Hollow hybrid spheres with silica inner shell for non-deformable, core exchangeable properties

Core exchangeable polymer-silica hybrid capsules with solvent-selective permeability were fabricated, in which the internal silica layer, formed from pre-included precursors, has the role of a framework to prevent irreversible deformation of the hollow capsules.     

Non-covalent reconfigurable microgel colloidosomes with a well-defined bilayer shell

Microgels are extremely interfacially active and are widely used to stabilize emulsions. However, they are commonly used to stabilize oil-in-water emulsions due to their intrinsic hydrophilicity and initially dispersed in water. In addition, there have been no attempts to control microgel structural layers that are formed at the interface and as a result it limits applications of microgel in advanced materials. Here, we show that by introducing octanol into poly(N-isopropylacrylamide-co-methacrylic acid) (PNIPAM-co-MAA) microgels, octanol-swollen microgels can rapidly diffuse from the initially dispersed oil phase onto the water droplet surface. This facilitates the formation of microgel-laden interfacial layers with strong elastic responses and also generates stable inverse water-in-oil Pickering emulsions. These emulsions can be used as templates to produce microgel colloidosomes, herein termed ‘microgelsomes’, with shells that can be fine-tuned from a particle monolayer to a well-defined bilayer. The microgelsomes can then be used to encapsulate and/or anchor nanoparticles, proteins, vitamin C, bio-based nanocrystals or enzymes. Moreover, the programmed release of these substances can be achieved by using ethanol as a trigger to mediate shell permeability. Thus, these reconfigurable microgelsomes with a microgel-bilayer shell can respond to external stimuli and demonstrate tailored properties, which offers novel insights into microgels and promise wider application of Pickering emulsions stabilized by soft colloids.

Inverse W/O Pickering emulsions and reconfigurable microgelsomes with a well-defined bilayer structure are prepared from octanol-swollen PNIPAM-co-MAA microgels and the combination of binary microgels, which promise wider application of soft colloids.     

Hollow titania spheres with movable silica spheres inside

We demonstrate a flexible method for preparing hollow TiO2 nanospheres with movable silica nanoparticles inside (HTNMSNs). In this method, we used monodisperse silica--polystyrene core--shell nanospheres (SiO2-PS-CSNs) sulfonated as templates and prepared the composite shell consisting of TiO2 and sulfonated polystyrene (SPS) through adsorbing or depositing tetrabutyl titanate gel into the SPS shell. Finally the HTNMSNs were obtained after removal of all polymers in the composite nanospheres by dissolution or calcinations. We investigated the dependence of the morphologies of HTNMSNs on the thickness of PS shells and the size of SiO2 cores and prepared rare earth doped HTNMSNs by a sol-gel process.     

Noncovalent anchoring of homogeneous catalysts to silica supports with well-defined binding sites

The efficient reversible functionalization of silica with catalytic sites using noncovalent interactions is described. We prepared silica materials with well-defined binding sites that selectively bind guest molecules that are equipped with the complementary binding motif, with the interaction between the two components being based on either hydrogen bonds or metal-ligand interactions. Several phosphine ligands functionalized with glycine-urea groups, required for hydrogen bond formation to the complementary host on the silica, have been prepared. The resulting noncovalently immobilized complexes have been used as a ligand system in the Pd-catalyzed allylic substitution and Rh-catalyzed hydroformylation of 1-octene. The supramolecular interaction between the transition-metal catalyst and the binding site located at the support is sufficiently strong to enable efficient catalyst recycling. In addition, the nature of the support facilitates the de- and refunctionalization of support, allowing the recycling of both homogeneous catalysts and the functionalized support. A rhodium catalyst based on a functionalized xantphos ligand was used in the hydroformylation of 1-octene in 11 consecutive reactions without showing catalyst deterioration or metal leaching.     

Direct coating of quantum dots with silica shell

This paper describes a method for direct coating of fluorescent semiconductor nanoparticles with silica shell. The fluorescent semiconductor nanoparticles used were CdSe _x Te_1–x nanoparticles coated with ZnS and succeedingly surface-modified with carboxyl groups, or quantum dots (Q-dots). The Q-dots were silica-coated by performing sol–gel reaction of tetraethyl orthosilicate (TEOS) using NaOH as a catalyst in the presence of the Q-dots. Quasi-perfect Q-dots/silica core-shell particles were formed at 5.0 M H₂O and 4.0 × 10⁻⁴ M NaOH. Under these concentrations of H₂O and NaOH, the particle size of Q-dots/silica particles could be varied from 20.1 to 38.1 nm as the TEOS concentration increased from 2.5 × 10⁻⁴ to 50 × 10⁻⁴ M. The Q-dots/silica particles showed fluorescence as well as the uncoated Q-dots.     

Fabrication of well-defined water-soluble core/shell heteronanostructures through the SiO2 spacer

A generalized approach for the fabrication of core/shell heteronanostructures through a simple chemical bath deposition method assisted by the bridging of SiO(2) spacer has been developed and a slow heterogeneous nucleation mechanism identified as the key to the success of this method.     

Template-free uniform-sized hollow hydrogel capsules with controlled shell permeation and optical responsiveness

This study has established a robust and straightforward method for the fabrication of uniform poly(vinylamine) hydrogel capsules without using templates that combines the dispersion polymerization and the sequential hydrolysis/cross-linking. The particle sizes are determined by the degree of cross-linking as well as by the cross-linking reaction time, while the shell thickness is independent of these variables. Diffusion-limited reactions occur at the periphery of the particles, leading to the formation of hydrogel shells with a constant thickness. The treatment of the surfaces of hollow hydrogel capsules with oppositely charged biopolymers limits the permeability through the shell of species even with low molecular weights less than 400 g/mol. Furthermore, we demonstrated that the hydrogel shell phase decorated with Au nanoparticles can be optically ruptured by exposure to laser pulse, a feature that has potential uses in optically responsive drug delivery.     

Preparation of hollow silica microspheres with controlled shell thickness in supercritical fluids

This article presents a novel route to prepare hollow silica microspheres with well-defined wall thickness by using cross-linked polystyrene (PS) microspheres as templates with the assistance of supercritical carbon dioxide (SC-CO₂). In this approach, the cross-linked PS templates can be firstly prepared via emulsifier-free polymerization method by using ethylene glycol dimethacrylate or divinylbenzene as cross-linkers. Then, the silica shell from the sol–gel process of tetraethyl orthosilicate (TEOS) which was penetrated into the PS template with the assistance of SC-CO₂ was obtained. Finally, the hollow silica spheres were generated after calcinations at 600 °C for 4 h. The shell thickness of the hollow silica spheres could be finely tuned not only by adjusting the TEOS/PS ratio, which is the most frequently used method, but also by changing the pressure and aging time of the SC-CO₂ treatment. Fourier transform infrared spectroscopy, transmission electron microscopy, and scanning electron microscope were used to characterize these hollow silica spheres.     

A novel tailored bimodal porous silica with well-defined inverse opal microstructure and super-microporous lamellar nanostructure

A novel tailored bimodal porous silica with well-defined inverse opal microstructure and super-microporous lamellar nanostructure has been successfully synthesized by simultaneous application of three-dimensional order polystyrene (PS) beads and an amphiphilic ionic liquid (AIL) as templates.     

A well-defined mesoporous amine silica surface via a selective treatment of SBA-15 with ammonia

2D double-quantum (1)H-(1)H NMR unambiguously shows that the "isolated" ≡Si-OH surface silanols of dehydroxylated SBA-15 are converted upon treatment with ammonia into single silylamine surface site ≡Si-NH(2). The "gem" di-silanols (=Si(OH)(2)) remain intact. Treatment using HMDS produces (=Si(OSiMe(3))(2)) but leaves ≡Si-NH(2) untouched. The resulting surface is hydrophobic and stable.     

Synthesis and investigation of barium titanate nanoparticles covered with silica shell

Matrix isolation of ferroelectric BaTiO₃ nanoparticles was executed by formation of protective silica shell (via hydrolysis and polycondensation of tetraethyl orthosilicate) on particles of precursor—barium titanyl oxalate. Synthesized BaTiO₃–SiO₂ composites have been characterized by IR spectroscopy, XRD, TEM, DTA/DTG methods.     

Magnetic properties and dye adsorption capacities of silica–hematite nanocomposites with well-defined structures prepared in surfactant solutions

Silica–hematite (α-Fe₂O₃) nanocomposites were synthesized by addition of aqueous solution containing ferrous ions (Fe²⁺), cetyltrimethylammonium bromide (CTAB) as a surfactant and tert-butanol (t-butanol) as a cosurfactant into colloidal silica solution. At alkaline atmosphere, silica surface with negative charges electrostatically attracts positively-charged iron hydroxide nuclei or particles which are stabilized by cationic CTAB molecules, and then silica–iron compound composites could be formed. Finally, the silica–hematite composite particles were obtained after calcination at 800 °C for 4 h. Through these processes, two types of composites having “core–shell type” or “decorated type” could be achieved. Morphology, BET surface area, crystallinity and magnetic properties of samples were analyzed by using TEM, BET, XRD and VSM, respectively. The “decorated type” composites had larger BET surface area and better magnetization. Also, to estimate the application in water treatment, adsorption properties of composites were studied through methylene blue (MB) adsorption which was characterized by UV–vis spectroscopy, involving collection of composites with neodymium magnet.     

Preparation of composite particles with magnetic silica core and fluorescent polymer shell

Dual functions of magnetic and fluorescent properties were created in composite particles that incorporated magnetite (Fe₃O₄) nanoparticles in particle cores of silica and fluorescent pyrene in particle shells of polystyrene. The Fe₃O₄ nanoparticles were prepared with a conventional homogeneous precipitation method and surface modified with a coupling agent of carboxyethylsilanetriol. The silica particles incorporating Fe₃O₄ nanoparticles were synthesized with a modified Stöber method in which the Fe₃O₄ nanoparticles were added to a system of tetraethylorthosilicate (TEOS)/ammonia/water/ethanol. Then, the magnetite/silica composite particles were coated with the pyrene/polystyrene shell in a soap-free emulsion polymerization, which was conducted in the presence of pyrene in a mixed solvent of water/ethanol. The composite particles prepared in the mixed solvent had both magnetic and fluorescent properties. The fluorescent spectrum of the particles with Fe₃O₄ was very similar to that without Fe₃O₄, indicating that the magnetic component within the core particles scarcely interfered with the fluorescent emission from the polymer shell.     

Superparamagnetic and fluorescent thermo-responsive core-shell-corona hybrid nanogels with a protective silica shell

We present the preparation and the characterization of the solution behavior and functional properties of superparamagnetic and/or fluorescent, thermo-responsive inorganic/organic hybrid particles with an intermediate protective silica shell and a smart polymer corona. These well-defined multifunctional nanogels were prepared via two consecutive encapsulation processes of superparamagnetic Fe(2)O(3) nanoparticles (NPs) and/or fluorescent CdSe(ZnS) semiconductor nanocrystals with a silica layer and a crosslinked poly(N-isopropylacrylamide) (PNIPAAm) polymer shell. First, the different NPs were entrapped into a silica shell using a microemulsion process. Therein, the precise adjustment of the conditions allows to entrap either several particles or single ones and to tailor the thickness of the silica shell in the range of 20-60 nm. In a second step, a polymer coating, i.e. thermosensitive PNIPAAm, was attached onto the surface of the multifunctional core-shell particles via free radical precipitation polymerization, furnishing multifunctional core-shell-corona hybrid nanogels. Analyses of the functional properties, i.e. optical brightness and magnetic moments, along with transmission electron microscopy reveal near monodisperse hybrid nanoparticles that retain the intrinsic properties of the original nanocrystals. Additionally, we demonstrate the drastically increased chemical stability due to the barrier properties of the intermediate silica layer that protects and shields the inner functional nanocrystals and the responsive character of the smart PNIPAAm shell.     

Hollow silica spheres with an ordered pore structure and their application in controlled release studies

Herein we report the synthesis and characterization of hollow silica spheres with a narrow size distribution, uniform wall thickness, and a worm-like pore structure. The formation of these spheres was monitored by confocal laser scanning microscopy and dynamic light scattering. A model for the molecular build-up of these silica hollow spheres is derived from these data in combination with studies of the as-made particles by transmission electron microscopy, scanning electron microscopy, pore size analysis, thermogravimetric analysis, and solid-state nuclear magnetic resonance. We further demonstrate that these spheres can be used for the encapsulation and subsequent release of different dye molecules.     

Access to well-defined isolated Fe(II) centers on silica and their use in oxidation

Well-defined Fe(II) isolated sites are obtained by reaction of diaryl-N,N'-diazadiene bis(neosilyl) iron (1) with an aerosil silica, SiO(2-(700)). This system can be used as a precursor for the catalytic oxidation of cyclohexene into cyclohexene oxide, cyclohexenol and cyclohexenone in the presence of H(2)O(2).     

A facile method for the preparation of monodisperse hollow silica spheres with controlled shell thickness

This article presents a facile, effective, mild synthesis process for well‐defined hollow spheres by using cationic polystyrene (PS) submicro‐particles as templates. In this approach, the cationic PS templates can be first prepared via emulsifier‐free polymerization by using the cationic monomer 2‐(methacryloyloxy) ethyltrimethylammonium chloride as comonomer, then, the silica shells from the sol‐gel process of tetraethoxysilane were coated on the surfaces of template particles via electrostatic interaction, finally the PS was dissolved in situ by modification of the reaction conditions in the same medium to form monodisperse hollow silica spheres with controlled shell thickness. Fourier transform‐infrared spectroscopy, thermogravimetric analysis, Brunauer‐Emmett‐Teller, transmission electron microscopy, and scanning electron microscope measurements were used to characterize these hollow silica spheres. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1332–1338, 2010     

Synthesis of micron-sized hollow silica spheres with a novel mesoporous shell of MCF

Micron-sized hollow silica spheres whose shells are made up of mesocellular silica foams(MCFs) have been synthesized by one-pot sol-gel method in benzene/water/P123 emulsion.The material is characterized with SEM,TEM,BET and ~(29)Si MAS NMR. The results show that the MCFs of the unique shell of hollow silica spheres were connected by large windows with a narrow distribution of～10 nm in diameter,the inner space of the hollow sphere is accessible.And the formation mechanism of the hollow silica spheres is ...