Multilayer Films from Templated TiO₂ and Structural Changes during their Thermal Treatment

This work is focused on synthesis, characterization, and determination of main parameters of the multilayer P123 templated TiO 2 films. The mesoporous multilayer thin films consist of TiO 2 nanoparticles on the F-doped SnO 2 (FTO) conductive glass substrates. The films were grown by implementing the protocol of supramolecular templating with the amphiphilic triblock copolymer, Pluronic P123. The templated multilayer films were manufactured by repeated dip coating followed by the thermal treatment at 350 °C for 2 h after deposition of each layer. It was found that the multilayer preparation technique at 350 °C has serious limitations. The structure does not further increase its specific surface area (roughness factor) after deposition of more than 3−5 layers. The new surface area added by deposition of the top layer is compensated by the reduction of the surface area lost due to the sintering of the bottom layers. The careful review of the analytical data suggests that the morphology of the P123 templated TiO 2 structure is likely the tightest arrangement of randomly positioned particles of a certain size on a given pore diameter. The bulk material consists of pores evenly formed in all directions while a denser crust is formed on the surface where the fusion was restricted in one direction at the interface with the air. Subsequent thermal treatments of the multilayer films were applied to improve the anatase crystallinity while keeping the open morphology and small particle size. The morphological changes of the mesoporous structure during the subsequent thermal treatment at 425−540 °C were investigated.