Highly Ordered, Hierarchically Porous TiO₂ Films via Combination of Two Self-Assembling Templates

Hierarchically mesoporous TiO2 films with a high degree of order and connectivity on the sub-100-nm scale are successfully fabricated by the dual-templating methods sequentially applied. In this approach, the self-assembly of block copolymers combined with sol-gel reaction is first used to generate highly ordered mesoporous films by optimizing their self-assembling behavior. At the next step, 50-nm PS nanoparticles are deposited on the mesoporous films generated in the previous step to produce the colloidal crystals, and their inverse structure with a high degree of order, otherwise, would not form the colloidal crystals but generate a colloidal glassy phase with poor order. In addition to the exceptionally high degree of order, mesoporous films exhibit a high porosity that spans from the top surface to the bottom surface throughout the entire film without clogging. Especially wide pores at the top layer enable functional materials of large size to access the inside the films with small pores, maximizing their performance. As a proof of concept, photocatalytic effects are examined for the mesoporous films with different structures. In terms of the template pattern, the line pattern and bowl structure are also shown to guide the self-assembly of colloidal particles when their characteristic size matches with the particle diameter, in addition to the hexagonal packing.