Fabrication and photocatalysis of mesoporous ZnWO4 with PAMAM as a template

Mesoporous ZnWO₄ was prepared with the template of PAMAM. The as-formed samples were characterized by X-ray diffraction (XRD), nitrogen absorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV-vis diffuse reflectance spectroscopy (DRS). It is found that the size of pore is in the range of 5-22 nm and that the porosity of ZnWO₄ is composed of aggregated ZnWO₄ nanoparticles. The photocatalytic activities towards degradation of rhodamine B (RhB) and malachite green (MG) under UV light has been investigated. The formation mechanism of mesoporous structures is proposed.     

Ligand-assisted hydrothermal synthesis of ZnWO4 rods and their photocatalytic activities

ZnWO₄ rods were prepared using a ligand-assisted hydrothermal method with ZnCl₂ and Na₂WO₄ in the presence of various amines as ligands for zinc ions. The choice of ligand was found to play an important role in the formation of ZnWO₄ rods. The aspect ratio of the ZnWO₄ rods increased with increasing ligand strength. XRD and HRTEM confirmed that the ZnWO₄ rods grow along the [1 0 0] direction. The photochemical activities of the ZnWO₄ rods for the decomposition of Rhodamine 6G were examined. The photocatalytic activity was found to depend on the aspect ratio of the ZnWO₄ rods.     

Hydrothermal synthesis and magnetic properties of Co0.2Cu0.03Fe2.77O4 nanoparticles

Co_0.2Cu_0.03Fe_2.77O₄ nanoparticles with different morphologies have been synthesized directly via a simple hydrothermal method. The effects of pH value, precursor concentration, reaction temperature and surfactant on the particle size were discussed. X-ray diffraction analyses showed that the as-synthesized Co_0.2Cu_0.03Fe_2.77O₄ nanoparticles possessed typical spinel structure. Scanning electron microscope images showed different morphologies of the particles, including truncated octahedron and octahedron. It was indicated that well-dispersed Co_0.2Cu_0.03Fe_2.77O₄ nanoparticles can be synthesized at pH values ranging from 11 to 13, and reaction temperature of 160 °C. The particle size decreased from 18 to 10 nm after the addition of sodium dodecyl sulphate at the pH value of 9. The magnetic measurement showed that the as-prepared Co-Cu spinel ferrite nanoparticles possessed hard magnetic property.     

Powder synthesis and characterization of nanocrystalline CeO2 via the combustion processes

Nanocrystalline CeO₂ powders were synthesized by the combustion reactions using citric acid and glycol as fuels and nitrate as an oxidant. The adiabatic flame temperatures in the auto ignition processes of the precursors were calculated theoretically. XRD measurements indicated that the powders produced in the combustion processes were cubic fluorite CeO₂ phase. The size and morphology of the particles and extent of agglomeration in the powders were studied using transmission electron microscopy (TEM) and the particle size analyzer respectively. Blue shifts of the absorption peak of the as-prepared powders were observed.     

Large-scale synthesis of ultralong Sb2S3 sub-microwires via a hydrothermal process

This paper describes an ethylene glycol (EG)-assisted approach to the large-scale ultralong Sb₂S₃ sub-microwires, formed by a simple hydrothermal reaction between SbCl₃ and Na₂S in the presence of distilled water. Transmission electron microscopy and scanning electron microscopy studies indicate that these Sb₂S₃ sub-microwires possess a diameter around 200 nm and length up to 100 μm. High-resolution transmission electron microscopy and selected area electron diffraction studies reveal that each Sb₂S₃ sub-microwire is a single-crystal along the [0 0 1] direction. The possible formation mechanism of the sub-microwires was discussed. The effects of volume ratio of EG/water, reaction temperature and the concentration of CO(NH₂)₂ on the morphology of Sb₂S₃ sub-microwires were also investigated.     

Characterization of nanosized Al2(WO4)3

Nanosized aluminum tungstate Al₂(WO₄)₃ was prepared by co-precipitation reaction between Na₂WO₄ and Al(NO₃)₃ aqueous solutions. The powder size and shape, as well as size distribution are estimated after different conditions of powder preparation. The purity of the final product was investigated by XRD and DTA analyses, using the single crystal powder as reference. Between the specimen and the reference no difference was detected. The crystal structure of Al₂(WO₄)₃ nanosized powder was confirmed by TEM (SAED, HRTEM). In additional, TEM locality allows to detect some W₅O₁₄ impurities, which are not visible by conventional X-ray powder diffraction and thermal analyses.     

High temperature annealing of micrometric Zn2SiO4:Mn phosphor powders in fluidized bed

Micrometric Zn_1.8Mn_0.2SiO₄ phosphor powders prepared by spray pyrolysis have been annealed between 900 and 1200 °C under ambient air atmosphere to investigate their luminescence properties. Two original gas-solid fluidization processes have been tested in order to limit sintering phenomena, and the post-treated products have been compared with those annealed using a conventional process in crucible. The crystallinity, the size distribution, the outer morphology and the luminescence properties of powders before and after treatment have been analysed. Massive sintering phenomena occur in crucible from 1000 °C, whereas the original granulometry and spherical morphology are preserved till 1100 °C in fluidized bed. The luminescence efficiencies are comparable for the three processes and shown to be maximal after annealing at 1200 °C. It has been established that residual ZnO and manganese ions at oxidation state higher than 2+, still present after treatment at 1100 °C, are detrimental to good luminescence efficiency. Both disappear from samples post-treated at 1200 °C.     

Structural study and luminescence of TlSrLa(AsO4)2

This work presents the crystal structure and luminescent properties of TlSrLa(AsO₄)₂. In this phase Tl⁺ ions are located in large tunnels delimited by chains of alternating (AsO₄) and (Sr,La)O₈ polyhedra. Thallium atoms are eightfold coordinated with C₁ symmetry. Large TlO distances are observed revealing a low stereochemical activity of the 6s² lone pair. Excitation and emission spectra of Tl⁺ in TlSrLa(AsO₄)₂ showed broad bands at lower energy than those observed in previous works. Excitation spectra are decomposed into multiple Gaussian bands and a theoretical analysis is made to explain the number of observed components. Two Gaussian components are revealed for emission spectra.     

Solvothermal synthesis of fusiform hexagonal prism SrCO3 microrods via ethylene glycol solution

Fusiform hexagonal prism SrCO₃ microrods were prepared by a simple solvothermal route at 120 °C, and characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and Fourier transform infrared (FT-IR) spectroscopy. By controlling the content of ethylene glycol (EG), it was found that ethylene glycol (EG) played an important role in the formation of such SrCO₃ microrods. Finally, effects of other solvents on the products, including 1,2-propanediol and glycerin, were also investigated.     

Fabrication of microspherical LiMnPO4 cathode material by a facile one-step solvothermal process

The microspherical LiMnPO₄ cathode material was successfully prepared for the first time by a simple one-step solvothermal process in the presence of critic acid. The reaction conditions (reactant concentration, reaction temperature) were used further to fabricate the size, surface coarseness and morphology of the microspherical LiMnPO₄. The as-prepared microspherical LiMnPO₄ at variant conditions exhibited remarkably different discharge capacity and rate capacity, indicating the potential of the suggested method in tuning the morphology and the structure of LiMnPO₄ to improve its electrochemical performance.     

Characterization of LiNbO3 nanocrystals prepared via a convenient hydrothermal route

LiNbO₃ nanocrystal was successfully prepared via a simple and convenient hydrothermal route using LiOH and Nb₂O₅ as the reactants. Transmission electron microscopy images shows that the as-prepared sample displays a flake-like shape of 40-100 nm. X-ray diffraction, IR spectrum and Raman spectra of the as-prepared sample indicates that the sample was well crystalline and of high purity.     

Controllable synthesis and optical properties of NdOHCO3 dodecahedral microcrystals

NdOHCO₃ dodecahedral microcrystals with an orthorhombic structure have been successfully synthesized by the hydrothermal method used urea as the precipitator. Experimental parameters, such as the reaction temperature, the reaction time, and the molar ratio of the starting reagents were examined. The as-synthesized products were characterized by powder X-ray diffraction, transmission electron microscopy, field-emission scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and photoluminescence. The possible growth process of NdOHCO₃ dodecahedral microcrystals was discussed.     

Synthesis of cerium hydroxycarbonate powders via a hydrothermal technique

CeOHCO₃ powders have been directly synthesized using a hydrothermal process at temperatures as low as 160°C. The well-dispersed powders are obtained in a short period of reaction time during hydrothermal reaction via the hydrolysis of urea. For synthesizing CeOHCO₃, the concentration of urea is found to be a crucial determinant, which has significant effects on the morphology of the derived powders. When low urea concentrations are provided, the formed particles are rhomboidal platelets. On the other hand, the high urea concentrations cause the shape of the powders to become prismatic. Increasing the concentration of urea tends to increase the particle size as well as the aspect ratio of CeOHCO₃ powders. After further heating at 500°C, a phase transformation from orthorhombic CeOHCO₃ to cubic CeO₂ takes place. The crystallinity and size of CeO₂ strongly depend on the particle size of CeOHCO₃.     

Synthesis and characterization of nanocrystalline MgAl2O4 spinel via sucrose process

Nanocrystalline MgAl₂O₄ spinel powder was synthesized using metal nitrates and a polymer matrix precursor composed of sucrose and polyvinyl alcohol (PVA). The precursor and the calcined powders were characterized by simultaneous thermal analysis (STA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). According to XRD results, the inceptive formation temperature of spinel via this technique was between 600 and 700 °C. The calcined powder at 800 °C for 2 h has faced shaped morphology and its crystallite size is in the range of 8-12 nm. Further studies also showed that the amount of polymeric matrix to metal ions has significant influence on the crystallite size of synthesized magnesium aluminate spinel powder.     

One-step hydrothermal process to prepare highly crystalline Fe3O4 nanoparticles with improved magnetic properties

Hydrothermal process was successfully used to synthesize Fe₃O₄ powder using ferrous chloride (FeCl₂) and diamine hydrate (H₄N₂·H₂O) as starting materials by carefully controlling the reaction conditions. The as-prepared Fe₃O₄ sample was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM), and its magnetic properties were evaluated on a vibrating sample magnetometer (VSM). The nanoscale (40 nm) Fe₃O₄ powder obtained at 140 °C for 6 h possessed a saturation magnetization of 85.8 emu/g, a little lower than that of the correspondent bulk Fe₃O₄ (92 emu/g). It is suggested that the well-crystallized Fe₃O₄ grains formed under appropriate hydrothermal conditions should be responsible for the increased saturation magnetization in nanosized Fe₃O₄.     

Luminescence properties of BaTiO3:Eu obtained via microwave stimulated hydrothermal method

BaTiO₃ nanocrystalline powders doped with the Eu³⁺ ions have been prepared using microwave stimulated hydrothermal method (MSHM). Structure, average grain size and morphology of the BaTiO₃:Eu³⁺ were analyzed by means of the X-ray powder diffraction measurements, Raman spectroscopy and SEM microscopy. The luminescence properties and decay times of the hydrothermal BT:Eu³⁺ nanocrystalline powders have been investigated as a function of the grain size, dopant concentration, preparation conditions and sintering temperature. It was found that the studied properties are strongly dependent on the grain size of BaTiO₃:Eu³⁺ nano-crystallites.     

Photoluminescence of nanocrystalline SrMgF4 prepared by a solution chemical route

SrMgF₄ was prepared by precipitation in aqueous solution. Alkaline earth metal acetates and ammonium fluoride were used as precursors. After drying and annealing the samples at different temperatures and times, single phase SrMgF₄ was obtained. By varying the annealing conditions, the mean crystallite size could be adjusted. Furthermore, the thermally treated samples displayed UV-excited intensive broad band luminescence in the visible region. The emissions colour and intensity can be adjusted by the tempering conditions. X-Ray diffraction, TEM-microscopy, fluorescence and IR-spectroscopy were used for analysis.     

The synthesis and selected properties of new compounds: Mg3Fe4(VO4)6 and Zn3Fe4(VO4)6

New compounds: Mg₃Fe₄(VO₄)₆ and Zn₃Fe₄(VO₄)₆ were obtained from a solid state reaction. The temperatures of melting of Mg₃Fe₄(VO₄)₆ and Zn₃Fe₄(VO₄)₆ amount to 950±5 and 850±5°C, respectively. The indexing results and the calculated unit cell parameters for both compounds are given and suggest that both phases are isotypic with Mn₃Fe₄(VO₄)₆. The IR spectra of the above-mentioned compounds are presented.     

A novel broadband emission phosphor Ca2KMg2V3O12 for white light emitting diodes

A novel broadband emission phosphor Ca₂KMg₂V₃O₁₂ was first synthesized by solution combustion method. The X-ray diffraction showed that Ca₂KMg₂V₃O₁₂ phase can be obtained at 600-900 °C through combustion route. The crystal structure of this material was refined by Rietveld method using powder X-ray diffraction. It crystallizes in cubic system and belongs to space group Ia3d with z = 8, a = 0.12500 nm. The excitation band of Ca₂KMg₂V₃O₁₂ peaks at 320 nm in a region between 260 nm and 425 nm, and the emission spectrum exhibits an intense band centered at about 528 nm covering from 400 nm to 800 nm. The colour coordinates of samples prepared at different ignition temperatures are in a range of x = 0.323-0.339, y = 0.430-0.447.     

Effect of pH value on particle morphology and electrochemical properties of LiFePO4 by hydrothermal method

Lithium iron phosphate was prepared by hydrothermal synthesis using LiOH·H₂O, FeSO₄·7H₂O and H₃PO₄ as raw materials. The effects of pH value of reaction solution on particle morphology and electrochemical property were investigated. The pH value of the reaction solution was adjusted in the range of 2.5-8.8 by dilute sulfuric acid and ammonia water. The samples were characterized by field-emission scanning electronic microscope (FE-SEM), X-ray powder diffraction (XRD), constant-current charge/discharge cycling tests and chemical analysis. The results indicated that the particles exhibited acute angle diamond flake-like morphology at pH = 2.5, and as the pH value increased, the particle became hexagon flake-like, round flake-like and irregular flake-like morphology gradually. The optimal sample synthesized at pH = 6.4 exhibited discharge capacities of 151.8 mAh g⁻¹ at 0.2 C rate and 129.3 mAh g⁻¹ at 3 C rate. It was found that pH value affected the morphologies and properties of the product by means of different crystal growth rates.