Large Area Honeycomb-Structured TiO₂ Film for Photocatalytic Water Splitting

We demonstrate the fabrication of a large area 2-dimensional (2-D) binary colloidal assembly of polymeric microspheres (μ-spheres) and TiO₂ nanoparticles (NPs). TiO₂ NPs near the surface of poly­(methyl methacrylate) (PMMA) μ-spheres in aqueous dispersion exerted attractive depletion force between μ-spheres, allowing the formation of the well-ordered composite monolayer having hexagonal close-packed (hcp) structure on the air–water interface which can be transferred to a solid substrate. Subsequent drying and calcination of the composite film resulted in an “egg plate” structured TiO₂ film. When additional TiO₂ dispersion was spin-coated on the composite monolayer, an interesting honeycomb structured TiO₂ film was obtained. After the photodeposition of Au NPs on the honeycomb structured TiO₂ film for an enhanced absorptivity of visible light, the film was tested as a photoelectrode for photocatalytic water splitting. Owing to the large surface area of the well-ordered 2-D porous structure, a photoanode with the honeycomb-structured TiO₂ thin film exhibited a 67 times higher photocurrent density (PCD) for water splitting compared to the value from nanoporous TiO₂ photoanode with the same thickness.