Abstract: MCM-41 mesoporous materials doped with Cerium, Neodymium, Europium and Erbium were synthesized by
hydrothermal methods. Powder X-ray diffraction (XRD), N₂ sorption and high resolution transmission electron microscopy-X-ray energy dispersive
spectroscopy techniques (HRTEM-EDX) were used to investigate the effects of Lanthanides to the structure of MCM-41. Results show that Lanthanides
have been incorporated into the framework and/or walls of the silica matrix. The ordering of the mesoporous structure is dependent
on the doping content and ionic diameters of Lanthanides. An increase in the content of Ln leads to the increase in the average pore diameter and
a decrease in the diameter of Ln leads to the decrease in the average pore diameter.

Key words: Lanthanides, MCM-41, incorporation