**4. Conclusions**

Regarding Nb-MCM-41 synthesis, the solids synthesized using incipient impregnation show a hexagonally ordered MCM-41 type mesoporous structure, as observed in the X-ray diffractograms. Solids obtained by the sol-gel method, meanwhile, did not present this type of structure. However, the mesoporosity of the systems is evident in the transmission electron micrographs that indicate a mesoporous-type ordered structure, although the family to which they correspond would still need to be determined.

Using incipient impregnation, better dispersion was observed on the silica, given that for up to 20% of incorporation, no Nb2O5 leaching was observed. This method thus shows greater advantages for niobium incorporation in silica. As such, greater dispersion appears to generate a less homogeneous pore size and a reduced photodegradation effect.

The Nb-MCM-41 mesoporous solids synthesized using the sol-gel method gave a greater photodegradation response than those synthesized through the incipient impregnation method. The highest effectiveness in photodegradation of the methylene blue molecule was obtained with the mesoporous solid synthesized through the sol-gel method, at a level of 20% Nb. This suggests that it is important to determine the structure obtained through the sol-gel method, to understand better the interaction between silica and niobium and the resulting effect on photodegradation. The results obtained in this study reiterate the importance of the method of synthesis used to obtain the mesoporous materials on their functionality.
