Synthesis of composite eccentric double-shelled hollow spheres

Eccentric double-shelled hollow polyethylacrylate (PEA)/polystyrene (PS) crosslinked composite spheres were synthesized by phase separation during swelling polymerization of their mother polymer hollow spheres. The group -NH₂ was introduced within the network by ammonization of PEA. Other materials for example silica could be favorably grown within the gel network by a sol-gel process. The polymer/silica hollow spheres gave the corresponding derivative hollow spheres with varied composition including SiO₂/carbon, carbon and β-SiC, with the eccentric double-shelled morphology retained.     

Hydrothermal synthesis of ZnO hollow spheres using spherobacterium as biotemplates

By using spherobacterium Streptococcus thermophilus as a natural biotemplate, ZnO hollow spheres have been synthesized in a simple hydrothermal method based on the surface biofunctionality of the microorganism, followed by calcination. The as-obtained products are characterized by techniques of XRD, FESEM, TEM and N₂ adsorption. Furthermore, a possible formation mechanism involving a two-step encapsulation process is proposed which has an effect on the bimodal pore structure of the products with pores in the mesoporous range. The research introduces a new concept to synthesize porous hollow spheres by using spherobacterium as a biological template and opens up a new pathway to synthesize hollow nanospheres, nanotubes and other kinds of 3D nanostructures with bacterium as the template via simple chemical routes.     

Fabrication and photocatalytic performance of Sn-doped titania hollow spheres using polystyrene as template

Sn-doped anatase hollow spheres were fabricated using a template method involving polystyrene spheres as core and anatase coating as shell. The synthesis route included the preparation of PS spheres, followed by their coating by Sn-doped TiO₂ sol-gel precursor and subsequent removal of the PS cores by pyrolysis and recrystallization at 500 °C for 2 h. The observation of minor amounts of rutile suggests that Sn promotes the anatase → rutile phase transformation. At doping levels of ≤ 1.0 mol% Sn, the unsaturated solubility and increasing defect densities enhanced nucleation. At 1.0–2.0 mol% Sn, the solubility remained unsaturated but increasing Sn incorporation reduced crystallinity owing to lattice deformation and partial amorphization. At 2.0–3.0 mol% Sn, solid solution saturation occurred, resulting in excess dopant precipitation, leading to grain boundary pinning and partial blockage of surface-active sites. Ionic radii, thermodynamic, phase equilibria, intervalence charge transfer, and defect chemistry considerations suggest that Sn⁴⁺ exhibits substitutional solid solubility in the TiO₂ lattice. The photocatalytic performance was in the order 1.0 > 1.2 > 1.5 ≈ 0.7 > 2.0 > 0.0 > 3.0 mol% Sn. This ranking is consistent with the dominant role of crystallinity such that, at ≤ 1.0 mol% Sn, the performance increased owing to enhanced nucleation from low defect density and increasing crystallinity while, at 1.0–2.0 mol% Sn, the performance decreased from increased lattice strain and effective partial amorphization, and, at 2.0–3.0 mol% Sn, it decreased from maximal lattice strain and blockage of active sites.     

Inward template synthesis of intact hollow spheres

A facile and general one-step approach is presented to synthesize hollow spheres with varied composition by an aerosol-assisted solvent evaporation process. The monomer of ethyl-2-cyanoacrylatemide contained in the aerosol droplets can form an outer shell by a fast polymerization around the droplets. Materials inside the droplets further grow inwardly against onto the interior surface of the first shell forming another shell forming composite hollow spheres. The hollow spheres are derived by dissolution of the outer shell, therefore the intact shell can be well preserved. Many approaches can be exploited forming the second shell for example sol-gel process of oligomers and phase separation from polymer solutions. Microstructure of the hollow spheres can be tuned from smooth to porous. The methodology is general.     

Facile synthesis of well-defined CeO2 hollow spheres with a tunable pore structure

Herein, SiO₂@CeO₂ composite microspheres were successfully prepared via a hydrothermal assisted layer-by-layer self-assembly method employing colloid SiO₂ as the template, which was fabricated by a typical Stöber method. Monodispersed CeO₂ hollow spheres with a narrow size distribution were achieved after etching colloid SiO₂ templates through NaOH. The resultant samples were characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM), Transmission electron microscopy (TEM), Fourier translation infrared spectroscopy (FT-IR), X-ray photoelectron spectrum (XPS), and Nitrogen adsorption–desorption isothermal. Specifically, the shell thickness and the mesoporous structure of the hollow sphere can be easily controlled by changing the concentration of cerium source.     

Facile synthesis and electrochemical performances of hollow graphene spheres as anode material for lithium-ion batteries

The hollow graphene oxide spheres have been successfully fabricated from graphene oxide nanosheets utilizing a water-in-oil emulsion technique, which were prepared from natural flake graphite by oxidation and ultrasonic treatment. The hollow graphene oxide spheres were reduced to hollow graphene spheres at 500°C for 3 h under an atmosphere of Ar(95%)/H₂(5%). The first reversible specific capacity of the hollow graphene spheres was as high as 903 mAh g^-1 at a current density of 50 mAh g^-1. Even at a high current density of 500 mAh g^-1, the reversible specific capacity remained at 502 mAh g^-1. After 60 cycles, the reversible capacity was still kept at 652 mAh g^-1 at the current density of 50 mAh g^-1. These results indicate that the prepared hollow graphene spheres possess excellent electrochemical performances for lithium storage. The high rate performance of hollow graphene spheres thanks to the hollow structure, thin and porous shells consisting of graphene sheets.

PACS

81.05.ue; 61.48.Gh; 72.80.Vp     

Optical properties of colloidal crystalline arrays composed of hollow polystyrene spheres

We have evaluated the optical properties of close‐packed and non close‐packed colloidal crystalline arrays made of hollow polystyrene spheres. Close‐packed colloidal crystalline arrays were fabricated by simple evaporation of dispersions, whereas nonclose‐packed colloidal crystalline arrays were fabricated by exploiting electrostatic interactions between the spheres in aqueous dispersion. Optical properties of the arrays were estimated from angle‐resolved reflection spectra. The Bragg diffraction peak of the colloidal crystalline array made of hollow spheres was of shorter wavelength than in the case of solid spheres, not only for the close‐packed array but also for the nonclose‐packed array. These shifts were caused by a decrease in the effective refractive index n_eff with decreasing particle refractive index. We have found that this relationship could be explained by the simple equation n_eff = n_particle?+ n_solvent (1 ? ?), where ? is the volume fraction of the particles, for both close‐packed and non close‐packed arrays. The current work suggests new possibilities for the creation of advanced colloidal crystals. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2364–2368, 2007     

Surfactant-free synthesis of Cu2O hollow spheres and their wavelength-dependent visible photocatalytic activities using LED lamps as cold light sources

A facile synthesis route of cuprous oxide (Cu₂O) hollow spheres under different temperatures without the aid of a surfactant was introduced. Morphology and structure varied as functions of reaction temperature and duration. A bubble template-mediated formation mechanism was proposed, which explained the reason of morphology changing with reaction temperature. The obtained Cu₂O hollow spheres were active photocatalyst for the degradation of methyl orange under visible light. A self-designed equipment of light emitting diode (LED) cold light sources with the wavelength of 450, 550, and 700 nm, respectively, was used for the first time in the photocatalysis experiment with no extra heat introduced. The most suitable wavelength for Cu₂O to photocatalytic degradation is 550 nm, because the light energy (2.25 eV) is closest to the band gap of Cu₂O (2.17 eV). These surfactant-free synthesized Cu₂O hollow spheres would be highly attractive for practical applications in water pollutant removal and environmental remediation.     

Novel CuS hollow spheres fabricated by a novel hydrothermal method

A thioglycolic acid (TGA) assisted hydrothermal process has been developed to synthesize submicron-sized copper sulfide (CuS) hollow spheres via the reaction between copper sulfate (CuSO₄) and thioacetamide (CH₃CSNH₂). X-ray diffraction, transmission electron microscopy and scanning electron microscopy were employed to characterize the obtained product. Furthermore, the possible mechanism and the critical factors for the TGA-assisted hydrothermal synthesis of the CuS hollow spheres have been preliminarily presented.     

Preparation of crystalline manganese oxides hollow spheres

Manganese oxides hollow spheres were synthesized by heating manganese carbonate precursors prepared by a one-step, solid-state method. Addition of sodium chloride (NaCl) and surfactant nonylphenyl ether (NP9), heating time and heating temperature played important roles in the synthesis process. The crystals were characterized by X-ray powder diffraction (XRD) and transmission electronic microscopy (TEM). It was shown that the product was pure and crystallized very well.     

Template method synthesis of mesoporous carbon spheres and its applications as supercapacitors

Mesoporous carbon spheres (MCS) have been fabricated from structured mesoporous silica sphere using chemical vapor deposition (CVD) with ethylene as a carbon feedstock. The mesoporous carbon spheres have a high specific surface area of 666.8 m²/g and good electrochemical properties. The mechanism of formation mesoporous carbon spheres (carbon spheres) is investigated. The important thing is a surfactant hexadecyl trimethyl ammonium bromide (CTAB), which accelerates the process of carbon deposition. An additional advantage of this surfactant is an increase the yield of product. These mesoporous carbon spheres, which have good electrochemical properties is suitable for supercapacitors.     

Adhesion between submicrometer polystyrene spheres

The sphere-substrate contact method was usually used to study adhesion theory because it is rather difficult to make two micrometer or submicrometer spheres contact precisely. Here, we used sphere-sphere contact method by a novel, simple process to investigate deformations of spheres. The polystyrene particles size ranges from 60 nm to 600 nm. We found that the polystyrene particles underwent plastic deformations due to van der Waals interaction. The contact radii were observed by the scanning electron microscope (SEM).     

Preparation of poly(β-hydroxybutyrate) and poly(lactide) hollow spheres with controlled wall thickness

In recent years, polymer microcapsules have attracted more and more attention because of their specific properties and applications in encapsulation and drug delivery. Great effort has been made to investigate the preparation methods, structure controls as well as the property designs for the polymer microcapsules. In this work, we reported an effective route for the preparation of poly(β-hydroxybutyrate) (PHB) and poly(lactic acid) (PLA) hollow spheres with controlled wall thickness, which involves the graft polymerization of the biodegradable polymers from the surface of silica spheres followed by removing the template cores. Nuclear magnetic resonance spectroscopy (NMR), thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and transmission electron microscope (TEM) have been used to prove the structure of the hollow sphere and the intermediates. The result reveals that with the increase of reaction time the wall thickness of the hollow sphere will increase gradually.     

Dye-sensitized solar cells based on hollow anatase TiO2 spheres prepared by self-transformation method

Dye-sensitized solar cells (DSSCs) are fabricated based on hollow anatase TiO₂ (HA-TiO₂) spheres synthesized by a chemically induced self-transformation (CIST) strategy using urea as a base catalyst, whose walls are composed of anatase nanocrystals and exhibit hierarchical porosity. TiO₂ hollow structured materials not only have low density, high specific surface areas, and hierarchically porous structures, but also exhibit high light-collection efficiency and fast motion of charge carriers. Effects of calcination temperatures on the performance of HA-TiO₂ solar cells are investigated and discussed. With increasing calcination temperatures, the light-electricity conversion efficiencies (η) increase. At 600 °C, HA-TiO₂ cells reach the highest efficiency. The performances of HA-TiO₂ cells are also compared with Degussa P-25 (P25) TiO₂ nanoparticle cells at the same film thickness, and their optimal efficiencies at 600 °C are 4.82 and 4.35%, respectively. The enhanced performance of HA-TiO₂ cells is due to their high surface area and hierarchically nanoporous structures when compared with the nonporous TiO₂ nanoparticles (P25).     

Highly porous metal organic framework derived NiO hollow spheres and flowers for oxygen evolution reaction and supercapacitors

In this study, metal-organic-framework (MOF) derived porous NiO hollow spheres and flowers were obtained using facile solvothermal synthesis and heat treatment. After pyrolyzing, the flower like and hollow spherical like morphology of NiO nanoparticles was successfully inherited from the initial MOF-based templates. The electrochemical studies demonstrated that the porous NiO hallow spheres unveiled a better supercapacitive performance (specific capacitance (C_s) = 1058 F g^?1 at current density (j) = 2 A g^?1) and oxygen evolution reaction (OER) catalytic activity (overpotential (?) = 323 mV) compared to porous NiO flowers (C_s = 857 F g^?1 at j = 2 A g^?1 and ? = 346 mV). Moreover, excellent capacity retention of over 93% was obtained in porous NiO-hs nanoparticles even after 5000 cycles. The fabricated NiO//Fe₂O₃ asymmetric supercapacitor delivered an energy density (E) of 35.75 W h Kg^?1 under power density (P) of 780 W kg^?1 and showed promising stability over 3000 cycles. Considering the ease of preparation and high catalytic activity and supercapacitive performance, these prous NiO hallow structures can be considered as a potential electrode material for next generation energy storage devices and OER catalysts.     

二氧化硅空心球的制备及研究

在乙醇/水的混合溶液中,采用聚乙烯吡咯烷酮（PVP）为分散剂,偶氮二异丁腈（AIBN）为引发剂,通过分散聚合法制备出聚苯乙烯（PS）微球。然后以微球为模板,PS粒子作为核,SiO_2作为壳,在600℃时经过热分解得到SiO_2空心球。通过热分析仪、扫描电子显微镜对制得的空心球进行了表征和分析,并讨论其影响因素。     

Synthesis and properties of magnetite/polypyrrole core–shell nanocomposites and polypyrrole hollow spheres

In this work a new route for preparation of core–shell nanoparticles composed of an iron oxide core and a polypyrrole (PPy) shell is explored. During the preparation procedure the initially formed iron(0) core is converted to magnetite. It is demonstrated, that the magnetite cores can completely be dissolved by reaction with acid. Furthermore the dissolution of iron oxide cores by electrolysis also is possible. The resulting PPy hollow spheres as well as the core–shell nanocomposites are electrochemically active.     

Synthesis of porous hollow silica spheres using functionalized polystyrene latex spheres as templates

Uniform sized and integrated hollow silica spheres with porous shells were prepared by using sulfuric and carboxylic acid-functionalized polystyrene latex spheres as templates, sodium silicate as a precursor, and cetyltrimethylammonium bromide as a shell structure-directing agent. When polystyrene-methyl acrylic acid latex spheres were used as the templates, the pores in the shells of the resultant hollow silica spheres were composed of both micropores and mesopores. The pores in the shells of the hollow silica spheres were mainly composed of mesopores when sulfonated polystyrene-methyl acrylic acid latex spheres were used as the templates. The shell thickness and the specific surface area of the hollow silica spheres increased with the increase in the surface acidity of the latex spheres.     

Efficient hydrogen production by photocatalytic water-splitting using Pt-doped TiO2 hollow spheres under visible light

Pt doped TiO₂ hollow spheres (Pt/HS-TiO₂) are prepared by a sol–gel method and characterized by XRD, SEM, TEM and UV-visible absorption spectra. In addition, Pt/HS-TiO₂ is employed as the catalyst for photocatalytic hydrogen production from water splitting under visible light irradiation. The results show that Pt/HS-TiO₂ with hollow sphere structure presents excellent photocatalytic hydrogen evolution performance. The hydrogen generation rate can reach more than 1023.71 μmol h⁻¹ g⁻¹ at room temperature and no obvious deactivation is observed after 30 h irradiation. Furthermore, the reactively of Pt/HS-TiO₂ could be reproduced in the repeated cycle. Therefore, Pt/HS-TiO₂ is a promising photocatalyst to efficiently generate hydrogen under visible-light irradiation at room temperature.     

Preparation of the stimuli-responsive ZnS/PNIPAM hollow spheres

Novel quantum dots ZnS/poly(N-isopropylacrylamide) (PNIPAM) hybrid hollow spheres were obtained by localizing free radical polymerization of NIPAM and crosslinker (MBA) at the peripheral of PCL nanoparticles, followed by biodegradation of PCL with an enzyme of the Lipase PS. The formation of ZnS/PNIPAM hollow spherical structures and the thermo-sensitive reversible properties was systematically investigated by transmission electron microscopy (TEM) and dynamic light scattering (DLS), respectively. The ZnS/PNIPAM hollow spheres possess the photoluminescence properties and a swelling and de-swelling at about 32 °C, which agrees well with the slight red shift in photoluminescence spectra.