Structural and morpholological properties of titanium dioxide-based sol-derived materials synthesized in different supercritical organic solvents

Abstract

TiO2-based sol-derived materials were synthesized by supercritical drying assisted sol–gel process. The effects of supercritical fluid (acetone, ethanol, and methanol) on structural and morphological properties of TiO2 nanocrystallites were investigated by XRD, infrared spectroscopy, SEM, and specific surface area measurements. The samples synthesized in acetone and ethanol are pure anatase and the brookite phase visibly appears when the methanol is used as supercritical fluid. The structural parameters are found to be dependent on supercritical drying conditions of fluids. The presence of Ti–O and Ti–O–Ti bonds was confirmed by FTIR measurements. EDAX analysis showed that the sample elaborated in ethanol is oxygen rich with higher cell parameters. SEM images show that the samples synthesized in acetone and methanol are formed by spherical and dispersed particles whereas the particles of the sample synthesized in supercritical ethanol are heavily agglomerated to form a denser monolithic block. BET measurements showed that the lowest pore diameter, the biggest pore volume, and the highest specific surface area are found in the TiO2-based sol-derived materials synthesized in supercritical methanol. The adsorption isotherm of the sample synthesized in supercritical methanol is found to be composed of two hysterisis loops probably due to the presence of two types of pores which increase the global pore volume. This result indicates that the adsorption capacity can be generally improved by increasing the specific surface area and pore volume of catalysts.