Ultraporous nanocrystalline TiO2-based films: synthesis, patterning and application as anti-reflective, self-cleaning, superhydrophilic coatings.

Crack-free, anatase-based optical coatings with a refractive index down to 1.27, a porosity up to 80 vol%, and a tunable thickness up to 1.5 µm were fabricated. The extraordinary stability of the porosity upon thermally induced crystallisation and template removal was attributed to the combined effects of the presence of 10% molar silica in the inorganic phase, a flash treatment at 500 °C, and the use of templates with different dimensions ranging from a few nanometers to 50 nm. The hierarchical porous system was directly patterned by UV lithography and used as multifunctional anti-reflective, self-cleaning coatings.