O2 trapping in silica nano-structures with high specific surfaces

We report an experimental investigation regarding the entrapping of O₂ molecules inside various silica nano-structured systems having specific surfaces from 50 to 1000 m²/g. By recording Raman spectra and Near Infrared O₂ emission we studied the O₂ content per mass unit. Our data show that the internal voids of these nanostructured systems can trap O₂ molecules diffusing from the surrounding air or from a pure O₂ atmosphere, whereas the concentration of O₂ that can be trapped in the silica near-surface layer is at least one order of magnitude lower. This low ability is consistently observed in non-porous and porous silica nanoparticles and in mesoporous silica systems. Furthermore, we observed that the O₂ emission appears in the measurements recorded for mesoporous systems as the MCM41 after thermal treatment at 1000 °C when the mesoporous structure collapses, as proved by the variations of the Raman spectra. Considering the high variability in structure and morphology of the ensemble of investigated samples we suggest that the fact that the thin near-surface layer of silica has a low ability in trapping O₂ molecules is a general property of the silica high specific surface systems.