Hydrophilicity and surface heterogeneity of TiO2-doped silica materials for membrane applications

Silica materials containing different amount of titania (namely from 0 to 33%) were prepared, characterized and tested to evaluate their hydrophilic features in order to design a good membrane material for water purification. XRD, HRTEM, nitrogen gas-volumetric adsorption at 77 K were applied to obtain a complete structural and morphological description of the systems. Material stability in alkaline solutions was clearly enhanced by adding TiO2 to the silica material. Adsorption microcalorimetry and microgravimetric measurements were used to study water and toluene adsorption, respectively, in order to assess the hydrophilic and hydrophobic behaviors of the materials using polar (water) and non-polar (toluene) probe molecules. Microcalorimetric data allowed to describe also the energetic features of the water adsorption giving interesting information on the microscopic environment of the adsorption sites. The analysis procedure applied in this study can constitute a valid approach to determine a priori the behaviors of membrane materials.