Synthesis and Characterization of Porous and Nonporous Monodisperse Colloidal TiO2 Particles
TL;DR: In this paper, the influence of different salt ions or polymer molecules on the size and distribution of the final titania particles was investigated, and electron microscopy, thermogravimetry, 1H-MAS NMR, X-ray absorption spectroscopy, and electrophoresis.
Abstract: Monodisperse spherical titania particles of variable sizes are produced in a sol−gel synthesis from Ti(EtO)4 in ethanol with addition of a salt or a polymer solution. The influence of different salt ions or polymer molecules on the size and the size distribution of the final particles was investigated. The amorphous hydrous titania particles were characterized by electron microscopy, thermogravimetry, 1H-MAS NMR, X-ray absorption spectroscopy, and electrophoresis. Nitrogen absorption measurements revealed that the addition of polymers yields hollow and porous titania colloids.
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TL;DR: In this article, a general method to coat colloids with silica is described, which is especially useful for colloidal particles that cannot be covered directly with SiO2 by a Stober-like growth process.
Abstract: A general method to coat colloids with silica is described. The amphiphilic, nonionic polymer poly(vinylpyrrolidone) (PVP) was adsorbed to various colloidal particles such as small gold colloids, gold-shell silica-core particles, small and large silver colloids, boehmite rods, gibbsite platelets, and positively or negatively charged polystyrene. After this functionalization the stabilized particles could be transferred to a solution of ammonia in ethanol and directly coated with smooth and homogeneous silica shells of variable thickness by addition of tetraethoxysilane in a seeded growth process. The length of the polymer used strongly influences the stability of the colloids and the homogeneity and smoothness of the initial silica coating. This method is especially useful for colloidal particles that cannot be covered directly with SiO2 by a Stober-like growth process. Compared to methods known from the literature for the coating of such particles, this new method is faster and requires neither the use o...
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TL;DR: A more detailed description of the biomedical areas where sol-gel materials have been explored and found to hold significant potential is given in this paper, where a generalized description of various solgel methods available and how these chemistries control the bulk properties of the end products is presented.
582 citations
TL;DR: The approach presented in this study demonstrates that simultaneous control of the physical properties, including specific surface area, mesoporosity, crystallinity, morphology, and monodispersity, of the titania materials can be achieved by a facile sol-gel synthesis and solvothermal process.
Abstract: Monodisperse mesoporous anatase titania beads with high surface areas and tunable pore size and grain diameter have been prepared through a combined sol−gel and solvothermal process in the presence of hexadecylamine (HDA) as a structure-directing agent The monodispersity of the resultant titania beads, along with the spherical shape, can be controlled by varying the amount of structure-directing agent involved in the sol−gel process The diameter of the titania beads is tunable from ∼320 to 1150 nm by altering the hydrolysis and condensation rates of the titanium alkoxide The crystallite size, specific surface area (from 89 to 120 m2/g), and pore size distribution (from 14 to 23 nm) of the resultant materials can be varied through a mild solvothermal treatment in the presence of varied amounts of ammonia On the basis of the results of small-angle XRD, high-resolution SEM/TEM, and gas sorption characterization, a mechanism for the formation of the monodisperse precursor beads has been proposed to illust
407 citations
TL;DR: It is shown using computer simulations that two structures that would enable a bandgap in the visible region, diamond and pyrochlore, can be self-assembled in one crystal structure from a binary colloidal dispersion.
Abstract: Three-dimensional photonic crystals, or periodic materials, that do not allow the propagation of photons in all directions with a wavelength in the visible region have not been experimentally fabricated, despite there being several potential structures and the interesting applications and physics that this would lead to1. We show using computer simulations that two structures that would enable a bandgap in the visible region, diamond and pyrochlore, can be self-assembled in one crystal structure from a binary colloidal dispersion. In our approach, these two structures are obtained as the large (Mg) and small (Cu) sphere components of the colloidal analogue of the MgCu2 Laves phase2, whose growth can be selected and directed using appropriate wall patterning. The method requires that the particles consist of different materials, so that one of them can be removed selectively after drying (for example, by burning or dissolution). Photonic calculations show that gaps appear at relatively low frequencies indicating that they are robust and open for modest contrast, enabling fabrication from more materials.
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3,136 citations
TL;DR: Reference LPI-ARTICLE-1988-002doi:101021/ja00212a033View record in Web of Science Record created on 2006-02-21, modified on 2017-05-12 as discussed by the authors.
Abstract: Reference LPI-ARTICLE-1988-002doi:101021/ja00212a033View record in Web of Science Record created on 2006-02-21, modified on 2017-05-12
529 citations
TL;DR: In this article, a monodisperse TiO2 powders were synthesized by controlled hydrolysis of dilute alcoholic solutions of titanium alkoxides, and the state of powder aggregation in dispersions and powder packing in the green bodies strongly affected the sintering behavior.
Abstract: Monodisperse TiO2 powders were synthesized by the controlled hydrolysis of dilute alcoholic solutions of titanium alkoxides. The state of powder aggregation in dispersions and powder packing in the green bodies strongly affected the sintering behavior. The sintering of uniformly packed powder compacts resulted in finegrained microstructures with >99% of theoretical density nt temperatures much lower than those required to sinter conventional TiO2 powders.
420 citations
TL;DR: In this paper, the formation of uniform silica particles is investigated and rates of silicon alkoxide reactions are reported and linked to particle growth rates, which are consistent with a particle growth mechanism involving reactions occurring in solution that proceed independently of the presence of particles.
419 citations
TL;DR: A kinetic model is described that explains the formation of dispersions of narrow size distribution in such systems of monodispersed colloids from homogeneous solutions and was tested for a system involving formation of uniform spherical gold particles by reduction of auric chloride in aqueous solutions.
377 citations