Showing papers in "Journal of Materials Chemistry in 2002"

Intercalation chemistry of layered double hydroxides: recent developments and applications

Abstract: Layered double hydroxides (LDHs) have been investigated for many years as host materials for a range of anion exchange intercalation reactions. In this role they have been used extensively as ion-exchange materials, catalysts, sorbents and halogen absorbers. More recently, there have been a tremendous number of new developments using these materials to store and deliver biologically active materials in vivo. Significant advances have been made recently on the characterisation of these materials, including structural studies and on the mechanism of intercalation using in situ techniques.

Growth and form of gold nanorods prepared by seed-mediated, surfactant-directed synthesis

Abstract: Gold nanorods were prepared via a seed-mediated sequential growth process involving the use of citrate-stabilised seed crystals and their subsequent growth in a series of reaction solutions containing [AuCl4]−, ascorbic acid and the cationic surfactant cetyltrimethylammonuim bromide (CTAB). Electron diffraction analysis and HRTEM images of mature nanorods showed superpositions of two specific pairs of crystallographic zones, either and or and , which were consistent with a cyclic penta-twinned crystal with five {111} twin boundaries arranged radially to the [110] direction of elongation. The nanorods have an idealised 3-D prismatic morphology with ten {111} end faces and five {100} or {110} side faces, or both. TEM studies of crystals at various stages of growth indicated that the seed crystals are initially transformed by growth and aggregation into decahedral penta-twinned crystals, 4% of which become elongated when a fresh reaction solution is added, whilst the remaining twins grow isometrically. Reiteration of this procedure increases the length of the existing nanorods, induces further transformation of isometric particles to produce a second (and third) population of shorter, wider nanorods, and increases the size of the isometric crystals. The data indicate that symmetry breaking in fcc metallic structures to produce anisotropic nanoparticles is based on an intrinsic structural mechanism (twinning) that is subsequently modulated extrinsically during growth in solution by specific adsorption of AuI–surfactant complexes on the side faces/edges of the isometric penta-twinned crystals and which is responsible for the preferential growth along the common [110] axis. We propose that the coupling of multiple twinning and habit modification is a general mechanism that applies to other experimental procedures (electrochemical, inverse micellar media) currently used to prepare metallic nanoparticles with a high aspect ratio.

Covalent chemistry of single-wall carbon nanotubes

Abstract: Despite the extraordinary promise of single-wall carbon nanotubes, their realistic application in materials and devices has been hindered by processing and manipulation difficulties. Now that this unique material is readily available in near kilogram quantities (albeit still at high cost), research into means of chemical alteration is in full swing. The covalent attachment of appropriate moieties is anticipated to facilitate applications development by improving solubility and ease of dispersion, and providing for chemical attachment to surfaces and polymer matrices. While it is clear that more investigation is needed to elucidate the nature and locality of covalently attached moieties, developments to date indicate that carbon nanotubes may indeed be considered a true segment of organic chemistry. In this contribution, we review the current state of carbon nanotube covalent chemistry, and convey our anxious expectation that further developments will follow.

Growth conditions for wurtzite zinc oxide films in aqueous solutions

Abstract: A pH above 9.0 was essential for the formation of wurtzite zinc oxide (ZnO) in aqueous solution systems. The addition of complexing agents to decrease the deposition rate was required for the direct growth of ZnO on the surface of substrates through heterogeneous nucleation. The nucleation of the crystals was promoted by undercoats derived from zinc acetate. Wurtzite ZnO films consisting of hexagonal columns with diameters of 20–100 nm were successfully prepared on various substrates under suitable conditions.

Synthesis and characterization of stable aqueous dispersions of silver nanoparticles through the Tollens process

Abstract: This paper describes a simple and convenient procedure based on the Tollens process for the preparation of silver nanoparticles with a relatively narrow distribution in size. The starting reagents were similar to those commonly used in the electroless deposition of silver. Only under appropriate conditions, mixing of these reagents was able to generate stable aqueous dispersions of silver colloids rather than thin films of silver deposited on the surfaces of objects immersed in the plating solution (including the interior surface of the container). We have demonstrated the capability and feasibility of this approach by forming silver nanoparticles with dimensions in the range of 20–50 nm. These silver nanoparticles could exist as very stable dispersions in water, or as submonolayer coating on microscale colloids. We have also explored the use of light scattering simulation to study the oxidation (by air) of these nanoparticles.

Synthesis and characterization of high-temperature hexagonal P2-Na0.6 MnO2 and its electrochemical behaviour as cathode in sodium cells

Abstract: A layered sodium manganese oxide, Na0.6MnO2, stable at temperatures above 800 °C, was synthesized by using a sol–gel method that employs Mn(acac)3 (ac = acetylacetonate), Na2CO3 and propionic acid to form the resin framework. This layered bronze possesses a hexagonal, P2-type structure, in which the distortion associated with Mn3+ is hardly perceptible. It reacts slowly, though reversibly, with atmospheric moisture, which causes the interlayer spacing in the structure to increase by ca. 2.5 A, through intercalation of water molecules into the interlayer gap occupied by Na+ ions. The anhydrous material was tested as a cathode in sodium cells. Although the electrochemical intercalation of Na+ occurs in two steps, the host retains its main structural features, with a slight tendency in the interlayer spacing to contract as the sodium content increases. The similarity between the discharge and charge profiles of the first cycles reveals a quasi-reversible nature in the intercalation process and that the cell can deliver a constant specific capacity of ca. 140 A h kg−1 at 0.1 mA cm−2 when cycled in a voltage window of 3.8–2.0 V. However, the continuous strains and distortions resulting from the insertion and extraction of Na+ ions cause the host structure to gradually collapse and yield an amorphous material after the first eight cycles. This leads to a progressive reduction of the cell capacity, irrespective of the specific voltage window used.

Novel red-emitting fluorene-based copolymers

Abstract: A series of novel soluble conjugated copolymers derived from 9,9-dioctylfluorene (DOF) and 4,7-di-2-thienyl-2,1,3-benzothiadiazole (DBT) were synthesized by a palladium-catalyzed Suzuki coupling reaction with different feed ratios of DOF to DBT. Owing to exciton confinement on the DBT site, exciton emission is centred on the DBT chromophore and gives rise to saturated red emission. Polyfluorene fluorescence is quenched completely at DBT concentrations as low as 1% in the solid film. Devices based on these copolymers emit a saturated red light. Chromaticity coordinates are around x = 0.70, y = 0.30 for the copolymers. The emission peaks are shifted from 628 nm to 674 nm when DBT content increases from 1 to 35%. The highest quantum efficiency achieved with device configuration of ITO/PEDT/PFO-DBT/Ba/Al was 1.4% for the copolymer with 15% DBT content.

Direct syntheses of ordered SBA-15 mesoporous materials containing arenesulfonic acid groups

Abstract: SBA-15 mesoporous silica has been functionalized with arenesulfonic acid groups by means of a one-step simple synthesis approach involving co-condensation of tetraethoxysilane (TEOS) and 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane (CSPTMS) in the presence of a poly(alkylene oxide) block copolymer (Pluronic 123) under acid silica-based catalysis. The resultant materials show hexagonal mesoscopic order and pores sizes up to 60 A, with acid exchange capacities of ca. 1.3 mequiv. H+ per g SiO2 and surface areas up to 600 m2 g−1. The sulfonic groups anchored to the silica surface of the pore walls are thermally stable to temperatures up to 380 °C and resistant to leaching in organic and aqueous solutions under mild conditions. 31P MAS NMR measurements of chemically adsorbed triethylphosphine oxide and the catalytic properties confirm the presence of Bronsted acid centers in these mesoporous materials containing arenesulfonic acid groups that are stronger than those found in propanesulfonic-modified SBA-15 and Al-MCM-41.

Formation and characterization of Au–Ag bimetallic nanoparticles in water-in-oil microemulsions

Abstract: Gold–silver bimetallic nanoparticles with varying mole fractions were synthesized in water-in-oil microemulsions of water/Aerosol OT/isooctane by the co-reduction of HAuCl4 and AgNO3 with hydrazine at 25 °C. TEM analysis revealed that the bimetallic nanoparticles were essentially monodisperse and had a mean diameter of 4–22 nm, increasing with an increase in the molar ratio of water to Aerosol OT (ω0) and Ag content. The UV/VIS absorption spectra of their solutions exhibited only one plasmon absorption and the absorption maximum of the plasmon band red-shifted almost linearly from 400 to 520 nm with increasing Au ∶ Ag molar ratio, revealing the formation of an alloy. Although the characteristic peaks for Au and Ag were too close to distinguish, the XRD analysis showed that the characteristic peaks for a Au–Ag bimetallic systems became broader and accordingly suggested the formation of bimetallic nanoparticles. The EDX analysis confirmed directly the formation of Au–Ag bimetallic nanoparticles. It showed that the composition of Au–Ag bimetallic nanoparticles was in good agreement with that of the feed solution but the outer layer of the particles was enriched in Ag. The HRTEM study indicated the resultant Au–Ag bimetallic nanoparticles contained single and multiple twins as well as stacking faults, and no mismatch was present. In addition, it was found that the formation rate of Au nanoparticles was much faster than that of Ag nanoparticles. This satisfactorily accounted for the composition distribution within a Au–Ag bimetallic nanoparticle.

Preparation of polychrome silver nanoparticles in different solvents

Abstract: Polychrome silver nanoparticles have been prepared by a soft solution approach under microwave irradiation from a solution of silver nitrate (AgNO3) in the presence of poly(N-vinyl-2-pyrrolidone) without any other reducing agent. Different morphologies of silver colloids with charming colors could be obtained using different solvents as the reaction medium. The structures of the silver colloids were determined by X-ray powder diffraction. UV-Vis spectroscopy was used to follow the reaction process and to characterize the optical properties of the resultant silver colloids. The influence of the solvent on the morphology of silver was investigated.

One-dimensional nanostructures of trigonal tellurium with various morphologies can be synthesized using a solution-phase approach

Abstract: This article describes a solution-phase, self-seeding approach to the large-scale synthesis of one-dimensional (1D) nanostructures of trigonal tellurium (t-Te) with diameters ranging from 50 to hundreds of nanometers, and lengths up to tens of micrometers. These highly anisotropic nanostructures were formed through the reduction of orthotelluric acid (or tellurium dioxide) by hydrazine at various refluxing temperatures. Nuclei formed in the reduction process had a strong tendency to grow along the c-axis due to the inherently anisotropic structure of t-Te. Depending on the solvent and refluxing temperature, the growth of t-Te nanostructures was found to follow two distinct paths. When the reaction was refluxed in water and at temperatures below 100 °C, the initial reduction products were a mixture of nanocrystallites of t-Te and spherical colloids of amorphous tellurium (a-Te). When this mixture was aged at room temperature, the a-Te colloids slowly dissolved into the solution and grew into nanowires on the nanocrystallites of t-Te. When the reaction was carried out in pure ethylene glycol (or mixtures with water) and refluxed at temperatures above 100 °C, the 1D nanostructures of t-Te were directly formed in the reduction process. The exact morphology of these anisotropic nanostructures was mainly controlled by the refluxing temperature (Tr); typical examples include spines (Tr < 100 °C), filaments (Tr = 100–160 °C), needles (Tr = 160–180 °C), and tubular structures (Tr > 180 °C). These uniform, relatively monodispersed 1D nanostructures could form stable dispersions in ethylene glycol or water, and be used as the building blocks or templates to generate more complex nanostructured materials.

Functional oligothiophenes as advanced molecular electronic materials

Abstract: The oligothiophene/fullerene dyad system shows marked photoinduced electron transfer from the oligomer to the attached fullerene at the terminal position, and is successfully put to practical use in the fabrication of photovoltaic cells. The further modified dyad system, attaching a thiol or disulfide anchoring group at another terminal position, can form a self-assembled monolayer (SAM) on a gold substrate, where the tethered molecules are unidirectionally ordered. In particular, the use of a tripodal anchoring group provides a powerful approach for the formation of a much denser and more stable SAM, which is beneficial for the high performance of SAM-based photovoltaic cells. The porphyrin/oligothiophene/fullerene triad system is designed to evaluate efficient intramolecular electron transfer from the terminal porphyrin to the other terminal fullerene through the central oligothiophene, revealing the high potential of oligothiophene as a long-range molecular wire. Other oligothiophenes incorporating pyrenes or terpyridines are developed as light-emitting materials useful for electroluminescent (EL) devices. In these devices, the pyrene-modified system also acts as a hole-transport layer, whereas the terpyridine-modified system acts as an electron-transport layer.

Double-cable polymers for fullerene based organic optoelectronic applications

Abstract: Conjugated polymers are used increasingly for the fabrication of electronic and optoelectronic devices like light emitting diodes (LEDs) and photovoltaic (PV) elements. A breakthrough in realising a promisingly efficient conversion of solar energy into electrical energy has been achieved by using blends of soluble electron-donor type conjugated polymers with fullerenes as electron-acceptor, transporting component. This “bulk heterojunction” approach suggests the preparation of intrinsically bipolar materials as a way to control both electronic and morphological properties at once. On these bases, the covalent grafting of fullerene moieties to conjugated backbones seems promising for the preparation of intrinsically bipolar polymeric materials (double-cable polymers) alternative to conjugated polymer/fullerene composites. The recent developments on the design, the characterisation and the application of this novel class of fullerene functional materials are reviewed.

Preparation and characterization of a novel magnetic nano-adsorbent

Abstract: A novel magnetic nano-adsorbent has been developed using Fe3O4 nanoparticles (13.2 nm) as cores and polyacrylic acid (PAA) as ionic exchange groups. The Fe3O4 magnetic nanoparticles were prepared by co-precipitating Fe2+ and Fe3+ ions in an ammonia solution and treating under hydrothermal conditions. PAA was covalently bound onto the magnetic nanoparticles via carbodiimide activation. Transmission electron micrographs showed that the magnetic nanoparticles remained discrete and had no significant change in size after binding the PAA. The X-ray diffraction patterns indicated the magnetic nanoparticles were pure Fe3O4 with a spinel structure, and the binding of PAA did not result in a phase change. Magnetic measurement revealed the magnetic nanoparticles were superparamagnetic, and their saturation magnetization was reduced only slightly after PAA binding. Fourier transform infrared spectroscopy, thermogravimetric and differential thermal analyses, and X-ray photoelectron spectroscopy confirmed the binding of PAA to the magnetic nanoparticles, suggested a binding mechanism for the PAA, and revealed the maximum weight ratio of PAA bound to the magnetic nanoparticles was 0.12. In addition, the ionic exchange capacity of the resultant magnetic nano-adsorbents was estimated to be 1.64 mequiv g−1, much higher than those of commercial ionic exchange resins. When the magnetic nano-adsorbents were used for the recovery of lysozyme, the adsorption/desorption of lysozyme was completed within 1 min due to the absence of pore-diffusion resistance. Also, the adsorption/desorption efficiency could reach almost 100% under appropriate conditions, and the recovered lysozyme retained 95% activity.

Synthesis of nickel nanoparticles in aqueous cationic surfactant solutions

Abstract: The synthesis of nickel nanoparticles by the reduction of nickel chloride with hydrazine in an aqueous solution of cationic surfactants CTAB/TC12AB was studied. It was found that an appropriate amount of NaOH, trace acetone, and an elevated temperature were necessary for the formation of pure nickel nanoparticles. Also, it was not necessary to perform the reaction under a nitrogen atmosphere. X-ray diffraction revealed the resultant particles were pure nickel crystalline with a face-centered cubic (fcc) structure. Their mean diameter was 10–36 nm, increasing with increasing nickel chloride concentration or decreasing hydrazine concentration. When the concentration ratio of hydrazine to nickel chloride was above 40, the mean diameter approached a constant value. The magnetic measurement on a typical sample with a mean diameter of 12 nm showed that the resultant nickel nanoparticles were superparamagnetic due to their extremely small size. The saturation magnetization, remanent magnetization, and coercivity were 32 emu g−1, 5.0 emu g−1, and 40 Oe, respectively. Also, the magnetization was observed to increase with decreasing temperature. All the observed magnetic properties essentially reflected the nanoparticle's nature.

Aluminosilicate mesostructures with improved acidity and hydrothermal stability

Abstract: Significant improvements in both the hydrothermal stability and the acidity of mesostructured aluminosilcates have been reported recently. New assembly pathways, along with post-synthesis treatment methods, have made it possible to form structures with thick and more highly crosslinked framework walls. The resulting structures are slow to degrade under hydrothermal conditions in comparison to conventional analogs. Also, improved methodologies for grafting Al centers into the walls of pre-assembled frameworks have afforded aluminosilicate mesostructures with enhanced acidity. The most promising strategy for improving the hydrothermal stability and acidity of aluminosilicate mesostructures, however, is based on the use of protozeolitic nanoclusters. These so-called “zeolite seeds” can be directly assembled into hexagonal, cubic, wormhole, and foamlike framework structures under a variety of assembly conditions. They also can be grafted into the walls of pre-assembled frameworks to form more stable acidic derivatives.

Carbon coating of anatase-type TiO2 and photoactivity

Abstract: Carbon coating of photocatalytic anatase-type TiO2 powders was successfully carried out by heating a powder mixture of poly(vinyl alcohol) and TiO2 under N2 gas flow at temperatures above 700 °C. All particles of TiO2 were covered by a carbon layer and looked black. For methylene blue (MB) in aqueous solution, carbon-coated anatase powders thus prepared showed marked adsorption and decomposition under UV irradiation and were confirmed to keep almost the same photoactivity as that without any carbon coating. Carbon coating of anatase-type TiO2 was found to give different merits for photoactive performance; suppression of phase transformation from anatase to rutile at high temperatures, quick adsorption of MB into the carbon layer, decomposition of adsorbed MB by TiO2 and prevention of the interaction of TiO2 with binder resin. Repeated cycles of adsorption and decomposition of methylene blue in aqueous solution were experimentally confirmed.

Solid–liquid reaction synthesis of layered machinable Ti3AlC2 ceramic

Abstract: Fully dense polycrystalline Ti3AlC2 was fabricated by a solid–liquid reaction synthesis and simultaneous in-situ hot pressing of a mixture of Ti, Al and graphite powders at 1500 °C and 25 MPa for 5 minutes and subsequently annealing at 1200 °C for 20 minutes. The effects of various parameters including composition of the initial elemental powders, temperature as well as the hot pressing pressure on the purity, formation and densification of Ti3AlC2 were examined. In addition, the reaction path for the formation of Ti3AlC2 was investigated by DTA, XRD, SEM and EDS, suggesting that the reaction path during the heating process could be reasonably described as follows: Al powder melted at some 660 °C and coated the Ti particles; at about 740 °C the exothermic reactions between Al and Ti occurred and Ti–Al intermetallics like TiAl and Ti3Al were formed; the diffusion of carbon in the Ti–Al intermetallics at elevated temperature resulted in the carbides Ti2AlC, Ti3AlC and TiC; and finally these carbides and the unreacted graphite reacted at about 1420 °C to yield Ti3AlC2.

Intelligent window coatings: atmospheric pressure chemical vapour deposition of vanadium oxides

Abstract: Thin films of the vanadium oxides, V2O5, VO2, VOx (x = 2.00–2.50) and V6O13 were prepared on glass substrates by atmospheric pressure chemical vapour deposition (APCVD) of vanadium tetrachloride and water at 400–550 °C. The specific phase deposited was found to be dependent on the substrate temperature and the reagent concentrations. The films were characterised by Raman microscopy, X-ray diffraction (XRD), Rutherford backscattering (RBS), scanning electron microscopy (SEM), energy dispersive analysis by X-rays (EDX), reflectance/transmittance and UV absorption spectroscopy. The VO2 films show by Raman microscopy and reflectance/transmittance spectroscopy, reversible switching behaviour at 68 °C associated with a phase change from monoclinic (MoO2 structure) to tetragonal (TiO2, rutile structure).

A scalable CVD synthesis of high-purity single-walled carbon nanotubes with porous MgO as support material

Abstract: The choice of support and catalyst materials has been proved to be critical to scalable chemical vapor deposition (CVD) synthesis of carbon nanotubes In our study, we found that porous MgO prepared by thermal decomposition of its salts was an eminent support material for CVD growth of single-walled carbon nanotubes (SWNTs) Compared with other kinds of supports such as SiO2, ZrO2, Al2O3 and CaO etc, the quality of as-grown SWNTs on MgO supports was stable; the effects of reaction conditions such as furnace temperature, flow rate of the gas and the types of catalysts and supports on the properties of as-prepared SWNT products were thoroughly investigated and characterized by micro-Raman spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermogravimetry (TG) techniques The results indicated that the yields of SWNTs on MgO supports could be up to about 120% with the addition of a small amount of assistant catalyst Mo salt The obtained purity of the as-grown products was higher than 90% after treatment with 4 M HCl The obvious advantages of using MgO supports include efficient and stable growth of SWNTs, scalable synthesis of SWNTs at low cost, and easy removal of the support in mild acid, causing little harm to the products

Chiral nanotubes of polyaniline synthesized by a template-free method

Abstract: Chiral nanotubes of polyaniline (PANI) were successfully synthesized by a template-free method in the presence of (S)-(−)-2-pyrrolidone-5-carboxylic acid [(S)-PCA)] or (R)-(+)-2-pyrrolidone-5-carboxylic acid [(R)-PCA] as the dopant for the first time. The tubular morphologies of the resulting PANI–(S)-PCA and PANI–(R)-PCA were confirmed by SEM and TEM images. The tubes are 80–220 nm in outer diameter and 50–130 nm in inner diameter. It was proposed that the micelles of aniline–(S)-PCA or (R)-PCA, which were formed due to the hydrophobic aniline and the hydrophilic -COOH group of PCA, played a “template” role during the formation of the chiral nanotubes. These chiral nanotubes showed optically active and electrical properties. In particular, a positive and a negative Cotton effect corresponding to a helical screw of the polymer main chains was observed in the chiral nanotubes. The structural characterization measured by FTIR and X-ray diffraction indicated that the configuration of PCA did not affect the main chains of the chiral nanotubes; however, short-range ordering at 2θ = 6.43 (d = 13.73 A) was significantly observed from the chiral nanotubes, which might result from the chiral character of the dopant.

Hierarchical battery electrodes based on inverted opal structures

Abstract: The synthesis of a novel battery electrode architecture based on an ordered arrangement of interconnected macropores is reported; the mesoporous vanadium oxide electrode is designed to have a hierarchical architecture, which is beneficial for mass transport and should reduce polarization accordingly.

Synthesis of closed PbS nanowires with regular geometric morphologies

Abstract: Closed PbS nanowires with regular geometric morphologies (ellipse and parallelogram shape) were synthesized in the presence of poly[N-(2-aminoethyl)acrylamide] in ethylenediamine/H2O (3∶1, v/v) solvent at 110–150 °C.

Polyaniline nanowires by electropolymerization from liquid crystalline phases

Abstract: Conductive polyaniline nanowires in emeraldine form can be deposited by potentiodynamic electropolymerization from a reverse hexagonal liquid crystalline phase where one-dimensional (1D) aqueous channels can serve as space-confined reactors. Polyaniline nanowire bundles with single-wire diameter of 50–70 nm and length of several microns were obtained from surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse hexagonal liquid crystalline phase. Impedance measurement suggests improved ordering of the reverse hexagonal liquid crystal under external electric field during the electropolymerization process. This enhanced ordering appears essential for the nanowire growth. The nanowires obtained can be easily collected by a simple washing process.

Photonic antenna system for light harvesting, transport and trapping

Abstract: Host–guest composites with photonic antenna properties are described. The material consists of cylindrical zeolite L crystals the channels of which are filled with chains of joined but electronically non-interacting dye molecules. Light shining on a crystal is first absorbed and the energy is then transported by the dye molecules inside the tubes to the desired part. Data on crystals in the size range of 30 nm up to 3000 nm are reported. The synthesis principle we are using is based on the fact that molecules can diffuse into individual channels. This means that given the appropriate conditions, they can also leave the zeolite by the same way. In some cases, however, it is desirable to block their way out, for stability reasons. This is done by adding a closure molecule. The general approach to connect the antenna function to its surroundings is to add “stopcock” molecules which generally consist of a head, a spacer and a label. They can either trap excitation energy on the external surface or inject excitation energy into the dye-loaded crystal. The stopcock molecules act as bridges between the dye molecules inside the channels and the outside world. Functionalisation of the closure and the stopcock molecules is an option for tuning e.g. wettability, refractive index, and chemical reactivity. The wide-ranging tunability of the dye–zeolite L composites makes them useful for many applications. We discuss demonstration experiments which show the process of energy transfer and energy migration as educational tools, applications as high quality and non-toxic pigments, use as strongly luminescent pigments applicable as colour-changing media for LEDs, options for realising nanoscaled laser materials, and finally the challenge for realising solid state solar cells based on sensitisation of a thin semiconductor layer by energy transfer, the reversal of which can also lead to a new generation of LEDs.

Synthesis and characterization of PtRu/C catalysts from microemulsions and emulsions

Abstract: Nanosized PtRu catalysts supported on carbon have been synthesized from inverse microemulsions and emulsions using H2PtCl6 (0.025 M)/RuCl3 (0.025 M)/NaOH (0.025 M) as the aqueous phase, cyclohexane as the oil phase, and NP5 (poly(oxyethylene)5 nonyl phenol ether) or NP9 (poly(oxyethylene)9 nonyl phenol) as the surfactant, in the presence of Carbon Black suspended in a mixture of cyclohexane and NP5 + NP9. The titration of 10% HCHO aqueous solution into the inverse microemulsions and emulsions resulted in PtRu/C catalysts, in which the PtRu particles were nanometers in size. The catalysts were characterized by TEM, XRD and XPS and the metal particles were found to inherit the Pt fcc structure with Pt and Ru mostly in the zero valence oxidation states, amidst some Pt(II), Pt(IV) and Ru(IV). The cyclic voltammograms for methanol oxidation on these PtRu/C catalysts showed higher electrocatalytic activities for the two microemulsion derived catalysts than the emulsion-derived electrocatalyst.

Liquid crystalline assemblies of ordered gold nanorods

Abstract: Gold nanorods have been prepared in aqueous solution using a seed-mediated growth approach in the presence of surfactant. We observe the formation of liquid crystalline phases in concentrated solutions of high aspect ratio (13–18) gold nanorods by polarizing microscopy, transmission electron microscopy, and small angle X-ray scattering. These phases, which are stable up to 200 °C, exhibit concentration-dependent orientational order.

Synthesis of rod-, twinrod-, and tetrapod-shaped CdS nanocrystals using a highly oriented solvothermal recrystallization technique

Abstract: Rod-, twinrod- and tetrapod-shaped CdS nanocrystals have been successfully prepared from the starting spherical CdS nanocrystals via a highly oriented solvothermal recrystallization technique. X-Ray powder diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and high-resolution transmission electron microscopy have been used to characterize the crystal structure and growth direction of the obtained sample. The present technique may open a new doorway to one-dimensional nanosized semiconductors from the same kind of materials with irregular shape or larger size.

On the structure of Li3Ti2(PO4)3

Abstract: The structure of the Nasicon-type phase Li3Ti2(PO4)3, obtained by chemical lithiation of LiTi2(PO4)3, has been characterised using neutron diffraction for the long range structure and 7Li NMR for more local information. The lithium atoms were precisely located from the neutron diffraction data, using nuclear difference Fourier maps. The lithium ions, which were known to be in the large M2 cavity, occupy two M3 and M′3 subsites (distorted tetrahedra) with occupation factors of 2/3 and 1/3, respectively. From these two intermediate sites, it was shown that the diffusion pathway between two M1 sites in these Nasicon-type structures consists of a set of seven face-sharing tetrahedra. A variable temperature 7Li MAS NMR study showed a set of signals due to a distribution of environments for a given Li+ ion, in terms of occupied or vacant M3/M′3 sites in its vicinity. Elevation of the temperature to 353 K leads to a reversible exchange of these signals, due to fast hopping of Li between the two sites within a given M2 cavity.

In situ micelle–template–interface reaction route to CdS nanotubes and nanowires

Abstract: CdS nanotubes and nanowires have been successfully synthesized via an in situ micelle–template–interface reaction (ISMTIR) route by adjusting the concentration of the surfactant. The whole reaction system is made up of SDS rod-like micelles as the template, CS2 as the oil phase and sulfur source, NH3 as the attacking agent and coordination-agent, and CdCl2 in water. It was found that SDS rod-like micelles were excellent templates for the growth of nanotubes and nanowires of small size. Due to a micelle diameter of 10–20 nm, the CdS nanotubes formed have an outer diameter of 15 nm on average and a wall thickness of ca. 5 nm, within the exciton diameter of bulk CdS. In particular, the formation of CdS nanowires was thought to occur by a “rolling-broken-growth” (RBG) process, in which the micelles could not support the strain of the CdS produced rolling. Thus, the diameter of as-obtained CdS nanowires was ca. 5 nm, within the exciton diameter, too. The UV-vis absorption spectra show the as-obtained CdS nanotubes and nanowires are well quantum-confined. In the future, this method is expected to be used to prepare other metal sulfide nanotubes and nanowires.