Niobia-stabilised anatase TiO2 highly porous mesostructured thin films

The thermal stability of anatase TiO2 mesoporous thin films has been considerably increased up to 800 °C by substituting a fraction of Ti cations by Nb. Mesoporous mixed oxide films Ti1−xNbxO2, with x = Nb/(Nb + Ti) ranging from 0 to 1, and homogeneous crystalline walls have been successfully prepared from chloride precursors and non-ionic block copolymer templates. They all exhibit a uniaxially distorted Im3m bcc mesostructure with the a lattice parameter ranging from 14 to 19 nm. Films have been characterised by simultaneous in situ SAXS and WAXS investigations during thermal treatment. Transmission electron microscopy and UV–visible ellipsometry were used to confirm the structure, the porosity and the good optical quality. A high porosity of 40% (pore size estimated at 7 nm) was maintained for the 10% Nb-doped films above the temperature of crystallisation and a bandgap of 3.40 eV has been measured after annealing at 500 °C.