Tuning the Interfacial Properties of Mesoporous Ionosilicas: Effect of Cationic Precursor and Counter Anion

Ionosilica are mesoporous silica-based hybrid materials containing covalently bound ionic groups. The mixed ionic mineral nature confers particular properties to these materials. Here, we focus on the tailoring of the interfacial properties of ionosilicas. Three materials were synthesized from three different oligosilylated ammonium precursors. Furthermore, anion exchange allowed replacing the halide in the parent ionosilicas by more hydrophobic anions, e.g., thiocyanate (SCN^–) and bis­(trifluoromethane)­sulfonimide (NTf₂^–). Both the constitution of the ammonium substructure of the precursor and the nature of the counteranion allow controlling the interfacial properties in terms of hydrophilicity and affinity toward different types of solvents. Although all studied ionosilica are highly hydrophilic mesoporous materials, significant differences and clear trends could be observed. As shown via competitive 1-butanol adsorption measurements in the liquid phase and solvent vapor adsorption from the gas phase, the interfacial properties of ionosilicas can be fine-tuned either by the use of more hydrophobic ammonium precursors or the incorporation of hydrophobic anions. We therefore show that ionosilicas combine high porosity, regular architecture on the mesoscopic level with an unmatched chemical versatility, induced by the high variability and the high number of homogeneously distributed ionic species. Ionosilicas appear as highly adaptable materials and can be considered as “designer materials”, which are interesting for applications in catalysis, sorption, and separation.