Highly Organized Mesoporous TiO2 Films with Controlled Crystallinity: A Li-Insertion Study

• Published in: Advanced functional materials Vol. 17; no. 1; pp. 123 - 132
• Main Authors: Fattakhova-Rohlfing, D., Wark, M., Brezesinski, T., Smarsly, B. M., Rathouský, J.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 05.01.2007; WILEY‐VCH Verlag
• Subjects: Block copolymers; Mesoporous materials; Mesoporous oxides; Template-directed assembly; Titania
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.200600425

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)20H), 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 °C, but treatment at 550–700 °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 °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 °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. Li insertion has been used to study the crystallization behavior of mesoporous TiO2 films (see figure) prepared by a novel poly(ethylene‐co‐butylene)‐b‐poly(ethylene oxide) block‐copolymer template. Such polymers allow the attainment of high crystallinity in the films by annealing at temperatures of up to 650 °C, whilst maintaining the 3D mesoporous structure.