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Mesoporous crystalline metal oxides
No full textMesoporous monocrystalline metal oxides (e.g. Co₃O₄, Cr₂O₃, NiO, CeO₂, In₂O₃
and WO₃) templated by SBA-15 or KIT-6 were synthesised successfully by using a
simple solvent-free approach, the so-called solid-liquid method, which was the
principal development of methodology in this project. A metal-containing precursor,
whose melting point is lower than its decomposition temperature, was directly ground
with a mesoporous silica and impregnated into the pores of the silica template after
melting when the temperature was increased above its melting point. The liquid
precursor then decomposed to form metal oxide inside the silica pores when the
temperature was further increased to its decomposition temperature and
crystallization temperature of the oxide. The structural characterisations of these
porous metal oxides were performed by using TEM, XRD and N₂
adsorption/desorption techniques. The solid-liquid method is convenient and
solvent-free. On the other hand, its limitation is that the precursor must have a
melting point lower than its decomposition temperature.
A novel porous single crystal of rutile TiO₂ as well as anatase nanocrystal-silica
composite was also synthesised successfully for the first time using SBA-15 and
KIT-6 as templates. These materials have interesting properties of proton conductivity,
Li insertion and photoactivity. Likewise, the characterisation of porous TiO₂ was
achieved by using XRD, TEM, SAED and N₂ adsorption/desorption. The residual
SiO₂ component in porous TiO₂ was detected by using the EDX technique.
Porous cubic metal oxides of Co₃O₄, NiO, CeO₂ and In₂O₃ were prepared using
novel mesoporous silicas FDU-12 and SBA-16, which contain spherical nanocavities
linked together by smaller windows. These porous materials have larger surface areas
than those templated by SBA-15 and KIT-6. Unlike the cubic metal oxides, syntheses
of porous crystals of non-cubic metal oxides such as rhombohedral Cr₂O₃, Fe₂O₃ and
hexagonal TiO₂, WO₃ were not successful when using cage-containing mesoporous
silicas as templates. The three-dimensional arrangements of nanospheres in porous crystals of cubic oxides mentioned above were observed by TEM and the
corresponding larger surface areas were confirmed by N₂ adsorption/desorption
technique.
Additionally, fabrication of porous crystals of other metal oxides such as MgO,
ZnO and ZrO₂ were unsuccessful by using either mesoporous silicas or mesoporous
carbons as templates. Possible drawbacks of using mesoporous silica and carbon as
templates were discussed
Radiation Effects in CMOS Isolation Oxides: Differences and Similarities With Thermal Oxides
Full text linkRadiation effects in thick isolation oxides of modern CMOS technologies are investigated using dedicated test structures designed using two commercial foundries. Shallow Trench Isolation and Pre-Metal Dielectric are studied using electrical measurements performed after X-ray irradiations and isochronal annealing cycles. This paper shows that trapping properties of such isolation oxides can strongly differ from those of traditional thermal oxides usually used to process the gate oxide of Metal Oxide Semiconductor Field Effect Transistors. Buildup and annealing of both radiation-induced oxide-trap charge and radiation-induced interface traps are discussed as a function of the oxide type, foundry and bias condition during irradiation. Radiation-induced interface traps in such isolation oxides are shown to anneal below 100°C contrary to what is usually observed in thermal oxides. Implications for design hardening and radiation tests of CMOS Integrated Circuits are discussed
Copper catalyzed one-pot synthesis of beta-ketophosphine oxides from ketones and H-phosphine oxides
No full textA facile and efficient copper catalyzed one-pot method has been developed for the formation of beta-ketophosphine oxides from ketones and H-phosphine oxides under air at room temperature, in which vinylhydrazinedicarboxylate was formed as the key intermediate. Preliminary mechanistic studies indicated that the reaction might involve a radical process and carbonyl oxygen atom of beta-ketophosphine oxides came from molecular oxygen. (C) 2017 Elsevier Ltd. All rights reserved
Porous anodic metal oxides
No full textAn equifield strength model has been established to elucidate the formation mechanism for the highly ordered alumina pore arrays and titanium oxide nanotubular arrays prepared via a common electrochemical methodology, anodisation. The fundamentals of the equifield strength model was the equilibrium between the electric field driven oxidation rate of the metal and electric field enhanced dissolution rate of oxide. During the anodic oxidation of metal, pore initiation was believed to generate based on dissolution rate difference caused by inhomogeneity near the metal/oxide interface. The ionic nanoconvection driven by the electric force exerted on the space charge layer in the vicinity of electrolyte/oxide interface is established to be the main driving force of the pore ordering at the early stage of the anodisation. While the equifield strength requirement governs the following formation of the single pore and the self-ordering of random distributed pore arrays during the anodisation process.
Hexagonal patterned Al2O3 nanopore arrays and TiO2 nanotubular arrays have been achieved by anodisation of corresponding metal substrates in proper electrolytes. The two characteristic microstructural features of anodic aluminium oxide (AAO) and anodic titanium oxide (ATO) were investigated using scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The observations of the hemispherical electrolyte/oxide and oxide/metal interfaces, uniform thickness of the oxide layer, as well as self-adjustment of the pore size and pore ordering can be well explained by the equifield strength model.
Field enhanced dissociation of water is extremely important in determination of the porosity of anodic metal oxide. The porosity of AAO and ATO films was found to be governed by the relative dissociation rate of water which is dependent on anodisation conditions, such as electrolyte, applied voltage, current density and electric field strength. Using an empirical method, the relations between the porosity of the AAO (ATO) films and the anodisation parameters, such as electric field strength, current density and applied voltage, have been established. Besides, the extent that an external electric field can facilitate the heterolytic dissociation of water molecule has been estimated using quantum-chemical model computations combined with the experimental aspect. With these achievements, the fabrication of anodic metal oxide films can be understood and controlled more precisely.
Additionally, the impacts of other factors such as the electrolyte type and the temperature effect on the morphology of the anodic products were also investigated. Some important experimental evidences on the pore diameters variation with applied voltage in the anodisation of aluminium and the titanium were obtained for future investigation of the anodic metal oxide formation processes
High resolution electron energy loss spectroscopy of manganese oxides: application to Mn3O4 nanoparticles
Full text linkManganese oxides particularly Mn3O4 Hausmannite are currently used in many industrial applications such as catalysis, magnetism, electrochemistry or air contamination. The downsizing of the particle size of such material permits an improvement of its intrinsic properties and a consequent increase in its performances compared to a classical micron-sized material. Here, we report a novel synthesis of hydrophilic nano-sized Mn3O4, a bivalent oxide, for which a precise characterization is necessary and for which the determination of the valency proves to be essential. X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and particularly High Resolution Electron Energy Loss Spectroscopy (HREELS) allow us to perform these measurements on the nanometer scale. Well crystallized 10–20 nm sized Mn3O4 particles with sphere-shaped morphology were thus successfully synthesized. Meticulous EELS investigations allowed the determination of a Mn3+/Mn2+ ratio of 1.5, i.e. slightly lower than the theoretical value of 2 for the bulk Hausmannite manganese oxide. This result emphasizes the presence of vacancies on the tetrahedral sites in the structure of the as-synthesized nanomaterial
Aerosol spray synthesis of powder perovskite-type oxides
No full textThe physicochemical properties and the performance of perovskite‐type oxides are highly dependent on the applied preparation method and correlated synthesis conditions. Spray synthesis methods are available for a wide range of perovskite‐type oxides for use in various applications, including catalysis. Besides enabling a cost‐effective/economic production of materials with a high throughput, reproducibility, and homogeneity, spray methods can offer materials with unusual structural properties that conventional synthesis methods are not able to confer. Taking catalytic applications of perovskite‐type oxides into consideration, various spray synthesis methods are reviewed with the aim to provide a compendium on characteristics of synthesis methods, structural properties, and performance of materials
A mild method for electrochemical reduction of Heterocyclic N-Oxides
No full textDeoxygenation of heteroaromatic N-oxides is commonly accomplished using chemical or enzymatic methods. In this work, we report on an expedient protocol for electrochemical reduction of pyridine N-oxide derivatives under mild conditions. A diverse range of mono- and bis-N-oxides were converted into the corresponding nitrogen bases in good yields. Importantly, the method is highly selective towards N-oxides and tolerates challenging halo and nitro substituents in the heteroaromatic ring
Transition metal oxides for high performance sodium ion battery anodes
Full text linkSodium-ion batteries (SIBs) are attracting considerable attention with expectation of replacing lithium-ion batteries (LIBs) in large-scale energy storage systems (ESSs). To explore high performance anode materials for SIBs is highly desired subject to the current anode research mainly limited to carbonaceous materials. In this study, a series of transition metal oxides (TMOs) is successfully demonstrated as anodes for SIBs for the first time. The sodium uptake/extract is confirmed in the way of reversible conversion reaction. The pseudocapacitance-type behavior is also observed in the contribution of sodium capacity. For Fe2O3anode, a reversible capacity of 386 mAh g-1at 100 mA g-1 is achieved over 200 cycles; as high as 233 mAhg-1is sustained even cycling at a large current-density of 5 A g-1
Thermodynamic analysis of two-step solar water splitting with mixed iron oxides
No full textA two-step thermochemical cycle for solar production of hydrogen from water has been developed and investigated. It
is based on metal oxide redox pair systems, which can split water molecules by abstracting oxygen atoms and reversibly
incorporating them into their lattice. After successful experimental demonstration of several cycles of alternating
hydrogen and oxygen production, the present work describes a thermodynamic study aiming at the improvement of
process conditions and at the evaluation of the theoretical potential of the process.
In order to evaluate the maximum hydrogen production potential of a coating material, theoretical considerations
based on thermodynamic laws and properties are useful and faster than actual tests. Through thermodynamic calculations it is possible to predict the theoretical maximum output of H2 from a specific redox-material under certain conditions. Calculations were focussed on the two mixed iron oxides nickel–iron-oxide and zinc–iron-oxide. In the simulation the amount of oxygen in the redox-material is calculated before and after the water-splitting step on the basis of laws of thermodynamics and available material properties for the chosen mixed iron oxides. For the simulation the commercial Software FactSage and available databases for the required material properties were used.
The analysis showed that a maximum hydrogen yield is achieved if the reduction temperature is raised to the limits of
the operation range, if the temperature for the water splitting is lowered below 8001C and if the partial pressure of oxygen during reduction is decreased to the lower limits of the operational range. The predicted effects of reduction temperature and partial pressure of oxygen could be confirmed in experimental studies. The increased hydrogen yield at lower splitting temperatures of about 8001C could not be confirmed in experimental results, where a higher splitting
temperature led to a higher hydrogen yield. As a consequence it can be stated that kinetics must play an important role especially in the splitting step
Bacterial reduction of N-oxides of tobacco- specific nitrosamines (TSNA)
Full text link1 Contrary to established metabolic pattern, a recent investigation of NNK metabolism produced in rat urine higher levels of 4-(methylnitrosamino)-1-(3-pyridyl)-1- butanone (NNK) and 4-(methylnitrosamino)-1-(3-pyri dyl)-1-butanol (NNAL) than their N-oxides, suggesting that reconversion of N-oxides could occur after urine formation. 2 To verify the possible role of bacteria in the reduction of NNK-N-oxide and NNAL-N-oxide to their respective parent compounds, NNK and NNAL, in smokers with urinary tract infection (UTI), the N-oxides were isolated from the urine of rats treated with 5-3HNNK and individually incubated at 37°C with ten bacterial species in sterile human urine under different pH regimens. After incubation with the bacteria, aliquots of culture media were analyzed by high pressure liquid chromatography (HPLC) with radiochemical detection. 3 Escherichia coli, Enterobacter cloacae, Klebsiella pneumoniae and Proteus mirabilis possessed varying capacity to regenerate NNK and NNAL from their N- oxides while others showed no detectable reductive capability within 24 h. 4 This result constitutes the first experimental evidence that in tobacco users with concomitant UTI, bacterial regeneration of the procarcinogenic NNK and NNAL from their N-oxides could occur in the bladder leading to increased carcinogen burden in these individuals
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