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Silica Nanospheres (silica + nanosphere)
Selected AbstractsCdS-Nanoparticle/Polymer Composite Shells Grown on Silica Nanospheres by Atom-Transfer Radical Polymerization,ADVANCED FUNCTIONAL MATERIALS, Issue 3 2005T. Cui Abstract In this paper we describe the combined use of surface-initiated atom transfer radical polymerization (ATRP) and a gas/solid reaction in the direct preparation of CdS-nanoparticle/block-copolymer composite shells on silica nanospheres. The block copolymer, consisting of poly(cadmium dimethacrylate) (PCDMA) and poly(methyl methacrylate) (PMMA), is obtained by repeatedly performing the surface-initiated ATRP procedures in N,N -dimethylformamide (DMF) solution at room temperature, using cadmium dimethacrylate (CDMA) and methyl methacrylate (MMA) as the monomers. CdS nanoparticles with an average size of about 3,nm are generated in situ by exposing the silica nanospheres coated with block-copolymer shells to H2S gas. These synthetic core,shell nanospheres were characterized using transmission electron microscopy (TEM), dynamic light scattering (DLS), thermogravimetric analysis (TGA), diffuse reflectance UV-vis spectroscopy, X-ray photoelectron spectroscopy (XPS), and powder X-ray diffraction (XRD). These composite nanospheres exhibit strong red photoluminescence in the solid state at room temperature. [source] Nanoporous, Ultralow-Dielectric- Constant Fluoropolymer Films from Agglomerated and Crosslinked Hollow Nanospheres of Poly(pentafluorostyrene)- block -Poly(divinylbenzene)ADVANCED MATERIALS, Issue 21 2005G.-D. Fu Nanoporous fluoropolymer films with dielectric constants below 2 are prepared via consecutive surface-initiated atom transfer radical polymerizations of pentafluorostyrene (PFS) and divinylbenzene (DVB) on silica nanospheres. After agglomeration of the nanospheres, crosslinking of the nanospheres by UV, and removal of the silica cores (see Figure), a nanoporous fluoropolymer film with a dielectric constant as low as 1.7 is formed. [source] BIOCHEMISTRY OF SILICA BIOMINERALIZATION IN DIATOMSJOURNAL OF PHYCOLOGY, Issue 2000M. Sumper Diatoms are well known for the intricate patterns of their silica-based cell walls. The complex structures of diatom cell walls are species specific and become precisely reproduced during each cell division cycle, indicating a genetic control of silica biomineralization. Therefore, the formation of the diatom cell wall has been regarded as a paradigm for controlled production of nanostructured silica. However, the mechanisms allowing biosilicification to proceed at ambient temperature at high rates have remained enigmatic. Recently, we have shown that a set of highly cationic peptides (called silaffins) isolated from Cylindrotheca fusiformis shells are able to generate networks of silica nanospheres within seconds when added to a solution of silicic acid. Different silaffin species produce different morphologies of the precipitated silica. Silaffins contain covalently modified Lys-Lys elements. One of these lysine residues bears a novel type of protein modification, a polyamine consisting of 6,11 repeats of the N-methyl-propylamine unit. In addition to the silaffins, additional polyamine-containing substances have been isolated from a number of diatom species that may be involved in the control of biosilica morphology. Scanning electron microscopic analysis of diatom shells isolated in statu nascendi provide insights into the processes of pattern formation in biosilica. A model will be discussed that explains production of nanostructured biosilica in diatoms on the basis of these experimental results. [source] Optical properties of thick metal nanohole arrays fabricated by electron-beam and nanosphere lithographyPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2009Ahmad Reza Hajiaboli Abstract Optically thick metallic nanohole structures were fabricated using two different methods , electron-beam and nanosphere lithography. The nanosphere lithography technique was based on self-assembling of polystyrene or silica nanospheres (0.560,1.25 ,m in diameter) followed by the deposition of a silver film. The holes size and periodicity of the patterns as well as optical properties (transmission and reflection in the Visible,NIR) of the structures were investigated. The extraordinary optical transmission (EOT) was studied experimentally in both structures and it was found to be dependent on the geometrical parameters (holes shape, diameter and periodicity of structures). As the samples were made for long range order, the effect of the defects like missing holes, change of periodicity or variation of the holes shape, were also studied. The experimental results, especially the position of the SPR band in the different nanohole structures, were compared with those found by simulation carried out with 3D FDTD (finite difference time domain). (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Entrapping Flavin-Containing Monooxygenase on Corrugated Silica Nanospheres and their Recyclable Biocatalytic ActivitiesCHEMCATCHEM, Issue 8 2010Archana Abstract Synthetic methods and biocatalytic activities of new classes of heterogeneous biocatalysts by immobilizing flavin-containing monooxygenase on corrugated and nanoporous silica nanospheres are reported. The nanoporous and corrugated silica nanospheres are synthesized by etching silica nanospheres with aqueous KOH solution. The etched nanospheres are proven to have increased surface area, corrugated, cage-like external surfaces, and, most importantly, more accessible and well-suited surfaces to immobilize bigger molecules, such as enzymes. Furthermore, the etched silica nanospheres contain hydrophilic and silanol groups that are conducive for anchoring enzymes. By utilizing the structures of the etched silica nanospheres, effective immobilization of flavin-containing monooxygenase 1 (FMO1) is demonstrated. The FMO1 immobilized etched silica nanospheres have shown efficient and recyclable biocatalytic activity for nicotine oxidation. [source] Mesoporous Silica Nanosphere-Supported Chiral Ruthenium Catalysts: Synthesis, Characterization, and Asymmetric Hydrogenation StudiesCHEMCATCHEM, Issue 3 2009David Abstract Chiral RuCl2,diphosphine,diamine complexes with a pendant siloxy group were synthesized and characterized by NMR spectroscopy and mass spectrometry. The Ru complexes were grafted onto three different types of mesoporous silica nanospheres (MSNs) through the siloxane linkage, and the resulting MSN-supported Ru catalysts were highly active for the asymmetric hydrogenation of aromatic ketones, to afford chiral secondary alcohols, and racemic arylaldehydes, to give chiral primary alcohols. Excellent activities and enantioselectivities were observed for these MSN-supported Ru catalysts owing to readily accessible and uniform catalytic sites within the large channels of MSNs (diameters of >2,nm) and short diffusion lengths for the organic compounds as a result of small nanoparticle sizes of less than 1,,m. This catalyst immobilization strategy with MSN supports should be amenable to the design of many highly active and enantioselective heterogeneous asymmetric catalysts. [source] Bimetallic Au,Ni Nanoparticles Embedded in SiO2 Nanospheres: Synergetic Catalysis in Hydrolytic Dehydrogenation of Ammonia BoraneCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2010Hai-Long Jiang Dr. Abstract Gold,nickel nanoparticles (NPs) of 3,4,nm diameter embedded in silica nanospheres of around 15,nm have been prepared by using [Au(en)2Cl3] and [Ni(NH3)6Cl2] as precursors in a NP-5/cyclohexane reversed-micelle system, and by in situ reduction in an aqueous solution of NaBH4/NH3BH3. Compared with monometallic Au@SiO2 and Ni@SiO2, the as-synthesized Au,Ni@SiO2 catalyst shows higher catalytic activity and better durability in the hydrolysis of ammonia borane, generating a nearly stoichiometric amount of hydrogen. During the generation of H2, the synergy effect between gold and nickel is apparent: The nickel species stabilizes the gold NPs and the existence of gold helps to improve the catalytic activity and durability of the nickel NPs. [source] | |||||||||||||