Highly photoactive porous anatase films obtained by deformation of 3D mesostructures

A transparent film of three-dimensional (3D) hexagonal (P6(3)/mmc) mesostructured titania was fabricated according to a modified procedure using triblock copolymer Pluronic P123. The precursor solution was diluted with ethanol and spin-coated to afford a transparent film with a thickness of less than 100 nm. The mesostructure was maintained (deteriorated) at 400 °C, converted to regularly arranged anatase nanopillars with sufficient porosity at 550 °C, and deformed at 700 °C to nanocrystals with intercrystalline mesospaces. The mesostructural variation was related to the degree of shrinkage of the film owing to condensation and crystallization of the titania frameworks. An anatase nanocrystal film having sufficient porosity and high crystallinity was most active in the photodegradation of methylene blue. Such intercrystalline mesospaces can be controlled by regular deformation of 3D mesostructures through anatase nanopillar structures. In addition to adequate crystallinity of the titania frameworks, smooth diffusion of target organic molecules and/or degraded organic compounds was important for effective photodegradation.