On the hydrothermal stability of MCM-41 mesoporous silica nanoparticles and the preparation of luminescent materials

MCM-41 nanoparticles have recently attracted growing scientific interest for applications in biomedical and diagnostic fields, nevertheless their use is limited because of the low hydrothermal stability, rendering them not suitable for functionalisation (i.e. dye molecules loading, anchoring of luminescent guests, etc.) in aqueous media. In this work, nanosized MCM-41 was hydrothermally stabilised by properly adapting post-synthesis hydrothermal restructuring treatment already used for conventional MCM-41 material (particle size in the micron range). A significant improvement of the hydrothermal stability of nanosized MCM-41 was reached: the pore array of the stabilized MCM-41 was not significantly modified after hydrothermal treatment at 333 K, whereas under the same conditions the parent MCM-41 became partially amorphized. The hydrothermal stabilisation is due to pore wall restructuring occurring during post-synthesis modification, and an increase of hydrophobicity of the silica surface. The improved hydrothermal stability of nanosized MCM-41 rendered this solid suitable for dye impregnation in aqueous media and allowed the preparation of a luminescent fluorescein/MCM-41 nanocomposite material, which in aqueous suspension showed an emission efficiency 5 times higher than an equimolar fluorescein solution.