Impact of the Synthetic Strategy on the Structure and Availability of Active Sites in Bifunctional Mesoporous Organic–Inorganic Hybrids

The development of organic-inorganic hybrid materials bearing both acidic and basic functionalities is a challenging task, as it requires preserving the integrity and availability of two distinct active sites within a single porous network, such as silica. In this study, we report a synthetic approach that combines established grafting and co-condensation methods to achieve a controlled distribution of acidic and basic sites in mesoporous silica. Although each strategy is well known individually, their deliberate integration provides a distinctive pathway to tune the spatial arrangement and mutual preservation of the two functionalities. A comprehensive, multi-technique characterization approach, including in situ analyses and probe molecule adsorption, was used to monitor structural and chemical changes in both the organic and inorganic components. The results reveal that the coexistence of acidic and basic groups is highly sensitive to the synthetic conditions and activation treatments. In particular, basic sites are prone to protonation during the conversion of thiol groups into strong sulphonic acid sites, resulting in a partial loss of basic activity. The extent of this effect depends on the specific preparation route. In conclusion, the combined synthetic and characterization approach offers valuable insights into the nature, stability, and availability of the functional sites, guiding the rational design of advanced bifunctional hybrid materials.