Hierarchical Porous TiO2 Films from Colloidal Composite Fluidic Deposition

We use a "structure director" colloidal composite to fabricate porous titanium oxide films having a hierarchical pore architecture consisting of mesopores regularly distributed in the macropore shell. The colloidal composite consists of polystyrene beads coated with (ammonium lactate)titanium dihydroxide deposited by means of a fluidic technique. The pore properties and interconnections are controlled at different length scales: a macroscale, which is imposed by the polystyrene beads; a mesoscale, which is controlled by the composition and by the thermal history of the composite; a nanometer-scale, controlled by the nanocrystal sintering in air. Our approach can be extended to a wide class of water-soluble metal oxide precursors; therefore, it opens interesting perspectives for "bottom-up" nanotechnology of functional arrays and devices.