Porous TiO 2/SiO 2 composite prepared using PEG as template direction reagent with assistance of supercritical CO 2

Abstract

Titania–silica mesoporous composites have been prepared using polyethylene glycol (PEG) 20,000 as a template direction reagent with the assistance of supercritical carbon dioxide (SC CO 2). For this preparation method, the composite precursors of tetrabutyl titanate (TBTT) and tetraethyl orthosilicate (TEOS) were dissolved in supercritical CO 2 and impregnated into PEG 20,000 using SC CO 2 as swelling agent and carrier. After removal of the PEG template by calcination in air at suitable temperatures, porous titania–silica composites were obtained. Effects of CO 2 pressure and temperature have been studied on the impregnation ratio during the supercritical fluid condition. The composite products were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), FTIR spectroscopy, nitrogen sorption–desorption experiments, scanning electronic microscope (SEM), and transmission electron microscope (TEM). XRD and nitrogen sorption–desorption experimental results indicate that the titania–silica composite crystallized in anatase phase and has a preferable BET surface area up to 301.98 m 2/g. It was also demonstrated that the microstructure and macroproperty of TiO 2/SiO 2 composites depend strongly on the experimental pressure during the impregnation process in SC CO 2. At suitable CO 2 pressure, silica even can be found in a single crystalline structure in nature by observation of TEM. At the same time, SEM indicates that the composite product existed in a spheric form or a cubic form inserted with many holes. So this work provides a new route to control and obtain the special micrography of TiO 2/SiO 2 composites with the aid of suitable polymer templates in supercritical CO 2.