Hydrothermal synthesis and photoluminescence properties of SrCO3

Well-crystallized strontium carbonate (SrCO₃) nanoparticles were successfully synthesized by a simple hydrothermal method. The products were characterized by X-ray diffraction (XRD), which is in good agreement with orthorhombic SrCO₃. Raman spectrum is in accordance with its crystal structure. Field emission scanning electron microscopy (FE-SEM) characterization indicates that the as-synthesized SrCO₃ nanoparticles are of mean size about 80 nm. The band gap of SrCO₃ was estimated by Wood and Tauc method through UV-visible reflection spectrum, showing a band gap value of 3.17 eV (391 nm). The photoluminescence properties of the as-synthesized SrCO₃ were measured at room temperature, which shows excellent emissions with two emission centers ranging from ultraviolet to red. The ultraviolet emission center locates at 390 nm, and the green emission center locates at 523 nm, respectively.     

Preparation of SrTiO<Subscript>3</Subscript> nanomaterial by a sol–gel-hydrothermal method

A new synthetic route to obtain high-purity strontium titanate, SrTiO₃, using the sol–gel-hydrothermal reaction of TiCl₄ and a SrCl₂ solution in an oxygen atmosphere has been developed. In the synthesized products the SrTiO₃ nanoparticles are nearly spherical and decrease in size with the reaction time (48 h) down to a diameter of about 40 nm. The microstructure and composition of the as-synthesized samples were investigated by X-ray diffraction (XRD), high-resolution TEM (HRTEM), Raman spectroscopy, atomic force microscopy (AFM), and energy-dispersive X-ray spectroscopy (EDX). All the samples were identified as cubic perovskite phase.     

Green hydrothermal synthesis and characterization of CdO2 nanoparticles

A green hydrothermal method has been developed for the synthesis of CdO₂ nanoparticles from Cd(OH)₂ powder and 6 vol.% H₂O₂ aqueous solution at 80-150 °C. The characterization results from X-ray diffraction, transmission electron microscopy, and thermal gravimetric and differential scanning calorimetry analysis disclosed that the resultant products were pure cubic phase CdO₂ nanoparticles with the sizes in the range of about 11-13 nm. The UV-vis absorption spectra revealed that the as-synthesized CdO₂ nanoparticles had similar optical band gaps of about 3.85 eV. The Raman spectra of the as-synthesized CdO₂ nanoparticles displayed two obvious peaks at about 348 and 830/833 cm^-1, a characteristic of pyrite-type IIB-peroxides.     

Hydrothermal synthesis and magnetic property of Cu3(OH)2V2O7·nH2O

Copper vanadium oxide hydroxide hydrate (Cu₃(OH)₂V₂O₇·nH₂O) nanoparticles with mean size of about 100 nm were successfully synthesized by a simple hydrothermal method. The structure and morphology of the as-synthesized products were characterized by X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Raman spectra, and Fourier transform infrared spectra (FTIR). The composition and purity of the as-synthesized Cu₃(OH)₂V₂O₇·nH₂O nanoparticles were characterized by Energy disperse spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The magnetic property of the as-synthesized Cu₃(OH)₂V₂O₇·nH₂O nanoparticles was characterized by vibrant sample magnetometer. Magnetic hysteresis curve indicate that the as-synthesized nanoparticles are of weak ferromagnetic property at room temperature.     

Synthesis of strontium ferrite nanoparticles by coprecipitation in the presence of polyacrylic acid

Strontium ferrite nanoparticles were prepared by coprecipitation in a PAA aqueous solution. The average diameter of the mixed hydroxide precipitates was 3.1 nm. From the thermal analysis by TGA/DTA and the phase analysis by XRD, it was shown that the appropriate molar ratio of Sr/Fe in aqueous solution was 1/8 and the precursor could yield pure strontium ferrite after calcination at above 700°C. The average diameters of the strontium ferrite nanoparticles calcined at 700 and 800°C were 34 and 41 nm, respectively. The magnetic measurements indicated that their saturation magnetization (57-59 emu/g) reached 85-88% of the theoretical one and increased with the decrease of temperature at 5-400 K. Their coercivity values (55-67 Oe) were much lower than those reported earlier, revealing the resultant nanoparticles were superparamagnetic. All the magnetic properties observed reflected the nature of nanoparticles and also concerned with their morphology and microstructure.     

Low temperature synthesis and characterization of strontium stannate–titanate ceramics

A novel modified chimie douce synthetic approach based on the gel to crystallite conversion (G–C) method has been developed to prepare strontium titanate SrTiO₃, strontium stannate SrSnO₃, and mixed strontium stannate–titanate SrSn_1−xTi_xO₃ (x = 0.05–0.5). The obtained materials were characterized by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). The formation of fully crystalline SrTiO₃ was observed in the temperature range of 800–1000 °C. The formation of monophasic SrSnO₃ occurs in the temperature range of 700–900 °C. At lower and higher temperatures the formation an impurity phases such as SrCO₃ and SnO₂ takes place. The same synthetic approach has been applied for the preparation of mixed strontium stannates–titanates SrSn_1−xTi_xO₃. The SEM images of SrTiO₃ samples indicated that the powder particles are 1–5 μm in size having approximately plate-like shape. Quite different surface morphology was determined for SrSnO₃ samples revealing the size of crystals from 500 nm to 40 μm. For the composition with x = 0.15, it was observed that the grain growth is uniform and the size of the grains is of the order of ∼2–5 μm.     

Citrate gel synthesis and characterization of (ZrO2)0.85(REO1.5)0.15 (RE = Y, Sc) solid solutions

By the citrate gel method, (ZrO₂)_0.85(REO_1.5)_0.15 (RE = Y, Sc) solid solutions in pure cubic fluorite structure were prepared at relatively low calcination temperatures. The existence of the strong coordination interaction between the COO⁻ groups of the ligands and metal ions could effectively prevent the segregation of metal ions during the gel formation. Upon heat treatment within 110-500 °C, the gel decomposed by multi-steps, with the formation of well-defined intermediate decomposition products, while, the bonding nature between COO⁻ groups and metal ions changed with temperature: unidentate (110-250 °C) → bridging (300-350 °C) → ionic (400-500 °C). The oxide powder resulted from the calcination of the gel at 800 °C is an assembly of mesoporous nanoparticles with uniform sizes, but agglomerated in lumps. It was confirmed that the chemical homogeneity, nanoparticle size uniformity and crystallinity, sinterability and electrical conductivity of (ZrO₂)_0.85(REO_1.5)_0.15 can be remarkably improved by avoiding the phase separation (solid/liquid) phenomenon during the preparation of the gels.     

Hydrothermal synthesis, structure and scintillation characterization of nanocrystalline Eu-doped Gd2O3 materials and its X-ray imaging applications

Nanocrystalline Gd₂O₃:Eu scintillators were successfully synthesized using a hydrothermal method and subsequent calcination treatment in the electrical furnace as an X-ray to visible light conversion material for an indirect X-ray image sensor. In this work, various Gd₂O₃:Eu scintillators were prepared in accordance with different synthesis conditions such as doped-Eu concentration, different calcination temperatures of 600-1400 °C and calcination time of 1-10 h. The transition of morphology from nanorods to particles was observed as the calcination temperature of Gd₂O₃:Eu scintillator increased. And the phase transformation of the sample from cubic to monoclinic structure was discovered at 1300 °C calcination temperature. In addition, scintillation properties such as luminescent spectra and light intensity under 266 nm UV illumination were measured as a function of calcination condition of as-synthesized Gd₂O₃:Eu powder. The nanocrystalline Gd₂O₃:Eu scintillator with a strong red light emission at near 611 nm wavelength under photo- and X-ray excitation will be employed for its potential X-ray image sensor applications in the future.     

Formation of SrTiO3 from Sr-oxalate and TiO2

SrTiO₃ powder has been prepared from Sr-oxalate and TiO₂ precursors, instead of using titanyl-oxalate. Sr-oxalate was precipitated from nitrate solution onto the surface of suspended TiO₂ powders. Crystallization of SrTiO₃ from the precursor was investigated by TGA, DTA and XRD analysis. It is evident that precursor, upon heating, dehydrates in two stages, may be due to the presence of two different types of Sr-oxalate hydrates. Dehydrated precursor then decomposes into SrCO₃ and TiO₂ mixture. Decomposition of SrCO₃ and simultaneous SrTiO₃ formation occur at much lower temperature, from 800 °C onwards, due to the fine particle size of the SrCO₃ and presence of acidic TiO₂ in the mixture. The precursor completely transforms into SrTiO₃ at 1100 °C. About 90 nm size SrTiO₃ crystallites are produced at 1100 °C/1 h, due to the lower calcination temperature and better homogeneity of the precursor.     

Fabrication and characterization of nearly monodisperse Co3O4 nanospheres

Nearly monodisperse Co₃O₄ nanospheres were fabricated via a facile polyethylene glycol 400-mediated solventhermal route followed by a calcination process at 500 °C. The structure, morphology, and properties of the products were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectrometry, and UV-vis spectrometry. The results showed that the products were Co₃O₄ nanospheres of 160-170 nm in diameter and were composed of nanoparticles of ca. 40 nm. The possible formation mechanism was discussed on the basis of experimental results. Furthermore, optical property of the products was characterized.     

Ionothermal synthesis of AlPO4-34 molecular sieves using heterocyclic aromatic amine as the structure directing agent

AlPO₄-34 was synthesized ionothermally in 1-butyl-3-methyl imidazolium bromide using heterocyclic aromatic amine as the structure directing agent (SDA). The as-synthesized products were characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM), nuclear magnetic resonance spectroscopy (NMR) and thermal gravimetric (TG) analysis. The factors affecting the crystallization were investigated. The results show that methyl-substituted heterocyclic aromatic amines can effectively direct to form AlPO₄-34 and reside in the channel solely. Meanwhile, the ionic liquid need not be consumed, it merely acts as a solvent. Hydrofluoric acid plays a crucial role in the synthesis process as a mineralizer. The morphology and crystallinity of the product can be controlled by the dosage of the SDA and the crystallization temperature. The synthesized product shows a good thermal stability, and maintains a very good crystalline structure after calcination at 550 °C in air.     

Green synthesis of ZnO2 nanoparticles from hydrozincite and hydrogen peroxide at room temperature

A green method based on the reaction between hydrozincite (Zn₅(CO₃)₂(OH)₆) powder and hydrogen peroxide (H₂O₂, 30 wt.%) in aqueous solution at room temperature was developed for the synthesis of ZnO₂ nanoparticles. Results from X-ray diffraction, transmission electron microscopy and Raman demonstrated that the resultant products were pure cubic phase ZnO₂ nanoparticles, whose sizes were in the range of 3.1-4.2 nm. Thermogravimetric analysis indicated that between 180 and 350 °C, the as-synthesized ZnO₂ nanoparticles had a weight loss of about 16.7%, consistent with the theoretical amount (16.4%) of the O₂ released from ZnO₂ decomposition (ZnO₂ = ZnO + 1/2O₂). The present method was green, simple and cost-effective, which should be suitable for large-scale production of multifunctional ZnO₂ nanoparticles.     

A facile route to sonochemical synthesis of magnetic iron oxide (Fe3O4) nanoparticles

A facile sonochemical approach was applied for the large scale synthesis of iron oxide magnetic nanoparticles (NPs) using inexpensive and non-toxic metal salts as reactants. The as-prepared magnetic iron oxide NPs has been characterized by XRD, TEM, EDS, and VSM. X-ray diffraction (XRD) and EDS analysis revealed that Fe₃O₄ NPs have been successfully synthesized in a single reaction by this simple method. Transmission electron microscopy (TEM) data demonstrated that the particles were narrow range in size distribution with 11 nm average particle size. Moreover, TEM measurements also show that the synthesized nanoparticles are almost spherical in shape. The magnetization curve from vibrating sample magnetometer (VSM) measurement shows that as-synthesized NPs were nearly superparamagnetic in magnetic properties with very low coercivity, and magnetization values were 80 emu/g, which is very near to the bulk value of iron oxide. The estimated value of mass susceptibility of as-synthesized nanoparticles is Xg = 5.71 × 10^− 4 m³/kg.     

Low temperature synthesis of Fe3O4 nanoparticles and its application in lithium ion batteries

Well dispersed Fe₃O₄ nanoparticles with mean size about 160 nm are synthesized by a simple chemical method at atmosphere pressure. The products are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and Raman spectrum. Electrochemical properties of the as-synthesized Fe₃O₄ nanoparticles as anode electrodes of lithium ion batteries are studied by conventional charge/discharge tests, showing initial discharge and charge capacities of 1140 mAh g⁻¹ and 1038 mAh g⁻¹ at a current density of 0.1 mA cm⁻². The charge and discharge capacities of Fe₃O₄ electrode decrease along with the increase of cycle number, arriving at minimum values near the 70th cycle. After that, the discharge and charge capacities of Fe₃O₄ electrode begin to increase along with the increase of cycle number, arriving at 791 and 799 mAh g⁻¹ after 393 cycles. The morphology and size of the electrode after charge and discharge tests are characterized by SEM, which exhibits a large number of dispersive particles with mean size about 150 nm.     

Facile synthesis of antimony-doped tin oxide nanoparticles by a polymer-pyrolysis method

In this article, antimony-doped tin oxide (ATO) nanoparticles was synthesized by a facile polymer-pyrolysis method. The pyrolysis behaviors of the polymer precursors prepared via in situ polymerization of metal salts and acrylic acid were analyzed by simultaneous thermogravimetric and differential scanning calorimetry (TG-DSC). The structural and morphological characteristics of the products were studied by powder X-ray diffraction (XRD) and transmission electron microscope (TEM). The results reveal that the ATO nanoparticles calcined at 600 °C show good crystallinity with the cassiterite structure and cubic-spherical like morphology. The average particle size of ATO decreases from 200 to 15 nm as the Sb doping content increases from 5 mol% to 15 mol%. Electrical resistivity measurement shows that the resistivity for the 10-13 mol% Sb-doped SnO₂ nanoparticles is reduced by more than three orders compared with the pure SnO₂ nanoparticles. In addition, due to its versatility this polymer-pyrolysis method can be extended to facile synthesis of other doped n-type semiconductor, such as In, Ga, Al doped ZnO, Sn doped In₂O₃.     

Solvothermal synthesis of SrMoO4:Ln (Ln = Eu, Tb, Dy) nanoparticles and its photoluminescence properties at room temperature

Rare-earth ions (Eu³⁺, Tb³⁺, Dy³⁺) doped SrMoO₄ nanoparticles were prepared by solvothermal route using oleic acid as surfactant to control the particle shape and size. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), photoluminescence spectra (PL) and the kinetic decay times were applied to characterize the obtained samples. The XRD patterns reveal that all the doped samples are assigned to the scheelite-type tetragonal structure of SrMoO₄ phase. In addition, the as-synthesized SrMoO₄:Ln (Ln = Eu³⁺, Tb³⁺, Dy³⁺) particles are high purity well crystallized and with the average size of 30-50 nm. The possible formation process of SrMoO₄:Ln (Ln = Eu³⁺, Tb³⁺, Dy³⁺) nanoparticles have been discussed as well. Upon excitation by ultraviolet radiation, the as-synthesized SrMoO₄:Ln (Ln = Eu³⁺, Tb³⁺, Dy³⁺) nanoparticles exhibit the characteristic emission lines of corresponding Eu³⁺, Tb³⁺, Dy³⁺, respectively.     

Hydrothermal synthesis of alpha Fe2O3 nanoparticles capped by Tween-80

Surface modified α-Fe₂O₃ nanoparticles capped by Tween-80 were prepared by the hydrothermal treatment of Fe(NO₃)₂.9H₂O at 200 °C. The spherical nanoparticles possessed good crystallinity with an average crystallite size of 21 nm. The presence of Tween-80 on the surface of α-Fe₂O₃ was confirmed by FTIR and Mössbauer analysis. The surfactant was effective in controlling the particle shape and restricted the particle growth to a narrow range around 40-60 nm as observed by scanning electron microscopy. The α-Fe₂O₃ nanoparticles obtained without Tween-80 were irregular in shape with a wide size distribution in the range of 150-300 nm.     

Low temperature molten salt synthesis of SrTiO3 submicron crystallites and nanocrystals in the eutectic NaCl-KCl

An eutectic NaCl-KCl molten salts method has been developed for the synthesis of SrTiO₃ submicron crystallites and nanocrystals from SrO₂ and two kinds (submicron and nano-sized) of TiO₂ powders at 700 °C, which was much lower than that (generally > 1000 °C) of the conventional solid state reactions. The characterization results from X-ray diffraction and X-ray photoelectron spectroscopy revealed that the obtained products were pure perovskite phase SrTiO₃ without any contamination of Na, K, and Cl ions. The scanning electronic microscopy and transmission electron microscopy images disclosed that the starting TiO₂ played an important role in the morphology and size of the obtained SrTiO₃: while the product derived from TiO₂ submicron crystallites comprised faceted submicron crystallites of about 95-184 nm, that derived from TiO₂ nanocrystals comprised quadrate nanocrystals of about 20-61 nm. Besides, based on the experiments without the molten NaCl-KCl eutectic, at different temperatures and times, and using different kinds of TiO₂, the possible formation mechanism of SrTiO₃ submicron crystallites and nanocrystals was proposed.     

Behavior of Cu nanoparticles ink under reductive calcination for fabrication of Cu conductive film

Cu nanoparticle ink was prepared from Cu nanoparticles that were coated with a gelatin layer at an average diameter of 46 nm. The Cu nanoparticle ink was applied on the polyimide substrate. Conductive films were fabricated using the Cu nanoparticle ink with a two-step annealing process consisting of oxidative pre-heating at 200 °C under 10 ppm O₂-N₂ mixed gas flow and reductive calcination at 250 °C under 3 vol.% H₂-N₂ mixed gas flow showed a low resistivity of 5 μΩ cm. The hydrolysis of the remaining gelatin layer by H₂O vapor, which was formed during the reduction of the Cu oxide by 3 vol.% H₂-N₂ mixed gas, was suggested. The results suggest the possibility of the removal of the gelatin layer without oxidative pre-heating and simultaneous sintering of Cu nanoparticles in reductive calcination.     

A novel synthetic route to Y2O3:Tb phosphors by bicontinuous cubic phase process

This study applies a novel approach to prepare the terbium-doped yttrium oxide phosphors (Y₂O₃:Tb³⁺) using the bicontinuous cubic phase (BCP) process. The experimental results show that the prepared precursor powder was amorphous yttrium hydroxide Y_1−xTb_x(OH)₃ with a spherical shape and primary size 30–50 nm. High crystallinity phosphors with body-centered cubic structures were obtained after heat treatment above 700 °C for 4 h. The primary size of the phosphors grew to 100–200 nm, and dense agglomerates with a size below 1 μm were formed during the calcination. The obtained Y₂O₃:Tb³⁺ phosphor had a strong green emitting at 542 nm. The optimum Tb³⁺ concentration was 1 mol% to obtain the highest PL intensity. This study indicates that the calcining temperature of 700 °C needed for high luminescence efficiency in this work is much lower than 1000 °C or above needed for the conventional solid-state method.