Facile synthesis and magnetic properties of manganese dioxide nanowires

A large number of MnO₂ nanowires were fabricated by a facile hydrothermal method. The nanowires have a tetragonal pyrolusite structure and a smooth surface. The common bulk defects such as dislocations, twinnings and stacking faults are not detected by HRTEM measurement. The magnetisation dependence of temperature indicates that the magnetisation, linearly and monotonically, increases with decreasing temperature in the range 300–80?K, revealing the paramagnetic properties of the nanowires. The first discharge capacity reaches 223.5?mA?h?g^?1, and the value of capacity steadily decreases during the following cycles, down to an acceptable 122.3?mA?h?g^?1 after 25 cycles. The high surface ratio of nanowires is the main reason for the excellent discharge cycle property of the MnO₂ nanowires.     

Effect of calcination conditions on phase formation and particle size of nickel niobate powders synthesized by solid-state reaction

The solid-state mixed oxide method via a rapid vibro-milling technique is explored in the preparation of single-phase nickel niobate (NiNb₂O₆) powders. The formation of the NiNb₂O₆ phase in the calcined powders has been investigated as a function of calcination conditions by TG-DTA and XRD techniques. Morphology, particle size and chemical composition have been determined via a combination of SEM and EDX techniques. It has been found that the minor phases of unreacted NiO and Nb₂O₅ precursors and the Ni₄Nb₂O₉ phase tend to form together with the columbite NiNb₂O₆ phase, depending on calcination conditions. More importantly, it is seen that optimization of calcination conditions can lead to a single-phase NiNb₂O₆ in an orthorhombic phase.     

Studies on the synthesis of CdCO3 nanowires and porous CdO powder

In the present study, we demonstrate the self transformation of aqueous cadmium acetate into CdCO₃ nanowires through hydrothermal reaction. The reaction temperature and the volume ratio of water to ethanol were found to be crucial for the formation of CdCO₃ nanowires. The nanowires are of single crystal in nature having width ∼ 17-30 nm as observed from selected area electron diffraction (SAED) pattern and transmission electron microscopic (TEM) results. The major weight loss found in thermogravimetric analysis (TGA) corresponds to the formation of CdO and CO₂. The powder X-ray diffraction (PXRD) patterns of CdCO₃ and CdO are respectively indexed to pure rhombohedral and cubic phases. The photoluminescence (PL) spectrum of CdO exhibits an emission peak at 483 nm due to the transition between the valence and conduction bands.     

Room-temperature synthesis of nanometric α-Bi2O3

Nanometric Bi₂O₃ powder was successfully synthesized by applying the method based on self-propagating room temperature reaction (SPRT) between bismuth nitrates and sodium hydroxide. X-ray powder diffraction (XRPD) and Rietveld's structure refinement method were applied to characterize prepared powder. It revealed that synthesized material is a single phase monoclinic α-Bi₂O₃ (space group P2₁/c with cell parameters a = 5.84605(4)Å, b = 8.16339(6) Å, c = 7.50788(6) Å and β = 112.9883(8)). Powder particles were of nanometric size (about 50 nm). Raman spectral studies conformed that the obtained powder is single phase α-Bi₂O₃. Specific surface area of obtained powder was measured by Brunauer-Emmet-Teller (BET) method.     

Solvothermal synthesis of In(OH)3 nanorods and their conversion to In2O3

In this work, we demonstrate that monodisperse indium hydroxide (In(OH)₃) nanorods constructed with parallel wire-like subunits have been fabricated via a acrylamide-assisted synthesis route without any template. NH₃ from the hydrolysis of acrylamide acts as the OH⁻ provider. The structure and morphology of as-prepared products have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and thermogravimetric analysis (TG). A detailed mechanism has been proposed on the basis of time-dependent experimental results. Furthermore, by annealing In(OH)₃ precursors at 500 °C for 3 h in air, In₂O₃ samples were obtained with the designed morphology.     

Large-scale hydrothermal synthesis of WO3 nanowires in the presence of K2SO4

WO₃ nanowires were fabricated by a hydrothermal method in the presence of K₂SO₄. The nanowires exhibit a well crystallized one-dimensional structure with 10 nm in diameter and several microns in length. Effects of other alkali salts (KNO₃, NaNO₃ and Na₂SO₄) on the morphologies of WO₃ nanocrystals were also investigated. The important role of K₂SO₄ salt in the WO₃ nanowires synthesis has been demonstrated.     

Facile synthesis of nanocrystalline spinel NiFe2O4 via a novel soft chemistry route

A novel soft chemistry route (rheological phase reaction method) was developed to synthesize nanocrystalline NiFe₂O₄. The as-prepared samples were characterized by powder X-ray diffractometer (XRD), transmission electron microscope (TEM) and vibrating sample magnetometer (VSM). The effects of the calcination temperature on the particle sizes and magnetic properties of the samples were investigated. The results indicated that the samples obtained by this method had the single-phase spinel. Particle sizes estimated from Scherrer's formula increased with the calcination temperature, which were consistent with the results of TEM. The magnetic properties of the samples were strongly affected by the calcination temperature. The coercivity initially increased and then decreased with increasing calcination temperature whereas the saturation magnetization continuously increased.     

Microwave-assisted synthesis of hierarchical Bi2O3 spheres assembled from nanosheets with pore structure

Hierarchical Bi₂O₃ spheres assembled from nanosheets with nanopore structure have been successfully synthesized by thermal decomposition of the precursor at 400 °C for 3 h in air, which was prepared using Bi(NO₃)₃·5H₂O and poly(vinylpyrrolidone) (PVP) by a microwave-assisted heating method in ethylene glycol (EG) at 150 °C for 10 min. The morphology of Bi₂O₃ is similar to that of the precursor. The products were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectrometry (FT-IR), field-emission scanning electron microscopy (FE-SEM), thermogravimetric analysis (TG) and differential scanning calorimetric analysis (DSC). XRD pattern showed that the product had a high degree of crystallinity. FE-SEM micrograph indicated that hierarchical Bi₂O₃ spheres had sizes around 10 μm.     

Selective synthesis of Bi2Se3 nanostructures by solvothermal reaction

Bi₂Se₃ nanobelts, nanoflakes and sheets embedded nanotubes were prepared via solvothermal process with different solvents. The reaction conditions influencing the synthesis of Bi₂Se₃ nanostructures such as solvents, and reaction temperatures were studied and optimized. Results indicated that the mixed solvent composed of triethanolamine and ethanol (TEA-EtOH) or triethanolamine and distilled water (TEA-H₂O) can decrease the threshold temperature (TT) of Bi₂Se₃. With the solvents TEA-EtOH and TEA-H₂O, we originally accomplished the shape-controlled synthesis of Bi₂Se₃ nanocrystals by controlling reaction temperature. Based on the viewpoint of crystallography about Bi₂Se₃, the possible growth mechanisms of Bi₂Se₃ nanostructures were discussed.     

Facile synthesis of MnV2O6 nanostructures with controlled morphologies

MnV₂O₆ nanostructures including nanorods, nanobelts, and nanosheets, have been synthesized by a facile hydrothermal reaction between Mn(CH₃COO)₂·4H₂O and commercial V₂O₅. The synthesized products are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The influences of synthetic parameters, such as, reaction time, temperature and medium, on the morphologies of the resulting products have been investigated. As the reaction temperatures increase from 120 °C to 180 °C, MnV₂O₆ nanorods and nanobelts are obtained, respectively. The time-dependent experimental results at 180 °C reveal that the sizes of MnV₂O₆ nanobelts increase gradually with the reaction proceeding. Interestingly, as the reaction is carried out with the aid of H₂O₂ solution, flower-like MnV₂O₆ nanosheets are formed.     

Synthesis of sphere-like Co3O4 nanocrystals via a simple polyol route

A simple polyol method was developed to synthesize uniform sphere-like Co₃O₄ nanocrystals in ethylene glycol. Powder X-ray diffraction (XRD) and electron diffraction (ED) showed that the as-prepared sample was indexed as the cubic spinel structure. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated that the Co₃O₄ nanocrystals were spherical with the crystallite size in the range of 90-110 nm. Infrared spectra and Raman spectra confirmed the formation of the Co₃O₄ nanocrystals. The magnetic properties of the Co₃O₄ nanocrystals were measured by using a superconducting quantum interference device (SQUID) magnetometer, which showed that the as-prepared sample exhibited a tiny hysteresis loop with the magnetization value of 2.4 emu/g and the coercivity of 110 Oe.     

Molten salt synthesis of single-crystal Co3O4 nanorods

The synthesis of the single-crystal Co₃O₄ nanorods by molten salt approach was reported for the first time. The products were characterized by Transmission electron microscopy (TEM), X-ray diffraction (XRD), High-resolution transmission electron microscopy (HRTEM) and Selected-area electron diffraction (SAED). TEM results indicate that these nanorods have diameters of about 150 nm and lengths of about 2 μm. According to the analysis of the SAED and HRTEM results, we drew the conclusion that these nanorods grew along an unusual [− 1,− 1,15] direction by Ostwald ripening mechanism.     

Synthesis and photoluminescent properties of Gd3O4Br:Er phosphors prepared by solid-state reaction method

Pure orthorhombic Gd₃O₄Br:Er³⁺ upconversion phosphors were synthesized by a solid-state reaction method and the structural properties of Gd₃O₄Br:Er³⁺ were investigated by X-ray diffraction; field emission scanning electron microscopy, Raman spectroscopy and Fourier transform infrared spectroscopy. The results show that Gd₃O₄Br has low phonon cutoff energy, indicating that Gd₃O₄Br:Er³⁺may have high luminescent efficiency. Intense green (514–582 nm) and strong red (645–692 nm) upconverted luminescence of Gd₃O₄Br:Er³⁺ were observed under 980 nm laser excitation. The bright green emission is visible to the naked eyes even for 1 mW of the pump power (980 nm) for Gd₃O₄Br:Er³⁺ (0.1%) samples, indicating that Gd₃O₄Br:Er³⁺ may be used as upconversion phosphors.     

Effect of calcination conditions on phase formation and particle size of Zn3Nb2O8 powders synthesized by solid-state reaction

The solid-state mixed oxide method via a rapid vibro-milling technique is explored in the preparation of single-phase Zn₃Nb₂O₈ powders. The formation of the Zn₃Nb₂O₈ phase in the calcined powders has been investigated as a function of calcination conditions by TG-DTA and XRD techniques. Morphology, particle size and chemical composition have been determined via a combination of SEM and EDX techniques. It has been found that the minor phases of unreacted ZnO and Nb₂O₅ precursors and the columbite ZnNb₂O₆ phase tend to form together with the Zn₃Nb₂O₈ phase, depending on calcination conditions. It is seen that optimization of calcination conditions can lead to a single-phase Zn₃Nb₂O₈ in a monoclinic phase.     

In2O3 nanowires for gas sensors: morphology and sensing characterisation

Thin and densely packed In₂O₃ nanowires have been synthesised on alumina substrates via transport and condensation method, starting from nanoparticles of indium or palladium as catalysts for the condensation process. Indium catalyst promoted wires growth according to vapour-solid (VS) mechanism, while palladium catalyst leads to wires formation based on vapour-liquid-solid (VLS) condensation. Electron microscopy and related diffraction analysis demonstrated that the wires are monocrystalline, with atomically sharp termination of the lateral sides, and are free from extended defects. The sensing properties of nanowires bundles have been tested to acetone using the flow through technique in the temperature range between 100 and 500 °C.     

Hydrothermal synthesis of magnetite nanoparticles via sequential formation of iron hydroxide precipitates

A novel method for preparing fine magnetite nanoparticles without using any additives and organic solvents has been developed. In this method, a sequential precipitates formation method, ferrous and ferric hydroxides are not coprecipitated but sequentially formed in an alkaline solution, and then the resulting suspension is subjected to a hydrothermal treatment. The obtained magnetite nanoparticles were characterised through scanning electron microscopy observation and X-ray diffraction analysis, and the particle size and magnetic properties were measured with a dynamic light scattering particle size analyser and a superconducting quantum interference device magnetometer, respectively. In order to prepare fine magnetite nanoparticles with a uniform size, both the formation sequence of ferrous and ferric hydroxide precipitates and the supersaturation of ferric hydroxide in the solution were essential. The ferromagnetic magnetite nanoparticles with a median size 8.5?nm were relatively easily obtained in the formation process in which a ferric sulphate solution was rapidly poured into a suspension of ferrous hydroxide particles prepared beforehand using ferric chloride and sodium hydroxide, whereas the median size of magnetite nanoparticles prepared via conventional coprecipitation route was 38.6?nm.     

One-pot synthesis of intestine-like SnO2/TiO2 hollow nanostructures

In the present study the intestine-like binary SnO₂/TiO₂ hollow nanostructures are one-pot synthesized in aqueous phase at room temperature via a colloid seeded deposition process in which the intestine-like hollow SnO₂ spheres and Ti(SO₄)₂ are used as colloid seeds and Ti-source, respectively. The novel core (SnO₂ hollow sphere)-shell (TiO₂) nanostructures possess a large surface area of 122 m²/g (calcined at 350 °C) and a high exposure of TiO₂ surface. The structural change of TiO₂ shell at different temperatures was investigated by means of X-ray diffraction and Raman spectroscopy. It was observed that the rutile TiO₂ could form even at room temperature due to the presence of SnO₂ core and the unique core-shell interaction.     

The production of flower-like NiFe2O4 superstructures consisting of nanosheets via the thermolysis of a heterometallic oxo-centered trinuclear complex

Flower-like NiFe₂O₄ superstructures consisting of nanosheets have been successfully synthesized by direct thermolysis of a heterometallic oxo-centered trinuclear complex [NiFe₂O(CH₃COO)₆(H₂O)₃·2H₂O] (NiFe-HOTC) at 400 °C for 6 h in a horizontal tube furnace. The composition and structure of the products were investigated by X-ray diffraction (XRD) and infrared spectra (IR). XRD analysis revealed a pure ferrite phase with high crystallinity. Morphological investigation by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed NiFe₂O₄ flowers with average diameter varying from 0.5 to 3 μm consist of nanosheets with average edge length in the range of 60-300 nm and thickness of about 30 nm. Furthermore, energy dispersive X-ray analysis (EDX) demonstrated that the atom ration of Ni, Fe and O is 1:2:4. In addition, magnetic measurements showed that the obtained flower-like NiFe₂O₄ are ferromagnetic at room temperature.     

Preparation and tribological properties of polyurethane/α-aluminum oxide hybrid films

This study focused on the preparation and tribological properties of polyurethane/α-aluminum oxide (PU/α-Al₂O₃) hybrid films. PU/α-Al₂O₃ hybrid films containing various nanoscaled α-Al₂O₃ contents were prepared by an effectively mechanical stirring method. The tribological properties of PU/α-Al₂O₃ hybrid films were investigated by a TABER type abrasion tester after 2000 cycles. The results of abrasion tests showed the abrasion resistance of the PU/α-Al₂O₃ hybrid film was increased as the α-Al₂O₃ content was increased. The abrasion resistance of the PU/α-Al₂O₃ hybrid film was significantly improved up to 27.4% by adding 2 wt.% nanoscaled α-Al₂O₃ particles. The surface morphologies of PU/α-Al₂O₃ hybrid films, before and after abrasion tests, were examined by scanning electron microscopy (SEM). For the loading of 2 wt.% α-Al₂O₃ particles, the SEM image of the worn surface of the PU/α-Al₂O₃ hybrid film showed much smoother than those of pure PU film and other PU/α-Al₂O₃ hybrid films.     

Optical and magnetic properties of elliptical hematite (α-Fe2O3) nanoparticles coated with uniform continuous layers of silica of different thickness

Elliptical-type α-Fe₂O₃ nanoparticles with/without silica shell have been prepared. The core particles were coated with uniform continuous layers of silica of two different thicknesses by hydrolysis of TEOS. The obtained HCP structure elliptical α-Fe₂O₃ nanoparticles with ∼ 240 nm length and 100 nm width is polycrystalline in nature. The thicknesses of SiO₂ shell coated on α-Fe₂O₃ are about 55 and 30 nm, respectively. The optical and magnetic properties of these nanoparticles have been investigated.