Sol-gel synthesis of SBA-15: Impact of HCl on surface chemistry

Surface functionalisation of mesoporous silicas is critical to their application as sorbents and catalyst supports. Here we report the impact of chloride on the physicochemical properties of SBA-15, notably the surface density of reactive hydroxyl groups. Bulk and surface properties were characterised by N2 porosimetry, X-ray diffraction, SEM, TEM, FTIR spectroscopy, and Inverse gas chromatography (IGC). Increasing the HCl concentration from 0.1 → 2.0 M during the sol-gel preparation of SBA-15 increased the surface silanol coverage two-fold, and slightly widened mesopores from 4.2 to 4.9 nm. IGC reveals that the specific surface energy and corresponding surface polarity of SBA-15 correlate with surface silanol properties, and hence tuning the HCl concentration during SBA-15 synthesis offers a facile route to hydrophilic or hydrophobic silicas, and in turn a means to control their functionalisation and sorptive properties.