Formation Of Hollow Structure Research Articles

Phase transition induced formation of hollow structures in colloidal lanthanide-doped NaYF4 nanocrystals

Formation of colloidal hollow structures in NaYF4 nanocrystals (NCs) with and without lanthanide ion doping has been observed and inves- tigated via the co-thermolysis of a mixture of trifluoroacetate precursors in trioctylphosphine oxide. The Kirkendall effect in this one-step reaction is driven by the monomer diffusion and crystal phase transition. It is found that three kinetic stages which include rapid precipitation of cubic phase NCs, cubic to hexagonal phase transition concurrent with an inward transport of NaF species, and vacancy diffu- sion are attributed to the hollow structure formation. X-ray energy dispersive spectroscopy (XEDS) point analysis is applied to examine the ions distribu- tion and crystalline components in the lanthanides (Yb and Er)-doped NaYF4 up-conversion nanophos- phors (UCNPs). The hollow structures increase the surface-to-volume of a single NC and thus have a significant effect on the photoluminescence of the lanthanide-doped NPs and provide synthetic applica- tions for achieving novel NaYF4-based NCs.

A Simple H2O2-assisted Method for the Synthesis of Intestine-like SnO2 Nanostructures at Room Temperature

Abstract Highly crystalline intestine-like SnO2 nanostructures with hollow interior have been synthesized by a one-step H2O2-assisted method at room temperature. A possible growth mechanism has been proposed. In the synthesis, H2O2 fulfills important functions in both forming the intestine-like morphology and promoting the formation of hollow structure.

Synthesis and characterization of hollow spherical copper phosphide (Cu 3P) nanopowders

In this paper, hollow spherical Cu 3P nanopowders were synthesized by using copper sulfate pentahydrate (CuSO 4⋅5H 2O) and yellow phosphorus in a mixed solvent of glycol, ethanol and water at 140–180 ∘C for 12 h. X-ray powder diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), electron diffraction pattern (ED) and transmission electronic microscopy (TEM) studies show that the as-synthesized nanocrystal is pure hexagonal phase Cu 3P with a hollow spherical morphology. Based on the TEM observations, a possible aggregation growth mechanism was proposed for the formation of Cu 3P hollow structures. Meanwhile, the effects of some key factors such as solvents, reaction temperature and reaction time on the final formation of the Cu 3P hollow structure were also discussed.

Hollow LiNi0.8Co0.1Mn0.1O2−MgO Coaxial Fibers: Sol−Gel Method Combined with Co-electrospun Preparation and Electrochemical Properties

Hollow LiNi0.8Co0.1Mn0.1O2−MgO coaxial fibers were prepared by employing the sol−gel proces combined with the coaxial electrospinning technique. The hollow coaxial fibers had a shell thickness of 30−60 nm and wall thicknesses of 300−500 nm. The polyvinyl pyrrolidone (PVP) had an important role in the formation of hollow structure. The electrochemical properties of hollow LiNi0.8Co0.1Mn0.1O2−MgO coaxial fibers were investigated by charge−discharge experiments. The hollow coaxial fibers as electrode materials showed a high discharge capacity and excellent cycle stability.

A facile route to hollow superparamagnetic magnetite/polystyrene nanocomposite microspheres via inverse miniemulsion polymerization

AbstractIn this article, we report a facile route to the preparation of hollow superparamagnetic magnetite/polystyrene nanocomposite microspheres via inverse miniemulsion polymerization at room temperature and under ambient pressure. Water droplets act as a soft template for the formation of hollow structure. Meanwhile, the existence of amphipathic magnetite nanoparticles (MPs) which can assemble at the interface of W/O is favorable to the interfacial polymerization of styrene, ensuring the formation of hollow nanocomposite microspheres. The final products were thoroughly characterized by X‐ray powder diffraction (XRD), fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), field‐emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), and X‐ray photoelectron spectroscopy (XPS), which showed the formation of hollow magnetite/polystyrene nanocomposite microspheres. Magnetic hysteresis loop measurements revealed that both MPs and hollow nanocomposite microspheres displayed superparamagnetism. The effects of the content of H2O, sorbitan monooleate (Span 80) and styrene and the dose rate on the morphology of nanocomposite microspheres were studied. Furthermore, the mechanism of the formation of the hollow magnetic microspheres was also discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3900–3910, 2008

A Facile Method for Preparation of Hollow Polyphenylsilsesquioxane Microspheres

Abstract Hollow polyphenylsilsesquioxane microspheres were fabricated under mild conditions from a mixture of water and phenyltriethoxysilane (PTES) with ammonia as catalyst. The pH value and the temperature of the reaction mixture are the crucial factors contributing to the formation of stable and regular polyphenylsilsesquioxane hollow spheres. A possible mechanism for the formation of hollow structure was proposed.

Assembly of Silver Nanoparticles into Hollow Spheres Using Eu(III) Compound based on Trifluorothenoyl-Acetone

The preparation of luminescent silver hollow spheres using Eu(III) compound based on trifluorothenoyl-acetone is described. The structure and size of silver hollow spheres were determined by TEM images. The result shows the formation of hollow structure and average size of the silver hollow spheres (0.9 μm). The silver hollow spheres were further characterized by UV absorption spectrum, SNOM and SEM images, suggesting them to be formed by self-assemble of some isolated silver nanoparticles. The luminescent properties of them were also investigated and they are shown to be high emission strength; moreover, they offer the distinct advantage of a lower packing density compared with other commercial luminescent products.

Hollow fibers of yttria-stabilized zirconia (8YSZ) prepared by calcination of electrospun composite fibers

8YSZ fibers were synthesized by calcination of PVP/zirconium oxychloride/yttrium nitrate composite fibers (PVP-Precursor) obtained by electrospinning. Scanning electron microscopy (SEM) indicated that the 8YSZ fibers are hollow and the gas released during organic binder decomposition resulted in the formation of hollow center in fibers. Proper controlling heating rate is necessary to the formation of hollow structure. Both X-ray diffraction (XRD) and Raman spectroscopy analysis indicated that the 8YSZ fibers have crystal structure of tetragonal phase. The hollow structure should make the fibers to have a higher resistance to sintering than solid fibers at elevated temperature. This result has important applications in catalytic combustion.

Formation of TiO 2 hollow microparticles by spraying water droplets into an organic solution of titanium tetraisopropoxide (TTIP) — Effects of TTIP concentration and TTIP-protecting additives

Hollow, spherical TiO 2 microparticles of several tens of micrometers in diameter can be prepared by spraying water into an organic phase containing titanium tetraisopropoxide (TTIP) as a titanium source. The concentration of TTIP did not affect the shell thickness. On the contrary, the shell thickness was increased with the concentration of the additives such as acetic acid and acetylacetone, having effects to protect TTIP from hydrolysis and condensation. The formation of a hollow particle was described by a simple model involving the hydrolysis of TTIP at the water–oil interface, the inward diffusion of hydrolyzed titanium hydroxide through the passage in the shell and its incorporation into the TiO 2 shell by condensation. The reduction of porosity of shell inhibits the diffusion, resulting in the formation of hollow structure. The simulation based on this model predicted that the shell thickness increased as the diffusion rate increased or the reaction rate decreased, and was independent of the outer TTIP concentration. These predictions were in qualitative agreement with the experimental results.

Hollow Amorphous Formation via Oxidation of Al Nanoparticles at Low Temperatures

Formation of hollow structure through oxidation of Al nanoparticles was studied by applying transmission electron microscopy. Al nanoparticles 6~8 nm in diameter were observed to become hollow particles after having been exposed to air at 295 K for a few minutes. An analysis of the Debye-Sherrer rings in the selected area diffraction patterns before and after oxidation showed that hollow oxide nanoparticles are amorphous. The formation mechanisms of hollow oxide are discussed based on the low-temperature oxidation mechanism of Al and on the comparison with our previous results of hollow ZnO formation via oxidation of Zn nanoparticles.

Mechanism of a self-templating synthesis of monodispersed hollow silica nanospheres with tunable size and shell thickness

This study clarifies the mechanism of the hollow structure formation in the simple self-templating preparation of monodispersed hollow silica structures; the role of the polarity of washing solvent in creating the hollow structure is emphasized.

Fabrication, characterization, and formation mechanism of hollow spindle-like hematite via a solvothermal process

As a novel hollow nanostructure, hollow spindle-like hematite with uniform size and morphology was solvothermally synthesized. These hollow polycrystalline particles with the length of 220–300 nm, the width of 70–100 nm, and the wall thickness of ca. 18 nm were characterized by TEM, FE-SEM, XRD, FT-IR, TGA, Mössbauer spectrum, and XPS methods. It was found that these hollow-structured particles were transformed from their original solid spindle particles. During the hollow structure formation process, the interiors of solid particles were preferentially dissolved while the retained exteriors were protected by coordinated sulfate ions. The formation mechanism was proposed as a coordination-assisted dissolution process occurred in a reverse microemulsion system.

Preparation of BaMgAl 10O 17:Eu blue phosphor by flame-assisted spray pyrolysis: photoluminescence properties of powder and film under VUV excitation

Flame-assisted spray pyrolysis was applied to prepare BaMgAl 10O 17:Eu (BAM) blue phosphor particles with spherical shape, which exhibited improved photoluminescence characteristics under vacuum ultraviolet (147 nm) excitation. It was found that simply controlling the property of the precursor solution to be sprayed was helpful to suppress the formation of hollow structure and made it possible to produce dense and spherical-shaped BAM particles by using the flame-assisted spray pyrolysis process. The film of prepared BAM powder was built up on slide glass. Then, the prepared spherical particles produced not only better uniform surface, but also higher particle density in comparison with the commercial BAM particles which have irregular shape. The photoluminescence intensity of the spherical-shaped BAM particles prepared by the flame-assisted spray pyrolysis was lower than that of the commercial powder. The phosphor film made from BAM particles with fine size and spherical shape, however, showed higher photoluminescence intensity than that prepared with the irregular-shaped commercial particles due to higher particle density and uniformity of the film.

Preparation of hollow silica microspheres in W/O emulsions with polymers

Micrometer-sized hollow silica particles were synthesized by sol–gel reaction in water-in-oil emulsion. To obtain hollow structures in silica particles, the viscosity of water droplets in W/O emulsion was controlled with polyethylene glycol (PEG) or polyvinylpyrrolidone (PVP). To stabilize the emulsion structure, hydroxypropyl cellulose (HPC) was added to the oil phase. Without HPC, the particles have an irregular shape and hardly have a particulate form. As the concentration of HPC increased from 0.8 to 1.4 wt%, the size of silica particles decreased from 10 to 1 μm. But above 1.4 wt%, the solution was very viscous, so that it was difficult to handle. Especially, the role of PEG or PVP in the water phase was very important, not only because it stabilized the W/O emulsion structure, but also because it influenced the formation of hollow structure. Interestingly, the hollow silica particles were formed when the molar ratio of water to TEOS (Rw) was 4 and the concentrations of PEG and HPC were 6 and 1.4 wt%, respectively. Also, when PEG was replaced with polyvinylpyrrolidone (PVP), hollow silica particles ranging from 3 to 7 μm were formed.

Mo(CH 3CN) 4(NO) 2](BF 4) 2 as a model for NO on a reduced [formula omitted] catalyst

A Co-Mo sulfide catalyst with tube-like structure was prepared through a low-temperature pre-sulfurization process using rod-like CoMoO4 as the precursor. The pre-sulfurization temperature greatly affected the total pore volume, the concentration of CoMoS species, the microstructure of (Co)MoS2 slabs and the catalytic desulfurization activity. The increased temperature can promote the formation of hollow structure and the sulfurization degree of the precursor. It was found that the excessive temperature induced the Co atoms to form more isolated Co9S8 species, hindering the formation of highly active CoMoS species. Therefore, appropriate temperature is more favorable to form the (Co)MoS2 slabs with shorter length and higher stacking number, leading to more coordinatively unsaturated sites, especially the corner sites. According to the results of hydrodesulfurization reaction, the reaction rate of dibenzothiophene and the yields of liquid products are highly depended on the number of surface-active sites, which are mainly originated from the Type II CoMoS species. Moreover, the extended pre-sulfurization time can further improve the catalytic desulfurization activity of the catalyst at an appropriate pre-sulfurization temperature.