Effects of Ti-precursor concentration and annealing temperature on structural and morphological properties of TiO2 nano-aerogels synthesized in supercritical ethanol

Abstract

TiO2 nano-aerogels are elaborated by using acid-modified sol–gel approach from titanium tetra isopropoxide under supercritical drying conditions of ethanol. The effects of Ti-precursor concentration and annealing temperature on structural and morphological properties of TiO2 nanoparticles are investigated by XRD, infrared spectroscopy, SEM and specific surface area measurements. It was found, from XRD analysis, that pure anatase phase is obtained for the aerogels synthesized with various precursor concentrations. The increase of sol concentration leads to a slight and uniform variation of TiO2 cell parameters. The specific surface area of aerogels particles decreases and the pore volume increases with increasing of Ti-concentration. The presence of Ti–O and Ti–O–Ti bonds is confirmed by FTIR measurements. EDAX analysis shows that TiO2 nano-aerogels are oxygen rich. SEM images put into evidence the almost spherical elaborated particles with an enhanced agglomeration at high precursor concentration. With the increase of annealing temperature, the mixture of the phases did not happen and the pure anatase to pure rutile transition phase temperature is found to be around 900 °C. The Ti–O–C bonds disappear with annealing temperature. The heat treatment leads not only to the changes in crystal structure but also in morphology of the elaborated aerogels grains.