Titania Nanostructured Films Derived from a Titania Nanosheet/Polycation Multilayer Assembly via Heat Treatment and UV Irradiation

A multilayer film of titania nanosheet crystallites and poly(diallyldimethylammonium chloride) has been modified via heat treatment or exposure to UV light. The resulting films in various chemical compositions and crystal structures have been characterized by X-ray diffraction, FT-IR spectroscopy, X-ray photoelectron spectroscopy, and spectroscopic ellipsometry. Thermal or photocatalytic decomposition of polycations in the nanosheet gallery was achieved by heating to 400 °C or UV irradiation, respectively, which produced inorganic multilayers composed of the nanosheets and charge-balancing cations such as ammonium and/or oxonium ions. The polycation removal brought about an improvement in the multilayer stacking order, accompanied by a decrease in inter-nanosheet distance by ∼35%. The nanosheet architecture as well as multilayer structure collapsed upon heating at 500 °C or higher, yielding ultrathin films of TiO 2 (anatase and then rutile). The films exhibited a wide range of optical and photochemical properties dependent on modifications.