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.