Effect of sol–gel modifications on formation and morphology of nanocrystalline lanthanum aluminate

LaAlO₃ powders are prepared by sol–gel method. The effect of preparation conditions on morphological properties and crystal formations are investigated. iso-Propanol/tert-butanol and ethyl acetoacetate/ethylene glycol monomethylether are used solvents and complexing agents, respectively. Samples are dried with conventional and freeze-drying methods and calcined between 600 and 1000 °C. TGA, DTA, XRD, SEM and TEM methods are used for characterization. It is observed that freeze-dried sample prepared with tert-butanol has the lowest LaAlO₃ formation temperature and uniform rhombohedral crystals. But conventionally dried sample, prepared with iso-propanol has smallest agglomerates at 1000 °C and does not show clear crystallization temperature in DTA analysis. The XRD peaks of LaAlO₃ crystal are observed at 600 °C for all samples prepared by various sol–gel conditions.     

Cyclic microwave-assisted synthesis of flower-like and hexapod silver bismuth sulfide

Nanostructured AgBiS₂ with the shapes of flowers and hexapods was successfully produced from AgNO₃, BiCl₃ and sulfur sources (thioacetamide and thiourea) in ethylene glycol, by a cyclic microwave process. The phase was detected using X-ray diffraction (XRD) and selected area electron diffraction (SAED). Their SAED patterns were also in accordance with those of the simulations. Scanning and transmission electron microscopies (SEM and TEM) revealed the gradual transformation of nanostructured flowers into nanostructured hexapods, due to the microwave power increases. Their photoluminescence (PL) emissions were detected at the same wavelength of 435 nm, although they were produced under different conditions.     

Synthesis of single-crystal GaN nanowires on Si(111) substrate by ammonification technology

GaN nanowires have been synthesized on Si(111) substrate through ammoniating Ga₂O₃/BN films under flowing ammonia atmosphere at the temperature of 900 °C. The as-synthesized GaN nanowires were characterized by X-ray diffraction (XRD), selected-area electron diffraction (SAED), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM) and transmission electron microscope (TEM). The results demonstrated that the nanowires are hexagonal wurtzite GaN and possess a smooth surface with diameters ranging from 40 to 100 nm and lengths up to several tens of micrometers. The growth mechanism of crystalline GaN nanowires is discussed briefly.     

Characterization of AgBiS2 nanostructured flowers produced by solvothermal reaction

AgBiS₂ nanostructured flowers were produced from CH₃COOAg, Bi(NO₃)₃.5H₂O and thiosemicarbazide (NH₂CSNHNH₂) using different solvents [ethylene glycol (EG), water (H₂O), polyethylene glycol with molecular weight of 200 (PEG200), and propylene glycol (PG)] in Teflon-lined stainless steel autoclaves. The phase and purity were detected using X-ray diffraction (XRD), controlled by the solvents. The product was purified AgBiS₂ produced by the 200 °C and 24 h reaction in EG, corresponding to selected area electron diffraction (SAED) and simulation patterns. Scanning and transmission electron microscopies (SEM and TEM) revealed the formation of nanostructured flowers — enlarged by the increase in the lengths of time and temperature. Their photoluminescence (PL) emissions were detected at the same wavelength of 382 nm (3.24 eV), although they were produced under different conditions.     

Design and development of SnO decorated BaTiO3 heterostructure device platform for ethanol vapor detection

Herein, we reported the SnO decorated BaTiO₃ heterostructure as well as pristine BaTiO₃ based ethanol gas sensing properties examined. Barium titanate (BaTiO₃) and tin oxide (SnO) materials have been successfully synthesized by the hydrothermal alkaline solution technique. Structural investigations carried out by X-ray diffraction (XRD) analysis suggested the cubic phase of BaTiO₃ and the tetragonal SnO phase of the materials. Transmission electron microscopy (TEM) suggested irregular nanospheres of BaTiO₃ and micro sheets of SnO. The macroporous nature of BaTiO₃ and mesoporous nature of SnO were confirmed through Brunauer–Emmett–Teller (BET) analysis.   The fabricated device of BaTiO₃/SnO heterostructure shows sensor response of 10% with the fast response/recovery time of 1.9/1.6 s at the operating temperature of 150 °C for 500 ppm of ethanol vapor. The highest performance for the BaTiO₃/SnO heterostructure device was found to be sensor performance of 343% for 500 ppm of ethanol vapor with fast response time of 2.4 s at the operating temperature of 250 °C and it shows excellent sensor response at higher temperature. 

     

A facile one-step route to nanocrystalline TiB2 powders

Nanocrystalline titanium diboride (TiB₂) has been prepared by the reaction of TiCl₄ with NaBH₄ in the temperature range of 500–700 °C in an autoclave. X-ray powder diffraction (XRD) patterns can be indexed as hexagonal TiB₂ with the lattice constants of a=3.032 and c=3.229 Å. Transmission electron microscopy (TEM) image shows particle morphology, with average size of 15 nm for the powder obtained at 600 °C. Selected area electron diffraction (SAED) pattern confirms the prepared hexagonal TiB₂. The oxidation behavior of TiB₂ is studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA).     

Fabrication and characterization of Ag/calcium silicate core-shell nanocomposites

The Ag/calcium silicate nanocomposite with core-shell nanostructure has been successfully synthesized using Ag solution, Ca(NO₃)₂·4H₂O and Na₂SiO₃·9H₂O in ethanol/water mixed solvents at room temperature for 48 h. Ag solution was previously prepared by microwave-assisted method in ethylene glycol (EG) at 150 °C for 10 min. The nanocomposites consisted of Ag core and an amorphous calcium silicate shell. The XRD and EDS results confirmed that the product was the Ag/calcium silicate nanocomposite. The TEM micrographs indicated that the Ag/calcium silicate nanocomposite was core-shell nanoparticles. The effects of Ca(NO₃)₂·4H₂O and Na₂SiO₃·9H₂O concentration on the shells of Ag/calcium silicate nanocomposite were investigated. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and energy-dispersive X-ray spectra (EDS). This method is simple, fast and may be extended to the synthesis of the other kinds of core-shell nanocomposites.     

Low temperature synthesis of nanocrystalline calcium aluminate compounds with surfactant-assisted precipitation method

Nanocrystalline calcium aluminates with different CaO:Al₂O₃ and surfactant/metal ion molar ratios were prepared by wet chemical synthesis method using Poly (ethylene glycol)-block-poly(propylene glycol)-block poly(ethylene glycol) (PEG–PPG–PEG, MW:5800) as surfactant. X-ray diffraction (XRD) and N₂ adsorption–desorption results showed that the increase in CaO:Al₂O₃ ratio decreased the specific surface area and increased the particle sizes of prepared samples while the surfactant/metal ion molar ratios were kept constant. These analyses also declared that for the sample with CaO:Al₂O₃ = 1:2 (CA2) addition of polymeric surfactant increased the specific surface area and decreased the crystallite size. Scanning electron microscopy (SEM) results confirmed that size of particles for CaO:Al₂O₃ = 1:6 (CA6) sample are smaller than CA2. Transmission electron microscopy (TEM) revealed no particular particle shape for the CA2 sample but it showed the high degree of crystallinity and single phase for the prepared sample at 1100 °C.     

Fabrication of three-dimensional snowflake-like bismuth sulfide nanostructures by simple refluxing

Three-dimensional snowflake-like bismuth sulfide nanostructures were successfully synthesized by simple refluxing at 160 °C in ethylene glycol, using bismuth citrate and thiourea as reactants. The crystal structures and morphologies of the products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDX). The Bi₂S₃ nanostructure was built up by highly ordered one-dimensional Bi₂S₃ nanorods, which was aligned in an orderly fashion. Ethylene glycol plays a critical role in the creation of bismuth sulfide three-dimensional nanostructures, which serves as an excellent solvent and structure director. Bismuth citrate, a linear polymer, also makes for the formation of the three-dimensional nanostructures.     

Synthesis and characterization of Bi2S3 nanorods by solvothermal method in polyol media

Bi₂S₃ nanorods were synthesized via a simple solvothermal process in polyol media through the reaction between Bi(NO₃)₃·5H₂O, urea and CS₂ at 150 °C for 15 h using diethylene glycol as solvent. The nanorods were characterized by XRD, TEM and SAED. The results showed that the products were well-crystallized orthorhombic phase with lattice parameters a = 11.15 Å, b = 11.3 Å and c = 3.984 Å, which are consistent with the value in standard JCPDS card No. 17-0320. DEG served as an excellent solvent and structure director. Besides, compared to water and EG as solvents, the DEG system can provide a mild and homogenous condition, which is favorable to anisotropic growth and increases the yield of high quality Bi₂S₃ nanorods. Based on the experimental results, the growth mechanism was discussed.     

A simple chemical route to Bi2S3 hierarchical columniform structures assembled by nanorod-based lamellae

Bi₂S₃ hierarchical columniform structures assembled by nanorod-built lamellae have been first synthesized by a simple wet chemical method through the reaction between Bi(NO₃)₃?5H₂O and CS₂ at 80 °C for 14 h using DMSO as solvent without any surfactants. These new Bi₂S₃ structures were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Compared to ethylene glycol and DMF, DMSO supplied an excellent chemical environment favorable to the generation of Bi₂S₃ quickly in heterogeneous condition. The influences of the synthetic parameters were discussed and a possible growth mechanism for the formation of these complex structures was proposed.     

Preparation of nano-CaO using thermal-decomposition method

CaO is an important inorganic material, which can be used as catalyst, toxic-waste remediation agent, adsorbent etc. In order to make use of CaO, nano-CaO was prepared by thermal-decomposition method using Ca(NO₃)₂.4H₂O as precursor, NaOH aqueous solution as precipitant, and ethylene glycol as medium in this paper. Characteristics of samples were measured by TGA, XRD, TEM et al techniques. The results showed that the size of nano-CaO about 14 nm could be obtained under the conditions (calcinations temperature 500 °C, calcinations time 1.5 h, heating rate of calcinations 5 °C/min). It is a very simple and effective method to prepare nano-CaO.     

Structural,electrical, and rheological properties of palladium/silver bimetallic nanoparticles prepared by conventional and ultrasonic-assisted reduction methods

Polyvinylpyrrolidone stabilized Pd/Ag bimetallic nanoparticles (NPs) with average particle sizes of 9 and 6 nm were synthesized by simultaneous reduction in the presence and absence of ultrasound waves, respectively. The prepared NPs were characterized by six methods including X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution-TEM (HRTEM), UV–vis spectroscopy, scanning tunneling microscopy (STM), and energy dispersive X-ray (EDX) analysis. The rheological properties of Pd/Ag NPs in ethylene glycol as a base fluid with various mass fractions of NPs from 2% to 5% at different temperatures were studied experimentally and theoretically. The experimental results showed that viscosity of Pd/Ag NPs in ethylene glycol increases with increasing particle mass fraction and decreases with increasing temperature. A maximum of 31.58% increase in viscosity of ethylene glycol at 20 °C was observed when 5% Pd/Ag NPs was added. Measurement of the electrical conductivity of nanofluids of Pd/Ag bimetallic NPs in distilled water at different mass fractions and temperatures was performed. A 3841% increase in electrical conductivity of distilled water at 25 °C was observed when 1% Pd/Ag NPs was added. Both the rheological and electrical properties of Pd/Ag bimetallic NPs were measured in ethylene glycol and distilled water, respectively for the first time.     

A simple solvothermal reduction route to copper and cuprous oxide

Pure copper nanocrystallites and cuprous oxide nanorods have been synthesized via solvothermal treatment of CuSO₄ or CuSO₄·5H₂O and NaOH in pure ethanol and mixed solution of ethanol and deionized water at 140 °C for 10 h, respectively. Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) were used to investigate the different morphologies of the as-synthesized products. X-ray powder diffraction (XRD) and selected area electron diffraction (SAED) were applied to characterize the composition and crystal phases of the products. It was proposed that the reducibility of ethanol was influenced by temperature and the addition of deionized water in the formation of different phases, which were realized by carefully controlling the experimental conditions.     

Preparation and characterization of high surface area nanosheet titania with mesoporous structure

High surface area nanosheet TiO₂ with mesoporous structure were synthesized by hydrothermal method at 130 °C for 12 h. The samples were characterized by XRD, SEM, TEM, SAED, and BET surface area. The nanosheet structure was slightly curved and approximately 50–100 nm in width and several nanometers in thickness. The as-synthesized nanosheet TiO₂ had an average pore diameter about 3–4 nm. The BET surface area and pore volume of the sample are about 642 m²/g and 0.774 cm³/g, respectively.     

Preparation and characterization of cobalt ferrite by the polymerized complex method

Magnetic nanoparticles of Co-ferrite were prepared by the polymerized complex method. Heating in vacuum of a precursor solution containing citric acid (CA), ethylene glycol (EG) and cobalt and iron salts with a molar ratio of Co/Fe/CA/EG=1/2/9/22.5 at 130 °C produced a brownish transparent polymeric gel, which have been characterized by IR and NMR spectroscopy. The results of both techniques suggest two types of reactions: the formation of metal-CA complexes and successive esterification reactions between CA and EG. The organic fraction was removed by controlled thermal treatments (200–800 °C) whereby the bimetallic oxide was formed. The powders obtained were characterized by X-ray diffraction (XRD), vibrational sample magnetometry (VSM) and transmission electron microscopy (TEM). XRD analysis showed the presence of CoFe₂O₄ at 400 °C. The saturation magnetization values of the samples increased as a function of calcination temperature and reached a maximum of 79.8 emu/g at 800 °C. The TEM images showed spherical nanoparticles with sizes between 20 and 40 nm.     

Cyclic microwave-assisted synthesis of Cu3BiS3 dendrites using l-cysteine as a sulfur source and complexing agent

Nanostructured Cu₃BiS₃ dendrites were successfully synthesized from CuCl, BiCl₃ and l-cysteine in ethylene glycol (EG), using cyclic microwave radiation (CMR). The phase was detected by X-ray diffraction (XRD) and selected area electron diffraction (SAED), and was in accordance with that obtained by the simulation. Scanning and transmission electron microscopic (SEM and TEM) techniques revealed the gradual transformation of nanoparticles to nanostructured dendrites, due to the increase of microwave power. Photoluminescence of Cu₃BiS₃ dendrites was a blue emission centered at 367 nm.     

Structural study of Li<Subscript>2</Subscript>MnO<Subscript>3</Subscript> by electron microscopy

Detailed crystallographic data on high-quality Li₂MnO₃ material has been obtained using a combination of X-ray diffraction (XRD), selected-area electron diffraction (SAED), high-resolution electron microscopy (HREM), and 0.1 nm probe high-angle annular dark-field imaging (HAADF) in a scanning transmission electron microscope. A high-purity Li₂MnO₃ powder was annealed at 950 °C for 3 days to obtain predominantly defect-free grains which average size was 3.0 ± 1.5 μm. Rietveld refinement indicated that the C2/m spacegroup provided the best fit for the XRD data. Electron diffraction patterns obtained along various zone axes, on defect-free oxide particles, could be uniquely indexed to the monoclinic structure. HREM and HAADF images of defect-free grains were consistent with a Li–Mn–Mn– arrangement, i.e., lithium ordering in the transition metal planes. Low-magnification TEM images occasionally revealed stacking defects within oxide particles. HREM images of sample areas containing defects revealed a low density of stacking faults within the monoclinic sequence, resulting in a trigonal P3 ₁ 12 local arrangement.     

Characterization and synthesis of KTa0.1Nb0.9O3 particles via high temperature mixing method under hydrothermal conditions

KTa_0.1Nb_0.9O₃ (KTN) particles with an orthorhombic perovskite structure have been synthesized via a high temperature mixing method (HTMM) under hydrothermal conditions. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and high-resolution transmission electron microcopy (HRTEM). The influence of alkaline concentration and solvent composition on the phase structure and morphology of the obtained powders was investigated. The results show that the well-crystallized KTN powders with sizes of 200–500 nm are successfully prepared at temperatures as low as 240 °C when the KOH concentration is 2.0 M and the isopropanol/water (I/W) volume ratio equals to 100/0.     

Short time reaction synthesis of nano-hexagonal boron nitride

Nano-hexagonal boron nitride (h-BN) was successfully prepared via rapid microwave-assisted synthesis using boric acid (H₃BO₃) and melamine (C₃H₆N₆) as raw materials. An investigation of the effect of the microwave energy on the synthesis process of nano h-BN was carried out. In addition, the preparation method of the precursor was also studied. Here, mixtures at different H₃BO₃:C₃H₆N₆ ratios (1:1 and 2:1 M) were prepared via wet and dryforms. Each precursor was heated under microwave energy for different reaction times. The microwave-synthesized nano-products were characterized by XRD, SEM, EDS, HRTEM and SAED. The results show that the reaction time and temperature that are typically 4.6 h (ramp time + soak time) and 1400–2100 °C, respectively (literature values), can be dramatically reduced to only 1.5 h (ramp time + soak time) and 1130–1210 °C, respectively, applying microwave heating. It was observed that the final product consists of crystalline h-BN nanoparticles of about 20 nm and disc-like morphology.