Effects of water content and pH on gel-derived TiO2–SiO2

Gel-derived TiO2–SiO2 particles with equal molar compositions and a specific surface area above 300 m2/g were prepared by controlling the molar ratio of H2O to alkoxides at about 10. The effects of molar ratios of H2O/alkoxides, pH of the starting solutions and temperatures of the calcination on the characteristics of the gel-derived TiO2–SiO2 were studied using BET, FT-IR, XRD, SEM and TEM. The results indicated that there was a critical value for H2O/alkoxides molar ratios in all pH conditions to give the highest specific surface areas and pore volumes of the derived specimens. The effects of pH of the starting solutions were not pronounced, in comparison with the effects of H2O/alkoxides molar ratio used. Although the calcination broke Ti–O–Si bonding, at elevated temperatures the mobility of the constituent elements in the structure was not sufficiently high, even at 1123 K, to rearrange the atoms to form the corresponding crystalline phases. Based on the experimental results obtained, three different mechanisms for sol–gel conversion were proposed to explain the effects of H2O/alkoxides molar ratios on the characteristics of gel-derived particles.