We for the first time demonstrated carbon-deposited TiO2 inverse opal (C-TiO2 IO) structures as highly efficient visible photocatalysts. The carbon deposition proceeded via high-temperature pyrolysis of phloroglucinol/formaldehyde resol, which had been coated onto the TiO2 IO structures. Carbon deposition formed a carbon layer and doped the TiO2 interface, which synergistically enhanced visible-light absorption. We directly measured the visible-light photocatalytic activity by constructing solar cells comprising the C-TiO2 IO electrode. Photocatalytic degradation of organic dyes in a solution was also evaluated. Photocatalytic dye degradation under visible light was only observed in the presence of the C-TiO2 IO sample and was increased with the content of carbon deposition. The IO structures could be readily decorated with TiO2 nanoparticles to increase the surface area and enhance the photocatalytic activity. Notably, the photocatalytic reaction was found to proceed in a viscous polymeric solution. A comparison of the mesoporous TiO2 structure and the IO TiO2 structure revealed that the latter performed better as the solution viscosity increased. This result was attributed to facile diffusion into the fully connected and low-tortuosity macropore network of the IO structure.

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Three-dimensional (3D) periodic nanopatterns have gained much interest due to their potential applications, ranging from photonics to biological tissue engineering. Here, 3D silica nanoparticle/SU8 composite patterns were fabricated by holographic lithography. Although a uniform composite photoresist film was obtained by mixing epoxy-functionalized silica nanoparticles, the unavoidable scattering by the silica nanoparticles sufficiently changed the photosensitivity of the photoresists, resulting in the decrease of pattern contrast. With careful optimization of the light exposure condition, as well as increased polymer rigidity due to uniform dispersion of the nanoparticles in the polymer matrix, we were able to obtain high contrast 3D nanopatterns with up to 5 wt% silica content. We characterized the mechanical properties by the nanoindentation technique. The incorporation of silica nanoparticles remarkably improved the mechanical stability of the resulting 3D patterns. The mechanical properties of the composite nanopatterns displayed a Young's modulus of 3.8 GPa and a hardness of 0.05 GPa.Although the 3D patterns have a pore volume of around 50%, these mechanical properties are similar to those previously reported for the bulk SU8 films.