Structural and chemical transformations in the products of the interaction of silica gel with vapours of TiCl4 and H2O

Titanium oxide structures were synthesised by a molecular layering method on the surface of silica (ShSKG, SBET = 270 m2/g, V = 0.94 cm3/g, d = 14 nm). The change in the mass of the sample during the deposition was measured in situ. The samples were characterised by elemental analysis of Ti (photocolorimetry) and Cl (mercurimetry), scanning electron microscopy, and energy-dispersive X-ray spectroscopy. In this study, the effect of the temperature (200 °C, 500 °C) and number of synthesis cycles (1–4) on the distribution of titanium oxide structures over a cross-section of silica was investigated, along with the chemical composition and the microstructure of the modified silica samples. All of the deposition steps carried out at 200 °C and 500 °C were self-limiting. Synthesis at 200 °C provided a uniform distribution of titanium oxide structures over a cross-section of silica, and no traces of phase formation were found by scanning electron microscopy. For the samples synthesised at 500 °C, the titanium concentration in the edge of the granule was 1.5 times higher than in the central regions. Titanium dioxide crystals were found on the external surface of the silica modified by four cycles at 500 °C (its concentration was approximately 3.5 wt% of the total titanium content in the sample). On the surface of this sample, oval agglomerates of a higher titanium concentration were observed. The structure of these agglomerates was globular, similar to the structure of the initial silica.