Understanding the Zr and Si interdispersion in Zr1−xSixO2 mesoporous thin films by using FTIR and XANES spectroscopy

Abstract

Zr–Si mixed mesoporous oxides were obtained in a wide range of proportions, from 0 to 30% and from 70 to 100% of Si, using Si(OEt)₄ and ZrCl₄ as precursors and Pluronic F127 as a template. The oxide mesostructure was characterized by transmission electron microscopy and 2D-small angle X-ray scattering. Fourier transform infrared spectroscopy measurements suggested a local homogeneous interdispersion of both cations. Further selective studies using X-ray Absorption Near Edge Structure (XANES) spectroscopy for separately Zr and Si local environments, allowed for demonstrating that the Zr coordination varies from close to 7 to 6, when its concentration in the mixed oxide is reduced. In addition, it was possible to determine that in mixed oxides with low Zr concentrations, Zr can fit into the spaces occupied by Si in SiO₂ pure oxide. An equivalent XANES result was obtained for Si, which is also compatible with the information obtained by FTIR. Furthermore, the Zr–O distance varied from close to 2.2 Å to 1.7 Å when the Zr concentration decreased. Finally, our study also demonstrates the usefulness of XANES to selectively assess the local structure (coordination, symmetry and chemical state) of specific atoms in nanostructured systems.