Surface hydroxyls in porous silica: a Raman spectroscopy study

The surface vibrational properties of sol–gel synthesized porous silica are investigated as a function of sample porosity. By considering the Raman contribution of the physisorbed water, the analysis of the fundamental O–H stretching range (3000–3800 cm−1) displays the vibrational modes related to Si–OH species on the surface of the porous matrix. The sample porosity affects the H-bonding interaction between OH-related groups and influences the hydrophilic character of the surface: a curvature effect can be hypothesized.