Synthesis and characterization of single-crystalline MnFe2O4 nanorods via a surfactant-free hydrothermal route

Uniform, high-quality, single-crystalline MnFe₂O₄ nanorods with diameter around 25 nm and length up to 500 nm, have been reproducibly synthesized via a surfactant-free hydrothermal route. The growth direction of the obtained nanowires was determined to be its [1 1 1] direction, resulting in the increase of saturation magnetization. Mn²⁺ is responsible for one-dimensional growth of the nanorods, and the effects of reaction time and solution concentration on the morphology and crystallization of the MnFe₂O₄ nanorods were investigated. Saturation magnetization of the nanorods is 74.0 emu/g, which is among the best value reported so far.     

Synthesis and properties of boron doped ZnO nanorods on silicon substrate by low-temperature hydrothermal reaction

Boron doped ZnO nanorods were fabricated by hydrothermal technique on silicon substrate covered with a ZnO seed layer. It is found that the concentration of boric acid in the reaction solution plays a key role in varying the morphology and properties of the products. The growth rate along the [0 0 0 1] orientation (average size in diameter) of the doped ZnO nanorods decreased (increased) with the increase of boric acid concentration. Based on the results of XRD, EDX and XPS, it is demonstrated that the boron dopants tend to occupy the octahedral interstice sites. The photoluminescence of the ZnO nanorods related to boron doping are investigated.     

Synthesis, characterization and catalytic properties of sol-gel derived mixed oxides

Alumina and 1:1 mixed oxides of Al₂O₃-ZrO₂, Al₂O₃-TiO₂, SiO₂-TiO₂ and ZrO₂-TiO₂ were synthesized via a sol-gel process by the so-called neutral amine route, followed by calcination at 600 °C. The mixed oxides were characterized before calcination by X-ray diffraction, revealing ordered hexagonal (Al₂O₃, Al₂O₃-ZrO₂, ZrO₂-TiO₂) and lamellar (SiO₂-TiO₂, Al₂O₃-TiO₂) structures. After calcination, all samples exhibited amorphous structures. Surface areas and pore characteristics of all materials were determined by nitrogen adsorption isotherms. The calcined oxides are active catalysts in the epoxidation of cyclooctene with tert-butyl hydroperoxide as oxidant. Epoxide yields from 14 to 45% were found for reaction times of 24 h. The titanium oxide containing catalysts are the most active and selective ones. On the other hand, the poisoning of acidic centers yields a decreasing activity while increasing selectivity.     

Synthesis,structural, optical and magnetic properties of Cu-doped ZnO nanorods prepared by a simple direct thermal decomposition route

Cu-doped ZnO nanorods (i.e. Cu = 1.75, 3.55, 5.17 and 6.39 at.%) have been successfully synthesized by simple, direct, thermal decomposition of zinc and copper acetates in air at 300 °C for 6 h. The prepared samples were characterized by X-ray diffraction (XRD) and transmission electron microscopy. The XRD results indicate that the 1.75 at.% Cu-doped ZnO sample has a pure phase with the ZnO wurtzite structure, while the impurity phases are detected with increasing Cu concentrations. It was found that the doping of Cu results in a reduction of the preparation temperature. The optical properties of the samples were also investigated by UV–visible spectroscopy and photoluminescence measurements. The results show that the Cu doping causes the change in energy-band structures and effectively adjusts the intensity of the luminescence properties of ZnO nanorods. X-ray photoelectron spectroscopy analysis implies that there are some oxygen vacancies in the samples and also indicates that all the doped samples are associated with the mixture of Cu ion states (Cu²⁺ and Cu¹⁺/Cu⁰). Magnetic measurements by vibrating sample magnetometry indicate that undoped ZnO is diamagnetic, whereas all of the Cu-doped ZnO samples exhibit room temperature ferromagnetic behavior. We suggest that Cu substitution and density of oxygen vacancies (V _o) may play a major role in the room temperature magnetism of the Cu-doped ZnO samples.     

Controlled synthesis of light rare-earth hydroxide nanorods via a simple solution route

Ln(OH)₃ (Ln=La, Pr, Nd, Sm, Eu, Gd) nanorods are synthesized without using any surfactants or templates at room temperature. The as-obtained nanorods are within 4–25 nm in diameter and up to 200 nm in length. The most important improvement is that the aspect ratio of the obtained nanorods can be effectively controlled by adjusting the reaction time and pH value of the reaction system. The as-synthesized nanorods are characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). It is interesting to find that both the inherent crystal structure of light lanthanide hydroxide and the chemical potential affect the formation of nanorods. The photoluminescence (PL) instrument is used to investigate the optical properties of the Eu(OH)₃ nanorods and its abnormal luminescence behaviors are observed.     

Synchrotron reflectivity spectra and optical properties of rare-earth oxides

The spectra of the complete set of optical functions for nine sesquioxides of rare-earth elements of the R₂O₃ group are obtained at 300 K in the energy range 0–50 eV. The calculations are carried out on the basis of synchrotron reflectivity spectra and computer programs using the Kramers-Kronig relations. The main features of the optical spectra and their dependence on the nature of rare-earth elements were determined.     

Structural and photoluminescent properties of Ni doped ZnO nanorod arrays prepared by hydrothermal method

Self-assembled Ni-doped zinc oxide (Zn_1−xNi_xO, x = 0.05, 0.10, 0.15, i.e., ZnNiO, nominal composition) nanorod arrays vertically grown on the ZnO seed layer covered glass along [0 0 1] direction were synthesized by hydrothermal method. Their images and structures have been characterized by scan electron microscope (SEM), X-ray diffraction (XRD) and Raman spectra, showing that Ni doping is beneficial to the formation of ZnO nanorods with hexagonal cross section and the enhancement of ZnO crystal quality. X-ray photoemission spectroscopy (XPS) study further demonstrated that Ni atoms were successfully doped into ZnO lattices. The photoluminescence (PL) spectra of ZnNiO samples show near bandedge emission (NBE) peaks at about 380 nm at a low excitation power and the NBE peak position redshifts while its intensity continuously increases with the increase of Ni doping concentration. With the excitation power increasing, the NBE peak redshifts from 380 nm to about 400 nm for ZnNiO nanorod arrays. The NBE mechanisms for ZnNiO nanorod arrays have been discussed, which is helpful for understanding their room temperature ferromagnetisms.     

Synthesis and characterization of brightly photoluminescent CdTe nanocrystals

A new synthesis procedure for the preparation of spherical shaped CdTe nanocrystals (NCs) is presented, exhibiting bright luminescence with exceptionally high quantum efficiency (up to 85%). The growth of these NCs occurs in a non-coordinating solvent, octadecene, with the addition of oleic acid/tri-octylphosphine stabilizers, CdO as a precursor for the Cd monomers and additional Cd metal particles as a supplementary Cd reservoir source. The dependence of the crystalline quality and the optical properties of the CdTe NCs, on the initial Cd:Te precursors’ molar ratio, and the reaction duration were investigated. It was demonstrated that the NCs’ properties improved significantly as the initial Cd:Te molar ratios are increased. The obtained NCs’ properties were correlated with measurements of the Cd⁰ concentration in Cd metal particles, CdTe NCs and in Cd monomer solutions.     

Synthesis of nanorods FePO4 via a facile route

Iron phosphate nanorods were synthesized via a novel facile route. The structure, composition, and morphology of the prepared material were characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM), respectively. The diffraction lines were indexed to the hexagonal structure. The diameter of these nanorods is about in the range of 20–30 nm and the length 50–100 nm. The preferential growth direction of the prepared material was the [100]. The reaction mechanism for the synthesis of FePO₄ nanorods was also primarily discussed. Compared to the bulky and the irregular nanoparticles, the nanometer ones will be more fascinating for application in many areas.     

Synthesis, structure, and photoluminescence properties of ZnSSe alloy nanorods

ZnSSe alloy nanorods were prepared on gold (Au)-coated Si (100) substrates by the thermal evaporation of a mixture of ZnSe and ZnS powders. The nanorods were straight, 70-150 nm in width, and up to a few tens of micrometers in length. Transmission electron microscopy and X-ray diffraction indicated that the nanorods were ZnSSe single crystals with a wurtzite-type hexagonal close-packed structure. The photoluminescence measurements showed that the ZnSe nanorods had a strong emission band centered at approximately 500 nm in the blue-green region. The blue-green emission band corresponding to the deep-level emission of the ZnSSe nanorods showed no shift. On the other hand, a shoulder of the band in the blue region corresponding to the near-band edge (NBE) emission band shifted continuously from 466 nm to a lower wavelength region with increasing composition x in ZnSe_1−xS_x from 0 to 0.41. The blue-green emission intensity of the ZnSSe nanrods also increased with increasing composition x. The enhancement of blue-green emission might be due to the increase in structural defects, such as dislocations and stacking faults in the nanorods.     

Synthesis and characterization of magnetite dodecahedron nanostructure by hydrothermal method

Magnetite dodecahedral nanocrystals were fabricated using ethlenediamine tetraacetic acid (EDTA)-mediated hydrothermal route. Scanning electron microscopy images displayed that the products were almost dodecahedrons. The length of two different ribs were about 300 and 200 nm, respectively. X-ray diffraction patterns showed that the products were the cubic inverse spinel structure. Fourier transform infrared spectrum directly provided evidence of the EDTA bound to a specific surface of the precipitated magnetic nanocrystal. Reaction medium, temperature and time played important roles in the formation of dodecahedral morphology. Based on the experimental results, the possible formation mechanism of such novel nanostructures was proposed. Also, the magnetic properties of the samples were characterized on a vibrating sample magnetometer (VSM).     

Analysis of the thermophysical properties of some rare-earth hydroxides through crystal field effects

A crystal field analysis of the experimental results on the magnetic susceptibilities and their anisotropies in Ho(OH)₃ and Tb(OH)₃ was made with a view to resolve the previous anomalies observed in the results of specific heat studies. A pronounced thermal effect on lattice specific heat has been observed in Ho(OH)₃ but not in Tb(OH)₃. For Er(OH)₃, the total specific heat was calculated with reasonable assumptions over a wide temperature range, but no experimental data are yet available for comparison.     

Synthesis and characterization of PbS nanorods and nanowires

 A surfactant assisted solvotermal approach for the controllable synthesis of PbS nanowires and nanorods is applied. The synthesis is based on decomposition of lead thiocyanate in boiling benzyl alcohol with Cetyl trimethyl ammonium bromide used as a surfactant. Nanowires of PbS (about 2–3 μm with an average diameter of 30–50 nm) and nanorods (200–300 nm in length with an axial ratio of 4–5) were synthesised. The nanostructures were characterized by high resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM), selected area electron diffraction (SAED) and X-ray diffraction analysis. The experimental results indicate that the reaction duration and concentration of surfactant play key roles in determining the final morphologies of PbS blocks building and also in their crystallinity. A possible mechanism for creation of PbS nanowires and nanorods is discussed.     

The photoluminescent properties of europium and terbium ions co-doped one-dimensional gadolinium orthophosphate nanorods and microcrystals

The europium/terbium ion-doped gadolinium orthophosphate nanorods and microcrystals phosphors were synthesized by the hydrothermal reaction and solid-phase reaction, respectively. The structures, morphologies, and luminescent behaviors were compared. The microcrystals can obtain higher quantum efficiency compared with nanorods because of the different structures (monoclinic and hexagonal). In the ultraviolet-visible region, the gadolinium ions absorbed energy then transferred to europium and terbium ions. The energy transfer from terbium to europium existed both in microcrystals and in nanorods, and it was confirmed that the energy transfer efficiency from terbium to europium in nanorods is higher than that in microcrystals.     

Synthesis, structure and electronic properties of ultranarrow CdS nanorods

We report on the one-step synthesis of ultra narrow wurtzite CdS nanorods using bench top chemical decomposition route. The synthesized CdS nanorods are of 1.8 nm in diameter and show major confinement along the radial dimension, which is well below the exciton Bohr radius of bulk CdS (2.5 nm). Structural and self-assembly properties of nanorods are studied using X-ray Diffraction (XRD) and small angle X-ray scattering (SAXS) measurements, which reveal preferred orientation of the nanorods along <00.2> direction with 2D supercrystalline spatial distribution. The estimated nanorod dimensions from XRD is corroborated with the transmission electron microscopy observations. UV–vis and photoluminescence spectroscopy reveals significant increase in the band gap in comparison to bulk CdS which is further tallied with the simulations using effective mass approximation (EMA). Formation of discrete structure of valence band and conduction band due to strongly quantum confined excitons in the radial direction is evidenced from EMA simulation. Combination of experimental and theoretical approach helps in understanding the structure–property relationship for ultranarrow CdS rods which might lead to nanorod based applications.     

Synthesis and characterization of novel vanadium dioxide nanorods

Novel vanadium dioxide nanorods were fabricated via a surfactant-assisted hydrothermal method at 180 °C for 48 h in the presence of cetyltrimethylammonium bromide (CTAB). The self-assembled samples were characterized by XRD, SEM, TEM, HRTEM and FT-IR. The results show that the products are nanorods, which are pure B phase vanadium dioxide with high crystallinity. The obtained nanorods have diameters of 40-60 nm with lengths up to 1-2 um. The probable formation mechanism of vanadium dioxide is also discussed.     

Some aspects concerning the characterization of iron oxides and hydroxides in soils and clays

A review of the systematic Mössbauer studies on the most encountered iron oxides and hydroxides is given in which the qualitative and quantitative aspects, helpful in the characterization of natural smaples, are emphasized. The present possibilities of Mössbauer spectroscopy in soil characterization are further illustrated from some examples of natural soils.Senior Research Associate at the National Fund for Scientific Research, Belgium.     

Nanoplate-like CuO: hydrothermal synthesis,characterization, and electrochemical properties

Plate-like nanocrystalline CuO was synthesized via the hydrothermal process using copper nitrate trihydrate as inorganic precursor and 1,3-diaminoprapane which acts as a structure-directing template. The morphology, the structure, the crystallinity and the composition were studied through x-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). It was found that the hydrothermal reaction time had a marked effect on the morphology and particularly, on the particle size and the nature of the resulting products. The optical properties of the as-synthesized CuO nanoplatelets were studied by UV-visible diffuse reflectance spectra (DRS) and the values of the band were found to be 1.93 eV. Electrochemical measurements have revealed a reversible redox behavior with a doping/de-doping process corresponding to reversible cation intercalation/de-intercalation. This process is easier for the smaller sized Li⁺ cation compared to the larger Na⁺ cation and to the largest K⁺ cation.