Highly organized mesoporous TiO2 films with controlled crystallinity:: A Li-insertion study

A study of electrochemical Li insertion combined with structural and textural analysis enabled the identification and quantification of individual crystalline and amorphous phases in mesoporous TiO2 films prepared by the evaporation-induced self-assembly procedure. It was found that the properties of the amphiphilic block copolymers used as templates, namely those of a novel poly(ethylene-co-butylene)-b-poly(ethylene oxide) polymer (KLE) and commercial Pluronic P123 (HO(CH2CH2O)(20)(CH2CH(CH3)O)(70)(CH2CH2O)(20)H), decisively influence the physicochemical properties of the resulting films. The KLE-templated films possess a 3D cubic mesoporous structure and are practically amorphous when calcined at temperatures below 450 degrees C. but treatment at 550-700 degrees C provides a pure-phase (anatase), fully crystalline material with intact mesoporous architecture. The electrochemically determined fraction of crystalline anatase increases from 85 to 100 % for films calcined at 550 and 700 degrees C, respectively. In contrast, the films prepared using Pluronic P123, which also show a 3D cubic pore arrangement, exhibit almost 50 % crystallinity even at a calcination temperature of 400 degrees C, and their transformation into a fully crystalline material is accompanied by collapse of the mesoporous texture. Therefore, our study revealed the significance of using suitable block-copolymer templates for the generation of mesoporous metal oxide films. Coupling of both electrochemical and X-ray diffraction methods has shown to be highly advisable for the correct interpretation of structure properties, in particular the crystallinity, of such sol-gel derived films.