Titania gels

Uchida, M., Kim, H.-M., Kokubo, T., Fujibayashi, S. and Nakamura, T. (2003) Structural dependence of apatite formation on titania gels in a simulated body fluid. Journal of Biomedical Materials Research, 64A, 164-170. 

Fig. 30. Spectra of three high area, amorphous, hydrous oxides of titanium compared with that of the crystalhne anhydrous oxide, rutile. One is a straight titania gel, two are coprecipitated with different elements to form mixed metal hydrous oxide gels.

Controlled porosity and surface area titania gels as novel photocatalytic washcoats... 

Titania gels produced in this study were formed by the acid hydrolysis of titanium tetra-isopropoxide [14]. Although all the sols were produced in a similar manner, the final pH for the formation was controlled by the addition of ammonium hydroxide. The acid hydrolysis of titanium tetra-isopropoxide may be considered as follows ... 

Using the sol-gel technique five titania gels were prepared at final pH for the formation of the gels ranging from pH 1-6.7. The nomenclature adopted in this study starts with the letters SG followed by the pH of formation and finally a letter to indicate the final heat-treatment temperature a, b, c, d, or e being equal to 60°C, 200°C, 300°C, 400°C or 500°C, respectively. The original five materials were prepared at pH s of 1.0, 3.0,4.5, 5.7 and 6.7. The results obtained on these five materials dried at 60°C will be first discussed. The sample prepared at a pH of 5.7 was then calcined at various temperatures. The effects on the Sbet, porosity and phase composition will be discussed separately. 

Textural Results for Titania gels prepared at different pH... 

Figure 6.11. A. O natural abundance MAS NMR spectra of zirconia polymorphs. The peak marked A is from oxygen in the alumina rotor. The asterisks denote spinning side bands. From Bastow and Stuart (1990) by permission of Elsevier Science. B. MAS NMR spectra of titania gel heated to various temperatures, showing the evolution of rutile at the expense of anatase. From Bastow et at. (1993) by permission of the Royal Society of Chemistry. C. Static and MAS O NMR spectra of cubic Y2O3. Adapted from Florian et at. (1995).

O MAS NMR spectra of titania gel heated to various temperatures. Note the gradual loss of the 0Ti4 resonance on heating. From Bastow et al. (1993) by permission of the copyright owners. 

Titania sol and gel prepared through the hydrolysis of tetrabutyl titanate in acid water solution are sensitive to ultraviolet (UV) irradiation and turn into blue color [137]. Electron spin-resonance measurement showed that the pho-tochromism was ascribed to the presence of titanium (III) ions in the Ti-O-Ti network. The titanium (III) ions could be oxidized by the oxygen in the atmosphere, and then the sol and gel faded slowly. The absorption peaks in the optical absorption spectra of the titania gel were attributed to the transition of 3-dimensional electrons of a trivalent titanium in certain environments. 

Bonsack, J.P., Ion-exchange and surface properties of titania gels from Ti(IV) sulfate solutions, J. Colloid Interf. Sci., 44, 430, 1973. 

Schneider and Baiker in their review on the many methods of preparation of titania gels in the form of xero- and aero-gels-[6], mentioned either amorphous or crystalline non... 

The XRD patterns as shown in Fig 1 obtained for all the samples after their reduction in hydrogen indicate the presence of unreduced platinum oxides even after HTR in the supported titania gel and mixed oxide sample. However, complete reduction to metallic platinum was observed on supported commercial titania system. It can be observed that the phase transformation of titania from anatase to rutile does not occur under the experimental... 

During the period 1937-1940 Higuchi proposed a modified capillary condensation theory to explain the isotherms of 18 sorbates on titania gel of the same lot. The new theory proposes that in sorption phenomena vapors may be adsorbed in two ways (a) adsorption due to the surface force of solid sorbents which is usually accomplished by forming a monomolecular film in the relatively low pressure range and (b) capillary condensation of sorbates into pores whose radii are larger than ca. 10 A and covered by an adsorption film. The capillary condensation is undoubtedly due to the vapor pressure depression of the sorbate liquid described by the Thompson equation. 

Ti02 H2O TX-35 or TX-45/decane/water C (addition of TIPO and photoactive species, Eu ", Nd ", pyrene) Preparation of photoactive microemulsion-derived titania gels [94]. 

The potential of microemulsion-derived titania gels as host matrices for photoactive ions and molecules was explored by Guizard et al. [94] with the dopants Eu , Nd " ", and pyrene. It was concluded that the gel matrix presented three types of host sites associated with the microporosity, the mesoporosity, and the macroporosity. 

FIGURE 2.75 MAS NMR spectrum of a dried silica/titania gel prepared at Si/Ti molar ratio 70/30, a rotor frequency of 12.5 kHz spinning side bands. (Adapted from Polyhedron, 19, Babonneau, F. and Maquet, J., Nuclear magnetic resonance techniques for the structural characterization of siloxane-oxide hybrid materials, 315-322, 2000, Copyright 2000, with permission from Elsevier.)... 

Bastow, T.J., Moodie, A.F., Smith, M.E., and Whitfield, H.J. 1993. Characterisation of titania gels by O nuclear magnetic resonance and electron diffraction. J. Mater. Chem. 3 697-702. 

Characterization with XRD, SEM, AFM, and ETA Figure 7.1. Preparation of mesoporous titania gels by surfactant templating (an example). 

The templated titania gel films were prepared by the following method. From the practical point of view, highly porous titania film is important. Titania sols were prepared by hydrolysis of TNB in ethanol solution with addition of EACAC using acid catalyst. The gel films were prepared by spin coating at 2,500 ipm for 30 s on silica glass substrates. Spin coating was repeated up to five times. The wet gel films were immersed into an ethanol solution of surfactants, CTAC or BTAC, at 60°C for 1 h, and dried at 90°C for 24 h (surfactant-modified gel films) [30-32]. The dried gel films were annealed at 500°C for 2 h. The preparation methods are summarized in Figure 7.2. 

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