dans une première étape, un procédé de synthèse de GaN finement divisé a été mis au point. La synthèse solvothermale de microcristaux de GaN a été réalisée par traitement d'un mélange réactionnel gallium/additif sous pression d'ammoniac. Ce matériau était destiné à servir de corps mère pour la croissance de monocristaux de GaN par un procédé de dissolution-transport-cristallisation. Dans une seconde étape, la solubilité du GaN ainsi obtenu a été évaluée dans le solvant ammoniac. Il s'est avéré qu'en raison de la forte covalence de la liaison Ga-N, ce composé n'a pu être solubilisé. En conséquence, le remplacement de GaN par un corps mère plus ionique et donc susceptible de se solubiliser plus facilement a été envisagé. Le composé Li₃GaN₂ a donc été synthétisé dans ce but. Enfin, la dernière partie présente les premiers travaux réalisés sur la solubilité de Li₃GaN₂ qui ont montré que ce composé était soluble dans l'ammoniac. En outre, la faisabilité du transport d'une espèce contenant du gallium du corps mère vers des germes a été abordée. Dans le futur, Li₃GaN₂ pourrait donc servir de corps mère pour la croissance de monocristaux de GaN.

Diamond cuboid-, rhombohedron- and hexagon-shaped nanocrystals as well as branched rods of the solid solution Co1-xMnxO have been synthesized via a solvothermal synthetic route from manganese formate and cobalt acetate at elevated temperature. Rhombohedra and hexagons have dimensions no larger than 50 nm on the longest axis, rods have branches up to 150 nm long and cuboids grow up to 250 nm on a side. X-ray and electron diffraction and transmission electron microscopy analyses show that these nanoparticles are single crystals of wurtzite-type and rock salt-type Co1-xMnxO. Varying the surfactant, water and precursor ratios allows control of particle size, morphology and stoichiometry. Extending growth time at high temperatures (>370°C) leads to the disappearance of the wurtzite phase due to Ostwald ripening. Longer reaction times at temperatures between 345-365°C lead to more crystalline wurtzite-lattice particles. These results show that nanoparticle morphologies and crystal lattices arise from crystal growth and Ostwald ripening at different rates selecting for either small, smooth-surfaced wurtzite lattice particles or large, dendritically-grown rock salt lattice particles.