Fabrication and characterization of titania inverse opals using supercritical carbon dioxide

Titania inverse opals (TIO) with macropores were synthesized via hydrolysis of titanium tetra-isopropoxide (TTIP) in supercritical carbon dioxide (scCO2). Colloidal polystyrene (PS) particles packed in a regular arrangement were used as a template. A mixture of scCO2, TTIP along with ethanol (EtOH) and distilled water was used as an impregnation medium to the voids of PS template. After the sol–gel coating reaction of the titania precursor in the voids and a subsequent thermal treatment, an inverted titania opal structure with high periodicity was obtained. The TIO was characterized by field emission scanning electron microscopy (FE-SEM), Raman spectroscopy and X-ray diffractometry (XRD). From the results of analysis, we conclude that the TIO synthesized in this study have anatase crystalline structure and have mean pore size diameter of 670–700 nm. The change in particle sizes is equivalent to only 2–5% shrinkage from the original PS latex spheres (715 nm). This represents much improved result compared to the products made by other methods where 20–30% shrinkage is common.