Uniform Silica

Another example is shown in Figure 9. In this case there was a fairly uniform silica penetration through the entire particle. The average silica concentration throughout the particle was about 8% SiO. ... 

Hydrothermal synthesis of the non-uniform silica gel used for preparative chromatography proceeds in a different fashion. Sodium silicate (IMa2Si03),1 obtained by alkaline fusion of very pure sand, is acidified to yield orthosilicic acid (Si(0H)4). This unstable acid initially dimerises then condenses further to yield a gel with a hydroxylated surface. Under conditions of controlled polymerisation, a hydrogel is obtained which is further calcinated to yield a very dense silica gel (xerogel). Some of the processes involved here are of the same type as those used to produce microspheres for analytical chromatography. 

Bonini, M., et al. (2006), Synthesis and characterization of magnetic nanoparticles coated with a uniform silica shell, Mater. Sci. Eng., 26(5-7), 745-750. 

Lu et al. [172] used a template assembled from uniform silica spheres to produce both an ordered macroporous Au-Ag nanostructure and an ordered hollow Au-Ag nanostructured film by electroless deposition. Both films showed SERS activity but were rather rough on the nanoscale and the authors attributed the surface enhancement to the presence of interconnected nanostructured aggregates and nanoscale roughness. 

Stober et al. (15) developed a method of preparing remarkably uniform silica particles with sizes ranging from 50 nm to >1 pm in diameter. Their recipe involves hydrolyzing silicon alkoxides in aqueous alcoholic solutions containing ammonia. The resulting solids are amorphous and are 11-15% porous. We chose to use the hydrolysis and condensation of tetraethylor-thosilicate, TEOS, in ethanol as a model precipitation reaction to study parameters leading to uniformity. 

Also plotted in Figure 8 is an estimate of thickness obtained from ratios of the Si and Al signals in the XPS spectra. This estimate results from the relationship between the measured Si Al ratio and the thickness t of a uniform silica coating (7) ... 

Figure 8. Silica layer thickness versus silica loading determined by TEM and XPS (ESCA) methods for silica-coated a-alumina particles. The theoretical curve was calculated for uniform silica coating of dense spherical a-alumina particles with equivalent 150-nm diameters. (Reprinted with permission from reference 7. Copyright 1989.)...

Silica-based SBA-15 materials, synthetised using triblock copolymers as templates, have a 2-dimensional hexagonal symmetry. PEO chains are deeply occluded within silica walls of SBA-15 and therefore the density of these walls, after calcination and elimination of PEO chains, may not be uniform. Hydrothermal treatment of SBA-15 can be used to increase their main mesopore diameter and decrease their wall thickness. Unique informations provided by modelling of XRD data complemented by TEM and N2 sorption show that calcined SBA-15 solids cannot be considered as ideal arrays of mesopores imbedded in a uniform silica matrix. The silica walls structure is complex as mesopores appear to be surrounded by a microporous corona of silica. We will also describe how this corona is affected by hydrothermal treatment. 

F.Y. Yang, Y. Chu, S.Y. Ma, Y.P. Zhang, and J.L. Liu, Preparation of uniform silica/ polypyrrole core/shell microspheres and pol3fpyrrole hollow microspheres by the template of modified silica particles using different modified agents, J. Colloid Interface Sci., 301(2), 470-478 (2006). 

Bogush GH, Zukoski CF (1991) Uniform silica particle precipitation—an aggregative growth model. J Colloid Interface Sci 142 19-34... 

To completely eliminate polar surface groups and reticulation of particles, sols of uniform silica particles were converted to organosols by esterification in the sol state... 

G.H. Bogush and C.F. Zukoski IV Uniform silica particle precipitation An aggregative growth model, J. Colloid Interface Sci., 142 (1991) 19 34... 

The rare earth tetrakis P-diketonate complex functionalized silica spheres are conveniently prepared by a one-pot synthesis method which is based on the modified Stober process [56]. The resulted luminescent nanoparticles are shown schematically in Fig. 8.9 (top). Because the introduction of siloxy-bearing rare earth complex precursor can result in coagulation, a step-by-step approach is adopted to implement the synthesis of uniform silica sphere. The rare earth complex precursors added into the reaction system in the second step can ensure the size uniformity of the nanoparticles furthest. As a result, the rare earth chelate mainly lies in the outer layer of the silica sphere, which has been shown schematically in Fig. 8.9 [55]. As shown in Fig. 8.9 (bottom), the nanoparticles obtained are uniform spheres, approximately 61 5 nm in diameter. And there is no obviously change in the particle size or morphology. All nanoparticles show relatively high luminescent lifetimes. Among the quantum efficiencies, the experiment values of Eu-TTA-SS (34.8 %)... 

Bele, M., Siiman, 0. and Matijevic, E. (2002) Preparation and flow cytometry of uniform silica-fluorescent dye microspheres. Journal of Colloid and Interface Science, 254, 274-82. 

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