A novel synthesis of micrometer silica hollow sphere

Silica microcapsules (hollow spheres) were synthesized successfully by a novel CTAB-stabilized water/oil emulsion system mediated hydrothermal method. The addition of urea to a solution of aqueous phase was an essential step of the simple synthetic procedure of silica hollow spheres, which leads to the formation of silica hollow spheres with smooth shell during hydrothermal process. The intact hollow spheres were obtained by washing the as-synthesized solid products with distilled water to remove the organic components. A large amount of silanol groups were retained in the hollow spheres by this facile route without calcination. The morphologies and optical properties of the product were characterized by transmission electron microscopy, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy. Furthermore, on the basis of a series of SEM observations, phenomenological elucidation of a mechanism for the growth of the silica hollow spheres has been presented.     

Submicrometer-sized hollow nickel spheres synthesized by autocatalytic reduction

A facile method to fabricate submicrometer-sized hollow nickel spheres by autocatalyzing the redox reaction around a sacrificial colloidal particle surface is presented in this paper. The size distribution of these spheres can be controlled by regulating the concentration of the alkali solution. The hollow nickel particles were characterized by field emission scanning electron microscopy, transmission electron microscopy and X-ray powder diffraction. The hollow spheres produced by this process may have potential applications in many fields, including chemistry, biotechnology and materials science.     

Template-free fabrication of TiO2 hollow spheres and their photocatalytic properties

Submicrometer-sized anatase TiO(2) hollow spheres were fabricated through a template-free solvothermal route using TiCl(4) as a raw material and a mixture of alcohols-acetone as solvent. Control of the hollow spheres' size was achieved by adjusting the ratio of alcohols to acetone. Products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution TEM, X-ray photoelectron spectra (XPS), X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and thermogravimetric (TG) analysis. It was found that the formation process of the TiO(2) hollow spheres might include the hydrolysis of Ti(IV) with the water formed from the solvothermal etherification reaction, the aggregation of the anatase TiO(2) nanoparticles, and the Ostwald ripening. Furthermore, the as-prepared TiO(2) hollow nanostructures exhibited good photocatalytic activity for the degradation of phenol.     

Assembled CuO hollow spheres from nanoparticles

CuO microspheres with hollow interiors were synthesized by a simple method using urea as an important reagent to generate soft-template. X-ray diffraction pattern, Infrared spectrum, electronic diffraction, field emission scanning electron microscopy images, transmission electron microscopy images and high-resolution transmission electron microscopy investigated the phase structures and morphologies of CuO microspheres. The hollow spheres may be formed through the assembling of nanoparticles with the assistance of gas bubbles and a self-generated template and aggregation process was proposed for the formation mechanism of the CuO spheres.     

Fabrication of Nickel hollow spheres by microemulsion-template-interface reaction route

Ni hollow spheres (NHSs) have been successfully synthesized through a microemulsion-template-interface reaction route. The structures of NHSs were characterized by X-ray powder diffraction (XRD), selected area electron diffraction (SAED), transmission electron microscopy (TEM). The results showed that the size of the NHSs was between 50 to 150 nm. The shell thickness of the NHSs is about 20 nm. In our method, the metal precursor and reducing agent dissolved in two different phases; they can react at oil/water interface. Thus, hollow spheres can be fabricated more easily.     

Preparation of polystyrene-encapsulated silver hollow spheres via self-assembly of latex particles at the emulsion droplet interface

In the present work, we have developed a novel route to wrap inorganic nanoparticles in polymer hollow spheres, which includes self-assembly polystyrene (PS) latex particles at the aqueous/oil interface, sintering and γ-ray radiation reduction. The Ag/PS composite microspheres were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and field-emission scanning electron microscopy (FESEM). The advantage of this method is that the PS shell thickness, permeability, the size of composite spheres, and the quantity of the encapsulated Ag nanoparticles can be easily adjusted, which gives the product a brilliant prospect in the field of catalysis.     

Synthesis of hollow spheres with mesoporous silica nanoparticles shell

Hollow spheres with mesoporous silica nanoparticles shell were synthesized with the use of cetyltrimethylammonium bromide (CTAB) and polystyrene (PS) hollow spheres as dual templates. The key to this study is that the uneven surface of the template provides nucleation sites for mesoporous nanoparticles, resulting in the formation of hollow spheres with mesoporous silica nanoparticles shell. The final products with hierarchical mesopores can be obtained through a simple one-step approach.     

Hydrothermal synthesis of PbS hollow spheres with single crystal-like electron diffraction patterns

PbS hollow spheres were successfully prepared by a sodium citrate-assisted hydrothermal process at 120 degrees C for 12 h, employing lead acetate trihydrate, thiourea and sodium citrate as precursors. The diameter of PbS hollow spheres is 200-400 nm, which is composed of about 50-80 nm nanoparticles. The synthesized product was characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), Fourier transform-infrared (FT-IR) spectroscopy, ultraviolet-visible spectrometer (UV-vis) and near-infrared absorption spectrometer (NIR). The effects of the reaction conditions on morphologies of PbS structures were investigated. Star-shaped and flat PbS crystals were obtained by changing some experiment conditions. The results show that temperature, sodium citrate concentration, sulfur sources and solvent play key roles on the final morphologies formation of PbS crystals. Especially, ED result indicates that PbS hollow spheres hold single crystal-like electron diffraction patterns. And the possible formation mechanism of hollow spheres was proposed.     

Shape-controlled synthesis and properties of dandelion-like manganese sulfide hollow spheres

Dandelion-like gamma-manganese (II) sulfide (MnS) hollow spheres assembled with nanorods have been prepared via a hydrothermal process in the presence of l-cysteine and polyvinylpyrrolidone (PVP). l-cysteine was employed as not only sulfur source, but also coordinating reagent for the synthesis of dandelion-like MnS hollow spheres. The morphology, structure and properties of as-prepared products have been investigated in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), selected area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM) and photoluminescence spectra (PL). The probable formation mechanism of as-prepared MnS hollow spheres was discussed on the basis of the experimental results. This strategy may provide an effective method for the fabrication of other metal sulfides hollow spheres.     

Facile preparation of titania hollow spheres by combination of the mixed solvent method and the sol-gel process and post-calcination

Polystyrene (core)-titania (shell) composite spheres consisting were readily prepared by a sol-gel process of titanium tetrabutoxide (TBOT) in a mixed solvent of ethanol/acetonitrile (3:1, v/v). Smooth and homogeneous titania coatings formed when the mixed solvent was dehydrated by anhydrous sodium sulfate. The thickness and surface roughness of titania coating increase with increase of the TBOT concentration. By adjusting the TBOT concentration in the range of 5.8-29.0 mM, the size of titania-coated PS spheres could be varied from 990 to 1125 nm. Calcination at elevated temperature gave dense, homogeneous, robust shells of anatase titania. The sizes of titania hollow spheres are 11.3-16.9% smaller than those of the titania-coated PS spheres as a result of calcination-induced shrinkage. The composite and hollow spheres were characterized by scanning electron microscopy, transmission electron microscopy and electron diffraction measurements. These core-shell organic-inorganic spheres and hollow ceramic spheres may have wide applications in catalysts, adsorbents, lightweight fillers, capsules, etc.     

Fabrication of hollow silica spheres and their application in polyacrylate film forming agent

Polystyrene (PS)/silica core/shell spheres were fabricated using mono-dispersed PS as templates by hydrolysis and condensation of two different silica precursors. The PS cores of PS/silica core/shell spheres were dissolved subsequently in the tetrahydrofuran medium to form mono-dispersed hollow silica spheres. The structures and morphologies of hollow silica spheres were characterized by scanning electron microscopy and transmission electron microscopy. Then, polyacrylate/hollow silica composite film forming agents were prepared via physical blending of polyacrylate and two different hollow silica spheres, and the water vapor permeability of their films were compared. The results showed that the structure of hollow silica spheres were very typical and obvious. The silica shell was continuous and uniform using tetraethylorthosilicate as precursor, which was accumulated by many silica seeds with size of 10–20 nm, and the thickness of silica shell was about 16.7 nm. However, the hollow silica spheres using tetraethylorthosilicate and vinyl triethoxysilane as precursors had mesoporous structure in the shell. The introduction of hollow silica spheres could significantly improve the water vapor permeability of polyacrylate film. At last, a possible mechanism for the formation of hollow silica spheres was proposed and the process of water vapor through polyacrylate/hollow silica composite films was modeled.     

Fabrication of hollow silica spheres in an ionic liquid microemulsion

Hollow silica spheres have been successfully synthesized by using the ionic liquid microemulsion droplets as the template. The morphology and microstructures of the silica spheres were investigated by scanning electron microscopy (SEM), high-resolution transmission electron microscope (HRTEM), and Nitrogen adsorption-desorption measurements. The obtained images showed that the average size of the silica spheres was almost between 150 and 300 nm. The Nitrogen adsorption-desorption investigation on the silica spheres indicated the amorphous structure on the interface. Both of these two results provide us new insights into this novel template and hollow silica spheres were for the first time prepared free of additional acid and alkali conditions. The possible mechanism for the formation of silica spheres has been put forward and discussed in details.     

Preparation and characterization of CdS hollow spheres

CdS hollow spherical particles with average diameter of 800 and 850 nm have been prepared using core/shell fabrication method with poly-(styrene-acrylic acid) (PSA) latex particles as template. TEM images show that smoothly coated core/shell composite particles have been fabricated by multicycles of coating in optimum concentration of reactants. CdS hollow spheres were obtained after removing the template by dissolving the polymer in the organic solvent, and the wall thickness is about 40-100 nm.     

A facile method for the preparation of hollow silver spheres

A new method for the preparation of hollow silver spheres was proposed. In the preparation process the mercapto groups played an important role in the process of forming starch/silver core-shell structure, which provided nucleation sites for the growth of a silver shell. Removal of the starch core is realized by degrading the starch template with α-amylase. The morphology of the starch/silver core-shell nanocomposite and the hollow silver spheres was characterized by TEM and AFM.     

Sol-gel synthesis of titania hollow spheres

TiO₂ hollow spheres are prepared by a convenient sol-gel method at room temperature. The products were characterized by XRD, FESEM, TEM and FT-IR. It was found that these spheres are hollow inside with outer diameters of 200-500 nm. The average mesoporous diameter is about 9.8 nm. And the BET surface area and specific pore volume are about 161.9 m²/g and 0.441 cm³/g, respectively.     

Directly ultraviolet photochemical deposition of silver nanoparticles on silica spheres: Preparation and characterization

A simple method was developed to directly deposit silver nanoparticles on the surface of silica spheres. The photochemical reduction was carried out by ultraviolet irradiation in air atmosphere at room temperature. The [Ag(NH₃)₂]⁺was reduced to silver atoms upon ultraviolet irradiation. Silver atoms subsequently deposited on the surface of silica spheres and agglomerated into silver nanoparticles. Silica spheres with silver nanoparticles of different size and density can be simply controlled by adjusting the UV-light irradiation time. The silver nanoparticles deposited on silica spheres were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, and field emission scanning electron microscopy.     

Efficient rapid microwave-assisted route to synthesize InP micrometer hollow spheres

The efficiencies of two methods of synthesizing InP micro-scale hollow spheres are compared via the analogous solution-liquid-solid (ASLS) growth mechanism, either through a traditional solvothermal procedure, or via a microwave-assisted method. Scanning electronic microscopy (SEM) images show that most of the as-grown samples are micrometer hollow spheres, which indicates the efficiency of both methods. For traditional solvothermal route, long time (10 h) is necessary to obtain the desired samples, however, for the microwave-assisted route, 30 min is enough for hollow spherical products. An optimal choice of microwave irradiating time allows reducing the reaction time from hours to minutes. The proposed ASLS growth mechanism has also been discussed in detail.     

Synthesis and photocatalytic oxidation properties of titania hollow spheres

The hollow spheres of anatase TiO₂ with higher photocatalytic activity have been fabricated by spherical CaCO₃ nanoparticles as a template, and titanium sulfate (Ti(SO₄)₂) as a precursor, and the CaCO₃ templates were dissolved subsequently in dilute HNO₃ solution. The TiO₂ hollow spheres samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and N₂ adsorption-desorption isotherms. The characterization results indicate that as prepared TiO₂ hollow spheres sample was transformed to anatase phase in calcined at 400 °C, and the anatase TiO₂ hollow spheres have a higher specific surface area and show much better photocatalytic activity than commercial P25 in the photodegradation of Rhodamine B under the UV irradiation.     

Synthesis of montmorillonite-chitosan hollow and hierarchical mesoporous spheres with single-template layer-by-layer assembly

In order to develop a facile and precisely controlled approach to synthesize hierarchical mesoporous materials with tailored property, in this work, a novel study was carried out to fabricate montmorillonite-chitosan hollow and hierarchical mesoporous spheres (MMTNS@CS-HMPHS) based on single-template layer-by-layer (LbL) assembly. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), specific surface area analysis and X-ray photoelectron spectroscopy (XPS) analyses were carried out to characterize the morphology and surface properties of MMTNS@CS-HMPHS. Benefitting from the unique lamellar structure of MMTNS, mesoporous channels are formed on the shell of MMTNS@CS hollow spheres, resulting in high surface area. Moreover, the surface functionalization and pore size of MMTNS@CS-HMPHS can be easily tuned, due to the tailored property through LbL assembly method. Besides the unique microstructure, MMTNS@CS-HMPHS also possesses the active sites generated from both MMT and chitosan, which greatly promotes its performance in fields of adsorption, drug delivery and catalyst supports, etc.     

A room-temperature synthesis of titanium nitride hollow spheres

Titanium nitride hollow spheres were synthesized by the reaction of TiCl4 and NaNH2 at room temperature. X-ray powder diffraction (XRD) pattern could be indexed as cubic TiN with the lattice constants of a = 4.236 A. Transmission electron microscopy (TEM) images showed hollow spheres with diameter about 200 nm. A possible formation mechanism of TiN hollow spheres was discussed.