Synthesis of mesoporous titania thin films with vertical pore channels and thick and crystalline walls

Mesoporous titania thin films with vertical pore channels and crystalline walls have been sought for a long time because such materials are considered to be useful in many applications, especially as electrodes in organic solar cells and dye-sensitized solar cells. In this paper, we report the syntheses and characterization of such materials. The syntheses are achieved by spin-coating of precursor solutions composed of TiCl₄ and a Pluronic triblock copolymer F-127 ((EO)₁₀₆(PO)₁₀₀(EO)₁₀₆ where EO is ethylene oxide and PO is propylene oxide) in 1-butanol in various ratios, followed by aging and calcination. The wall thickness can be varied in the range of 6-8 nm, larger than that obtained by using ethanol as the solvent, by controlling the composition of the precursor solution. The thick walls enable the use of high temperatures in the calcination, up to 500 °C in the present study, to induce the crystallization of the wall material into anatase. The pore structure of the 500 °C calcined films is characterized by vertical straight channels with smooth internal surfaces. The channels are arranged with the hexagonal symmetry when viewed from the top. The variable wall thicknesses are reflected in the band gaps of the films with the thickest one showing 3.29 eV.