Controlled preparation of hollow zinc oxide microspheres from aqueous solution using hexamethylenetetramine and cysteine

Zinc oxide particles were synthesized by precipitation from an aqueous solution of zinc nitrate tetrahydrate, R-(+)-cysteine and hexamethylenetetramine (HMTA, urotropine). Hollow microspheres of ZnO-cysteine hybrid material with a diameter of ca. 1 μm and a wall thickness ca. 50 nm were obtained. After heating up to 850 °C pure ZnO microspheres of roughly the same size were formed. The particles were characterized by XRD, SEM, FT-IR and TGA.     

Synthesis and photochromic properties of EDTA-induced MoO3 powder

In this study, the photochromic MoO₃ powder with novel morphology has been synthesized via hydrothermal method, using ethylene diamine tetraacetice acid (EDTA) as organic inducing agent. The influence of EDTA on the morphology, structure and photochromic properties of MoO₃ powder has been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), as well as ultraviolet and visible spectroscopy (UV-vis) and color difference meter. When the molar ratio of EDTA/Mo⁶⁺ is 0.05:1, the EDTA-induced MoO₃ powder is found to have 3D flower-like morphologies and excellent photochromic properties. Furthermore, the possible growth mechanism of the flower-like structure and the photochromic mechanism of MoO₃ powder are also discussed in detail.     

Effects of reaction time and citric acid contents on the morphologies of BaCO3 via PVP-assisted method

BaCO₃ with different morphologies, such as dumbbell-like, pillar-like, peanut-like and ellipsoid-like have been successfully synthesized using citric acid (CA) as chelating ligand via a simple polyvinylpyrrolidone (PVP)-assisted method. The effects of the pH of the starting solutions, reaction time and the molar ratio of CA/Ba²⁺ on the morphologies of BaCO₃ were investigated. X-ray diffraction (XRD), transmission electron microscope (TEM) and the infrared (IR) spectrum of the sample are used to characterize the obtained products.     

Controllable synthesis of hydroxyapatite nanocrystals via a dendrimer-assisted hydrothermal process

The morphology and size of hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ (denoted HAP) can be controlled under hydrothermal treatment assisted with different dendrimers, such as carboxylic terminated poly(amidoamine) (PAMAM) and polyhydroxy terminated PAMAM. The structure and morphology were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR) and transmission electron microscopy (TEM). IR spectra were also used to investigate the complexation of Ca²⁺ with PAMAM. The results revealed that the inner cores of the PAMAM dendrimers are hydrophilic and potentially open to calcium ions, since interior nitrogen moieties serve as complexation sites, especially in case of the polyhydroxy terminated PAMAM. And the reasonable mechanism of crystallization was proposed that it can be attributed to the localization of nucleation site: external or interior PAMAM. Additionally, the PAMAM dendrimer with carboxylic and polyhydroxy groups has an effective influence on the size and shape of hydroxyapatite (HAP) nanostructures. Different crystal morphology was accomplished by adsorption of different dendrimers onto specific faces of growing crystals, altering the relative growth rates of the different crystallographic faces and leading to different crystal habits.     

Formation of novel morphologies of aragonite induced by inorganic template

A glass-slice was used as a template to induce formation and assembly of aragonite. Thermodynamic theory was applied to explain the production of the aragonite. Transformation of three-dimensional nucleation to template-based two-dimensional surface nucleation caused the production of aragonite. Hemisphere, twinborn hemisphere and flower-shaped particles were produced by direction of the glass-slices. Planes were always appeared in these as-synthesized samples because the nucleation and the growth of these samples were adsorbed at the surfaces of the glass-slices. The formation mechanism of the as-formed sample was proposed. Compared with organic template, the present study provides a facile method to apply inorganic template to prepare functional materials.     

Synthesis and crystallographic study of Pb-Sr hydroxyapatite solid solutions by high temperature mixing method under hydrothermal conditions

The solid solutions in the system of Pb and Sr hydroxyapatite, Sr_10−xPb_xHAp (x = 0-10), were successfully synthesized by high-temperature mixing method (HTMM) at 160 °C for 12 h under hydrothermal conditions. The samples were characterized by X-ray diffraction, chemical analysis and electron microscopic observation, and the site of the metal ions in the solid solutions was analyzed with the Rietveld method. The lattice constants, both a and c, of the solid solutions varied linearly with Pb content. It was found that Pb ions in the solid solutions preferentially occupied the M(2) site in the apatite structure. HTMM gives Sr-Pb HAp solid solutions much better crystallization. However, due to the formation of intermediate compound of Pb₃O₂(OH)₂ in the Pb(NO₃)₂·4H₂O solution before mixing with (NH₄)₂HPO₄ solution at 160 °C, HTMM causes the decrease of crystallization of the samples with high Pb content.     

Selenium nanowires and nanotubes synthesized via a facile template-free solution method

Trigonal selenium (t-Se) nanowires and nanotubes were successfully prepared on a large scale via an environment-friendly synthetic process, in which no templates or surfactants were employed. These t-Se nanowires having a width of 70-100 nm and length up to tens of micrometers were synthesized in absolute ethanol at room temperature, while t-Se nanotubes with outer diameter ranging from 180 to 350 nm were obtained at 85 °C in water system. SEM and TEM analyses of the samples obtained at different stages indicated that the formation of these t-Se 1D nanostructures was governed by a “solid-solution-solid” growth process. The amorphous Se (a-Se) nanoparticles were initially generated and then would transform into crystal seeds for the subsequent growth of nanowires or nanotubes. Detailed experiments found that temperature and solvents as well as concentrations of starting materials were crucial to the formation of final morphology.     

Single crystal growth of Mn2N using an In-Na flux

Hexagonal platelet and pyramidal single crystals of Mn₂N were prepared by using an In-Na flux at 700 °C and 5 MPa of N₂ pressure. The crystal structure (space group P6₃/mmc) with lattice parameters a=2.8185(6) Å and c=4.5371(12) Å was confirmed by X-ray single-crystal diffraction. Nitrogen atoms statistically occupy a half of the octahedral interstitial sites in a hexagonal closest packing arrangement of Mn atoms.     

Crystal growth and structure determinations of potassium hafnates: K2Hf2O5 and K4Hf5O12

Crystals of K₂Hf₂O₅ and K₄Hf₅O₁₂ were grown from molten potassium hydroxide flux. The crystal structures were determined by single-crystal X-ray diffraction. K₂Hf₂O₅ crystallizes in the space group Pnna of the orthorhombic system, with unit cell dimensions of a = 5.780(1) Å, b = 10.640(2) Å, and c = 8.666(2) Å. This compound contains infinite chains of HfO₆ octahedra that form a channel structure. K₄Hf₅O₁₂ crystallizes in the space group of the trigonal system, with unit cell dimensions of a = 5.7877(2) Å and c = 10.3693(7) Å. This compound possesses a layered structure with six-coordinate Hf in three different coordination environments (trigonal prismatic, distorted octahedral, and regular octahedral).     

Crystal growth and structure refinement of monoclinic Li2TiO3

Colorless platelet crystals of monoclinic Li₂TiO₃ with a maximum size of 5.0 mm × 5.0 mm × 0.5 mm were successfully grown by a flux method at 1373 K using a LiBO₂-Li₂O system flux. The stoichiometric chemical composition of Li₂TiO₃ was determined by the SEM-EDX, ICP-AES and density measurement using the single crystal samples. The thermal conductivity of the Li₂TiO₃ single crystals was evaluated using hot-disk method. A single-crystal X-ray diffraction study confirmed the monoclinic Li₂SnO₃-type structure, space group C2/c and the lattice parameters of a = 5.0623(5) Å, b = 8.7876(9) Å, c = 9.7533(15) Å, β = 100.212(11)°, and V = 427.01(9) Å³. The crystal structure was refined to the conventional values of R = 2.4% and wR=3.3% for 2187 independent observed reflections. The cationic arrangement of (LiTi₂) layers in Li₂TiO₃ was precisely revealed by the structure analysis.     

Fabrication and dissolution behavior of hollow hydroxyapatite microspheres intended for controlled drug release

Hollow hydroxyapatite (HA) microspheres were fabricated by a simple spray drying method in this study. Moreover, the dissolution behavior of these hollow HA microspheres after immersion in simulated body fluid (SBF) was also studied. The results indicated that the dissolution of the HA microspheres in SBF is not homogeneous in a layer-by-layer fashion but was preferential at different locations of the particle surface. Generically, dissolution preferentially occurs on the location with looser structure and high porosity of the microspheres. The degradable HA microspheres are expected to have potential applications in bone local drug delivery systems.     

Single crystal growth and structure refinements of CsMxTe2−xO6 (M = Al, Ga, Ge, In) pyrochlores

Single crystals of CsM_xTe_2−xO₆ pyrochlores with M = Al, Ga, Ge, and In have been grown from a TeO₂ flux. Structure refinements from single crystal X-ray diffraction data are reported. These results are used to discuss deviations from ideal stoichiometry that result in electronic conductivity presumably related to mixed valency of tellurium.     

ZnO single crystals: Synthesis and characterization

Zinc oxide crystals grown in a single basic mineralizer in hydrothermal autoclaves are of poor quality. The crystals are transparent, pale green or pale yellow in color depending on different technical growth conditions. The quality of crystals under different conditions was observed by X-ray rocking curves measurement. The use of ultra-pure nutrient improves their perfection and purity. Zinc oxide bulks that were grown by the hydrothermal method in a mixture of KOH and LiOH aqueous solutions are of good quality.     

Size and morphology-controlled Ni2[Fe(CN)6]·xH2O Prussian Blue analogue fabricated via a hydrothermal route

Nanocrystalline Prussian Blue analogue Ni₂[Fe(CN)₆]·xH₂O was synthesized through hydrothermal process at 180 °C for 24 h with NiSO₄·6H₂O and K₄[Fe(CN)₆]·3H₂O as precursors. The effects of reactant concentration and protective matrix (Polyethylene glycol 400, PEG-400) on the size and morphology of nanoparticles were investigated. The as-synthesized products were identified as face-centered cubic structure by powder X-ray diffraction. Field-emission scanning electron microscopy and transmission electron microscopy images showed that well dispersed nanoparticles with fairly narrow size distribution were successfully prepared.     

Effect of rotation of feed and seed rods on the quality of Na0.75CoO2 single crystal grown by traveling solvent floating zone method

High purity Na_0.75CoO₂ single crystals have been grown by floating zone method. We found the rotation of feed and seed rods play a crucial role in growing high quality single crystal. Systematic investigations suggest the occurrence of a phase separation at microscopic level, such as the separation into Na-rich and Na-poor domains during the growth, and formation of impurity phase(s) depending on growth conditions. Na_xCoO₂ (x = 0.30, 0.60) crystals have been prepared by sodium deintercalation from Na_0.75CoO₂. Powder X-ray and energy dispersive X-ray analyses have confirmed the phase purity and homogeneity of the samples. Magnetic susceptibility measurements of x = 0.60 and 0.75 crystals indicate a bulk phase transition at 22 K and an anomaly around 339 K and 334 K respectively which are attributed to structural transition. In addition some unique features related to Na_0.60CoO₂ were observed.     

Synthesis of vanadium oxide nanofibers and tubes using polylactide fibers as template

A new method to produce vanadium oxide nanofibers with dimensions <140 nm and tubes is reported. Vanadium oxide was coated on polylactide fibers by a sol-gel method using a reaction mix of ammonium vanadate and acetic acid as starting materials and water as solvent. Vanadium oxide tubes, of about 1 μm in diameter, were formed when this coated fiber was heated in nitrogen and oxygen at 300 and 250 °C for 1 h. Hydrothermal treatment of the polylactide fibers with the reaction mix at 160 °C for 12 h followed by heating in oxygen at 300 °C for 1 h formed vanadium oxide nanofibers, 60-140 nm in width and several microns in length. Electrochemical studies reveal that these vanadium oxide nanofibers are redox active and readily undergo reversible reactions with lithium in non-aqueous cells.     

Preparation of polyaniline nanotubes array based on anodic aluminum oxide template

In this article, the highly ordered polyaniline (PANI) nanotubes array was prepared by in situ polymerization using anodic aluminum oxide (AAO) as template. Polymerization of aniline was confined in the one-dimensional nanochannel of AAO template. The aniline was adsorbed and polymerized preferentially on the pore walls of template. The structure of PANI nanotubes array was characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), selected area electron diffraction (SAED) and dynamic force microscope (DFM). The results show that PANI nanotubes are synthesized successfully in the nanopores of template, the diameter and length of PANI nanotubes are closed to the pore diameter and thickness of AAO template, respectively, the arrangement of PANI nanotubes is very regular and uniform, the crystal form of PANI nanotubes is hexagonal, different from pseudo-orthorhombic crystal form of PANI bulk sample, and cell parameters a and b are 0.5008 nm. The change of crystal form is due to the confinement of AAO template, which makes the molecular chain of PANI arrange more ordered.     

Composition dependent phase connectivity, dielectric and magnetoelectric properties of magnetoelectric composites with Pb(Mg1/3Nb2/3)0.67Ti0.33O3 as piezoelectric phase

Ferrite (Ni_0.6Co_0.4Fe₂O₄) phase, ferroelectric (Pb(Mg_1/3Nb_2/3)_0.67Ti_0.33O₃) phase and magnetoelectric composites of (x)Ni_0.6Co_0.4Fe₂O₄ + (1 − x)Pb(Mg_1/3Nb_2/3)_0.67Ti_0.33O₃ with x = 0.15, 0.30 and 0.45 were prepared using solid-state reaction technique. Presence of Ni_0.6Co_0.4Fe₂O₄ and Pb(Mg_1/3Nb_2/3)_0.67Ti_0.33O₃ was confirmed using X-ray diffraction technique. The scanning electron microscopic images were used to study the microstructure of the composites. Connectivity scheme present in the magnetoelectric (ME) composites are discussed from the microscopic images. Variation of dielectric constant and dielectric loss with temperature for all the composites was studied. Here we report the effect of Ni_0.6Co_0.4Fe₂O₄ mole fraction on connectivity schemes between Ni_0.6Co_0.4Fe₂O₄ and Pb(Mg_1/3Nb_2/3)_0.67Ti_0.33O₃ composite. The variation of magnetoelectric voltage coefficient with dc magnetic field shows peak behaviour. The maximum value of magnetoelectric voltage coefficient of 9.47 mV/cm Oe was obtained for 0.15Ni_0.6Co_0.4Fe₂O₄ + 0.85Pb(Mg_1/3Nb_2/3)_0.67Ti_0.33O₃ composites. Finally we have co-related the effect of Ni_0.6Co_0.4Fe₂O₄ content and dielectric properties on magnetoelectric voltage coefficient.     

Synthesis of potassium hexatitanate whiskers starting from metatitanic acid and potassium carbonate and sulfate by calcination method

Potassium hexatitanate whiskers were synthesized starting from metatitanic acid (H₂TiO₃), potassium carbonate and sulfate by calcination method. The effects of mole ratios of K₂CO₃ to metatitanic acid (H₂TiO₃), content of potassium sulfate, and calcination temperature on the crystallinity and morphology of the resultant potassium titanate whiskers were investigated by X-ray diffraction and scanning electron microscopy. Well crystallized potassium hexatitanate whiskers with an average length of 7.3 μm and an average diameter of 0.62 μm were synthesized when the molar ratio of K₂CO₃ to metatitanic acid was kept at 1:3.5 and the calcination temperature was up to 1150 °C. The presence of K₂SO₄ favored the formation of thin potassium hexatitanate whiskers as compared to the absence of K₂SO₄. The whiteness and brightness of the synthesized potassium hexatitanate whiskers were comparable to that of rutile TiO₂ pigment.     

Preparation of SrCe0.95Yb0.05O3−α perovskite for use as a membrane material in hollow fibre fabrication

In this study, a pure orthorhombic perovskite SrCe_0.95Yb_0.05O_3−α (SCYb) ceramic powder was prepared using a chelated water-soluble complex method at relatively low temperatures. Common chelating ligands such as citric acid and EDTA were employed for the synthesis of complex-based precursors, followed by thermal decomposition of the precursors at high temperatures. Thermal behaviour, crystal phases, and structures of the prepared ceramic powders were characterised by TGA/DTA, XRD and SEM techniques, respectively. Clean and single-phase SCYb submicron-sized powders were obtained after sintering at a temperature of 1000 °C for 4 h. Gas-tight hollow fibre having a maximum bending strength of 60 MPa have been fabricated from the SCYb powders synthesised from the chelated water-soluble complex method.