Doughnut-like wrinkled fibrous nano silica architecture as a novel and effective reusable green heterogeneous nanocatalyst for the Hantzsch reaction

In the present study, we engineered a novel amphoteric monodisperse colloid (MOS - KCC-1) featuring a unique doughnut-like wrinkled fibrous nanosilica structure. This research focused on designing a novel internally cross-linked wrinkled fibrous organosilica nanocomposite incorporating organic basic bridges within its framework. To achieve this, a trivalent organosilane bridging agent was synthesized via a facile nucleophilic substitution reaction between cyanuric chloride and (3-aminopropyl)triethoxysilane. Subsequently, this triazine organosilica (TS) cross-linker was integrated into the pore walls of dendritic fibrous nanostructured silica using a sol-gel process under open-vessel reflux conditions. The resulting heterogeneous hybrid nanocomposite, KCC-Triazine, was characterized by FT-IR, FE-SEM, TEM, XRD, TGA, BET and EDX mapping. The rationale behind this design was that the wrinkled fibrous structure, with its numerous pores and slits, would function as a nanoreactor and serve as an excellent catalyst in organic transformations due to the presence of organic basic units within the pore walls. Given the utility of polyhydroquinoline (PHQ) and polyhydroacridine (PHA) scaffolds as nitrogen-based heterocycles with diverse biological activities, the catalytic performance of the nanocomposite was evaluated in the synthesis of these classes of compounds via the one-pot, four-component Hantzsch condensation reaction between aldehydes, active methylene compounds and NH₄OAc under solvent-free conditions. The combination of high catalytic activity and good reusability, along with the convenience of solvent-free conditions, makes this method an attractive option for the facile and efficient synthesis of basic nitrogen-containing heterocycles. Furthermore, the nanocatalyst can be easily separated from the reaction mixture and reused multiple times without a significant loss in activity, offering both economic and environmental advantages.