Synthesis of porous hollow silica spheres using polystyrene-methyl acrylic acid latex template at different temperatures

Porous hollow silica spheres were prepared by using polystyrene-methyl acrylic acid latex as a template and cetyltrimethylammonium bromide as a wall structure-directing agent starting from tetraethoxysilane. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), FT-infrared spectroscopy (FT-IR) and nitrogen adsorption/desorption were used to characterize the hollow silica spheres. When silica-coated latex composites were prepared at room temperature, hollow silica spheres with micropores in the walls were formed after removing the latex templates by calcination. When silica-coated latex composites were aged at a higher temperature of 150 °C, intact mesoporous hollow silica spheres were formed after calcination treatment.     

Template synthesis of nanostructured silica with hollow core and mesoporous shell structures

Silica capsules with hollow macroporous core–mesoporous shell (HCMS) were synthesized through template-assisted replication of submicrometer-size polystyrene spheres as templates. The silica mesoporous shell exhibited highly ordered hexagonal structure as confirmed by X-ray diffraction pattern and TEM image. The pore diameter and BET surface area of this sample were found to be 2.1 nm and 1387 m²/g, respectively.     

A novel approach to fabrication of superparamagnetite hollow silica/magnetic composite spheres

We described a method for synthesizing hollow silica/magnetic composite spheres using sulfonic acid functionalized hollow silica spheres (SAFHSS) as templates. The Fe₃O₄ nanoparticles were deposited on or imbedded in the hollow silica shell by a precipitation reaction. The morphologies, composition and properties of the hollow composite spheres were characterized by transmission electron microscopy, Fourier transform infrared analysis, X-ray diffraction measurement and vibrating-sample magnetometry measurement. The results indicated crystal sizes and amount of the Fe₃O₄ nanoparticles on the SAFHSS. The magnetic properties of the hollow composite spheres were controlled by adjusting the proportion between Fe²⁺ and Fe³⁺ and iron ion total concentration. When appropriate loading species were added into the system, superparamagnetite hollow composite spheres were obtained. The method also could be applicable to prepare other superparamagnetite hollow silica/ferrite composite spheres.     

Preparation of titania hollow spheres by catalyst-free hydrothermal method and their high thermal stabilities

TiO₂ hollow spheres have been prepared by hydrothermal method using carbon spheres as hard templates based on template-directed deposition and calcination in order to remove templates. The morphology and structure of samples were systematically characterized by using various techniques, including XRD, zeta analyzer, SEM, TEM, DRS and FTIR. In this approach, the anatase phase was retained for temperatures up to 900 °C. Moreover, negative charged titania is deposited onto the negative charged surface of carbon spheres, which is proved by nanoparticle size analyzer. Therefore, a possible formation mechanism of TiO₂ hollow spheres was proposed. TiO₂ hollow spheres calcined at 550 °C exhibited the superior photocatalytic activity for the degradation of Rhodamine B, 2.9 times greater than that of Degussa P25. Furthermore, thermal stability of TiO₂ hollow spheres was examined. Fortunately, we found that hollow structures could still be visible distinctly after calcining at 900 °C.     

Synthesis, characterization and antibacterial action of hollow titania spheres

Hollow titania spheres were synthesized using the cationic polystyrene lattices which were prepared by polymerization in suspension of styrene using 2,2′-azobis (2-methylpropionamidine) dihydrochloride (AMPA) as an initiator. These cationic colloidal particles were dispersed in absolute ethanol in the presence of poly(vinylpyrrolidone) (PVP), solution of sodium chloride (NaCl) and mixed with ethanolic solutions of titanium tetraisopropoxide (TTIP). Subsequently, hollow spheres of titania compounds were obtained by calcinations of the so-coated polystyrene lattices at elevated temperature in air. The hollow titania spheres were characterized with scanning electron microscopy (SEM), FT-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and differential thermal analysis (DTA). Moreover, antibacterial action of illuminated hollow titania spheres on pure culture of Escherichia coli (E. coli) was studied. A decrease of E. coli concentration was observed after illumination of bacteria in the presence of hollow titania spheres.     

Synthesis of magnetic hollow silica using polystyrene bead as a template

In this paper, we report a new route to synthesize novel magnetic hollow silica nanospheres (MHSNs) using polystyrene particles as sacrificial templates, and TEOS and Fe₃O₄ as precursors. TEM, EDS, XRD, and SQUID were applied to characterize MHSNs. TEM and EDS results show that the MHSNs consist of about 200 nm of hollow cores and ∼35 nm shells with ∼10 nm of Fe₃O₄ nanoparticles embedded. The polystyrene beads were successfully removed by immersing the as-prepared silica nanocomposite in a toluene solution. XRD results demonstrate that the Fe₃O₄ magnetic nanoparticles still keep spinel structure even heated at low temperature. The surface status of the polystyrene beads and Fe₃O₄ nanoparticles has an important effect on the formation of the MHSNs. The MHSNs present a superparamagnetism at room temperature by SQUID measurement. The MHSNs have potential applications in biosystem and nanomedicine.     

Uniform Fe3O4–PANi/PS composite spheres with conductive and magnetic properties and their hollow spheres

Core–shell multifunctional composite spheres consisting of Fe₃O₄–polyaniline (PANi) shell and polystyrene (PS) core were fabricated using core–shell-structured sulfonated PS spheres (with uniform diameter of 250 nm) as templates. PANi was doped in situ by sulfonic acid resulting the composite spheres are well conductive. Dissolved with solvent, PS cores were removed from the core–shell composite spheres and hollow Fe₃O₄–PANi spheres were obtained. Removing the PANi and PS components by calcinations produced hollow Fe₃O₄ spheres. The cavity size of the hollow spheres was uniformly approximate to 190 nm and the shell thickness was 30 nm. The cavity size and the shell thickness can be synchronously controlled by varying the sulfonation time of the PS templates. The shell thickness in size range was of 20–86 nm when the sulfonation time was changed from 1 to 4 h. These resulting spheres could be arranged in order by self-assembly of the templates. Both the Fe₃O₄–PANi/PS composite spheres and the hollow Fe₃O₄ spheres exhibit a super-paramagnetic behavior. Scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray powder scattering were used to characterize these as-prepared spheres. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis of hollow silver spheres using poly-(styrene-methyl acrylic acid) as templates in the presence of sodium polyacrylate

Hollow silver spheres were successfully prepared by reducing AgNO₃ with ascorbic acid and using negatively charged poly-(styrene-methyl acrylic acid) (PSA) spheres as templates in the presence of sodium polyacrylate as a stabilizer. Firstly, silver cations adsorbed on the surface of PSA spheres via electrostatic attraction between the carboxyl groups and silver cations were reduced in situ by ascorbic acid. The silver nanoparticles deposited on the surface of PSA spheres served as seeds for the further growth of silver shells. After that, extra amount of AgNO₃ and ascorbic acid solutions were added to form PSA/Ag composites with thick silver shells. In order to obtain compact silver shells, the as-prepared PSA/Ag composites were heated at 150 °C for 3 h. Then hollow silver spheres were prepared by dissolving PSA templates with tetrahydrofuran.     

Synthesis of hollow ferrite nanospheres for biomedical applications

Hollow ferrite spheres of 220-340 nm diameter were synthesized at 60 °C as multi-functionalized magnetic carriers which are potentially applicable both as drug delivery systems (DDS) and hyperthermia treatment. We found that SH and OH groups on the silica template spheres enabled the fabrication of continuous ferrite shells of 20-30 nm in thickness. Transmission electron microscopy and energy-dispersive spectroscopy revealed that the templates were dissolved by a NaOH solution, yielding hollow particles exhibiting saturation magnetization of 78 emu/g. The results suggested that the ferrite shells are porous and the pores work as pathway for releasing drugs from the hollow particle inside.     

Synthesis of nanostructured polymer materials with different morphologies: Nanoporous ordered networks and hollow capsules

Nanostructured polymer materials with interesting morphological variation, which include three dimensionally interconnected uniform nanoporous network arrays (volume- and surface-templated ordered arrays) and hollow core spheres were synthesized by inducing different polymerization process of phenol and formaldehyde as a precursor over silica templates (ordered silica colloidal crystals or individual silica particles). The pore sizes of the resulting nanostructured polymer materials can be easily controlled by monitoring the sizes of silica spheres, while their morphologies were modulated by controlling the initiation sites of the acid-catalyzed condensation reaction of the same polymer precursor and by modifying silica templates.     

Preparation and photocatalytic activity of nitrogen-doped TiO2 hollow nanospheres

TiO₂ hollow nanospheres were prepared using silicon oxide as a template. N-doped titanium oxide hollow spheres, TiO_2−xN_x were synthesized by reacting TiO₂ hollow spheres with thiourea at 500 °C. XRD and XPS data showed that oxygen was successfully substituted by nitrogen through the nitrogen-doping reaction, and finally N-doped TiO₂ hollow spheres were formed. The N-doped TiO₂ hollow spheres showed new absorption shoulder in visible light region so that they were expected to exhibit photocatalytic activity in the visible light. The photocatalytic activity of N-doped TiO₂ hollow spheres under visible light was similar to that of normal spherical TiO_2−xN_x in spite of the structural difference.     

First-order hyperpolarizability of ZnS nanocrystal quantum dots studied by hyper-Rayleigh scattering

Hyper-Rayleigh scattering technique was used to measure for the first time the first-order hyperpolarizability (β) of ZnS nanocrystals with 2.5 nm mean diameter. Results show that the ‘per ZnS particle’ β value is 2.34×10⁻²⁷ esu and the ‘per ZnS formula unit’ β value is 1.63×10⁻²⁸ esu. An increase by at least two orders of magnitude in the β value per ZnS formula unit is found when compared with bulk ZnS. Two possible contributions originating from nanocrystal surface electric field and solvent field were experimentally excluded. Other two contributions, bulk-like contribution and surface contribution, are considered. Especially, the latter is emphasized due to the special surface structure of nanocrystals.     

Confinement-induced colloidal attractions in equilibrium

The Poisson-Boltzmann theory for colloidal electrostatic interactions predicts that charged colloidal spheres dispersed in water should repel each other, even when confined by charged surfaces. Direct measurements on highly charged polystyrene spheres, however, reveal strong, long-ranged confinement-induced attractions that have yet to be explained. We demonstrate that anomalous attractions also characterize the equilibrium pair potential for more weakly charged colloidal silica spheres sedimented into a monolayer above a glass surface. This observation substantially expands the range of conditions for which mean-field theory incorrectly predicts the sign of macroions' interactions, and provides new insights into how confinement induces long-ranged like-charge attractions.     

Synthesis, characterization and photodegradation study of mixed-phase titania hollow submicrospheres with rough surface

Titania hollow submicrospheres with mixed phase (anatase-brookite or anatase-rutile) were synthesized via the combination of hydrothermal treatment and calcination of submicrospheres consisting of a polystyrene core and an amorphous TiO₂ shell. After hydrothermal treatment, amorphous titania shell could be transformed to anatase-brookite shell consisting of loose packed titania nanocrystals, which could be further converted to anatase-brookite (below 700 °C) or anatase-rutile titania (700-800 °C) hollow spheres with rough surface via calcination. The loose packing of titania nanocrystals not only inhibited the transformation temperature from anatase to rutile, but also provided titania hollow submicrospheres with high photodegradation activity of Rhodamine B. The photocatalytic activity of titania hollow spheres increased firstly then decreased when the calcination temperature was varied in the range of 450-800 °C, while hollow spheres obtained via calcinating at 700 °C exhibited the highest photocatalytic activity, which was five times higher than that of counterpart without hydrothermal treatment.     

Enhanced photoelectrochemical performance of ZnO photoanode with scattering hollow cavities

Abstract ZnO nanoparticles with average diameter of 12 nm were used to fabricate ZnO photoanodes by electrohydrodynamic (EHD) technique for dye-sensitized solar cells (DSSCs). To enhance the light scattering and conversion efficiency, the ZnO film with scattering hollow cavities (HCs) was realized by calcining polystyrene spheres (PSs) in the film. The films had strong light scattering ability and the overall light to electricity conversion efficiency (η) was improved and reached 5.5% under illumination of simulated solar light (AM-1.5, 100 mW/cm²).     

Efficient Entrapment of Dye in Hollow Silica Nanoparticles: Direct Evidence Using Fluorescence Spectroscopy

Using hollow silica nanoparticles we demonstrate a simple and highly efficient way of removing hydrophilic dye (Rhodamine B) from water by encapsulation within these hollow spheres. The hollow silica spheres were obtained by using a surfactant templated procedure. Using fluorescence spectroscopy, we also show the evidence of the dye being absorbed within the hollow core of the silica shell (which is crucial for many applications) and differentiate from the adsorption of dye on the surface of the silica shell. It was found that that up to 94 % of the hydrophilic dye could be entrapped using these hollow shells within 72 h of exposure. Fluorescence spectroscopy shows a red shift in the dye encapsulated in the hollow silica which is due to aggregation of the dye and enables us to follow quantitatively the uptake of the dye molecules by the silica shells with time. The evidence for the encapsulation of the dye in these hollow spheres was reinforced by carrying out a comparative study, using solid silica particles.

Potato starch-based activated carbon spheres as electrode material for electrochemical capacitor

Potato starch-based activated carbon spheres (PACS) were prepared from potato starch by stabilization, carbonization followed by activation with KOH. The obtained PACS are hollow and retain the original morphology of potato starch with decrease in size, as shown by scanning electron microscopy. Modification of textural properties of the PACS was achieved by varying the carbonization temperature and the ratio of KOH/PCS. The results of N₂ adsorption isotherms indicate that the samples prepared are mainly microporous. The electrochemical behaviors of the hollow PACS were studied by galvanostatic charge-discharge, cyclic voltammetry, and impedance spectroscopy. The results indicate that high specific capacitance of 335 F/g is obtained at current density 50 mA/g for PACS with specific surface area 2342 m²/g. Only a slight decrease in capacitance, to 314 F/g, was observed when the current density increases to 1000 mA/g, indicating a stable electrochemical property.     

One-pot synthesis of uniform hollow cuprous oxide spheres fabricated by single-crystalline particles via a simple solvothermal route

Uniform Cu₂O hollow spheres fabricated by single-crystalline particles (smaller than 20 nm) are facile synthesized in ethylene glycol (EG) solution by a simple solvothermal route without using pre-fabricated templates and reductive agents. EG in this protocol is not only used as a solvent, complexing agent, and reducing agent, but also served as a structure-directing agent for the formation of hollow structure. By control of reaction conditions, such as reaction time, temperature, and the anions, the morphology and structure of the hollow spheres can be tuned. A coordination adsorption and oriented attachment and Ostwald ripening mechanism is proposed for explaining the formation process of hollow Cu₂O spheres in EG solution; and importantly, the hollow Cu₂O spheres exhibit an excellent property for the electro-catalytic oxidization of ascorbic acid in acetic acid buffer solution. Moreover, the hollow spherical Cu₂O particles could be potentially applied in catalysis, sensor, and as model for fundamental research.     

Two-dimensional ‘hat-scratch’ periodic structures induced by a single femtosecond laser pulse on silica glass

Two-dimensional ‘hat-scratch’ structures are fabricated on silica glass by the interference of three non-coplanar beams originating from a single femtosecond laser pulse. The scanning electron microscope (SEM) characterizations show that the as-formed structures are composed of hat holes and scratch marks. The experimental results indicate that the structures are dependent on the intensity of laser beam. The formation of the two-dimensional ‘hat-scratch’ structures is mainly due to the combined laser ablation effects including ionization, shock wave, plasma expansion, and phase explosion.     

Synthesis of hollow silica-sulfur composite nanospheres towards stable lithium-sulfur battery

Herein, porous hollow silica nanospheres were prepared via a facile sol-gel process in an inverse microemulsion, using self-assemblies of chiral amphiphile as a soft template and fine water droplets as a hard template. The shells of the hollow silica nanospheres are composed of flake-like nanoparticles with dense big holes on the surface. After covering a layer of sulfur on the silica nanospheres, followed by hydrothermal treatment in a D-glucose aqueous solution, silica-sulfur and silica-sulfur-carbon nanospheres were successfully fabricated. The silica-sulfur composites exhibit a stable capacity of 454 mAh g^?1 at current density of 335 mA g^?1 after 100 cycles with capacity retention of 85%, demonstrating a promising cathode material for rechargeable lithium-sulfur batteries. We believe that the approach for synthesis of porous hollow silica nanospheres and its carbon spheroidal shell can also be applicable for designing other electrode materials for energy storage.