Controlled synthesis of different morphological YF3 crystalline particles at room temperature

YF₃ crystalline particles with different crystal structures and different morphologies have been synthesized via a simple solution route by varying the fluoride source (NH₄F, HF, NH₄F·HF) and molar ratio of Y³⁺/F⁻ at room temperature. They were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray photoelectron spectrum (XPS).     

Room temperature synthesis of Li-doped MnO2 and its electrochemical activity

A new method was developed to synthesize a uniform round-shaped Li-doped MnO₂ by ozonation of acidic MnSO₄ in the presence of Li⁺ ions. X-ray diffraction study showed that the prepared compound was of a hexagonal-closed-packed (hcp) crystal structure with an average crystallite size of ~ 103 nm. The merging of 221/240 and 061/002 lines suggested a high microtwinning defect. Chemical composition has been explained in terms of Ruetschi's cation vacancy model. The electrochemical properties were studied by recording discharge profile in 9 M KOH at 1 mA/0.1 g and 100 Ω/0.5 g. The discharge proceeded with homogenous solid-state reduction into MnOOH followed by subsequent formation of Mn(OH)₂ via dissolution-precipitation mechanism.     

A green hydrothermal route to GaOOH nanorods

GaOOH nanorods were synthesized by a green hydrothermal method at 200 °C using nanocrystalline Ga₂O₃ powders and distilled water as the starting materials, and characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and thermogravimetric and differential scanning calorimetry (TG-DSC) analysis.     

Synthesis and photocatalytic behaviour of 3D flowerlike bismuth oxide formate architectures

By virtue of structural understanding, bismuth oxide formate (BiOCOOH) was first put forward to be a novel photocatalyst candidate. 3D flowerlike architectures have been successfully synthesized through a facile and economical route, which was free from any surfactant and template. The product was characterized by the study of X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM) and electron diffraction (ED), and the crystal structure of BiOCOOH was revealed. Besides, the formation mechanism of the BiOCOOH flowerlike architectures was also discussed. From the results of photocatalytic tests, the synthesized BiOCOOH architectures exhibited excellent photocatalytic activity for rhodamine-B (RhB) degradation under the simulated solar light irradiation. Therefore, this novel 3D flowerlike BiOCOOH architectures show significance of potential application in environment protection problems.     

Shape-controlled synthesis of high-purity CrO2 under HTHP

High-purity CrO₂ powders were prepared under high temperature (400 °C-600 °C) and high pressure (1 GPa-5 GPa) conditions. The shape, size and the grain boundary density of the CrO₂ powders can be tuned via simply changing the experiment conditions, such as temperature and pressure. Magnetic properties of the CrO₂ powders prepared under different conditions were investigated also. The saturation magnetizations of the samples are consistent with the best value ever reported. The synthesis of CrO₂ powders with controlled morphology should be of interest in tunneling magnetoresistance research.     

Catalytic synthesis of large-scale GaN nanorods

A novel rare earth metal seed was employed as the catalyst for the growth of GaN nanorods. Large-scale GaN nanorods were synthesized successfully through ammoniating Ga₂O₃/Tb films sputtered on Si(1 1 1) substrates. Scanning electron microscopy, X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy were used to characterize the structure, morphology, and composition of the samples. The results demonstrate that the nanorods are high-quality single-crystal GaN with hexagonal wurtzite structure. The growth mechanism of GaN nanorods is also discussed.     

Selected-control synthesis of Te nanowires and Te/C nanocables by adjusting hydrothermal temperature

Single-crystalline Te nanowires with an average diameter of 70 nm and Te/C nanocables with a smooth core about 50-100 nm in diameter and a surrounding sheath about 60 nm in thickness were obtained through the reduction of Na₂TeO₃ with glucose in the presence of cetyltrimethylammonium bromide (CTAB) under hydrothermal conditions at 130 °C and 170 °C. The products were characterized in detail by multiform techniques: X-ray diffraction, energy-dispersive X-ray analysis, scanning electron microscopy, and transmission electron microscopy. In the process, the temperature was found to play important roles in determining the produced Te nanowires and Te/C nanocables.     

Preparation and characterization of a series of diol di-stearates as phase change heat storage materials

A series of solid-liquid phase change materials, diol di-stearates, were prepared via esterification of stearyl chloride with the respective diol (1,2-ethanediol, 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol and 1,10-decanediol) using pyridine as acid absorbent, and were then characterized by FT-IR, WAXD, POM, DSC and TGA measurements. All of the resulting diol di-stearates were apt to crystallize due to structural symmetry and flexibility of long alkyl groups. The DSC results indicated that the melting point of the prepared diol di-stearates varied from 38.5 °C to 56.4 °C, and phase change enthalpy lies in the range 134 kJ/kg-189 kJ/kg.     

PAM-assisted synthesis of single-crystalline CuI nanorods

Single-crystalline cuprous iodide semiconductor nanorods were fabricated via a facile and efficient room-temperature solution process by using polyacrylamide (PAM) as a structure-directing agent, followed by heat treatment at 180 °C. The diameter and length of the nanorods were estimated to be ca. 50 nm and ca. 1 μm, respectively. And the phase-transformation temperature and decomposition temperature of the as-prepared CuI nanorods were deduced from the DSC curve of the products, which decreased markedly compared with those of the bulk CuI material. Moreover, a possible growth mechanism of the CuI nanorods based on polymer-crystal interactions in a mild aqueous solution is proposed.     

Improved thermoelectric performance of highly-oriented nanocrystalline bismuth antimony telluride thin films

Improved thermoelectric performance of highly-oriented nanocrystalline bismuth antimony telluride thin films is described. The thin films are deposited by a flash evaporation method, followed by annealing in hydrogen. By optimizing the annealing conditions, the resulting thin films exhibit almost perfect orientation with the c-axis normal to the substrate, and are composed of nano-sized grains with an average grain size of 150 nm. The in-plane electrical conductivity and Seebeck coefficient were measured at room temperature. The cross-plane thermal conductivity of the thin films was measured by a 3ω method, and the in-plane thermal conductivity was evaluated by using an anisotropic factor of thermal conductivity based on a single crystal bulk alloy with almost the same composition and carrier concentration. The measured cross-plane thermal conductivity is 0.56 W/(m K), and the in-plane thermal conductivity is evaluated to be 1.05 W/(m K). Finally, the in-plane power factor and figure-of-merit, ZT, of the thin films are 35.6 μW/(cm K²) and 1.0 at 300 K, respectively.     

Hydrothermal synthesis and characterization of bismuth titanate regular tetrahedron crystallites

Bi₁₂TiO₂₀ (BTO) single crystals were synthesized by a hydrothermal process in KOH solution at 180 °C for 4 h from Ti(OC₄H₉)₄ and Bi(NO₃)₃·5H₂O compounds. The effects of processing parameters on the growth and morphology of BTO single crystals were investigated. The KOH concentration, reaction time and temperature had a great effect on the phase composition and morphology of the resultant crystals. BTO phase could not be obtained with KOH concentrations lower than 3 M or higher than 5 M. XRD, SEM and TEM were used to characterize the samples. BTO single crystals were regular tetrahedron in morphology and 10 μm or so in size.     

Synthesis and photoelectrochemical properties of thin bismuth molybdates film with various crystal phases

Bismuth molybdate films with various phase structures including α-Bi₂Mo₃O₁₂, β-Bi₂Mo₂O₉, γ-Bi₂MoO₆, and γ′-Bi₂MoO₆ are fabricated on the indium-tin oxide glass substrates from an amorphous heteronuclear complex via the dip-coating method by appropriate adjustment of the reaction conditions. α-Bi₂Mo₃O₁₂, β-Bi₂Mo₂O₉, and γ-Bi₂MoO₆ film can be obtained at 400 °C, 500 °C, and 500 °C for 1 h, respectively. At 500 °C, γ′-Bi₂MoO₆ can be obtained for 4 h. Film formation process is proposed based on the experimental results. Thin γ-Bi₂MoO₆ films exhibit high photoresponse under visible light irradiation. Incident photon to current conversion efficiency of thin γ-Bi₂MoO₆ film starts to increase near 450 nm. And, it can reach 4.1% at 400 nm. The top of the valence band and bottom of the conduction band are roughly estimated to be − 0.71 and 1.69 eV, respectively. In contrast, γ′-Bi₂MoO₆ generated weak photocurrent; α-Bi₂Mo₃O₁₂ and β-Bi₂Mo₂O₉ film has no photoresponse under visible light irradiation. The reason for the difference in the visible light response was discussed.     

Surface tension of pure liquid bismuth and its temperature dependence: Theoretical calculations

A theoretical method for calculating the surface tension of liquid metals as a function of temperature is proposed. A mathematical equation, based on statistical thermodynamics, is applied to calculate the surface tension of pure liquid bismuth, in the temperature range 545-620 K. The calculated surface tension of liquid bismuth was found to be 388 mJ/m², which is in excellent agreement with the reported experimental values (374-417 mJ/m²). The surface tension of bismuth decreases linearly with temperature, confirming a negative slope.     

Synthesis of sodium iron silicate(NaFe(III)[SiO3]2) nanorods and electrochemical characterization

Sodium iron silicate (NaFe(III)[SiO₃]₂) nanorods have been synthesized using iron nitrate (Fe(NO₃)₃) and sodium silicate (Na₂SiO₃) solutions by means of hydrothermal method. The mixture solution is processed in hydrothermal autoclave first at 180-200 °C for two days and then dried at 70 °C to obtain nanotructured NaFe(III)[SiO₃]₂. It was revealed that NaFe(III)[SiO₃]₂ nanorod with the average diameter of ~ 15 nm and length of several hundreds nm was confirmed by X-ray power diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Cyclic voltammeter (CV) and electrochemical impedance spectra (EIS) investigations show that this kind of NaFe(III)[SiO₃]₂ nanostructures have evident and stable electrochemical redox behavior between potential range of − 0.1-0.55 V in alkaline solution.     

Synthesis of CdS nanorods by reacting CdCl2 nanorods with H2S at room temperature

We report the synthesis of CdS nanorods by reacting CdCl₂ nanorods with H₂S at room temperature. The preparation method was based on CdCl₂ nanorods employed as chemical template. The length and the diameter of the obtained CdS nanorods are about tens micron and 120−300 nm, respectively. The phase and the crystallographic structure of the products were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The composition of the products was investigated by X-ray photoelectron spectroscopy (XPS).     

Controlled oxidative synthesis of Bi nanoparticles and emission centers in bismuth glass nanocomposites for photonic application

Here we demonstrate an oxidative process to control metallic bismuth (Bi⁰) nanoparticles (NPs) creation in bismuth glass nanocomposites by using K₂S₂O₈ as oxidant and enhanced transparency of bismuth glasses. Formation of Bi⁰ NPs has been monitored by their distinct surface plasmon resonance (SPR) band at 460 nm in the UV-visible absorption spectra. It is further confirmed by the transmission electron microscopy (TEM) images which disclose the formation of spherical Bi⁰ NPs whereas the selected area electron diffraction (SAED) pattern reveals their crystalline rhombohedral phase. These glasses are found to exhibit visible and near infrared (NIR) luminescence bands at 630 and 843 nm respectively on excitation at 460 nm of the SPR band. It is realized that the luminescence center of bismuth species is an uncertain issue, however, it is reasonable to consider that the emission band at 630 nm is due to the combination of ²D_5/2 → ⁴S_3/2 of Bi⁰ and ²P_3/2 (1) → ²P_1/2 of Bi²⁺ transitions, and that of NIR emission band at 843 nm is attributed to the ²D_3/2 → ⁴S_3/2 of Bi⁰ transition.     

A simple solution route to controlled synthesis of ZnS submicrospheres, nanosheets and nanorods

ZnS nanostructures with different morphologies of submicrospheres, nanosheets and nanorods were synthesized by solution precipitation of thiourea with Zn(NO(3))(2) in the presence of block copolymer at low temperature. The sizes and morphologies of ZnS can be controlled simply by?changing the processing parameters. The results show that the ZnS submicrospheres are of 250-500?nm in diameter, nanosheets are 2.5?μm × 5.5?μm with an estimated thickness of 20-30?nm, and nanorods are 2-5?nm in diameter and 10-30?nm in length. Keeping the precursor system in an autoclave at 105?°C results in the formation of ZnS submicrospheres; ultrasonication and keeping the system at room temperature leads to the formation of ZnS nanosheets; and long-time continuous ultrasonication and keeping the system in an autoclave at 105?°C induces the formation of uniform ZnS nanorods. We argue that the reaction temperature and P123 may play crucial roles in the formation of three ZnS structures in this work. The morphologically controllable synthesis strategies may be extended to the shape-controlled production of nanostructures of other inorganic materials.     

Hydrothermal synthesis of oriented MnS nanorods on anodized aluminum oxide template

High-density aligned MnS nanorods with a narrow length distribution were prepared on an anodized aluminum oxide (AAO) template under a hydrothermal condition. MnS nanomaterials with different shapes were obtained using different precursor concentrations in the reaction solution. The porous surface of the AAO template and the precursor concentrations may play key roles in the initial nucleation stage of growing oriented MnS nanorods.     

Room temperature synthesis and characterization of different morphological TbF3 nano/microcrystals

At room temperature, a simple solution-based procedure employing NaBF₄ as the fluoride source has been developed to selectively prepare different morphological TbF₃ nano/microcrystals (disks, peanuts and spindles) with an orthorhombic structure. The crystal structure, morphology and photoluminescence properties of the as-prepared TbF₃ crystals were investigated by x-ray powder diffraction (XRD), scanning electron microscopy (SEM) and fluorescence spectrophotometer. The results revealed that large-scale and uniform disks with a mean thickness of 20 nm can be easily synthesized, and the spindle-like and peanut-like TbF₃ crystals were assembled from nanodisks. The effects of synthesis parameters such as NaBF₄, reaction time and molar ratio of the reactants were systematically investigated. The room temperature PL properties of these different morphological TbF₃ microcrystals were measured.     

Microwave hydrothermal synthesis of lanthanum oxyfluoride nanorods for photocatalytic nitrogen fixation: Effect of Pr doping

Photocatalytic fixation of nitrogen has been recognized as a green and promising strategy for ammonia synthesis under ambient conditions. However, the efficient reduction of nitrogen remains a challenge due to high activation energy of nitrogen and low utilization of solar energy. Herein, lanthanum oxyfluoride with different doping content of Pr³⁺ (LaOF:xPr³⁺) upconversion nanorods were synthesized by microwave hydrothermal method. Results indicated that the doping of Pr³⁺ generated considerable defects on the surface of LaOF which acted as the adsorption and activation center for nitrogen. Meanwhile, the Pr³⁺ ion narrowed the band gap and broadened the light response range of LaOF because LaOF:Pr³⁺ can upconvert visible light into ultraviolet light, which excite LaOF nanorods and improve the utilization of solar light. The doping amount of Pr³⁺ had critical effect on the photocatalytic nitrogen fixation performance which reached as high as 180 μmol·L⁻¹·h⁻¹ when the molar ratio of Pr³⁺ to LaOF was optimized to be 2%.