Silica coatings of titania

Furlong Surface Chemistry of Silica Coatings of Titania... 

We also include in this class of quasi-2D nanostructured materials Titania deposited inside ordered mesoporous silica (because an inner coating of mesoporous silica may be realized), or nano-dot type Titania particles well dispersed in the ordered porous matrix. We do not consider here solids which contain linear or zig-zag type TiOTiO-nanowires in a microcrystalline porous framework, such as ETS-4 and ETS-10, notwithstanding the interest of these materials also as photocatalysts,146-151 because these nanowires are located inside the host matrix, and not fully accessible from the gas reactants (the reactivity is essentially at pore mouth). 

The solid-state Si SPE NMR spectra of SBA-15 and the titania surface-coated SBA-15 (Ti-SBA-15) are in accord with this expectation. The spectrum of SBA-15 displays a broad as)mimetric peak at 109 ppm (Q" sites) with shoulders at —101 ppm (Q sites) and 90 ppm(Q sites) in the area ratio 79 19 2. The NMR spectrum of Ti-SBA-15 (one layer) shows a reduction of the band intensity relative to the intensity. The normalized Q Q Q site populations become 85 13 2. No asymmetry is observed in the Q site band. Repetition of the monolayer deposition to form a double layer of titania on silica yields a material whose Si NMR spectrum is indistinguishable from that of the Ti-SBA-15 with a monolayer coverage. As expected, the titania-insulated silica resonances are unperturbed by the second titania layer. 

Silica has been used both as a core and shell material. For example, monodis-persed silica spheres were coated with titania by decomposing titanyl sulfate, TiOS04, in acidic solutions at 90°C (146). The particles so produced showed good hiding power, to be useful as paper whiteners (147). Due to the uniformity of the cores and shells, the optical properties of such dispersions were predictable and reproducible, as shown in Figure 1.1.22, which compares the scattering coefficient,... 

Fig. 1,1.22 Scattering coefficient ( Soa) versus the optical size (2-rrr/X) of silica particles coated with layers of titania of different thickness, incorporated in a cellulose matrix, r. Radius of coated particles 5, thickness of the titania shell X, wavelength in the medium.

Two ways of incorporating titania onto Cr/silica catalysts are used, and each has certain advantages. In the simplest method the silica surface is coated with a layer of titania by allowing a titanium ester to react with the hydroxyl groups. 

For the formation of silica nanotubes around [Pt(NH3)4](HC03)2 nanofibers, acting as templates, a coating mechanism, comparable to that given by Caruso et al. for the coating of polystyrene spheres with silica or titania [11], can be discussed. 

Improved color strength and very high luster are produced by the combination of precise thickness silica flake substrate materials, selected for their interference chro-maticity, and by deposition of titania or iron oxide coating layers of the precise thickness required to generate the same interference color. These pearl luster pigments show stronger chromaticity L a b -values than can be produced with mica-based designs. 

PZC/IEP of Silica Coating Deposited on Titania from Ethoxide Electrolyte T Method Instrument pH, Reference... 

PZC/IEP of Titania Coating on Silica Deposited from Pre-Existing Titania Particles... 

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