Chemical control in precipitation of spherical zirconia particles

Monodisperse spherical zirconia particles are precipitated by hydrolysis of alcoholic solutions of zirconium alkoxides in the presence of long-chain carboxylic acids. The particle size can be finely tuned from 0.1 to 2.5 m by controlling the concentration of zirconium alkoxide, the water/zirconium ratio, the nature of alcohol from ethanol to butanol, the nature of carboxylic acid from caproic to oleic acid and its concentration. The relationships between the induction time before nucleation, the particle size and all the above parameters are tentatively explained on the grounds of the solubility of the carboxy-alkoxide derivatives and their tendency to form micelles. Calcination of precipitated powders between 300 and 600 C produces mixtures of varying composition from cubic to monoclinic phases of small crystallite sizes, and brings out the loss of surface area and organic content. Different conditions of drying powders lead to variously ordered microstructures.     

Synthesis and characterization of Ce-doped mesoporous anatase with long-range ordered mesostructure

The effect of cerium cation on the formation of titania crystallites using H⁺ as catalyst under mild condition has been investigated. The results indicated that the presence of cerium cation can improve the selectivity of producing anatase crystallites and inhibit the growth of crystallites. The Ce-doped mesoporous titania with highly crystallized pore walls consisting of anatase nanoparticles was synthesized by anatase crystallites assembly. The long-range ordered mesostructure was characterized by low angle and wide angle X-ray diffraction (XRD), N₂ adsorption-desorption, transmission electron microscopy (TEM) and selected area electron diffraction (SAED).     

Direct synthesis of shaped carbon nanoparticles with ordered cubic mesostructure

Shaped, mesoporous carbon nanoparticles (MSP-3) were prepared in high yield by a simple direct synthesis using a block copolymer surfactant as the mesopore-directing agent and a colloidal crystal to mold the external shape of the particles. The product consisted of monodisperse nanocubes and uniform nanospheres or tetrapods. The nanocubes contained regularly spaced, cagelike mesopores. The orientation of the cubic unit cell describing the mesopore symmetry coincided with the templated external cube faces.     

Synthesis,structural and magnetic characterization of highly ordered single crystalline BiFeO3 nanotubes

In this work, we report on the fabrication of highly ordered single crystalline BiFeO₃ (BFO) nanotubes by a sol–gel technique using two-step anodic aluminum oxide (AAO) as template. We prepared BFO nanotubes with dimensions of 65 nm in diameter and 3 μm in length, as confirmed by scanning electron microscopy (SEM) measurements. The obtained single crystalline nanotubes present the expected pure phase (BiFeO₃) as confirmed by energy-dispersive X-ray spectroscopy (EDX), selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). In addition to the antiferromagnetic behavior, the magnetization curves of the BFO nanotubes also present a ferromagnetic response, which holds from 2 to 300 K. This desirable behavior is associated to the break of the antiferromagnetic helical spin ordering of the BFO nanotubes. Besides the magnetocrystalline anisotropy, the large length-to-diameter ratio induced an uniaxial shape anisotropy, attested by the applied magnetic field angle measurements.     

Preparation and characterisation of magnetically ordered columnar structures of barium ferrite particles

In this study, we report on the columnar structures of barium ferrite particles that were prepared from water suspensions by applying a magnetic field during drying. Commercial barium ferrite (BaFe₁₂O₁₉) monodomain particles were used, and the surfaces of the particles were treated with an organic surfactant to reduce their agglomeration. The columnar structures were obtained by drying the water suspensions of BaFe₁₂O₁₉ particles on Al₂O₃ substrates under an applied magnetic field of 1?T. After the degradation of the organic components, the samples were sintered at 1350°C. X-ray powder diffraction, scanning electron microscopy and magnetic measurements were used to characterise the samples. When the magnetic field was applied perpendicularly to the sample plane, the as-deposited sample exhibited a higher coercivity (H _c?=?5434?Oe) and a higher squareness ratio (SQR?=?0.76) than the sintered sample (H _c?=?625?Oe, SQR?=?0.58). However, the sintered sample showed a higher anisotropy of the magnetic behaviour than the as-deposited sample.     

Preparation of highly crystalline graphitic nanocarbon for the electro-oxidation of methanol

Highly crystalline graphitic nanocarbons (GNC) have been prepared by the wet-air treatment of hydrothermallyderived graphitic porous carbon. The materials were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and electrochemical methods. The experimental results revealed that the treatment temperature has a significant effect on the morphology and degree of graphitic crystallinity. When GNC was treated at 450 °C under a wet-air atmosphere, the product (GNC-450) consisted of aggregates of silkworm-shaped carbon nanoparticles with enhanced graphitic characteristics. GNC-450 was evaluated as a catalyst support in the electro-oxidation of methanol. The Pt/GNC-450 catalyst contained smaller Pt particles and had a higher electrochemically active surface area than a commercial carbon black-supported Pt catalyst. In the electro-oxidation of methanol, the Pt/GNC-450 catalyst showed the highest performance among the Pt catalysts examined in this study. The superior catalytic performance appears to be closely related to the enhanced graphitic characteristics with highly dispersed Pt nanoparticles on the graphitic layers, which have a positive effect on the electrochemical performance.     

Acoustic control of materials with developed mesostructure

On the basis of generalization of the results of a series of theoretical and experimental investigations, we have formulated the scientific foundations of the synthesis of qualitatively new acoustic methods for predicting the properties and controlling the structure and defectiveness of multicomponent materials. On the example of powder and fibrous materials and their compositions, ceramics, foam-metals, honeycomb structures, diamond composites, multilayer constructions, and products made of them, we have shown that acoustic methods can serve as a reliable tool for obtaining information on the effective properties of the material as a whole and the parameters of ensembles or separate elements of its mesolevel. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 4, pp. 53–65, July–August, 2007.     

Precise control of highly ordered arrays of nested semiconductor/metal nanotubes

Lithographically defined microporous templates in conjunction with the atomic layer deposition (ALD) technique enable remarkable control of complex novel nested nanotube structures. So far three-dimensional control of physical process parameters has not been fully realized with high precision resolution, and requires optimization in order to achieve a wider range of potential applications. Furthermore, the combination of composite insulating oxide layers alternating with semiconducting layers and metals can provide various types of novel applications and eventually provide unique and advanced levels of multifunctional nanoscale devices. Semiconducting TiO₂ nanotubes have potential applications in photovoltaic devices. The combination of nanostructured semiconducting materials with nested metal nanotubes has the potential to produce novel multifunctional vertically-ordered three-dimensional nanodevices. Platinum growth by ALD has been explored, covering the initial stages of the thin film nucleation process and the synthesis of high aspect ratio nanotube structures. The penetration depth of the Pt into porous templates having various pore sizes and aspect ratios has been investigated. Several multi-walled nested TiO₂-Pt nanotubes in series have been successfully fabricated using microporous Si templates. These innovative nested nanostructures have the potential to produce novel multifunctional vertically-ordered three-dimensional nanodevices in photovoltaic and sensing technologies.      

Supersaturation operation for quality control of crystalline particles in solution crystallization

The crystallization is widely used in chemical processes, and is one of unit operation which deals with crystallization phenomena. The purposes of crystallization are to separate desired component and to produce crystalline particles. However, phenomena of crystallization are not simple and the relationships between operation conditions and product specification are complicated. The driving force of crystallization is supersaturation in non-equilibrium process. So the operation strategy for designing supersaturation is important in order to keep high quality such as size distribution, crystal morphology and polymorph. In this paper, the relationships between supersaturation and crystal qualities are discussed, and the operation design methods are introduced to control crystal qualities in solution crystallization.     

Electron microdiffraction studies of zirconia particles

A batch of zirconia was prepared at a pH of 2.95 using a sol-gel technique. The crystal structures formed during 500 °C calcination was followed by X-ray diffraction. The tetragonal phase was the major component after the initial calcination period of 15.5 h; however, it gradually transformed to the monoclinic crystal form during 200 h of calcination at 500 °C. Electron microdiffraction was employed in the present investigation to determine the crystal structure of individual particles, and to identify whether these particles contained twin variants. A technique has been developed to get a dispersion of agglomerated particles by condensing and spreading the beam on the agglomerates at 200 kV. The data revealed that some of the individual zirconia particles are featureless and some of them appear to contain single or multiple twin variants.     

Low temperature synthesis and visible light driven photocatalytic activity of highly crystalline mesoporous TiO2 particles

Mesoporous TiO2 powder materials with a high crystallinity have been prepared by evaporation induced self assembly (EISA) process using titanium tetraisopropoxide (TTIP) and pluronic P123 surfactant (EO20PO70EO20) as titanium source and structure-directing reagent, respectively. The prepared materials were characterized by low and wide-angle X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), optical absorption, and N2 adsorption-desorption experiments. The crystallinity of the materials was controlled by varying the calcination temperature. The resulting TiO2 materials showed highly crystalline structure with uniform particle size which increases from 11.8 to 23.8 nm with increasing the calcination temperature from 400 to 600 degrees C, respectively, whereas the specific surface area decreases from 125 to 40 m2/g. TEM and XRD results revealed that the calcination temperature of 600 degrees C is the best condition to obtain highly crystalline mesoporous TiO2. The photocatalytic activity of the TiO2 mesoporous materials with different crystallinity and textural parameters has been studied in the decomposition of methylene blue (MB) dye molecules under visible light irradiation. Among the mesoporous TiO2 materials studied, the material with the highest crystallinity, prepared at 600 degrees C, showed the best photocatalytic performance in the decomposition of MB under visible light in a short time.     

Preparation of stable micron-sized crystalline irbesartan particles for the enhancement of dissolution rate

Purpose: In this study, micron-sized crystalline drug particles of irbesartan (IBS) were prepared to improve its stability and dissolution rate.

Method: The approach to crystalline particles was based on the liquid precipitation process by which the amorphous particles were prepared. Pharmaceutical acceptable additives were used as the crystallization agent to convert the amorphous drug into crystalline particles. High pressure homogenization (HPH) process has been employed to reduce the size of the crystalline particles, and the micron-sized particles were obtained by the freeze-drying process.

Results: Different additives show different influences on the polymorphic form of IBS. Polyvinylpyrrolidone (PVP) and hydroxypropyl methylcellulose (HPMC) were effective in stabilizing amorphous particles instead of converting amorphous drug into crystalline particles, while poloxamer407 (F127) and tween80 (T80) could convert the amorphous drug into crystalline particles. T80 was also effective in controlling the particle size than that of F127. After HPH, crystalline particles with an average of 0.8 μm were obtained. The freeze-dried micron-sized crystalline particles exhibited significantly enhanced in vitro dissolution rate when compared to the raw drug. SEM, FT-IR, XRD, DSC and dissolution rate studies indicated that the micron-sized particles were stable during 6 months storage.

Conclusion: The preparation of micron-sized crystalline drug particles is an effective way to improve the stability and dissolution rate of irbesartan.     

Facile fabrication of hierarchically porous carbonaceous monoliths with ordered mesostructure via an organic organic self-assembly

A simple strategy for the synthesis of macro-mesoporous carbonaceous monolith materials has been demonstrated through an organic-organic self-assembly at the interface of an organic scaffold such as polyurethane (PU) foam. Hierarchically porous carbonaceous monoliths with cubic (Im m) or hexagonal (p6mm) mesostructure were prepared through evaporation induced self-assembly of the mesostructure on the three-dimensional (3-D) interconnecting struts of the PU foam scaffold. The preparation was carried out by using phenol/formaldehyde resol as a carbon precursor, triblock copolymer F127 as a template for the mesostructure and PU foam as a sacrificial monolithic scaffold. Their hierarchical pore system was macroscopically fabricated with cable-like mesostructured carbonaceous struts. The carbonaceous monoliths exhibit macropores of diameter 100–450 μm, adjustable uniform mesopores (3.8–7.5 nm), high surface areas (200–870 m²/g), and large pore volumes (0.17–0.58) cm³/g. Compared with the corresponding evaporation induced self-assembly (EISA) process on a planar substrate, this facile process is a time-saving, labor-saving, space-saving, and highly efficient pathway for mass production of ordered mesoporous materials. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. This article is published with open access at Springerlink.com     

Preparation, characterization and photocatalytic performance of Nd-doped titania nanoparticles with mesostructure

Nd³⁺-doped titania nanoparticles with mesostructures were synthesized via hydrothermal process by using cetyltrimethylammonium bromide (CTAB) as directing and pore-forming agent. The obtained materials were characterized by XRD, nitrogen adsorption-desorption, TEM and DRS. The existence of neodymium ion affect significantly the phase transition of the amorphous to anatase, and the band-gap energy was reduced because of the defect energy level induced by the 4f atomic orbital of Nd³⁺ with the optimal content of 1.5 at.% Nd. Density functional theory calculations can explain the band-gap narrowing. The maximum photocatalytic activity corresponds to the 0.5 at.% Nd³⁺-doped anatase nanopowders with mesostructures, which is higher than that of undoped samples.     

Preparation of micro-sized and monodisperse crystalline silver particles used for silicon solar cell electronic paste

In this paper, monodisperse crystalline silver particles in microscale were prepared via chemical reduction method and the reaction conditions were systematically investigated. Gelatin was used as surfactant to prevent the agglomeration of silver particles. The crystallized and mono-disperse silver particles were obtained at the optimal synthesis condition (1.2 mol/L silver nitrate, 0.8 mol/L ascorbic acid, gelatin/silver = 0.025 wt% and pH = 1.5). The average particle size of the silver particles is 1–2 μm and the tap density of silver particles is over 5.0 g/cm³. The pH value is a key factor for preparation of crystallized silver particles. When the pH value increases from 1.0 to 4.0, the morphology of silver particles changes from polyhedron crystalline to spherical particles. The silver particles were used for preparation of the lead-free silver paste for monocrystalline silicon solar cell and the solar cell grid electrode has low resistivity and high adhesion strength.     

亚微米球形ZrO_2颗粒材料的水热法合成及表征

以Zr(NO_3)_4·5H_2O和CO(NH_2)_2为原料,乙醇为溶剂,通过水热法合成亚微米级球形ZrO_2颗粒;用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、傅里叶红外光谱仪(FT-IR)、热重-差热分析仪(TGA-DTA)、紫外-可见光吸收光谱仪(UVVis)对ZrO_2颗粒进行分析表征,研究工艺条件对球形ZrO_2颗粒尺寸和形貌的影响。结果表明:通过水热法合成的球形ZrO_2颗粒粒径分布较窄,添加适量的表面活性剂、无机盐溶液及水对产物的尺寸与形貌具有一定的影响;添加适量水可获得粒径分布更窄的球形ZrO_2颗粒,且热处理对球形ZrO_2颗粒的粒径大小和形状影响不大。     

Preparation of highly ordered Fe-SBA-1 and Ti-SBA-1 cubic mesoporous silica via sol-gel processing of silatrane

Silatrane prepared from fumed silica and triethanolamine (TEA) was used as a precursor for the sol-gel synthesis of M-SBA-1 (M = Fe and Ti) at room temperature using cetyltrimethylammonium bromide as a template, and dilute solutions of ferric chloride and titanium glycolate as metal sources. Powder X-ray diffraction (XRD) showed the mesoporous materials to be well-ordered cubic structures, while N₂ adsorption/desorption measurements yielded high surface areas. Diffuse reflectance UV-visible spectroscopy demonstrated that iron (Fe³⁺) and titanium (Ti⁴⁺) were incorporated in the framework of the calcined materials to loadings of 6 wt.% Fe and 10 wt.% Ti without perturbing the ordered mesoporous structure.