Fabrication of TiO₂ binary inverse opals without overlayers via the sandwich-vacuum infiltration of precursor

A sandwich-vacuum method was demonstrated for the fabrication of titania (TiO₂) binary inverse opals with an open surface. In this method, a moisture-stable TiO₂ precursor was backfilled into the interstitial spaces of polystyrene binary colloidal crystals (PS bCCs), which served as a template. Removal of the template by calcination yielded TiO₂ binary inverse opals with a 3D-ordered macroporous (3DOM) structure. Optical reflectance spectra revealed the existence of a pseudostop band gap in the 3DOM TiO₂ samples. The position of the pseudostop band gap shifted to the low-wavelength region as the number ratio of small over large PS spheres was increased in the template. The sandwich-vacuum method proved to be simple and rapid for the fabrication of TiO₂ binary inverse opals without overlayers in large domains. The 3DOM TiO₂ materials were used as a photocatalyst for the degradation of benzoic acid. Results showed that in comparison to TiO₂ nanoparticles prepared under the same sintering conditions, the 3DOM TiO₂ materials displayed enhanced photocatalytic activity.