Fabrication of nanostructured metal nitrides with tailored composition and morphology

Unprecedented multi-channel TiN micro/nanotubes as well as various metal nitride nanofibers, including TiN, VN, NbN and ternary metal nitride nanofibers, were fabricated by a template free electrospinning method combined with post-nitridation.     

Ultrasound-assisted synthesis of nanostructured transition metal oxides

Ultrasound pretreatment of aqueous solutions of cetyltrimethylammonium bromide as a structure- directing agent has been applied to prepare nanostructured mesoporous Mn, Fe, and Ni oxides. After removal of the template by triple extraction with a water–ethanol solution of sodium acetate or ammonium chloride, air-calcined samples of oxide materials prepared in such a way possess surface areas of about 300–450 m²/g and are thermally stable up to 300°C.     

General, spontaneous ion replacement reaction for the synthesis of micro- and nanostructured metal oxides

A novel spontaneous ion replacement route based on the solubility difference as the driving force to synthesize a number of metal oxides has been established. We present a comprehensive study on the ion replacement reaction for chemical synthesis of micro- and nanostructured Mn2O3, ZnO, CuO, CdO, Al2O3, and CaO samples. This novel approach described herein is derived from the solubility difference between two carbonate salts, in which a metal cation can be driven from one liquid phase into another solid phase in the solution system. The resulting metal carbonate salts are initially formed and subsequently calcined to form highly crystallined metal oxides. The variation of pH values, reaction temperature, and reagent shapes can vary the solubility of these two carbonate salts, which thus changes the final morphology of metal oxides. The present work makes a progress to simply and mildly synthesize metal oxides with various morphologies, due to the fact that materials with a desired morphology are a key engineering step toward their shape-dependent chemical and physical properties.     

The combustion synthesis of iron group metal fine powders

The new approach has been developed for the synthesis of nickel (Ni), cobalt (Co) and iron (Fe) powders from the appropriate oxides by the solid combustion method. The reduction was made by sodium azide (NaN₃) at the presence of carbon in the argon atmosphere. The variation of combustion temperature and velocity was performed by using alkali metal salt as an inert diluent. The values of combustion parameters were measured and also the temperature distribution in a combustion wave are obtained. The geometric sizes of reactionary zones and the activation energy of the process were estimated. The optimum conditions for single-phase metal powder synthesis were found. Powders fabricated in this way had cubic structure and particles size about 0.5-2.0 μm for Ni, Co and 1-3 μm for Fe. In a number of cases the formation of spherical particles with the average size about 5-15 μm were observed.     

Block copolymer based composition and morphology control in nanostructured hybrid materials for energy conversion and storage: solar cells, batteries, and fuel cells

The development of energy conversion and storage devices is at the forefront of research geared towards a sustainable future. However, there are numerous issues that prevent the widespread use of these technologies including cost, performance and durability. These limitations can be directly related to the materials used. In particular, the design and fabrication of nanostructured hybrid materials is expected to provide breakthroughs for the advancement of these technologies. This tutorial review will highlight block copolymers as an emerging and powerful yet affordable tool to structure-direct such nanomaterials with precise control over structural dimensions, composition and spatial arrangement of materials in composites. After providing an introduction to materials design and current limitations, the review will highlight some of the most recent examples of block copolymer structure-directed nanomaterials for photovoltaics, batteries and fuel cells. In each case insights are provided into the various underlying fundamental chemical, thermodynamic and kinetic formation principles enabling general and relatively inexpensive wet-polymer chemistry methodologies for the efficient creation of multiscale functional materials. Examples include nanostructured ceramics, ceramic-carbon composites, ceramic-carbon-metal composites and metals with morphologies ranging from hexagonally arranged cylinders to three-dimensional bi-continuous cubic networks. The review ends with an outlook towards the synthesis of multicomponent and hierarchical multifunctional hybrid materials with different nano-architectures from self-assembly of higher order blocked macromolecules which may ultimately pave the way for the further development of energy conversion and storage devices.     

Thin metal nanostructures: synthesis,properties and applications

Two-dimensional nanomaterials, especially graphene and single- or few-layer transition metal dichalcogenide nanosheets, have attracted great research interest in recent years due to their distinctive physical, chemical and electronic properties as well as their great potentials for a broad range of applications. Recently, great efforts have also been devoted to the controlled synthesis of thin nanostructures of metals, one of the most studied traditional materials, for various applications. In this minireview, we review the recent progress in the synthesis and applications of thin metal nanostructures with a focus on metal nanoplates and nanosheets. First of all, various methods for the synthesis of metal nanoplates and nanosheets are summarized. After a brief introduction of their properties, some applications of metal nanoplates and nanosheets, such as catalysis, surface enhanced Raman scattering (SERS), sensing and near-infrared photothermal therapy are described.     

Macrocyclic sulfamides: synthesis, hybridization, and metal binding properties

Four cyclophanes incorporating the cyclosulfamide sub-unit have been synthesised in high yield. The X-ray crystal structures of three of them, and of cyclosulfamide itself, provide useful insight into the hybridisation of such compounds. The ionophoric properties of the macrocycles are also reported, with the sulfamides showing unusual selectivity for rubidium (benzyl trimer), barium (pyridyl dimer) and silver (pyridyl dimer and trimer).     

Site-resolved X-ray scattering studies,II the morphology in injection-molded PP foams

PP-structural foam moldings, composed of three co-axial cylinders were produced on an on-line injection molding machine in a pre-pressurized mold cavity by the classical low-pressure process and an alternative low-pressure process. Melt temperature, injection direction and sprue diameter were varied. Cross-sections cut from the middle of the small cylinder in longitudinal orientation were investigated by site-resolved X-ray scattering techniques in three different experiments: (i) wide-angle scans of the cross-sections, resulting in two-dimensional intensity maps; (ii) measurements of azimuthal intensity distributions of the principal PP reflections, for selected positions in the cross-sections; (iii) again for selected positions, small-angle measurements interpreted in terms of long periods. The comparison of the results derived from the different samples in the different experiments allows far-reaching statements about the influence of melt temperature, sprue dimension and position, and the type of process on the morphology and texture in the smallest cylinder of the moldings.     

Polyurea-functionalized multiwalled carbon nanotubes: synthesis, morphology, and Raman spectroscopy

An in situ polycondensation approach was applied to functionalize multiwalled carbon nanotubes (MWNTs), resulting in various linear or hyperbranched polycondensed polymers [e.g., polyureas, polyurethanes, and poly(urea-urethane)-bonded carbon nanotubes]. The quantity of the grafted polymer can be easily controlled by the feed ratio of monomers. As a typical example, the polyurea-functionalized MWNTs were measured and characterized in detail. The oxidized MWNTs (MWNT-COOH) were converted into acyl chloride-functionalized MWNTs (MWNT-COCl) by reaction with neat thionyl chloride (SOCl2). MWNT-COCl was reacted with excess 1,6-diaminohexane, affording amino-functionalized MWNTs (MWNT-NH2). In the presence of MWNT-NH2, the polyurea was covalently coated onto the surfaces of the nanotube by in situ polycondensation of diisocyanate [e.g., 4,4'-methylenebis(phenylisocyanate)] and 1,6-diaminohexane, followed by the removal of free polymer via repeated filtering and solvent washing. The coated polyurea content can be controlled to some extent by adjusting the feed ratio of the isocyanato and amino groups. The structure and morphology of the resulting nanocomposites were characterized by FTIR, NMR, Raman, confocal Raman, TEM, EDS, and SEM measurements. The polyurea-coated MWNTs showed interesting self-assembled flat- or flowerlike morphologies in the solid state. The signals corresponding to that of the D and G bands of the carbon nanotubes were strongly attenuated after polyurea was chemically tethered to the MWNT surfaces. Comparative experiments showed that the grafted polymer species and structures have a strong effect on the Raman signals of polymer-functionalized MWNTs.     

Changes in the composition of synthesis products upon transitioning from self-ignition to combustion

Changes in the chemical composition of condensed products upon switching from synthesis in the self-ignition mode to combustion synthesis is studied by approximate analytical and numerical means for condensed substances that react via competing reaction pathways. It is shown that these different modes of synthesis produce different compositions of the reaction products. The conditions required for transitioning from one mode of combustion initiation (thermal explosion) to another (ignition) are determined. It is found that this transition can occur upon changing the temperature of a heater by just two characteristic intervals. A scaling procedure that allows the calculation results obtained at zero dimensionless temperature of the heater to be used to determine the effect its non-zero dimensionless temperature has on the ignition mode and the composition of the obtained products is proposed. Calculations show that materials with different distributions of the chemical composition along the sample can be obtained by deliberately changing the temperature of the heater.     

Low-cost and facile synthesis of mesocellular carbon foams

Mesocellular carbon foam composed of nanometer sized primary particles was synthesized using hydrothermally synthesized MSU-F silica as a template and poly(furfuryl alcohol) as a carbon source.     

Low temperature nanostructured lithium titanates: controlling the phase composition, crystal structure and surface area

Low temperature lithium titanate compounds (i.e., Li₄Ti₅O₁₂ and Li₂TiO₃) with nanocrystalline and mesoporous structure were prepared by a straightforward aqueous particulate sol–gel route. The effect of Li:Ti molar ratio was studied on crystallisation behaviour of lithium titanates. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that the powders were crystallised at the low temperature of 500 °C and the short annealing time of 1 h. Moreover, it was found that Li:Ti molar ratio and annealing temperature influence the preferable orientation growth of the lithium titanate compounds. Transmission electron microscope (TEM) images showed that the average crystallite size of the powders annealed at 400 °C was in the range 2–4 nm and a gradual increase occurred up to 10 nm by heat treatment at 800 °C. Field emission scanning electron microscope (FE-SEM) analysis revealed that the deposited thin films had mesoporous and nanocrystalline structure with the average grain size of 21–28 nm at 600 °C and 49–62 nm at 800 °C depending upon the Li:Ti molar ratio. Moreover, atomic force microscope (AFM) images confirmed that the lithium titanate films had columnar like morphology at 600 °C, whereas they showed hill-valley like morphology at 800 °C. Based on Brunauer–Emmett–Taylor (BET) analysis, the synthesized powders showed mesoporous structure containing pores with needle and plate shapes. The surface area of the powders was enhanced by increasing Li:Ti molar ratio and reached as high as 77 m²/g for the ratio of Li:Ti = 75:25 at 500 °C. This is one of the smallest crystallite size and the highest surface areas reported in the literature, and the materials could be used in many applications such as rechargeable lithium batteries and tritium breeding materials.     

A rapid polyol combustion strategy towards scalable synthesis of nanostructured LiFePO4/C cathodes for Li-ion batteries

In the present study, carbon-coated lithium iron phosphate (LiFePO₄/C) is prepared directly by a polyol-assisted pyro-synthesis performed under reaction times of a few seconds in open-air conditions. The polyol solvent, tetraethylene glycol (TTEG), acts as a low-cost fuel to facilitate combustion and the released exothermic energy promotes the nucleation and growth processes of the olivine nanoparticles. In addition, phosphoric acid (used as the phosphorous source) acts as a catalyst to accelerate polyol carbonization. The structure analysis of the as-prepared LiFePO₄/C using X-ray, neutron diffraction and ⁷Li NMR studies suggested the efficacy of the rapid technique to produce highly crystalline phase-pure olivine nanocrystals. The electron microscopy and particle-size distribution studies revealed that the average particle diameters lie below 100 nm and confirmed the presence of a surface carbon layer of 2–3 nm thickness. The thermal and elemental studies indicated that the carbon content in the sample was approximately 5 %. The prepared LiFePO₄/C cathode delivered capacities of 162 mA h g^-1 at 0.1 °C rates with impressive capacity retention for extended cycling. The polyol-assisted pyro-synthesis, which evades the use of external energy sources, is not only a straightforward, simple and timely approach but also offers opportunities for large-scale LiFePO₄/C production.     

Thermal annealing of Au nanorod self-assembled nanostructured materials: morphology and optical properties

Three-dimensional Au nanorod and Au nanoparticle nanostructured materials were prepared by layer-by-layer self-assembly. The plasmonic properties of the Au nanorod and Au nanoparticle self-assembled nanostructured materials (abbreviated as AuNR and AuNP SANMs) are tunable by the controlled self-assembly process. The effect of thermal annealing at 180 and 500 degrees C to the morphologies, plasmonic properties and surface-enhanced Raman scattering (SERS) responses of these SANMs were investigated. According to the experimental results, these properties correlate with the structure of the SANMs.     

Effect of solvent composition on oxide morphology during flame spray pyrolysis of metal nitrates

The effect of solvent composition on particle formation during flame spray pyrolysis of inexpensive metal-nitrates has been investigated for alumina, iron oxide, cobalt oxide, zinc oxide and magnesium oxide. The as-prepared materials were characterized by electron microscopy, nitrogen adsorption, X-ray diffraction (XRD) and disc centrifugation (XDC). The influence of solvent parameters such as boiling point, combustion enthalpy and chemical reactivity on formation of either homogeneous nanoparticles by evaporation/nucleation/coagulation (gas-to-particle conversion) or large particles through precipitation and conversion within the sprayed droplets (droplet-to-particle conversion) is discussed. For Al(2)O(3), Fe(2)O(3), Co(3)O(4) and partly also MgO, the presence of a carboxylic acid in the FSP solution resulted in homogeneous nanoparticles. This is attributed to formation of volatile metal carboxylates in solution as evidenced by attenuated total reflectance spectroscopy (ATR). For ZnO and MgO rather homogeneous nanoparticles were formed regardless of solvent composition. For ZnO this is attributed to its relatively low dissociation temperature compared to other oxides. While for MgO this is traced to the high decomposition temperature of Mg(NO(3))(2) together with Mg(OH)(2)?MgO transformations. Cobalt oxide (Co(3)O(4)) nanoparticles made by FSP were not aggregated but rather loosely agglomerated as determined by the excellent agreement between XRD- and XDC-derived crystallite and particle sizes, respectively, pointing out the potential of FSP to make non-aggregated particles.     

溶液燃烧法一步合成纳米NiO和Ni

以硝酸镍为氧化剂,乙二醇为燃料,采用溶液燃烧法在300℃合成了纳米NiO和金属Ni.采用X射线衍射仪(XRD)和扫描电子显微镜(SEM)系统地研究了不同燃料、燃料/氧化剂比对合成产物的晶相组成和微观形貌的影响.结果表明:燃料种类和燃料/氧化剂比对合成产物晶相组成的影响显著.通过控制乙二醇/硝酸镍的比例,可以在空气气氛中...     

Highly hydrophilic copolymers of N,N-dimethylacrylamide, acrylamido-2-methylpropanesulfonic acid, and ethylenedimethacrylate: nanoscale morphology in the swollen state and use as exotemplates for synthesis of nanostructured ferric oxide

The polymer framework of water-swollen copolymers of N,N-dimethylacrylamide, acrylamido-2-methylpropanesulfonic acid, and ethylenedimethacrylate (nominal cross-linking degrees of 4, 8, and 20 mol %) is composed of highly expanded domains, with "pores" not less than 6 nm in diameter. When the 4% cross-linked copolymer (DAE 26-4) is swollen with a 10(-4) M solution of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) in water, MeOH, EtOH, or nBuOH, the molecules of the paramagnetic probe rotate rapidly (τ<1000 ps) and as fast as in the bulk liquid in the case of water. The swelling degree of DAE 26-4 is related to the Hansen solubility parameters of a number of liquids, including linear alcohols up to n-octanol. It is also found that the rotational correlation time of TEMPOL in the copolymer swollen by water and the lightest alcohols increases with decreasing specific absorbed volume. Time-domain NMR spectrometry of water-swollen DAE 26-4 shows that sorption of only 14% of the liquid required for its complete swelling is enough for full hydration of the polymer chains. Accordingly, in fully swollen DAE 26-4 the longitudinal relaxation time of water closely approaches the value of pure water. {(13)C} CP-MAS NMR on partially and fully water swollen samples of DAE 26-4 shows that swelling increases the mobility of the polymer chains, as clearly indicated by the narrowing of the best-resolved peaks. DAE 26-4 was used as an exotemplate for the synthesis of nanocomposites composed of the polymer and nanostructured Fe(2)O(3) through a series of ion-exchange/precipitation cycles. After the first cycle the nanoparticles are 3-4 nm in diameter, with practically unchanged size after subsequent cycles (up to five). In fact, the nanoparticle size never exceeded the diameter of the largest available pores. This suggests that the polymer framework controls the growth of the nanoparticles according to the template-controlled synthesis scheme. Selected-area electron diffraction, TEM, and high-resolution electron microscopy show that the nanostructured inorganic phase is composed of hematite.