Morphologies Of Microcrystals Research Articles

Fabrication of anatase titanium dioxide microspheres via homogeneous precipitation method

Titanium dioxide (TiO2) microspheres have been successfully prepared using titanium tetrachloride (TiCl4) as the starting material, ethanol (or methanol) as the solvent and urea as the homogeneous precipitant. Powder X-ray diffraction and SEM are used to characterise various properties of the obtained anatase microcrystals. Under the experimental conditions (temperature 110°C; time 12 h), the TiO2 products are almost all in this spherical morphology. The microsphere surfaces are smooth, which exhibit a sphere-like morphology with a diameter ranging from 2 to 5 μm. It is found that the morphologies of anatase microcrystals strongly depend on the hydrothermal conditions, in which urea plays an important role during the whole process. This work has provided a simple and effective method to synthesise anatase in aqueous solution, which may also be applicable to the preparation of other compounds.

Crystal growth of organic energetic materials: pentaerythritol tetranitrate

Abstract The energy output performance and thermal stability of organic energetic materials have a strong dependence on the porosity, particle morphology, and micro-scale crystal structure. This paper reviews the growth habit of pure pentaerythritol tetranitrate (PETN) crystals and the effect of metal impurities on microcrystal morphology of PETN films. The pure crystal growth shows that PETN molecules diffuse on the surface and nucleate in a two-dimensional layer-by-layer fashion; the final structure is controlled by the deposition flux. Also, the effect of metal cation impurities has a strong impact on the thermal stability and crystal structure, and is dependent on the doping level.

Time-dependent hydrothermal synthesis and self-evolution mechanism of Cu2O microcrystals

Abstract The successive and circulatory evolution of Cu 2 O microcrystal morphology and the reduction from Cu 2 O to Cu have both been investigated by carefully adjusting the hydrothermal heating time. The evolutions of the Cu 2 O morphology, which were from octahedrons to octahedrons, from plump-hexapods to perfect hexabranches, have been attained for the first time. The results of our work clearly demonstrate the effect of hydrothermal heating time on Cu 2 O microcrystal morphology without surfactant or template, with the same initial solution composition, the same solution concentration and the same temperature. In particular, the mechanism of circulatory evolution of Cu 2 O microcrystal morphology and that of reduction from Cu 2 O to Cu have both been investigated in detail.

Preparation of Self-Assembled Crystalline Microparticles with Bispyridyl Zn-Porphyrin

Well-defined solid-state microcrystalline structures from bispyridyl Zn-porphyrin have been successfully synthesized. The coordinative interactions between pyridine and Zn are main responsible for this translation of porphyrin molecular building blocks to crystalline microscopic objects. The hexagonal plates are obtained from acetonitrile and rhombus plates are grown from toluene solution. With a simple manipulation during the microcrystal growth, such as growth temperature and time, the morphologies can be controlled by adopting different molecular packing. Consequently, morphologies of microcrystals have been diversified.

Controlled synthesis of Ag2O microcrystals with facet-dependent photocatalytic activities

Ag2O microcrystals with different morphologies have been successfully synthesized by using various complexing agents. To achieve kinetic control of the growth of the Ag2O microcrystals, [Ag(NH3)2]+ complexing ions are required to restrict the release rate of silver ions before adding NaOH solution. The complexing anions play an important role in the growth process of the Ag2O microcrystals. This kinetic control leads to five morphologies of Ag2O microcrystals (cubic, octahedral, rhombic dodecahedra, polyhedra with 18 faces and rhombicuboctahedral), which exhibit facet-dependent photocatalytic activity for the degradation of methyl orange (MO) under visible light irradiation. The cubic Ag@Ag2O photocatalyst with exposed {100} facets showed the greatest activity of all the other morphologies of the photocatalysts. The mechanism of dramatic enhancement of the photocatalytic activity of Ag@Ag2O with exposed {100} facets was discussed in detail from three aspects, including the highest surface energy of the {100} facet, the larger difference value between the weighted average of the effective mass of holes and electrons along the [100] direction, and the suitable redox potentials of the (100) surface.

Controlled Synthesis and Photoluminescent Properties of Cu2O Microcrystals with Different Morphologies

Abstract Cu2O microcrystals with cubic, spherical, and octahedral morphologies were easily synthesized in aqueous solution under the assistance of ultrasonic irradiation. The obtained products were characterized by using X-ray power diffractometry (XRD) and field emission scanning electronic microscopy (FE-SEM). The morphologies of Cu2O microcrystals could be controlled by simply adjusting NaOH concentration. It is believed that the difference in the growth rate of Cu2O crystal facets led to the formation of different morphologies of microcrystals, which exhibited good room-temperature photoluminescence properties with new green emission peaks at 530 nm, making them have potential applications as phosphors and biolabels.

Fabrication of octahedral Atacamite microcrystals via a hydrothermal route

Octahedral Atacamite (Cu2Cl(OH)3) microcrystals have been successfully fabricated via a convenient hydrothermal route in the absence of any external inorganic additives or organic structure-directing agents. Powder X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy spectra are used to characterise various properties of the obtained Atacamite microcrystals. It is found that the morphologies of Atacamite microcrystals strongly depend on the hydrothermal conditions, in which urea plays an important role during the whole process. This work has provided a simple and effective method to synthesise Atacamite in aqueous solution, which may also be applicable to the preparation of other copper-based compounds.

Simple Synthetic Manipulation Allowing for Morphological Diversity of Porphyrin-Based Microcrystals

Amphiphilic (porphyrin)Sn(OH)2 molecular building block can directly translate into well-defined solid-state microcrystalline structures. The crystalline diamond plates are obtained from ethanol and crystalline square plates are grown from methanol solution. With a simple synthetic manipulation during the microcrystal growth, the morphologies can be controlled by adopting different molecular packing. Consequently, morphologies of microcrystals have been diversified. Furthermore, the macroscopic crystals were obtained in the presence of cetyltrimethylammonium bromide (CTAB).

Study on morphologies of Co microcrystals produced by solvothermal method with different solvents

Cobalt microcrystals with different sizes and morphologies were fabricated via a facile solvothermal method. The effects of different solvents on the sizes and morphologies are investigated separately. Flowerlike cobalt with around tens of microns in diameter is obtained in ethanol. Meanwhile, of microdisks and octadecahedra with the edge lengths about several microns are fabricated in ethylene glycol and glycerol, respectively. Reduction potential and viscosity rank of the solvents play the important roles in controlling the sizes and morphologies of cobalt. Moreover, room-temperature magnetic measurement shows that the magnetic properties of cobalt microcrystals depend on their morphologies.

An efficient microwave-assisted hydrothermal synthesis of BaZrO3 microcrystals: growth mechanism and photoluminescence emissions

The effect of different synthetic conditions (both template and chloride precursor concentration) on the morphologies of BaZrO3 microcrystals was systematically investigated. Three different templates, polyethylene glycol (PEG), cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulfate (SDS), and two different chloride concentrations were used in the experiments. BaZrO3 microcrystals were obtained using the microwave assisted hydrothermal method (MWHT) at 140 °C for 40 min. BaZrO3 microstructures were characterized by powder X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), Fourier transform Raman spectroscopy (FT-Raman) and photoluminescence (PL) measurements. The growth mechanism for the formation of BaZrO3 with decaoctahedron-shape was analyzed in detail, and we have found that the nature of the mechanism follows a non-classical growth process involving mesoscale self-assemblies of nanoparticles. Based on these findings, a relationship between the morphology and the photoluminescent behavior is proposed.

Uranium in Framboidal Pyrite from a Naturally Bioreduced Alluvial Sediment

Samples of a naturally bioreduced, U-contaminated alluvial sediment were characterized with various microscopic and spectroscopic techniques and wet chemical extraction methods. The objective was to investigate U association and interaction with minerals of the sediment. Bioreduced sediment comprises approximately 10% of an alluvial aquifer adjacent to the Colorado River, in Rifle, CO, that was the site of a former U milling operation. Past and ongoing research has demonstrated that bioreduced sediment is elevated in solid-associated U, total organic carbon, and acid-volatile sulfide, and depleted in bioavailable Fe(III) confirming that sulfate and Fe(III) reduction have occurred naturally in the sediment. SEM/EDS analyses demonstrated that framboidal pyrites (FeS(2)) of different sizes ( approximately 10-20 microm in diameter), and of various microcrystal morphology, degree of surface weathering, and internal porosity were abundant in the <53 microm fraction (silt + clay) of the sediment and absent in adjacent sediments that were not bioreduced. SEM-EMPA, XRF, EXAFS, and XANES measurements showed elevated U was present in framboidal pyrite as both U(VI) and U(IV). This result indicates that U may be sequestered in situ under conditions of microbially driven sulfate reduction and pyrite formation. Conversely, such pyrites in alluvial sediments provide a long-term source of U under conditions of slow oxidation, contributing to the persistence of U of some U plumes. These results may also help in developing remedial measures for U-contaminated aquifers.

A template‐free route for controlled synthesis of dumbbell‐like Sb2S3 microcrystals

AbstractLarge amounts of dumbbell‐like Sb2S3 microcrystals were synthesized via a simple solvothermal treatment method. Various techniques such as x‐ray diffraction (XRD), field‐emission scanning electron microscope (FESEM), high‐resolution transmission electron microscope (HRTEM), selected area electron diffraction (SAED), and photoluminescence spectrometry (PL) have been used to characterize the obtained products. The results showed that the products belong to the orthorhombic Sb2S3 phase, and the dumbbell‐like Sb2S3 microcrystals were composed by uniform microrods. Besides, the morphologies of Sb2S3 microcrystals could be changed from microshperes to dumbbell‐like microcrystals by only adjusting the reaction solvent. The solvent effects are discussed in detail. Furthermore, the PL properties of the obtained Sb2S3 microcrystals clearly show shape effects. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Exchange of Fluorinated Cyanine Dyes between Different Types of Silver Halide Microcrystals Studied by Imaging Time-of-Flight Secondary Ion Mass Spectrometry

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is used to study dye adsorption on silver halide (AgBr or Ag(Br,I)) microcrystals. The dyes are labeled with fluorine to allow their detection at the surface of the microcrystals by means of atomic ions. In this study, particular attention is paid to dye adsorption selectivity as a function of microcrystal morphology and to the possibility of dye exchange between different types of microcrystals. Using a gallium (Ga+) liquid metal ion gun operating at 25 keV as the primary ion source, secondary ion images with a lateral resolution of 65 nm have been collected. This high lateral resolution makes it possible to distinguish between octahedral and cubic AgBr crystals even with an edge length of only 0.4 μm, based on their bromide images. It also enables us to detect and localize the fluorine-labeled dyes at the surface of these microcrystals. When larger cubic crystals with an edge length of 0.8 μm are used, the site selectivity of the fluorine-labeled...

The effect of electrostatic field on the micro-crystal morphology of polymer films

The micro-crystal morphology of the films of isotactic polypropylene (iPP), poly(3-dodecylthiophene) (P3DDT) and iPP/P3DDT blend grown in different electrostatic environments has been investigated by using scanning electron microscope. The experimental results show that the micro-crystal morphology of polymer films was strongly dependent on electrostatic field. It was found that the micro-crystal morphology of the films of iPP, P3DDT and iPP/P3DDT blend grown in the electrostatic field was in the form of dendrite crystals, in which main stems were aligned in the field direction, and some branches of P3DDT were ruptured. However, the micro-crystals of the films of iPP, P3DDT and iPP/P3DDT blend have no crystal orientation in the absence of electrostatic field.