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.