The chemical stability of surface species formed by reaction between silica gel and titanium tetrachloride

Hydrolytic stability of the Si–O–Ti bonds in the chemical assembly of titania nanostructures on silica surfaces

“…The limitation on T h was associated with the fact that heating of silicas containing chemisorbed TiCl x groups above the T chs temperature led to disproportionation between titanium-containing structures to evolve TiCl 4 into the gas phase and an increase in the multiplicity of the bond formed by an individual group with the support surface. 48,76 Vapour-phase hydrolysis of samples obtained following the TiCl 4 chemisorption at different T chs reduced the intensity of the band corresponding to the Si7O7Ti bond by 25% ± 30% (see Figs 3,4). These spectral changes pointed to the decrease in the number of anchor bonds formed by titanium-containing groups, i.e., in the course of hydrolysis a part of Si7O7Ti bonds were broken.…”

“…48,76 However, according to analytical studies and calculations, such processes could not change the total number of bonds of titanium oxychloride groups with the silicon support surface (i.e., the total number of Si7O7Ti bonds). Hence, it can be assumed that the increase in the absorption band intensity observed for the Si7O7Ti bond in the IR spectra was associated with an increase in the degree of connectivity of an individual TiCl x group due to its interaction with the silanol groups that did not react earlier with TiCl 4 .…”

“…4,8,14,58,59,76 Reactions with titanium tetrachloride could involve isolated (or terminal) (1), geminal (2) and vicinal (3) OH groups of silica.…”

Thermal Transformations of Titanium Oxochloride Nanostructures on Silica Surface

“…An additional important factor that affects the nature of chemisorption and the structure of the forming surface groups is the temperature at which the stage of TiCl 4 chemisorption is carried out (T CS ) or the products obtained are calcined (T T ) [14316]. It may be assumed, on the basis of the results of [14,15], that transformations caused by thermal instability of the titanium oxochloride groups synthesized may occur in the forming surface monolayer in the course of synthesis at temperatures higher than 200oC. The aim of this study was to examine TiCl 4 chemisorption on silica and the subsequent thermal transformations of the reaction products in the temperature range 253 600oC.…”

“…A calculation of the amount of OH groups consumed in and chloride ions in the surface groups synthesized, which is apparently due to their thermal instability [14,15].…”