Effects of different Ti-doping methods on the structure of pure-silica MCM-41 mesoporous materials

Pure-silica mesoporous materials doped by titanium have been prepared by direct synthesis method and post-synthetic impregnation method. The effects of different Ti-doping methods on the structure of pure-silica mesoporous materials have been researched. X-ray diffraction, transmission electron microscopy, scanning electronic microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray absorption spectrum and nitrogen adsorption-desorption isotherms have been employed to characterize the products. It has been found that structural properties were strongly related to the amount and the way of titanium introduction. The mesoporous ordering of the samples that have been prepared by direct synthesis method and post-synthetic method became poor with the increasing of titanium amount. The XANES and EXAFS spectra confirmed that the titanium have been inserted into the framework of MCM-41. The titanium grafted in the Ti-MCM-41 in fourfold coordination, and the titanium doped in the Ti/MCM-41 in higher coordination sites.