Infrared absorption spectra and structure of TiO2-SiO2 composites

Abstract

The composites xTiO 2 -(1-x)SiO 2 (x = 0.1, 0.5, 0.9) were obtained by coprecipitation from solutions of alkoxides: tetraethoxysilane (TEOS) and titanium tetraisopropoxide (TIPT). Intermolecular interaction of the components of the composite is apparent in the IR absorption spectra in the 928-952 cm -1 region, and is connected with bending vibrations of the Si-O-Ti bond.Introduction. Composites based on titanium and silicon dioxides have begun to be used relatively recently as catalysts and photocatalysts for various processes, protective coatings, components of glasses with low linear thermal expansion coefficient, and waveguide materials [1][2][3][4][5][6][7]. The method for obtaining the composite determines the nature and extent of interactions between components. For mechanical mixing of the individual phases, weak van der Waals interaction occurs. Thorough mixing of the components at the molecular level when obtaining the composite by sol-gel or coprecipitation methods leads to a substantial change in the properties of the end product: the appearance of new catalytically active centers, a shift in the onset of crystallization for the titanium-containing component toward higher temperatures, and accordingly an increase in the thermal stability of the structural and adsorption characteristics of the composite [7]. Formation of Si-O-Ti bonds at the TiO 2 -SiO 2 interface leads to an appreciable change in the electronic structure of the titanium atoms in the composite [8,9]. One possible method for estimating the interaction between components is IR spectroscopy. The absorption band observed in the 910-960 cm -1 region is due to characteristic vibrations of the Si-OH and Si-O-Ti bonds. Its position depends on the chemical composition of the sample and the resolution of the instrument [10,11]. We know that for exhaustive dehydration of SiO 2 , the band in the 940-950 cm -1 region, due to bending vibrations of the Si-OH bond, disappears in the absorption spectra. After appropriate heat treatment of the composite, absorption in this region will be due only to bending vibrations of the Si-O-Ti bond and thus it becomes possible to study the nature and extent of intermolecular interaction between titanium and silicon oxides by IR spectroscopy, which was the subject of this work.The Experiment. The composite was obtained by the coprecipitation method. For this purpose, the specified amounts of tetraethoxysilane (TEOS) and titanium tetraisopropoxide (TIPT) were mixed with isopropyl alcohol, then a solution of water (or ammonium hydroxide) in alcohol was added dropwise with vigorous stirring. The suspension was stirred for 1 h, the residue was separated by filtration and washed with water until the organic components were no longer present. The samples were dried at 120 o C for 5 h and calcined at 350 o C and 650 o C for 3 h. The individual titanium and silicon oxides were obtained under similar conditions. Table 1 gives the conditions for obtaining powders of the individual titanium and silicon oxides and the composit...

Amine‐Tethered Solid Adsorbents Coupling High Adsorption Capacity and Regenerability for CO2 Capture From Ambient Air

“…950 cm À1 ) bonds seemed to be perturbed in the T-PEI/silica, possibly because of TiÀO and TiÀN vibrations, which were not present in the A-PEI/silica material. [31,[35][36][37] The presence of the polymer in the hybrid materials could be identified by using the CÀH stretching vibrations that appeared around 2800 to 2900 cm À1 in all PEI-containing materials. [28][29]38] Similarly, the characteristic absorptions observed in the PEI/silica materials at approximately 1460, 1570, and 1650 cm À1 could be attributed to the CÀH bending, secondary amine NÀH bending, and primary amine NÀH bending modes, respectively.…”

Erratum to: Nanoscale composite materials in the system SiO2–TiO2

“…1) together with the absorption bands characteristic of the individual titania and silica, exhibits the presence of the absorption band in the range of 928-949 cm -1 , which refers to the characteristic vibrations of Si-O-Ti bonds [9]. At the same time, the ''core SiO 2 -shell TiO 2 '' composite in this range does not contain a similar absorption band (curve 2, Fig.…”

“…Less studied are the composite materials in the system SiO 2 -TiO 2 , although they are known to exist in several different morphologies: co-precipitated powders, xerogels, mesostructured composite materials with the ''core-shell'' morphology, where each of the components with equal probability can act as the core or the shell [8]. Various methods of obtaining such composite materials are determined not only by the nature of the interaction between different components [9,10], but also by resistance to thermal stress [11], various surface properties, which open new perspectives and possibilities for their practical application [12][13][14][15][16][17][18][19].…”

Hydrogen Dissolution in the TiO2–SiO2–FeO and TiO2–SiO2–MnO Based Welding-Type Fluxes

“…And the composition of the flux results in significant changes in the molten structure where the hydrogen can dissolve as a free hydroxyl ion (OH -) or an incorporated hydroxyl (Si-OH). , a weak transmittance band is observed, which has been suggested to be the bending vibration of surface absorbed H2O on SiO2 according to Marashkevich et al 10) No apparent difference was observed with changes in FeO/SiO2 indicating that the surface absorbed H2O is relatively not a factor. At lower wavenumbers of 940 cm -1 , a ridge is observed, which is the hydroxylated silica bending vibration of Si-OH.…”

“…For an acidic oxide slag system, lower FeO/SiO2 or increased SiO2 content increases the bridged oxygen in the network structure, where H2O can dissociate and be incorporated into the silicate structure as Si-OH, which increases the hydrogen solubility. Near 930 cm -1 , studies 10) have shown the existence of a Ti-O-Si bending vibration, but was not pronounced. This may suggest that the hydrogen dissolution is relatively more affected by concentration changes in FeO and SiO2 than the TiO2 additions.…”