XANES-PCA analysis of Ti-species in MCM-41 mesoporous silica synthesized by different methods

Abstract

MCM-41 mesoporous silica was prepared with Ti incorporated in the structure by two different ways: hydrothermal and atmospheric pressure by sol–gel method. To evaluate each synthesis, these materials were in situ investigated through X-ray absorption fine structure (XAFS) spectroscopy in different stages of the synthesis. X-ray absorption structure at the near edge region (XANES) gives the coordination of Ti and the relative concentration of Ti-species present in the mesoporous materials, obtained by differ- ent synthesis. The Principal Component Analysis (PCA) of XANES spectra indicate that mesoporous silica modified by Ti synthesized by hydrothermal method has species with majority of Ti tetrahedrally coor- dinated. This coordination is increased up to six when the sample is hydrated. In the case of the sol–gel synthesis, Ti-sites have higher mean coordination, independently from the degree of hydration.