Nanostructured copper oxide semiconductors : a perspective on materials, synthesis methods and applications

The oxides of copper (CuxO) are fascinating materials due to their remarkable optical, electrical, thermal and magnetic properties. Nanostructuring of CuxO can further enhance the performance of this important functional material and provide it with unique properties that do not exist in its bulk form. Three distinctly different phases of CuxO, mainly CuO, Cu2O and Cu4O3, can be prepared by numerous synthesis techniques including, vapour deposition and liquid phase chemical methods. In this article, we present a review of nanostructured CuxO focusing on their material properties, methods of synthesis and an overview of various applications that have been associated with nanostructured CuxO.

Pyrene based conjugated materials: synthesis, characterization and electroluminescent properties

In this work, three novel pyrene cored small conjugated molecules, namely 1,3,6,8-tetrakis(6-(octyloxy)naphthalene-2-yl)pyrene (PY-1), 1,3,6,8-tetrakis((E)-2-(6-(n-octyloxy)naphthalene-2-yl)vinyl)pyrene (PY-2) and 1,3,6,8-tetrakis((6-(n-octyloxy)naphthalene-2-yl)ethynyl)pyrene (PY-3) have been synthesized by Suzuki, heck and Sonogashira organometallic coupling reactions, respectively. The effects of single, double and triple bonds on their optical, electrochemical, and thermal properties are studied in detail. These are all materials fluorescent and they have been used in organic light-emitting diodes (OLEDs) and their electroluminescent properties have been studied.

Novel materials synthesis by mechanical alloying/milling

An account is given of the research that has been carried out on mechanical alloying/milling (MA/MM) during the past 25 years. Mechanical alloying, a high energy ball milling process, has established itself as a viable solid state processing route for the synthesis of a variety of equilibrium and non-equilibrium phases and phase mixtures. The process was initially invented for the production of oxide dispersion strengthened (ODS) Ni-base superalloys and later extended to other ODS alloys. The success of MA in producing ODS alloys with better high temperature capabilities in comparison with other processing routes is highlighted. Mechanical alloying has also been successfully used for extending terminal solid solubilities in many commercially important metallic systems. Many high melting intermetallics that are difficult to prepare by conventional processing techniques could be easily synthesised with homogeneous structure and composition by MA. It has also, over the years, proved itself to be superior to rapid solidification processing as a non-equilibrium processing tool. The considerable literature on the synthesis of amorphous, quasicrystalline, and nanocrystalline materials by MA is critically reviewed. The possibility of achieving solid solubility in liquid immiscible systems has made MA a unique process. Reactive milling has opened new avenues for the solid state metallothermic reduction and for the synthesis of nanocrystalline intermetallics and intermetallic matrix composites. Despite numerous efforts, understanding of the process of MA, being far from equilibrium, is far from complete, leaving large scope for further research in this exciting field.

High-Spin and Emissive Molecular Materials: Synthesis and Characterization of New Polynuclear Ni(II) Complexes from the Use of Aromatic Schiff Bases as Bridging Ligands

The employment of the bridging/chelating Schiff bases, N-salicylidene-4-methyl-o-aminophenol (samphH2) and N-naphthalidene-2-amino-5-chlorobenzoic acid (nacbH2), in nickel cluster chemistry has afforded eight polynuclear Ni(II) complexes with new structural motifs, interesting magnetic and optical properties, and unexpected organic ligand transformations. In the present thesis, Chapter 1 deals with all the fundamental aspects of polynuclear metal complexes, molecular magnetism and optics, while research results are reported in Chapters 2 and 3. In the first project (Chapter 2), I investigated the coordination chemistry of the organic chelating/bridging ligand, N-salicylidene-4-methyl-o-aminophenol (samphH2). The general NiII/tBuCO2-/samphH2 reaction system afforded two new tetranuclear NiII clusters, namely [Ni4(samph)4(EtOH)4] (1) and [Ni4(samph)4(DMF)2] (2), with different structural motifs. Complex 1 possessed a cubane core while in complex 2 the four NiII ions were located at the four vertices of a defective dicubane. The nature of the organic solvent was found to be of pivotal importance, leading to compounds with the same nuclearity, but different structural topologies and magnetic properties. The second project, the results of which are summarized in Chapter 3, included the systematic study of a new optically-active Schiff base ligand, N-naphthalidene-2-amino-5-chlorobenzoic acid (nacbH2), in NiII cluster chemistry. Various reactions between NiX2 (X- = inorganic anions) and nacbH2 were performed under basic conditions to yield six new polynuclear NiII complexes, namely (NHEt3)[Ni12(nacb)12(H2O)4](ClO4) (3), (NHEt3)2[Ni5(nacb)4(L)(LH)2(MeOH)] (4), [Ni5(OH)2(nacb)4(DMF)4] (5), [Ni5(OMe)Cl(nacb)4(MeOH)3(MeCN)] (6), (NHEt3)2[Ni6(OH)2(nacb)6(H2O)4] (7), and [Ni6(nacb)6(H2O)3(MeOH)6] (8). The nature of the solvent, the inorganic anion, X-, and the organic base were all found to be of critical importance, leading to products with different structural topologies and nuclearities (i.e., {Ni5}, {Ni6} and {Ni12}). Magnetic studies on all synthesized complexes revealed an overall ferromagnetic behavior for complexes 4 and 8, with the remaining complexes being dominated by antiferromagnetic exchange interactions. In order to assess the optical efficiency of the organic ligand when bound to the metal centers, photoluminescence studies were performed on all synthesized compounds. Complexes 4 and 5 show strong emission in the visible region of the electromagnetic spectrum. Finally, the ligand nacbH2 allowed for some unexpected organic transformations to occur; for instance, the pentanuclear compound 5 comprises both nacb2- groups and a new organic chelate, namely the anion of 5-chloro-2-[(3-hydroxy-4-oxo-1,4-dihydronaphthalen-1-yl)amino]benzoic acid. In the last section of this thesis, an attempt to compare the NiII cluster chemistry of the N-naphthalidene-2-amino-5-chlorobenzoic acid ligand with that of the structurally similar but less bulky, N-salicylidene-2-amino-5-chlorobenzoic acid (sacbH2), was made.

Liquid crystalline hexabenzocoronenes as organic molecular materials - synthesis, characterization and application

Die vorliegende Arbeit 'Liquid Crystalline Hexabenzocoronenes as Organic Molecular Materials - Synthesis, Characterization and Application' war durch drei Schwerpunkte definiert:1. Verbesserung der Synthese von Hexabenzocoronen Derivaten mit sechsfacher Alkyl-Substitution,2. Entwicklung von molekularen Materialien mit verbesserten Eigenschaften wie zum Beispiel Löslichkeit und Verarbeitbarkeit,3. Einsatz der entwickelten Moleküle in optoelektronischen Bauteilen wie zum Beispiel organischen Solarzellen und Feld-Effekt-Transistoren.Mit Hilfe einer neuen Syntheseroute ist es gelungen Aryl-Aryl und Aryl-Alkyl Kupplungen sehr spät in der Reaktionssequenz von Hexabenzocoronenen einzusetzen. Dies führte zu einer Vielzahl substituierter HBC Derivate. Die Einführung eines Phenyl Spacers zwischen den HBC Kern und die äußeren Alkylketten, wie zum Beispiel in HBC-PhC12, hatte eine Vielzahl positiver Effekte wie dramatisch verbesserte Löslichkeit und Flüssigkristallinität bei Raumtemperatur zur Folge. Die Kombination dieser Phänomene ermöglichte die Bildung hochgeordneter Filme, welche sehr wichtig für den Einsatz in organischen Bauelementen sind. Mit Hilfe von STM Techniken an der Fest-Flüssig Phasengrenze wurden hochgeordnete 2-D Strukturen der HBC Moleküle gefunden. Die Kombination von extrem hoher kolumnarer Ordnung, bestimmt mit Hilfe der Festkörper NMR Spektroskopie, mit einer konstant hohen Ladungsträgerbeweglichkeit, führte zu dem sehr erfolgreichen Einsatz von HBC-PhC12 in organischen Solarzellen.

Engineered zeolitic materials: synthesis and application

Les zéolithes étant des matériaux cristallins microporeux ont démontré leurs potentiels et leur polyvalence dans un nombre très important d’applications. Les propriétés uniques des zéolithes ont poussé les chercheurs à leur trouver constamment de nouvelles utilités pour tirer le meilleur parti de ces matériaux extraordinaires. Modifier les caractéristiques des zéolithes classiques ou les combiner en synergie avec d’autres matériaux se trouvent être deux approches viables pour trouver encore de nouvelles applications. Dans ce travail de doctorat, ces deux approches ont été utilisées séparément, premièrement avec la modification morphologique de la ZSM-12 et deuxièmement lors de la formation des matériaux de type coeur/coquille (silice mésoporeuses@silicalite-1). La ZSM-12 est une zéolithe à haute teneur en silice qui a récemment attiré beaucoup l’attention par ses performances supérieures dans les domaines de l’adsorption et de la catalyse. Afin de synthétiser la ZSM-12 avec une pureté élevée et une morphologie contrôlée, la cristallisation de la zéolithe ZSM-12 a été étudiée en détail en fonction des différents réactifs chimiques disponibles (agent directeur de structure, types de silicium et source d’aluminium) et des paramètres réactionnels (l’alcalinité, ratio entre Na, Al et eau). Les résultats présentés dans cette étude ont montré que, contrairement à l’utilisation du structurant organique TEAOH, en utilisant un autre structurant, le MTEAOH, ainsi que le Al(o-i-Pr)3, cela a permis la formation de monocristaux ZSM-12 monodisperses dans un temps plus court. L’alcalinité et la teneur en Na jouent également des rôles déterminants lors de ces synthèses. Les structures de types coeur/coquille avec une zéolithe polycristalline silicalite-1 en tant que coquille, entourant un coeur formé par une microsphère de silice mésoporeuse (tailles de particules de 1,5, 3 et 20-45 μm) ont été synthétisés soit sous forme pure ou chargée avec des espèces hôtes métalliques. Des techniques de nucléations de la zéolithe sur le noyau ont été utilisées pour faire croitre la coquille de façon fiable et arriver à former ces matériaux. C’est la qualité des produits finaux en termes de connectivité des réseaux poreux et d’intégrité de la coquille, qui permet d’obtenir une stéréosélectivité. Ceci a été étudié en faisant varier les paramètres de synthèse, par exemple, lors de prétraitements qui comprennent ; la modification de surface, la nucléation, la calcination et le nombre d’étapes secondaires de cristallisation hydrothermale. En fonction de la taille du noyau mésoporeux et des espèces hôtes incorporées, l’efficacité de la nucléation se révèle être influencée par la technique de modification de surface choisie. En effet, les microsphères de silice mésoporeuses contenant des espèces métalliques nécessitent un traitement supplémentaire de fonctionnalisation chimique sur leur surface externe avec des précurseurs tels que le (3-aminopropyl) triéthoxysilane (APTES), plutôt que d’utiliser une modification de surface avec des polymères ioniques. Nous avons également montré que, selon la taille du noyau, de deux à quatre traitements hydrothermaux rapides sont nécessaires pour envelopper totalement le noyau sans aucune agrégation et sans dissoudre le noyau. De tels matériaux avec une enveloppe de tamis moléculaire cristallin peuvent être utilisés dans une grande variété d’applications, en particulier pour de l’adsorption et de la catalyse stéréo-sélective. Ce type de matériaux a été étudié lors d’une série d’expériences sur l’adsorption sélective du glycérol provenant de biodiesel brut avec des compositions différentes et à des températures différentes. Les résultats obtenus ont été comparés à ceux utilisant des adsorbants classiques comme par exemple du gel de sphères de silice mésoporeux, des zéolithes classiques, silicalite-1, Si-BEA et ZSM-5(H+), sous forment de cristaux, ainsi que le mélange physique de ces matériaux références, à savoir un mélange silicalite-1 et le gel de silice sphères. Bien que le gel de sphères de silice mésoporeux ait montré une capacité d’adsorption de glycérol un peu plus élevée, l’étude a révélé que les adsorbants mésoporeux ont tendance à piéger une quantité importante de molécules plus volumineuses, telles que les « fatty acid methyl ester » (FAME), dans leur vaste réseau de pores. Cependant, dans l’adsorbant à porosité hiérarchisée, la fine couche de zéolite silicalite-1 microporeuse joue un rôle de membrane empêchant la diffusion des molécules de FAME dans les mésopores composant le noyau/coeur de l’adsorbant composite, tandis que le volume des mésopores du noyau permet l’adsorption du glycérol sous forme de multicouches. Finalement, cette caractéristique du matériau coeur/coquille a sensiblement amélioré les performances en termes de rendement de purification et de capacité d’adsorption, par rapport à d’autres adsorbants classiques, y compris le gel de silice mésoporeuse et les zéolithes.

Imidazolium-Based Organic Structure Directing Agents for the Synthesis of Microporous Materials

The central theme of this thesis is the use of imidazolium-based organic structure directing agents (OSDAs) in microporous materials synthesis. Imidazoliums are advantageous OSDAs as they are relatively inexpensive and simple to prepare, show robust stability under microporous material synthesis conditions, have led to a wide range of products, and have many permutations in structure that can be explored. The work I present involves the use of mono-, di-, and triquaternary imidazolium-based OSDAs in a wide variety of microporous material syntheses. Much of this work was motivated by successful computational predictions (Chapter 2) that led me to continue to explore these types of OSDAs. Some of the important discoveries with these OSDAs include the following: 1) Experimental evaluation and confirmation of a computational method that predicted a new OSDA for pure-silica STW, a desired framework containing helical pores that was previously very difficult to synthesize. 2) Discovery of a number of new imidazolium OSDAs to synthesize zeolite RTH, a zeolite desired for both the methanol-to-olefins reaction as well as NOX reduction in exhaust gases. This discovery enables the use of RTH for many additional investigations as the previous OSDA used to make this framework was difficult to synthesize, such that no large scale preparations would be practical. 3) The synthesis of pure-silica RTH by topotactic condensation from a layered precursor (denoted CIT-10), that can also be pillared to make a new framework material with an expanded pore system, denoted CIT-11, that can be calcined to form a new microporous material, denoted CIT-12. CIT-10 is also interesting since it is the first layered material to contain 8 membered rings through the layers, making it potentially useful in separations if delamination methods can be developed. 4) The synthesis of a new microporous material, denoted CIT-7 (framework code CSV) that contains a 2-dimensional system of 8 and 10 membered rings with a large cage at channel intersections. This material is especially important since it can be synthesized as a pure-silica framework under low-water, fluoride-mediated synthesis conditions, and as an aluminosilicate material under hydroxide mediated conditions. 5) The synthesis of high-silica heulandite (HEU) by topotactic condensation as well as direct synthesis, demonstrating new, more hydrothermally stable compositions of a previously known framework. 6) The synthesis of germanosilicate and aluminophosphate LTA using a triquaternary OSDA. All of these materials show the diverse range of products that can be formed from OSDAs that can be prepared by straightforward syntheses and have made many of these materials accessible for the first time under facile zeolite synthesis conditions.

Synthesis of novel solid materials from carbon dioxide and carbon monoxide

The increase of atmospheric CO2 has been identified as the primary cause for the observed global warming over the past century. The geological and oceanic sequestration of CO2 has issues, such as cost and leakage as well as effects on sea biota. The ideal solution should be the conversion of CO2 into useful materials. However, most processes require high energy input. Therefore, it is necessary to explore novel processes with low energy demands to convert CO2 to useful solid materials. Amorphous carbon nitride and graphone received much attention due to their unusual structures and properties as well as their potential applications. However, to date there has been no attempt to synthesize those solid materials from CO2. Lithium nitride (Li3N) and lithium imide (Li2NH) are important hydrogen storage materials. However, their optical properties and reactivity has not yet studied. This dissertation research is aimed at the synthesis of carbon nitrides and graphone from CO2 and CO via their reaction with Li3N and Li2NH. The research was focused on (1) the evaluation of Li3N and Li2NH properties, (2) thermodynamic analysis of conversion of carbon dioxide and carbon monoxide into carbon nitride and other solid materials, (3) synthesis of carbon nitride from carbon dioxide, and (4) synthesis of graphone from carbon monoxide. First, the properties of Li3N, Li2NH, and LiNH2 were investigated. The X-ray diffraction measurements revealed that heat-treatment at 500°C introduce a phase transformation of β-Li3N to α-Li3N. Furthermore, the UV-visible absorption evaluation showed that the energy gaps of α-Li3N and β-Li3N are 1.81 and 2.14 eV, respectively. The UV-visible absorption measurements also revealed that energy gaps are 3.92 eV for Li2NH and 3.93 eV for LiNH2. This thermodynamic analysis was performed to predict the reactions. It was demonstrated that the reaction between carbon dioxide and lithium nitride is thermodynamically favorable and exothermic, which can generate carbon nitride and lithium cyanamide. Furthermore, the thermodynamic calculation indicated that the reaction between carbon monoxide and lithium imide can produce graphone and lithium cyanamide along with releasing heat. Based on the above thermodynamic analysis, the experiment of CO2 and Li3N reaction and CO and Li2NH were carried out. It was found that the reaction between CO2 and Li3N is very fast and exothermic. The XRD and element analysis revealed that the products are crystal lithium cyanamide and amorphous carbon nitrides with Li2O and Li2CO3. Furthermore, TEM images showed that carbon nitrides possess layer-structure, namely, it is graphene-structured carbon nitride. It was found that the reaction between Li2NH and CO was also exothermic, which produced graphone instead of carbon nitride. The composition and structures of graphone were evaluated by XRD, element analysis, TEM observation, and Raman spectra.

Synthesis and characterisation of nanoscale magnesium oxide powders and their application in thick films of Bi2Sr2CaCu2O8

Nanoscale MgO powder was synthesized from magnesite ore by a wet chemical method. Acid dissolution was used to obtain a solution from which magnesium containing complexes were precipitated by either oxalic acid or ammonium hydroxide, The transformation of precipitates to the oxide was monitored by thermal analysis and XRD and the transformed powders were studied by electron microscopy. The MgO powders were added as dopants to Bi2SrCa2CuO8 powders and high temperature superconductor thick films were deposited on silver. Addition of suitable MgO powder resulted in increase of critical current density, J(c), from 8,900 Acm(-2) to 13,900 Acm(-2) measured at 77 K and 0 T. The effect of MgO addition was evaluated by XRD, electron microscopy and critical current density measurements. (C) 1998 Elsevier Science B.V.

In-situ combustion synthesis of ultrafine TiB2 particles reinforced Cu matrix composite

Due to the lower strength of pure copper (Cu), ceramic particulate or whisker reinforced Cu matrix composites have attracted wide interest in recent years [1–3]. These materials exhibit a combination of excellent thermal and electrical conductivities, high strength retention at elevated temperatures, and high microstructural stability [3]. The potential applications include various electrodes, electrical switches, and X-ray tube components [4].

RF plasma sputtering deposition of hydroxyapatite bioceramics : synthesis, performance, and biocompatibility

Hydroxyapatite (HA) coatings have numerous applications in orthopedics and dentistry, owing to their excellent ability to promote stronger implant fixation and faster bone tissue ingrowth and remodeling. Thermal plasma spray and other plasma-assisted techniques have recently been used to synthesize various calcium phosphate-based bioceramics. Despite notable recent achievements in the desired stoichiometry, phase composition, mechanical, structural, and bio-compatible properties, it is rather difficult to combine all of the above features in a single coating. For example, many existing plasma-sprayed HA coatings fall short in meeting the requirements of grain size and crystallinity, and as such are subject to enhanced resorption in body fluid. On the other hand, relatively poor interfacial bonding and stability is an obstacle to the application of the HA coatings in high load bearing Ti6Al4V knee joint implants. Here, we report on an alternative: a plasma-assisted, concurrent, sputtering deposition technique for high performance biocompatible HA coatings on Ti6Al4V implant alloy. The plasma-assisted RF magnetron co-sputtering deposition method allows one to simultaneously achieve most of the desired attributes of the biomimetic material and overcome the aforementioned problems. This article details the film synthesis process specifications, extensive analytical characterization of the material's properties, mechanical testing, simulated body fluid assessments, biocompatibility and cytocompatibility of the HA-coated Ti6Al4V orthopedic alloy. The means of optimization of the plasma and deposition process parameters to achieve the desired attributes and performance of the HA coating, as well as future challenges in clinical applications are also discussed.

Synthesis and luminescent properties of star-burst D-Pi-A compounds based on 1,3,5-triazine core and carbazole end-capped phenylene ethynylene arms

Two new star-burst compounds based on 1,3,5-triazine core and carbazole end-capped phenylene ethynylene arms (1a and 1b) were synthesized and characterized. Their photophysical properties were investigated systematically via spectroscopic and theoretical methods. Both compounds exhibit strong 1π–π⁎ transitions in the UV region and intense 1π–π⁎/intramolecular charge transfer (1ICT) absorption bands in the UV–vis region. Introducing the carbazole end-capped phenylene ethynylene arm on the 1,3,5-triazine core causes a slight bathochromic shift and enhanced molar extinction coefficient of the 1π–π⁎/1ICT transition band. Both compounds are emissive in solution at room temperature and 77 K, which exhibit pronounced positive solvatochromic effect. The emitting state could be ascribed to 1ICT state in more polar solvent, and 1π–π⁎ state in low-polarity solvent. The high emission quantum yields (Φem=0.90~1.0) of 1a and 1b (in hexane and toluene) make them potential candidates as efficient light-emitting materials. The spectroscopic studies and theoretical calculations indicate that the photophysical properties of these compounds can be tuned by the carbazole end-capped phenylene ethynylene arm, which would also be useful for rational design of photofunctional materials.

Synthesis and properties of willemite Zn2SiO4, and M2+: Zn2SiO4 (M = Co and Ni)

Fine particles of willemite, alpha -Zn2SiO4, were prepared by both solution combustion and sol-gel methods. Both processes yield single-phase, large-surface area (26- and 78-m(2)/g), sinteractive willemite powders. Thermal evolution of crystalline phases was studied using X-ray powder diffraction patterns. The combustion method favors low-temperature formation of willemite compared to the sol-gel method. The powders, when uniaxially pressed and sintered at 1300 degreesC, achieved 78-80% theoretical density. The microstructures of the sintered body show the presence of equiaxed 0.5- to 4-mum grains. Blue pigments of willemite doped with Co2+ and Ni2+ were also prepared by the combustion process.