Processing of macroporous titania thin films:: From multiscale functional porosity to nanocrystalline macroporous TiO2

Titania thin films with hierarchical pore structure (macropores and nested mesopores) were obtained in one step by a combination of sol-gel synthesis with controlled phase separation. Poly(ethylene glycol) (M-w = 2000) induces a phase separation upon film formation, producing macropores with controllable diameters between 0.1 and 2 mu m. The macroporous texture can be tuned by changing the synthesis conditions and the post-treatment. The inorganic walls present mesoporosity with an interpore separation of 3-4 nm. The porous TiO2 wall surface can be modified by incorporating organic functions by post-grafting. An adequate post-synthesis treatment leads to nanocrystalline walls (anatase) without microcracks. The films thus produced can find potential applications as optical or photovoltaic materials, sensors, depollutants, and so forth.