Synthesis of Bi2Te3 nanopowders by vacuum arc plasma evaporation

Starting from elemental bismuth and tellurium, bismuth telluride (Bi₂Te₃) nanopowders were successfully prepared by vacuum arc plasma evaporation (VAPE) technique for the first time. The phase composition in the obtained nanopowders is closely related with the Bi:Te atomic ratio in starting precursor. The microstructure and morphology of the samples were characterized via X-ray diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). Compositional analysis was also carried out by energy dispersive analysis of X-rays (EDAX). The as-synthesized Bi₂Te₃ nanopowders have a rhombohedral crystal structure with lattice parameters a = 4.381 Å and c = 30.310 Å. The average particle size is about 35 nm obtained from TEM and confirmed from XRD results.     

Formation of LiNi0.5Co0.5VO4 nano-crystals by solvothermal reaction

LiNi_0.5Co_0.5VO₄ nano-crystals were solvothermally prepared using a mixture of LiOH·H₂O, Ni(NO₃)₂·6H₂O, Co(NO₃)₂·6H₂O and NH₄VO₃ in isopropanol at 150–200 °C followed by 300–600 °C calcination to form powders. TGA curves of the solvothermal products show weight losses due to evaporation and decomposition processes. The purified products seem to form at 500 °C and above. The products analyzed by XRD, selected area electron diffraction (SAED), energy dispersive X-ray (EDX) and atomic absorption spectrophotometer (AAS) correspond to LiNi_0.5Co_0.5VO₄. V–O stretching vibrations of VO₄ tetrahedrons analyzed using FTIR and Raman spectrometer are in the range of 620–900 cm⁻¹. A solvothermal reaction at 150 °C for 10 h followed by calcination at 600 °C for 6 h yields crystals with lattice parameter of 0.8252 ± 0.0008 nm. Transmission electron microscope (TEM) images clearly show that the solvothermal temperatures play a more important role in the size formation than the reaction times.     

Large-scale synthesis of WO3 nanoplates by a microwave-hydrothermal method

Tungsten oxide (WO₃) nanoplates were synthesized by a 270 W microwave-hydrothermal reaction of Na₂WO₄·2H₂O and citric acid (C₆H₈O₇·H₂O) in deionized water. X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED) were used to reveal the synthesis of WO₃ complete rectangular nanoplates in the solution of 0.2 g citric acid for 180 min, with O-W-O FTIR stretching modes at 819 and 741 cm⁻¹, and two prominent O-W-O Raman stretching modes at 804 and 713 cm⁻¹. The 2.71 eV indirect energy gap, and 430-460 nm blue emission wavelength range of WO₃ complete rectangular nanoplates were determined using UV-visible and photoluminescence (PL) spectrometers. The formation mechanism was also proposed according to the experimental results.     

Biomimetic synthesis of spherical nano-hydroxyapatite in the presence of polyethylene glycol

Spherical nano-hydroxyapatite (nano-HA) was synthesized successfully by a biomimetic method using Ca(NO₃)₂·4H₂O and (NH₄)₃PO₄·3H₂O as reagents in the presence of polyethylene glycol (PEG). The crystalline phase, microstructure, chemical composition, and morphology of the obtained samples were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). The results show that spherical nano-HA with diameter of 30–50 nm can be synthesized in the presence of a certain concentration (2–6%) of PEG. The crystallinity of HA powder synthesized in the presence of PEG was higher than that synthesized in the absence of PEG, but the crystallinity of HA reduced with increasing the concentration of PEG. The electrical conductivity (EC) of the solution revealed that PEG reduced the transfer rate of Ca²⁺ in the process of HA crystallization, indicating the interaction between PEG and HA. The possible mechanism of formation spherical nano-HA was discussed.     

Synthesis of nano-crystalline NiO-YSZ by microwave-assisted combustion synthesis

Nano-crystalline NiO-YSZ composite powders have been successfully prepared by microwave-assisted combustion of a gel derived from an aqueous solution containing ZrO(NO₃)₂·6H₂O ,Y(NO₃)₃·6H₂O, Ni(NO₃)₂·6H₂O and glycine. The as-prepared powders were examined using X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) techniques. It was found that the process took only a few seconds to obtain NiO-YSZ composite powders. The as synthesized composite powder was a homogeneous mixture of YSZ, NiO and Ni phases with crystallite size of 24.2, 33.6 and 25.3 nm respectively.     

Growth and optical properties of cerium dioxide nanocrystallites prepared by coprecipitation routes

Nanosized cerium dioxide (CeO₂) powders have been synthesized using coprecipitation methods and cerium nitrate hexahydrate (Ce(NO₃)₃·6H₂O) as the starting material. The growth and optical properties of nanosized CeO₂ powders were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), nano-beam electron diffraction (NBED), high resolution TEM (HRTEM), and ultraviolet–visible (UV–vis) absorption spectrophotometry. The XRD result shows that the dried CeO₂ precursor powders (both before and after calcination at various temperatures and times) contained a single crystalline phase of CeO₂. In the dried precursor powders, the crystallites of CeO₂ measured 10.4 nm and 66.8 nm before and after calcination at 1273 K for 240 min, respectively. The indirect band gap energy (_Ei$E_i$) of CeO₂ decreased from 3.03 eV to 2.68 eV as the crystallite size increased from 10.4 nm to 66.8 nm, whereas the direct band gap energy (_Ed$E_d$) of CeO₂ also decreased from 3.79 eV to 3.38 eV.     

Sonochemical preparation of PbWO4 crystals with different morphologies

PbWO₄ was prepared from Na₂WO₄·2H₂O and Pb(OAc)₂·3H₂O in a solution containing a cationic surfactant (N-cetyl pyridinium chloride) using the sonochemical process (ultrasonic irradiation). The product morphologies, characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), were controlled by the surfactant, pH values and ultrasonic irradiation times. X-ray diffraction (XRD) and selected area electron diffraction (SAED) studies revealed diffraction patterns in good agreement with the simulation model, along with Fourier transform infrared (FTIR) and Raman analyses showed a W–O stretching band consistent with tetragonal PbWO₄. Photoluminescent properties of the pine tree shaped products were also investigated.     

Transformation of cubic AgBiS2 from nanoparticles to nanostructured flowers by a microwave-refluxing method

Cubic AgBiS₂ nanoparticles and flower-like clusters were successfully synthesized by microwave refluxing of CH₃COOAg, Bi(NO₃)₃·5H₂O and thiosemicarbazide (NH₂NHCSNH₂) in ethylene glycol. The phase was detected by X-ray diffraction (XRD) and selected area electron diffraction (SAED). The SAED pattern was also in accordance with that of the simulation. Scanning and transmission electron microscopy (SEM and TEM) revealed the gradual transformation of nanoparticles into flower-like clusters by increasing microwave power. Their UV–visible absorption and photoluminescence (PL) emission were detected by spectrometry. Possible formation mechanism of nanoparticles and nanostructured flowers was also proposed according to the experimental results.     

Glycothermal process for barium magnesium tantalate nanopowders synthesis

Barium magnesium tantalate Ba(Mg_1/3Ta_2/3)O₃ (BMT) nanopowders were synthesized at a low temperature of 220 °C through glycothermal reaction by using Ba(OH)₂·8H₂O, Mg(NO₃)·6H₂O, and TaCl₅ as precursors and 1,4-butanediol as solvent. It is demonstrated that higher synthesis temperatures and co-precipitation of magnesium and tantalum improve the incorporation of magnesium into BMT nanopowders under glycothermal treatment and produce a homogeneous, stoichiometric powder. The glycothermally derived BMT nanopowders are very reactive and provide a high-density sintered body with 97.1% of theoretical density at a low temperature of 1350 °C. The average grain size of the sintered ceramics was 1.2 ± 0.2 μm and relatively uniform in comparison with the ceramics sintered with powders produced from the conventional method.     

Soft template synthesis of mesoporous Co3O4/RuO2·xH2O composites for electrochemical capacitors

Co₃O₄/RuO₂·xH₂O composites with various Ru content (molar content of Ru = 5%, 10%, 20%, 50%) were synthesized by one-step co-precipitation method. The precursors were prepared via adjusting pH of the mixed aqueous solutions of Co(NO₃)₂·6H₂O and RuCl₃·0.5H₂O by using Pluronic123 as a soft template. For the composite with molar ratio of Co:Ru = 1:1 annealed at 200 °C, Brunauer-Emmet-Teller (BET) results indicated that the composite showed mesoporous structure, and the specific surface area of the composite was as high as 107 m² g⁻¹. The electrochemical performances of these composites were measured in 1 M KOH electrolyte. Compared with the composite prepared without template, the composite with P123 exhibited a higher specific capacitance. When the molar content of Ru was rising, the specific capacitance of the composites increased significantly. It was also observed that the crystalline structures as well as the electrochemical activities were strongly dependent on the annealing temperature. A capacitance of 642 F/g was obtained for the composite (Co:Ru = 1:1) annealed at 150 °C. Meanwhile, the composites also exhibited good cycle stability. Besides, the morphologies and textural characteristic of the samples were also investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM).     

Synthesis of nanocrystalline lithium niobate powders via a fast chemical route

Lithnium niobate (LiNbO₃) can be obtained by mixing lithium nitrate (LiNO₃), ammonium niobate oxalate hydrate (C₄H₄NNbO₉) and glycine and then calcining at 600 °C for 1 h. The thermal analysis, structure, and morphology of the as-prepared LiNbO₃ were characterized by thermogravimetric and differential thermal analyses (TG/DTA), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The crystallization temperature of LiNbO₃ precursor is 580 °C based on the TG/DTA results. After being calcined at 600 °C, the structure of the LiNbO₃ synthesized using various ratios of glycine to metal nitrates (Ψ-value) was formed with a particle size of about 29-38 nm, as found by XRD analysis. The crystal size has the lowest value at Ψ = 2, and the highest level of crystallization is at Ψ = 3.     

Graphene nanosheets-tungsten oxides composite for supercapacitor electrode

Graphene nanosheets-tungsten oxides (tungsten oxide/tungsten oxide hydrate mixture) (GNS-W) composite was successfully synthesized using a facile approach. WO₃/WO₃·H₂O mixtures were deposited on the graphene nanosheets (GNS) to form the GNS-W composite. The GNS-W composite was characterized by X-ray diffraction (XRD), Raman spectrum, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The as-prepared GNS-W composite was directly fabricated into a supercapacitor electrode for potential energy storage application, and electrochemically tested by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. The GNS-W composite electrode exhibits a better electrochemical performance than that of the WO₃/WO₃·H₂O mixtures electrode. A high specific capacitance of about 143.6 F g⁻¹ at a current density of 0.1 A g⁻¹ for the GNS-W composite delivers significant improvement than that for the WO₃/WO₃·H₂O mixtures and GNS electrodes. The impedance studies also suggest that the GNS-W composite electrode shows the lower resistance and high conductivity due to the good interaction between the graphene nanosheets and the WO₃/WO₃·H₂O mixtures. The good electrochemical performance for the GNS-W composite may be attributed to the interaction between the WO₃/WO₃·H₂O mixtures and the edges of graphene nanosheets, which increases the ion diffusion rate as well as the conductivity.     

Effect of the addition ZrO2–Al2O3 on nanocrystalline hydroxyapatite bending strength and fracture toughness

Nanocrystalline hydroxyapatite powder has been synthesized from a Ca(NO₃)₂·4H₂O and (NH₄)₂HPO₄ solution by the precipitation method. In the next step we prepared ZrO₂–Al₂O₃ powder. After preparation, the powder was dried at 80 °C and calcined at 1200 °C for 1 h. Various amounts (HAP–15 wt% ZA, HAP–30 wt% ZA) of powder were mixed with the hydroxyapatite by ball milling. The powder mixtures were pressed and sintered at 1000 °C, 1100 °C and 1200 °C for 1 h. In order to study the structural evolution, X-ray diffraction (XRD) was used. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to estimate the particle size of the powder and observe fracture surfaces. Results show that the bending strength of pressed nanocrystalline HAP was improved significantly by the addition 15 wt% of ZrO₂–Al₂O₃ powders at 1200 °C, but the fracture toughness was not changed, however when 30 wt% of ZA powders were added to nanocrystalline HAP, the bending strength and fracture toughness of the specimens decreased at all sintering temperature.     

Synthesis of LaAlO3 powder using triethanolamine

LaAlO₃ powders were successfully synthesized by pyrolysis of complex compounds of lanthanum and aluminum with triethanolamine (TEA). The precursors and the derived powders were characterized by simultaneous thermogravimetry analysis (TG) and differential scanning calorimetry analysis (DSC), X-ray diffractometry (XRD), specific surface area measurements, and transmission electron microscopy (TEM). Pure LaAlO₃ phase was obtained at 775 °C for 2 h or 750 °C for 4 h, without formation of any intermediate phase. Pores were found from TEM images of LaAlO₃ powders prepared at 800 °C for 2 h.     

Growth behavior of nanosized ceria powders prepared by coprecipitation routes

Nanosized ceria (CeO₂) powders were obtained by coprecipitation routes of cerium nitrate hexahydrate [Ce(NO₃)₃·6H₂O]. The growth behavior of the nanosized CeO₂ powders was investigated by X-ray diffraction, transmission electron microscopy and selected area electron diffraction. The XRD results showed that the dried precursor powders contained a single crystalline phase of CeO₂, and only a single phase of CeO₂ appeared when the dried precursor powders were calcined at different temperatures for various durations. Moreover, the crystallite size of CeO₂ increased on increasing the calcination temperature and duration. The kinetics equation of the nanosized CeO₂ powders grown between 673 and 1273 K for various durations is described as     

Biomolecule and surfactant-assisted hydrothermal synthesis of PbS crystals

PbS crystals were hydrothermally synthesized using Pb(NO₃)₂, l-cysteine, and N-cetyl pyridinium chloride in solutions with different pH values at 140 °C. Flower-like, granular and truncated cubic PbS crystals composing of Pb and S were detected using an X-ray diffractometer (XRD), a scanning electron microscope (SEM), a transmission electron microscope (TEM), a selected area electron diffraction (SAED) technique and an energy dispersive X-ray (EDX) analyzer. In addition, a Raman spectrometer revealed the presence of the first and second overtone modes at 436 and 602 cm⁻¹, respectively. Emission spectra of the products were detected at 412 nm using a photoluminescence (PL) spectrometer.     

Sol−gel-based hydrothermal method for the synthesis of 3D flower-like ZnO microstructures composed of nanosheets for photocatalytic applications

Self-assembled 3D flower-like ZnO microstructures composed of nanosheets have been prepared on a large scale through a sol−gel-assisted hydrothermal method using Zn(NO₃)₂·6H₂O, citric acid, and NaOH as raw materials. The product has been characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The optical properties of the product have been examined by room temperature photoluminescence (PL) measurements. A possible growth mechanism of the 3D flower-like ZnO is proposed based on the results of experiments carried out for different hydrothermal treatment times. Experiments at different hydrothermal treatment temperatures have also been carried out to investigate their effect on the final morphology of the ZnO. The photocatalytic activities of the as-prepared ZnO have been evaluated by photodegradation of Reactive Blue 14 (KGL) under ultraviolet (UV) irradiation. The experimental results demonstrated that self-assembled 3D flower-like ZnO composed of nanosheets could be obtained over a relatively broad temperature range (90−150 °C) after 17 h of hydrothermal treatment. All of the products showed good photocatalytic performance, with the degree of degradation of KGL exceeding 82% after 120 min. In particular, the sample prepared at 120 °C for 17 h exhibited superior photocatalytic activity to other ZnO samples and commercial ZnO, and it almost completely degraded a KGL solution within 40 min. The relationship between photocatalytic activity and the structure, surface defects, and surface areas of the samples is also discussed.     

Structural and thermal analysis of in situ synthesized C–WC nanocomposites

Nanostructure of carbon encapsulated tungsten carbide (WC@C) has been prepared using reaction between metallic magnesium (Mg), acetone (C₃H₆O) and tungsten trioxide (WO₃) in an autoclave at 600 °C. The resultant powders were characterized by X-ray diffraction (XRD), differential thermal analysis/thermal gravimetric analysis and transmission electron microscopy (TEM). The XRD results showed that the optimization of the reaction time facilitates the reduction as well as carburization of the tungsten source. The apparent activation energy for decarburization of carbide phase was also evaluated from the data of thermal analysis to find the thermal stability of carbide phase. TEM image showed that the synthesized sample consisted of particles with an average size of 35 nm.     

Synthesis and characterization of ZnxMg1 − xGa2O4:Co fabricated by low-temperature burning method

A series of Zn_xMg_1 − xGa₂O₄:Co²⁺ spinels (x = 0, 0.25, 0.5, 0.75, and 1.0) was successfully produced through low-temperature burning method by using Mg(NO₃)₂·4H₂O, Zn(NO₃)₂·6H₂O, Ga(NO₃)₃·6H₂O, CO(NH₂)₂, NH₄NO₃, and Co(NO₃)₂·6H₂O as raw materials. The product was characterized by X-ray diffraction, transmission electron microscopy, and photoluminescence spectroscopy. The product was not merely a simple mixture of MgGa₂O₄ and ZnGa₂O₄; rather, it formed a solid solution. The lattice constant of Zn_xMg_1 − xGa₂O₄:Co²⁺ (0 ≤ x ≤ 1.0) crystals has a good linear relationship with the doping density, x. The synthesized products have high crystallinities with neat arrays. Based on an analysis of the form and position of the emission spectrum, the strong emission peak around the visible region (670 nm) can be attributed to the energy level transition [⁴T₁(⁴P) → ⁴A₂(⁴F)] of Co²⁺ in the tetrahedron. The weak emission peak in the near-infrared region can be attributed to the energy level transition [⁴T₁(⁴P) → ⁴T₂(⁴F)] of Co²⁺ in the tetrahedron.     

Synthesis of calcium phosphate-based composite nanopowders by mechanochemical process and subsequent thermal treatment

One-step mechanochemical process followed by thermal treatment has been used to produce calcium phosphate-based composite nanopowders. Effects of milling and subsequent heat treatment on the phase transition as well as structural features were investigated. The products were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM) techniques. The results revealed that the dominant phases after mechanical activation were hydroxyapatite, anatase (TiO₂), and periclase (MgO), while after thermal annealing process at 700 °C hydroxyapatite along with geikielite (MgTiO₃) and periclase (MgO) were the major phases. In addition, decomposition of hydroxyapatite to tricalcium phosphate (β-TCP) occurred after heat treatment in the range 900–1100 °C which resulted in the formation of tricalcium phosphate-based composite nanopowders. Evaluation of structural features of the samples calculated by X-ray diffraction profiles analysis indicated that the average crystallite size of hydroxyapatite after 10 h of milling and subsequent heat treatment at 700 °C were about 21 and 34 nm, respectively. TEM and SEM studies exhibited that the considerable morphological changes at temperatures ≥900 °C had to be ascribed not only to grain growth, but also for the transformation of hydroxyapatite to β-TCP.