Ordered macro-mesoporous nc-TiO₂ films by sol-gel method using polystyrene array and triblock copolymer bitemplate

Ordered macro-mesoporous titania (TiO₂) film with a mesoporous anatase nanocrystalline wall was synthesized by simultaneous application of polystyrene (PS) array colloidal crystal and triblock copolymer P123 as templates, and tetrabutyl orthotitanate as titanium source. Mesoporous structure was optimized through solvent species, amount of P123, and the addition of hydrochloric acid. Permeation of mesoporous TiO₂ precursors into PS array template was examined by altering the sol concentration. The results show that the mesoporous anatase nanocrystalline titania (nc-TiO₂) formed has a Brunauer-Emmett-Teller surface area of 89.55 m²/g typically and an average mesoporous size of 5.67 nm. Sol concentration, characterized by viscosity, surface tension, and contact angle between the sol and PS template, dominates the perfection of macro-mesoporous structure. Optical transmittance for the mesoporous film keeps a high level (above 70%) beyond the wavelength of 400 nm, ∼10% higher than that of the macro-mesoporous film. The band gap of macro-mesostructure TiO₂ film is 3.00 eV, which is not only lower than the 3.25 eV of the mesoporous film, but is also lower than the 3.18 eV of P25 TiO₂, because of the defect level from the surface state of macroporous structure.