In-Situ X-ray Diffraction Study of the Crystallization Kinetics of Mesoporous Titania Films

Abstract

In this work, we examine the kinetics of titania crystallization in periodic templated mesoporous thin films with a goal of understanding the relationship between atomic-scale crystallization and nanometer-scale structural change. The anatase crystallization proceeds via a surface-nucleation mechanism that rapidly produces relatively large titania grains. The activation energy for this process is about 210 ± 40 kJ/mol. As the crystallization proceeds, the periodic mesoscale order changes as the particles begin to impinge on the pore volume. The activation energy for this nanoscale restructuring is approximately 140 ± 30 kJ/mol, on the same order of magnitude as that observed for the crystallization. By studying the competition between these two processes, we are able to define the optimal conditions for kinetically controlled crystallization of the mesoporous material without appreciable change in the nanometer-scale structure. The grain growth behavior in the wall structure is also examined and is found to be directly affected by the presence of the inherent pore volume. These data contribute to the current understanding of the crystallization process in mesoporous oxide films and may be generally useful for developing crystalline titania-based materials with tunable nanoscale architectures.